Hydrogen adsorption in different carbon nanostructures

常用分析化学专业英语词汇absorbance 吸光度absorbent 吸附剂absorption curve 吸收曲线absorption peak 吸收峰absorptivity 吸收系数accident error 偶然误差accuracy 准确度acid-base titration 酸碱滴定acidic effective coefficient 酸效应系数acidic effective curve 酸效应曲线acidity constant 酸度常数activity 活度activity coefficient 活度系数adsorption 吸附adsorption indicator 吸附指示剂affinity 亲和力aging 化amorphous precipitate 无定形沉淀amphiprotic solvent 两性溶剂amphoteric substance 两性物质amplification reaction 放大反响analytical balance 分析天平analytical chemistry 分析化学analytical concentration 分析浓度analytical reagent (AR) 分析试剂apparent formation constant 表观形成常数aqueous phase 水相argentimetry 银量法ashing 灰化atomic spectrum 原子光谱autoprotolysis constant 质子自递常数au*ochrome group 助色团back e*traction 反萃取band spectrum 带状光谱bandwidth 带宽bathochromic shift 红移blank 空白blocking of indicator 指示剂的封闭bromometry 溴量法buffer capacity 缓冲容量buffer solution 缓冲溶液burette 滴定管calconcarbo*ylic acid 钙指示剂calibrated curve 校准曲线calibration 校准catalyzed reaction 催化反响cerimetry 铈量法charge balance 电荷平衡chelate 螯合物chelate e*traction 螯合物萃取chemical analysis 化学分析chemical factor 化学因素chemically pure 化学纯chromatography 色谱法chromophoric group 发色团coefficient of variation 变异系数color reagent 显色剂color transition point 颜色转变点colorimeter 比色计colorimetry 比色法column chromatography 柱色谱plementary color 互补色ple* 络合物ple*ation 络合反响ple*ometry ple*ometrictitration 络合滴定法ple*one 氨羧络合剂concentration constant 浓度常数conditional e*traction constant 条件萃取常数conditional formation coefficient 条件形成常数conditional potential 条件电位conditional solubility product 条件溶度积confidence interval 置信区间confidence level 置信水平conjugate acid-base pair 共轭酸碱对constant weight 恒量contamination 沾污continuous e*traction 连续萃取continuous spectrum 连续光谱coprecipitation 共沉淀correction 校正correlation coefficient 相关系数crucible 坩埚crystalline precipitate 晶形沉淀cumulative constant 累积常数curdy precipitate 凝乳状沉淀degree of freedom 自由度demasking 解蔽derivative spectrum 导数光谱desiccant; drying agent 枯燥剂desiccator 保干器determinate error 可测误差deuterium lamp 氘灯deviation 偏差deviation average 平均偏差dibasic acid 二元酸dichloro fluorescein 二氯荧光黄dichromate titration 重铬酸钾法dielectric constant 介电常数differential spectrophotometry 示差光度法differentiating effect 区分效应dispersion 色散dissociation constant 离解常数distillation 蒸馏distribution coefficient 分配系数distribution diagram 分布图distribution ratio 分配比double beam spectrophotometer 双光束分光光度计dual-pan balance 双盘天平dual-wavelength spectrophotometry 双波长分光光度法electronic balance 电子天平electrophoresis 电泳eluent 淋洗剂end point 终点end point error 终点误差enrichment 富集eosin 曙红equilibrium concentration 平衡浓度equimolar series method 等摩尔系列法Erelenmeyer flask 锥形瓶eriochrome black T (EBT) 铬黑Terror 误差ethylenediaminetetraacetic acid (EDTA) 乙二胺四乙酸evaporation dish 蒸发皿e*change capacity 交换容量e*tent of crosslinking 交联度e*traction constant 萃取常数e*traction rate 萃取率e*traction spectrphotometric method 萃取光度法Fajans method 法斯法ferroin 邻二氮菲亚铁离子filter 漏斗filter 滤光片filter paper 滤纸filtration 过滤flue* 溶剂fluorescein 荧光黄flusion 熔融formation constant 形成常数frequency 频率frequency density 频率密度frequency distribution 频率分布gas chromatography (GC) 气相色谱grating 光栅gravimetric factor 重量因素gravimetry 重量分析guarantee reagent (GR) 保证试剂high performance liquid chromatography (HPLC) 高效液相色谱histogram 直方图homogeneous precipitation 均相沉淀hydrogen lamp 氢灯hypochromic shift 紫移ignition 灼烧indicator 指示剂induced reaction 诱导反响inert solvent 惰性溶剂instability constant 不稳定常数instrumental analysis 仪器分析intrinsic acidity 固有酸度intrinsic basicity 固有碱度intrinsic solubility 固有溶解度iodimetry 碘滴定法iodine-tungsten lamp 碘钨灯iodometry 滴定碘法ion association e*traction 离子缔合物萃取ion chromatography (IC) 离子色谱ion e*change 离子交换ion e*change resin 离子交换树脂ionic strength 离子强度isoabsorptive point 等吸收点Karl Fisher titration 卡尔•费歇尔法Kjeldahl determination 凯氏定氮法Lambert-Beer law 朗泊-比尔定律leveling effect 拉平效应ligand 配位体light source 光源line spectrum 线状光谱linear regression 线性回归liquid chromatography (LC) 液相色谱macro analysis 常量分析masking 掩蔽masking inde* 掩蔽指数mass balance 物料平衡matallochromic indicator 金属指示剂ma*imum absorption 最大吸收mean, average 平均值measured value 测量值measuring cylinder 量筒measuring pipette 吸量管median 中位数mercurimetry 汞量法mercury lamp 汞灯mesh [筛]目methyl orange (MO) 甲基橙methyl red (MR) 甲基红micro analysis 微量分析mi*ed constant 混合常数mi*ed crystal 混晶mi*ed indicator 混合指示剂mobile phase 流动相Mohr method 莫尔法molar absorptivity 摩尔吸收系数mole ratio method 摩尔比法molecular spectrum 分子光谱monoacid 一元酸monochromatic color 单色光monochromator 单色器neutral solvent 中性溶剂neutralization 中和non-aqueous titration 非水滴定normal distribution 正态分布occlusion 包藏organic phase 有机相ossification of indicator 指示剂的僵化outlier 离群值oven 烘箱paper chromatography(PC) 纸色谱parallel determination 平行测定path lenth 光程permanganate titration 高锰酸钾法phase ratio 相比phenolphthalein (PP) 酚酞photocell 光电池photoelectric colorimeter 光电比色计photometric titration 光度滴定法photomultiplier 光电倍增管phototube 光电管pipette 移液管polar solvent 极性溶剂polyprotic acid 多元酸population 总体postprecipitation 后沉淀precipitant 沉淀剂precipitation form 沉淀形precipitation titration 沉淀滴定法precision 精细度preconcentration 预富集predominance-area diagram 优势区域图primary standard 基准物质prism 棱镜probability 概率proton 质子proton condition 质子条件protonation 质子化protonation constant 质子化常数purity 纯度qualitative analysis 定性分析quantitative analysis 定量分析quartering 四分法random error 随机误差range 全距(极差)reagent blank 试剂空白Reagent bottle 试剂瓶recording spectrophotometer 自动记录式分光光度计recovery 回收率redo* indicator 氧化复原指示剂redo* titration 氧化复原滴定referee analysis 仲裁分析reference level 参考水平reference material (RM) 标准物质reference solution 参比溶液relative error 相对误差resolution 分辨力rider 游码routine analysis 常规分析sample 样本,样品sampling 取样self indicator 自身指示剂semimicro analysis 半微量分析separation 别离separation factor 别离因数side reaction coefficient 副反响系数significance test 显著性检验significant figure 有效数字simultaneous determination of multiponents 多组分同时测定single beam spectrophotometer 单光束分光光度计single-pan balance 单盘天平slit 狭缝sodium diphenylamine sulfonate 二苯胺磺酸钠solubility product 溶度积solvent e*traction 溶剂萃取species 型体(物种)specific e*tinction coefficient 比消光系数spectral analysis 光谱分析spectrophotometer 分光光度计spectrophotometry 分光光度法stability constant 稳定常数standard curve 标准曲线standard deviation 标准偏差standard potential 标准电位standard series method 标准系列法standard solution 标准溶液standardization 标定starch 淀粉stationary phase 固定相steam bath 蒸气浴stepwise stability constant 逐级稳定常数stoichiometric point 化学计量点structure analysis 构造分析supersaturation 过饱和systematic error 系统误差test solution 试液thermodynamic constant 热力学常数thin layer chromatography (TLC) 薄层色谱titrand 被滴物titrant 滴定剂titration 滴定titration constant 滴定常数titration curve 滴定曲线titration error 滴定误差titration inde* 滴定指数-titration jump 滴定突跃titrimetry 滴定分析trace analysis 痕量分析transition interval 变色间隔transmittance 透射比tri acid 三元酸true value 真值tungsten lamp 钨灯ultratrace analysis 超痕量分析UV-VIS spectrophotometry 紫外-可见分光光度法volatilization 挥发Volhard method 福尔哈德法volumetric flask 容量瓶volumetry 容量分析Wash bottle 洗瓶washings 洗液water bath 水浴weighing bottle 称量瓶weighting form 称量形weights 砝码working curve 工作曲线*ylenol orange (*O) 二甲酚橙zero level 零水平异步处理dispatch_async(dispatch_get_ global_queue(0, 0), ^{// 处理耗时操作的代码块... [self test1];//通知主线程刷新dispatch_async(dispatch_get_ main_queue(), ^{//回调或者说是通知主线程刷新，NSLog(............); });。

广东药科大学学报Journal of Guangdong Pharmaceutical University Mar.2024,40(2)分子印迹聚合物对血液中野百合碱-血红蛋白加合物的分析葛燕辉1，2，郑远茹1，郭景灿1，江芷惠1[1.广东药科大学药学院，广东广州510006；2.广东药科大学附属第一医院（临床医学院），广东广州510080]摘要：目的基于分子印迹技术，建立快速检测体内野百合碱和血红蛋白加合物的方法。

方法以制备的野百合碱-血红蛋白加合物为模板分子，经表面印迹聚合法制备野百合碱-血红蛋白分子印迹聚合物，用作固相萃取介质识别造模大鼠血液中的血红蛋白加合物。

结果理化性质表征结果显示聚合层成功接枝在碳纳米管表面，且聚合物具备良好的热稳定性；将聚合物作为固相萃取介质，对造模大鼠血液进行分析，结果显示聚合物血红蛋白加合物具有较强的吸附能力（吸附量达90.86mg/mg），该结果与肝脏病理检测结果呈正相关性。

结论所制备的聚合物可以快速分析体内血红蛋白加合物的含量，与肝脏病理结果相结合，为肝小静脉闭塞症的无创伤诊断提供新的研究思路。

关键词：野百合碱；血红蛋白加合物；分子印迹聚合物；肝小静脉闭塞症；无创诊断中图分类号：R917文献标识码：A文章编号：2096-3653（2024）02-0076-07DOI:10.16809/ki.2096-3653.2024011802Analysis of Monocrotaline-hemoglobin adducts in blood using molecularly imprinted polymersGE Yanhui1,2*,ZHENG Yuanru1,GUO Jingcan1,JIANG Zhihui1(1.School of Pharmacy,Guangdong Pharmaceutical University,Guangzhou510006,China;2.The First Affiliated Hospital, Guangdong Pharmaceutical University,Guangzhou510080,China)*Corresponding author Email:*****************.cnAbstract:Objective To establish a rapid analytical method for in vivo binding of monocrotaline and hemoglobin based on molecular imprinting technology.Methods The prepared monocrotaline hemoglobin adduct (Mct@BHb)was used as a template molecule to prepare molecularly imprinted polymers(Mct@BHb@MIPs)by using surface imprinting polymerization method,and then the Mct@BHb@MIPs were used as an extraction medium to adsorp toxic markers in rat blood.Results The results showed that the polymer layer was successfully grafted onto the surface of MWCNs,and the polymer exhibited good thermal stability after characterization.The Mct@BHb@MIPs were used as a solid-phase extraction medium to analyze the blood of model rats,and the results showed that the polymer hemoglobin adducts had good adsorption capacity(adsorption amount reached90.86mg/mg).The analysis results were consistent with liver pathological detection.Conclusio n The polymerprepared by this research can quickly analyze the content of hemoglobin conjugates in vivo,which provides new research ideas for non-invasive diagnosis of hepatic small vein occlusion,combined with pathological results.Key words:monocrotaline;hemoglobin adduct;molecularly imprinted polymers;hepatic veno-occlusive disease;non-invasive diagnosis含有吡咯双烷类生物碱（pyrrolizidine alkaloids，PAs）的中药在治疗疾病过程中易引发肝小静脉闭塞病（hepatic veno-occlusive disease,HVOD）[1]，而目前我国有100多种含PAs的中药在临床上使用（约占《中药大辞典》收载量的1%），使得中药潜在的肝毒性问题不得不引起重视[2-3]。

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吸附氢分子的振动态及熵的计算王小霞;刘鑫;张琼;陈宏善【摘要】The entropy and enthalpy changes upon absorption determine the equilibrium adsorption states,the adsorption/desorption kinetics,and the surface reaction rates.However,it is difficult to measure experimentally or calculate theoretically the entropy of adsorption state.Hydrogen is considered as the most promising candidate to solve the global energy problems,and the storage by adsorption on light porous solids constitutes a main avenue to research field.An ideal storage system should be able to operate under ambient conditions with high recycling capacity and suitable uptake-release kinetics.The entropy of adsorbed H2 molecules is of great significance for determining the optimum conditions for hydrogen storage and for designing the storage materials.To the best of our knowledge,however,the only report on the entropy of the adsorbed H2 molecules is that adsorbed on alkali-metal exchanged zeolites at temperatures around 100 K.Due to different assumptions of the entropy changes,the values of the optimum enthalpy AH reported in the publications cover a wide range.In this paper,the adsorptionstates,vibrational modes,and the entropies of H2 molecules adsorbed on (MgO)9 and (AlN)12 clusters are studied by using first principal method.The computation is performed by the second-order perturbation theory (MP2) with the triple zeta basis set including polarization functions 6-311G(d,p).The very-tight convergence criterion is used to obtain reliablevibration frequencies.Analysis shows that six vibrational modes of the adsorption complexes can be attributed to the vibration of H2 molecule.For these normal modes,the amplitudes of the displacements of cluster atoms are usually two orders smaller than those of the hydrogen atoms.As the vibrational frequency is inversely proportional to the square root of the mass,the zero-point energy has an important influence on the adsorption energy.The ZPE correction exceeds half of the adsorption energy,and the adsorption on the anions is not stable after including the correction.Under the harmonic approximation,the normal vibration modes are independent,so the entropy of adsorbed H2 molecules can be calculated by using the vibrational partition function based on the vibrational frequencies.The results indicate that the entropy values depend mainly on the two lowest in-phase vibrational frequencies and it is not directly related to the adsorption strength but determined by the shape of the potential energy surface.In a temperature range of 70-350 K and at a pressure of 0.1 MPa,there is a good linear correlation between the entropy of adsorbed H2 and the entropy of gas-phase.The entropy of H2 decreases about 10.2R after adsorption.%用第一性原理方法研究了H2在(MgO)9及(AlN)12团簇上的吸附态、振动模式及熵.分析表明,吸附体系的振动中有六个简正模式可归为氢分子的振动;由于氢分子质量很小,零点能修正对吸附能有重要影响.利用振动配分函数计算了吸附氢分子的熵,表明吸附态H2的熵主要决定于较低的同相振动的频率,并不完全与吸附强度相关;在标准大气压下70-350 K的温度范围内,吸附H2的熵与气态H2的熵之间存在很好的线性关系,吸附后H2的熵减小约10.2R.【期刊名称】《物理学报》【年(卷),期】2017(066)010【总页数】7页(P85-91)【关键词】团簇;H2吸附;振动态;吸附H2的熵【作者】王小霞;刘鑫;张琼;陈宏善【作者单位】西北师范大学物理与电子工程学院,甘肃省原子分子物理与功能材料重点实验室,兰州 730070;西北师范大学物理与电子工程学院,甘肃省原子分子物理与功能材料重点实验室,兰州 730070;西北师范大学物理与电子工程学院,甘肃省原子分子物理与功能材料重点实验室,兰州 730070;西北师范大学物理与电子工程学院,甘肃省原子分子物理与功能材料重点实验室,兰州 730070【正文语种】中文用第一性原理方法研究了H2在(MgO)9及(AlN)12团簇上的吸附态、振动模式及熵.分析表明,吸附体系的振动中有六个简正模式可归为氢分子的振动;由于氢分子质量很小,零点能修正对吸附能有重要影响.利用振动配分函数计算了吸附氢分子的熵,表明吸附态H2的熵主要决定于较低的同相振动的频率,并不完全与吸附强度相关;在标准大气压下70—350 K的温度范围内,吸附H2的熵与气态H2的熵之间存在很好的线性关系,吸附后H2的熵减小约10.2R.PACS∶36.40.—c,31.15.A—,68.43.Bc DOI∶10.7498/aps.66.103601气体或液体分子在固体表面的吸附涉及广泛的应用领域,在吸附态下分子的平动被限制,而分子具有振动或转动运动.吸附过程的焓变和熵变决定了吸附的平衡状态、吸脱附的动力学、表面反应的反应速率常数等重要物理量,但对吸附态的熵理论计算和实验测量都比较困难[1,2].氢气作为潜在的理想能源,吸附态的熵对于确定最佳的存储条件以及存储材料的选择都十分重要[3,4].Yang等[5]基于van’t Hof f方程分析了吸附熵变对于存储条件的影响,Tang等[6]测量了MSiH3(M=K,Rb,Cs)体系脱附过程的熵变并讨论了熵和焓的补偿作用.氢分子的物理吸附能很好地用朗缪尔模型描述,吸附平衡常数K=exp(∆S0/R−∆H/RT),∆S0为标准大气压下的吸附熵变[7];而对于氢分子物理吸附态的熵,仅有100 K左右H2吸附在分子筛中的实验研究报道[8].在有关讨论固体储氢的文献中,由于对吸附态的熵假定不同,给出的最佳储存条件差别很大.例如Bhatia和Myer[7]假定吸附的熵变为8R,给出室温下储氢的理想吸附能为15.1 kJ/mol;而Li等[9]和Garberoglio等[10]假定不同的熵变并给出了完全不同的理想吸附能.最近Campbell和Sellers[1]测量了多种气体吸附态的熵,但并未包含H2的吸附.本文利用第一性原理方法,研究了H2在(MgO)9及(AlN)12团簇上的吸附,分析了吸附H2的振动态并计算了吸附态H2的熵.氢分子的吸附结构优化及振动频率计算釆用二阶微扰理论(MP2)[11],基函数选取了包括极化函数的三ξ基组6-311 G(d,p)[12];为了得到可靠的振动频率,结构优化采用了verytight的收敛条件(原子上的最大力为0.000002 a.u.,最大位移0.000006 a.u.).计算用Gaussian09程序[13]完成.对吸附体系的振动进行分析,得到吸附H2的配分函数,利用熵与配分函数的关系[14]计算H2吸附态的熵,式中N为阿伏伽德罗常数,k为玻尔兹曼常数,β=1/(kT).3.1 吸附态H2的振动模式氢分子很小不易极化,吸附一般较弱.MgO和AlN都是典型的离子团簇,能够对H2形成较强的吸附[15,16].对于MgO团簇,我们选取了稳定的岩盐和管状(MgO)9[17,18],而对AlN团簇我们选择了笼状的(AlN)12幻数结构[19,20].对H2吸附结构的优化表明,稳定的吸附方式是H2吸附在单个原子上,其中H2在阳离子上以侧位方式吸附,在阴离子上以端位方式吸附.笼状(AlN)12中所有Al或N原子都等价,对于H2在 (MgO)9上的吸附,我们选择了在岩盐结构四配位Mg/O原子(Mg4c,O4c)和管状结构三配位Mg/O原子(Mg3c,O3c)上的吸附.吸附态的熵决定于氢分子的振动频率,而振动频率依赖于吸附强度,因此我们选取具有不同吸附强度的结构以便于考察吸附态的熵与吸附强度的关系.图1给出了六种吸附结构,也给出了各吸附结构的吸附能∶其中Ecluster,EH2为团簇与自由H2的能量,Ecluster@H2为吸附体系的能量. 对于一个N粒子体系,将其势能在平衡位置做级数展开,引入质量权重的位移坐标qi=则在简谐近似下忽略三次及以上的高次项,因选取平衡位置处Ue=0,则(3)式中仅剩二次项,是正定的实对称矩阵,可用正交矩阵L=[lij]将其对角化.对角化后有Nf(线性分子为3N−5,非线性分子为3N−6)个非负本征值ki,对应的本征矢为在上述变换下,体系振动的哈密顿量分离变量求解则得到一系列独立的简谐振动.在每个振动模式中所有原子都以相同的频率、相位振动,(5)式给出的Qi称为简正坐标.H2吸附在团簇上后,吸附体系比原团簇多出六个振动自由度,通过GaussView对振动模式逐一甄别,发现有六个简正振动可归为氢分子,图2为H2吸附在岩盐(MgO)9上的简正振动模式.对图1各吸附结构中H2的简正振动模式对应的简正坐标进行仔细核查,发现团簇原子的振幅比氢分子的振幅一般小两个数量级.在H2的六个振动模式中,沿着H2到吸附位方向的同相振动用FTz表示,与之垂直的同相振动中,频率较低的用FTx表示、频率较高的用FTy表示;H2以端位方式吸附在阴离子上时,与FTz相对应的异相振动即为H2内的伸缩振动ωH-H,而以侧位方式吸附在阳离子上时,ωH-H与FTy对应;另外两个异相振动相当于H2的转动,分别用F Rθ和FRϕ表示.表1列出了图1各吸附态H2的振动频率.除Al原子上的FTy外,其他FTx与FTy 的振动频率都在100 cm−1以下,表明势能面的底部较平.FTz的振动频率和吸附强度相关,H2吸附在阳离子上时FTz约为300 cm−1,在阴离子上时为100 cm−1多.H2吸附在阳离上时FRθ和FRϕ对应的频率差别较大,而在阴离子上时两个频率比较接近.用相同算法得到的自由氢分子的振动频率ωH-H为4533.23 cm−1,由于吸附后H2内的结合减弱,从表1中可看出ωH-H约降低100 cm−1.3.2 零点能对H2吸附能的影响(4)式给出的力常数与折合质量成反比,对应的振动频率与质量的平方根成反比;对于H2的六个简正模式,折合质量近似为H2的质量,所以其振动频率较高,零点能修正对吸附能有较大的影响.因频率计算比较费时,在许多研究储氢的文献中并没有考虑零点能的修正[21−26].表2列出了(2)式定义的吸附能∆E、零点能修正∆ZPE以及考虑零点能修正以后的吸附能Eb.对于零点能修正表2中列出了用两种方法计算的值,第一种是其中ZPEcluster,ZPEH2为团簇与自由H2的零点能,ZPEcluster@H2为吸附体系的零点能.第二种是利用表1的频率直接求得,鉴于吸附后H2内的振动频率明显降低,考虑了伸缩振动频率的变化ħ∆ωH-H/2∶从表2可以看出两种方法计算的零点能非常一致,再次验证了我们甄选氢分子简正模式的正确性.表2数据表明,在阳离子Mg3c,Al和Mg4c上零点能修正达到了∆E 的64%,88%和97%,因此修正后吸附能大幅减小;而在阴离子上零点能修正都已超过了∆E,因此在阴离子上的吸附不稳定.3.3 氢分子吸附态的熵在简谐近似下,N粒子体系的振动近似为Nf=3N−6个独立的简谐振动的迭加,其振动配分函数为其中θvj=ħωj/k为振动特征温度.由(1)式得到振动熵它们为各简正模式的熵的和.由于H2的振动和其他简正模式独立,根据表1中的振动频率便可得到吸附态H2的熵值Sads.Gaussian程序在进行频率计算时直接给出了体系在标准状态下的振动熵值,由于气态H2的振动频率很高,常温下处在振动基态对熵无贡献,将吸附体系与团簇的振动熵值相减也给出H2吸附态的熵.表3给出了利用(10)式计算的标准态下H2吸附态的熵Sads与∆S,两者也非常一致.图3为不同温度下吸附态H2的熵,温度较低时熵值增加较快,超过150 K时Sads 随温度近似做线性变化.(10)式表明振动熵对低频比较敏感,H2吸附态的熵值主要由两个同相的振动频率FTx和FTy决定;FTz与吸附强度相关,而FTx和FTy主要由势能面底部形状决定,因此吸附态的熵并不完全与吸附强度相关.如在Mg3c上的吸附最强,但在Al上吸附的熵值最小.为了研究H2吸附前后的熵变,我们进一步考察了H2吸附态的熵和气态熵Sgas的关系.气态H2的振动对熵无贡献,平动的熵容易由下式算出∶双原子分子的转动配分函数为其中θr=ħ2/(2Ik)(I为转动惯量).由于H2是同核双原子分子,仲氢(核自旋波函数为交换反对称的单重态)只能处在l为偶数的转动能级上,而正氢(核自旋波函数为交换对称的三重态)只能处在l为奇数的转动能级上.利用熵与配分函数的关系可得到仲氢和正氢的转动熵计算分别取了前四项,当温度低于350 K时上述两式能保证计算的精度高于10−6.由于自旋禁阻效应,常温下制备的H2当温度降低时仲氢和正氢并不相互转变而保持1∶3的比例,对仲氢和正氢的熵加权平均可得到气态H2的转动熵S(R).图4为仲氢、正氢、气态H2的转动熵以及气态H2的总熵S(T+R)(平动+转动)随温度的变化,当T高于150 K时转动熵及总的熵都随温度近似做线性变化.图5给出了标准大气压下温度从70 K到350 K时吸附态与气态H2熵的关系,可以看出二者具有较好的线性关系,对数据做线性拟合对于H2在Mg3c,Mg4c和Al上的吸附,a分别为0.98,1.05和0.95;S0分别为−81.6,−85.58和−85.95.即斜率接近1,而吸附后H2的熵减小约10.2R.因为H2的质量小,平动、转动及振动熵与温度的关系与较重的分子都有明显的差别,因此拟合结果相较Campbell给出的斜率0.7和截距−3.3R不同[1].但这一结果却偶然地与特鲁顿规则非常接近,即在沸点(饱和蒸气压为1 bar)时非极性液体的吸附熵与气相熵近似为线性关系,斜率为1时截距为−10.3R.选取了H2在岩盐和管状(MgO)9及笼状(AlN)12上的吸附,计算了振动频率,分析了吸附H2的振动,计算了吸附的熵变.对吸附体系振动模式的分析表明,氢分子的振动可以从其他简正模式中独立出来,属于H2的六个简正模式中团簇原子的振幅小两个数量级.由于振动频率与质量的平方根成反比,对氢分子的吸附,零点能修正超过了吸附能的一半,修正后阴离子上的吸附能为正.鉴于氢分子的振动与其他简正模式独立,可以利用氢分子的振动频率计算吸附H2的熵,因较低的两个同相振动频率主要由势能面底部形状决定,吸附态的熵并不完全与吸附强度相关.在标准大气压下温度从70 K到350 K变化时,H2吸附态的熵与气态熵之间存在很好的线性相关,吸附后H2的熵减小约10.2R.感谢国家超级计算机中心在广州和深圳提供的计算资源.The entropy and enthalpy changes upon absorption determine the equilibrium adsorption states,the adsorption/desorption kinetics,and the surface reaction rates.However,it is difficult to measure experimentally or calculate theoretically the entropy of adsorption state.Hydrogen is considered as the most promising candidate to solve the global energyproblems,and the storage by adsorption on light porous solids constitutes a main avenue to research field.An ideal storage system should be able to operate under ambient conditions with high recycling capacity and suitable uptake-release kinetics.The entropy of adsorbed H2molecules is of great significance for determining the optimum conditions for hydrogen storage and for designing the storage materials.To the best of our knowledge,however,the only report on the entropy of the adsorbedH2molecules is that adsorbed on alkali-metal exchanged zeolites at temperatures around 100 K.Due to different assumptions of the entropy changes,the values of the optimum enthalpy∆H reported in the publications cover a wide range.In this paper,the adsorptionstates,vibrational modes,and the entropies of H2 molecules adsorbedon(MgO)9and(AlN)12clusters are studied by usingfirst principal method.The computation is performed by the second-order perturbation theory(MP2)with the triple zeta basis set including polarization functions 6-311G(d,p).The very-tight convergence criterion is used to obtain reliable vibration frequencies.Analysis shows that six vibrational modes of the adsorption complexes can be attributed to the vibration of H2molecule.For these normal modes,the amplitudes of the displacements of cluster atoms are usually two orders smaller than those of the hydrogen atoms.As the vibrational frequency is inversely proportional to the square root of the mass,the zero-point energy has an important influence on the adsorption energy.The ZPE correction exceeds half of the adsorption energy,and the adsorption on the anions is not stable after including the correction.Underthe harmonic approximation,the normal vibration modes are independent,so the entropy of adsorbed H2molecules can be calculated by using the vibrational partition function based on the vibrational frequencies.The results indicate that the entropy values depend mainly on the two lowest in-phase vibrational frequencies and it is not directly related to the adsorption strength but determined by the shape of the potential energy surface.In a temperature range of 70–350 K and at a pressure of 0.1 MPa,there is a good linear correlation between the entropy of adsorbed H2and the 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DOI∶10.7498/aps.66.103601*Project supported by the National Natural Science Foundation of China(GrantNos.11164024,11164034).†Corresponding author.E-mail:***************.cn。

Computational Investigation of Adsorption of Molecular Hydrogen on Lithium-Doped CorannuleneY.Zhang,†L.G.Scanlon,‡M.A.Rottmayer,‡and P.B.Balbuena*,†Department of Chemical Engineering,Texas A&M Uni V ersity,College Station,Texas77843,and Air Force Research Laboratory,Energy Storage&Thermal Sciences Branch,Wright-Patterson Air Force Base,Ohio45433Recei V ed:June24,2006;In Final Form:August14,2006Density functional theory and classical molecular dynamics simulations are used to investigate the prospectof lithium-doped corannulene as adsorbent material for H2gas.Potential energy surface scans at the level ofB3LYP/6-311G(d,p)show an enhanced interaction of molecular hydrogen with lithium-atom-doped corannulenecomplexes with respect to that found in undoped corannulene.MP2(FC)/6-31G(d,p)optimizations of4H2-(Li2-C20H10)yield H2binding energies of-1.48kcal/mol for the H2-Li interaction and-0.92kcal/mol forthe H2-C interaction,whereas values of-0.94and-0.83kcal/mol were reported(J.Phys.Chem.B2006,110,7688-7694)for physisorption of H2on the concave and the convex side of corannulene using MP2-(full)/6-31G(d),respectively.Classical molecular dynamics simulations predict hydrogen uptakes in Li-dopedcorannulene assemblies that are significantly enhanced with respect to that found in undoped molecules,andthe hydrogen uptake ability is dependent on the concentration of lithium dopant.For the Li6-C20H10complex,a hydrogen uptake of4.58wt%at300K and230bar is obtained when the adsorbent molecules are arrangedin stack configurations separated by6.5Å,and with interlayer distances of10Å,hydrogen uptake reaches6.5wt%at300K and215bar.1.IntroductionHydrogen has been proposed as a potential clean fuel,1but in order to be commercially employed,it is critical to develop compact,low-cost,and safe storage materials.The U.S.Depart-ment of Energy(DOE)set up the criteria of storing6.5wt% of hydrogen(density of62.5Kg/m3)for an ideal energy hydro-gen carrier.Other than storage in high-pressure tanks as gas or cryogenic hydrogen,different advanced hydrogen storage mater-ials have been extensively studied,including metal hydrides (MHs),2-5carbon-based,6-13and organometallic materials.14-19 The main mechanism of hydrogen adsorption on metal hydrides is chemisorption,and thus the desorption of hydrogen occurs at temperatures above500K and/or the hydrogen uptake capacity is low,about2wt%,due to the presence of heavy metals.2-5Hydrogen adsorption in carbon-based and organo-metallic materials is caused by anometallic materials14-19possess a low density,high surface area,and are porous materials.Hydrogen adsorption on organometallic materials shows about4.5wt%at77K and1wt%at room temperature and20bar.18,20The low hydrogen uptake at room temperature is the main disadvantage for the use of organome-tallic materials as adsorbents.With the advent of nanotechnol-ogy,carbon-based materials,including nanotubes,nanofibers, and activated carbon materials,have been analyzed experimen-tally and theoretically.6-13,21-23However,as a result of weak interactions between H2and pure carbon,these materials do not show sufficient storage capacity for commercial use under room temperature working conditions.Since Chen et al.24reported that alkali-metal-doped carbon nanotubes exhibit remarkable hydrogen uptake,a great deal of experimental and theoretical work has been done to investigate the hydrogen adsorption in metal-doped carbon materials.25-31 These studies showed that charge transfer from the alkali metal to these carbon materials polarize hydrogen molecules.As a result,a charge-induced dipole moment enhances the adsorption of hydrogen at ambient conditions.Besides,doping also increases the space to bind additional amounts of H2.30We have recently reported hydrogen adsorption on corannu-lene,a bowl-shaped molecule32with higher electron density in peripheral-carbon atoms than in inner-carbon atoms.33MP2 calculations yielded binding energies in the range-0.94to -0.83kcal/mol between a single hydrogen molecule andcorannulene,depending on the adsorption site.33Molecular dynamics(MD)simulations of crystalline corannulene predicted about0.79wt%of H2at72bar at273K and0.68wt%at300 K,in very good agreement with experimental results.33On the basis of MD simulations of corannulene stacks with different interlayer separations,we observed that the main factors that affect the hydrogen uptake capacity include the pressure applied to the system,temperature of adsorption,and the available space in the adsorbent assembly.For corannulene molecules arranged in stacks,it was observed that,as the interlayer distance(ILD) increases,the hydrogen uptake increases significantly.Thus,the adsorption of an alkali metal may enhance H2storage,not only due to the induction of dipole moments but also because of the generation of additional available space for H2storage. Experimentally,ball milling has been proved to effectively increase the lithium doping concentration in carbon materials, and this technique is ready to be extended to industrial scales.34 Kang35found the stable complex of pyrene-Li4where the ratio of Li to C is1:4.Deng et al.30found that the most stable ratio*Corresponding author.E-mail:balbuena@.†Department of Chemical Engineering,Texas A&M University.‡Air Force Research Laboratory,Energy Storage&Thermal SciencesBranch,Wright-Patterson Air Force Base.22532J.Phys.Chem.B2006,110,22532-2254110.1021/jp063963e CCC:$33.50©2006American Chemical SocietyPublished on Web10/13/2006of Li:C is1:6and1:8for Li-graphite intercalation compound (Li-GIC)at its equilibrium interlayer distance,while it is1:3 for Li-pillared graphene sheet(Li-PGS)for interlayer separa-tions greater than8Å.In this paper,we report ab initio and density functional theory(DFT)studies of the doping of lithium atoms to the corannulene molecule as well as on its interactions with H2.We also analyze the effect that doping of Li atoms to corannulene has on H2uptake capacity at finite temperatures and pressures using classical MD simulations.We investigate two types of structures,one with six lithium atoms doped on a single corannulene molecule and the other with five lithium atoms,which leads to Li to C ratios between1:3and1:4, consistent with results from other groups.30,35putational Methods2.1.Ab Initio and DFT Calculations.The Gaussian03 package36was used to undertake the molecular orbital theory calculations.Previous theoretical studies on corannulene indi-cated that a hybrid DFT method combined with double- plus polarization basis sets would well reproduce the structural parameters of corannulene37,38and protonation and lithiumcation binding on corannulene.32,39In this paper,we use B3LYP/ 6-31g(d,p)for geometry optimization of lithium-atom-doped corannulene complexes and B3LYP/6-311g(d,p)for potential energy surface scans.The optimized geometries are followed by frequency calculations to prove that the stationary points are local minima and find the zero point energy corrections. Single point calculations and full optimizations using second-order Mo¨ller-Plesset perturbation theory(MP2)with the6-31G-(d,p)basis set are performed to obtain more accurate binding energies accounting for weak van der Waals forces that are responsible for the H2/corannulene interaction based on phys-isorption.2.2.Classical MD Simulations.The derivation of the force fields for H2-corannulene interactions was reported previ-ously.33Lennard-Jones(LJ)parameters were derived using the LJ parameters for the Li atom,D Li-Li)0.025kcal/mol,and x Li-Li)2.451Å,40corresponding to the form:These parameters and eq1were used to generate a new set of parameters according to the equivalent formyielding LiLi)0.0275kcal/mol andσLiLi) 2.18Å.The Lorentz-Berthelot mixing rules were used to obtain the LJ cross parameters Li-H)0.0432kcal/mol andσLi-H)2.57Å.For the dipole-induced interaction,the dipole moment of the Li3-C20H10-Li2complex(3.856D)calculated at the level of B3LYP/6-311G(d,p)and the Li polarizability of2.43×10-23 cm3(ref41)were used to define an average pair interaction calculated as:The dipole-induced interaction between Li and H2(equation3) was added to eq2to generate new data using the nonbonded interaction parameters Li-H)0.0432kcal/mol andσLi-H) 2.57Å,and a new fitting of these data to the form of the LJ eq 2yielded Li-H)0.9kcal/mol andσLi-H)2Å,which are the parameters used in the MD simulations.The DL_POLY program,42version2.14,was used for all MD simulations.A cutoff value of10Åwas used for nonbonded interactions,and periodic boundary conditions in three dimen-sions were applied to the simulation cell.The simulations were run in the canonical NVT ensemble at temperatures of273K and300K and pressures up to250bar.Details of the assembled system are provided in the Results and Discussion Section.The total simulation time for each P and T is800ps,with300ps for the equilibration period and500ps for the production period. The evaluations of H2uptake are based on the500ps production period.3.Results and Discussion3.1.Doping of Li Atoms to Corannulene.Corannulene isa bowl-shape molecule with C5V symmetry.Figure1shows the structure of corannulene optimized at the level of B3LYP/6-311G(d,p).There are three types of carbon atoms:the outmost 10carbons bonded to one hydrogen each are named as“rim”carbons(C r),the innermost five carbons on the five-membered ring as“hub”carbons(C h),while the remaining five carbons connecting between the rim and hub carbon atoms are designated as“bridge”carbons(C b).The calculation shows that rim carbon atoms possess higher electron density than hub and bridge carbon atoms,thus the dipole vector would point toward the five-membered ring.The calculated dipole moment of corannulene is2.18D,which is close to the experimental data of2.07D.43The structural information and Mulliken charge distribution of corannulene are shown in Table1.Recent DFT studies35of Li-aromatic sandwich compounds, R-nLi-R,where R is benzene,naphthalene,or pyrene,reported that the Li atom was preferentially adsorbed over the six-membered ring instead of over individual or pairs of C atoms. For a single Li ion,it was found that the Li cation was bounded on the convex side over a six-membered ring of corannulene at the level of B3LYP/6-311G(d,p)//B3LYP/6-31G(d,p).32The data in Table2indicate that complexation of a Li ion at the convex side is more stable than at the concave side,which is in agreement with the results of Frash et al.,32whereas,for the Li atom,complexation at the concave side is more stable(by1.2 kcal/mol)than at the convex side.E vdw )DIJ{-2[x IJ x]6+[x IJ x]12}(1)E vdw )4 {[σIJr]12-[σIJ r]6}(2)Γh ij )-7759.74r6meV(3)Figure1.Optimized structure of corannulene at the level of B3LYP/6-311G(d,p).TABLE1:DFT(B3LYP/6-311G(d,p))Structural Parametersand Mulliken Charge Distribution in Corannulene aatom charge atom pair bond distance(Å)angle(deg)C h-0.04C h-C h 1.42C h-C h-C b122.88C b0.00C h-C b 1.38C h-C b-C r114.43C r-0.07C b-C r 1.45C b-C r-C r121.96H+0.09C r-C r 1.40C r-C b-C r129.78a The atomic charges are average values.Adsorption of Molecular H on Lithium-Doped Corannulene J.Phys.Chem.B,Vol.110,No.45,200622533The Mulliken charges on the various atoms (labels as in Figure 1)shown in Table 2suggest that the higher charge of the Li cation may be the reason for the stronger binding to the corannulene molecule.Multiple Li atoms can be adsorbed either at the concave or at the convex side.Figure 2shows attachment of five Li atoms on corannulene at the level of B3LYP/6-31G(d,p).Considering the effect of charge transfer from Li to C atoms and thus the repulsion between two positively charged lithium atoms,the initial geometries were arranged with Li atoms over the outer six-membered rings on either side.In the initial configuration,all five Li atoms were located at the same side (either convex or concave)of the corannulene molecule,and the optimized structure resulted always with the five Li atoms attached to the concave side,over the six-membered rings,as shown in Figure 2a.Thus,when the optimization was started locating the Li atoms over the convex side,there was an inversion of curvature of the corannulene molecule,in agreement with the tendency shown in Table 2for a single Li atom.Similarly,when the initial configuration contains two Li atoms on one side and three on the other side,the energetically favorable optimized conforma-tions contain more Li atoms on the concave side,that is,three Li atoms on the concave side and the other two Li atoms on the convex side (Figure 2b);this conformation has lower energy than that in Figure 2a by minimizing repulsion effects.Frequency calculations indicate that both complexes in Figure 2are local minima.Comparison of the respective energies is shown in Table 3,along with related structural information.The Li 5-C 20H 10and Li 3-C 20H 10-Li 2complexes have σV symmetry,as shown in Figure 2.Table 3illustrates that there is charge transfer from Li atoms to corannulene molecules,resulting in positive charges on Li atoms of Li 5-C 20H 10and Li 3-C 20H 10-Li 2.Overall,the total charge on Li atoms in Li 3-C 20H 10-Li 2is higher than those in Li 5-C 20H 10.Thus,C atoms of corannulene are more negatively charged in the first complex,resulting in higher electrostatic interaction and shorter distances from Li atoms to six-membered rings of corannulene in Li 3-C 20H 10-Li 2than in Li 5-C 20H 10.Each of the three Li atoms (1Li,4Li,and 5Li)on the concave side of Li 3-C 20H 10-Li 2locate close to the center of a six-membered ring,whereas the two attached to the convex side of Li 3-C 20H 10-Li 2are closer to a six-membered ring than those on the concave side of Li 5-C 20H 10.The calculated energies show that Li 3-C 20H 10-Li 2is about 4kcal/mol more stable than Li 5-C 20H 10;the binding energy per Li atom is -23.91kcal/mol-Li in Li 3-C 20H 10-Li 2and -23.11kcal/mol-Li in Li 5-C 20H 10.The doping of six Li atoms on corannulene is illustrated in Figure 3,which shows four different combinations tested on the basis of the results obtained for complexes with five Li atoms.Figure 3a displays the complex Li 6-C 20H 10,where the first five Li atoms are doped over six-membered rings on the concave side,and the sixth lithium atom is in the center over these five Li atoms.Alternatively,with the sixth Li atom doped at the convex side,we obtain the Li 5-C 20H 10-Li complex (Figure 3b).Both Li 6-C 20H 10and Li 5-C 20H 10-Li have σV symmetry,with the atoms labeled 1Li and 6Li located on theTABLE 2:Structural and Energetic Properties and Mulliken Charges in Complexes of Corannulene with a Lithium Cation/Atom Attached to a Six-Membered Ring,Optimized at the B3LYP/6-31G(d,p)Levelcharges on atoms (e)complex with corannulene Li -C distance(Å)electronic energy(hartrees)binding energy (kcal/mol)Li C r C b C h Li +on the concave side 2.28-2.31-775.52514-47.50.44-0.120.12-0.03Li +on the convex side 2.29-2.44-775.52700-48.70.46-0.130.15-0.06Li on the concave side 2.22-2.25-775.68264-16.80.33-0.150.11-0.05Li on the convex side2.14-2.38-775.68073-15.60.31-0.160.17-0.08Figure 2.Optimized (B3LYP/6-31G(d,p))conformations of corannulene complexed with five Li atoms doped at different positions.(a)Five Li atoms doped at the concave side over six-membered rings,Li 5-C 20H 10.(b)Three lithium atoms doped at the concave side and two at the convex side over six-membered rings,Li 3-C 20H 10-Li 2.22534J.Phys.Chem.B,Vol.110,No.45,2006Zhang et al.symmetry plane.Another complex contains the first five Li atoms doped as in the complex Li 3-C 20H 10-Li 2,and the sixth Li atom is attached either to the concave or to the convex side over a six-membered ring,forming Li 4-C 20H 10-Li 2(Figure 3d)and Li 3-C 20H 10-Li 3(Figure 3c).These complexes are no longer symmetric after optimization.Frequency calculations on the optimized structures of these complexes also indicate they are local minima,except for Li 5-C 20H 10-Li,which is a saddle point.Table 4summarizes partial structural and energetic informa-tion.The most important difference is the negative charge over the Li atom on top of Li 6-C 20H 10,which may favor electrostatic Li -Li interactions,resulting in Li 6-C 20H 10being 9kcal/mol more stable than Li 3-C 20H 10-Li 3.The binding energies per mole of Li are -25.03and -23.53kcal/mol-Li for Li 6-C 20H 10and Li 3-C 20H 10-Li 3,respectively.The relatively large binding energies of the Li 6and Li 5complexes of corannulene might indicate stable Li adsorption on corannulene,with the ratio of Li:C between 1:4and 1:3.The lithium doping concentration is in agreement with results reported by other groups.30,353.2.Adsorption of H 2on Li-Doped Corannulene Com-plexes.3.2.1.Li 6-C 20H 10and Li 5-C 20H 10-Li.Adsorption of H 2is studied on the most stable complexes at each doping concentration,i.e.,on Li 6-C 20H 10and on Li 3-C 20H 10-Li 2.To obtain a qualitative comparison of the interaction strengths of H 2in corannulene and Li-doped corannulene,we computed a potential energy scan,as shown in Figure 4,which illustrates that no attractive interactions between hydrogen and the corannulene molecule are detected at this level of theory when a head-on H 2molecule approaches the corannulene moleculeTABLE 3:Li-Doped Corannulene Complexes:Structural Information and Electronic Energy (Ha)and Binding Energy (kcal/mol of Li)at the Level of B3LYP/6-31G(d,p)distance Li -C (Å)acomplex Li label (as shown in Figure 2)charge of Li(e)Li -C r Li -C bLi -C h Li 5-C 20H 1010.32 2.142.653.072,30.14 2.23,2.24 2.30,2.33 2.32,2.344,50.25 2.14,2.17 2.51,2.55 2.82,2.86Li 3-C 20H 10-Li 210.45 2.212.292.362,30.48 2.13,2.19 2.27,2.53 2.18,2.414,50.222.13,2.22 2.25,2.472.42,2.51electronic energy (Ha)zero point energy (Ha)binding energy (kcal/mol of Li)Li -7.49098C 20H 10-768.164830.23195Li 5-C 20H 10-805.803840.23366-23.11Li 3-C 20H 10-Li 2-805.810220.23260-23.91aWhen two values are shown,each one represents two pairs of the distance of Li -C in σv complexes.TABLE 4:Li -Corannulene Complexes:Structural Information,Electronic Energy (Ha),and Binding Energy Per Li Atom (kcal/mol-Li)at the Level of B3LYP/6-31G(d,p)adistance Li -C (Å)complex Li label (shown in Figure 3)Li charge Li -C r Li -C bLi -C h Li 6-C 20H 1010.22 2.16 2.673.162,30.31 2.19,2.20 2.27,2.31 2.34,2.364,50.26 2.14,2.18 2.55,2.64 2.97,3.026-0.23 5.08 4.76 4.55Li 5-C 20H 10-Li10.45 2.102.573.052,30.14 2.17,2.22 2.31,2.40 2.43,2.444,50.21 2.07,2.15 2.46,2.49 2.75,2.7960.51 2.152.422.25Li 4-C 20H 10-Li 210.26 2.22,2.28 2.33,2.45 2.44,2.5220.47 2.14,2.19 2.27,2.51 2.21,2.3330.45 2.12,2.13 2.36,2.43 2.24,2.3140.15 2.23,2.37 2.23,2.55 2.37,2.5150.05 2.18,2.18 2.51,2.52 2.81,2.8460.49 2.149,2.157 2.518,2.585 2.92,2.98Li 3-C 20H 10-Li 310.30 2.32,2.37 2.35,2.46 2.36,2.4220.45 2.17,2.22 2.31,2.50 2.21,2.3330.20 2.13,2.25 2.26,2.63 2.24,2.4640.15 2.17,2.28 2.29,2.54 2.50,2.6550.35 2.17,2.39 2.31,2.62 2.57,2.7560.392.17,2.17 2.40,2.412.29,2.32electronic energy(Ha)zero point energy(Ha)binding energy (kcal/mol-Li)Li -7.49098C 20H 10-768.164830.23195Li 6-C 20H 10-813.350080.23616-25.03Li 5-C 20H 10-Li -813.345990.23443-24.61Li 4-C 20H 10-Li 2-813.347630.23374-24.78Li 3-C 20H 10-Li 3-813.335680.23309-23.53aEach value in σv symmetry complexes,Li 6-C 20H 10and Li 5-C 20H 10-Li,represents two pairs of the distance of Li -C.Adsorption of Molecular H on Lithium-Doped Corannulene J.Phys.Chem.B,Vol.110,No.45,200622535along pathways a,b,c,and d (Figure 4).However,when H 2approaches Li 6-C 20H 10(pathway e)or Li 3-C 20H 10-Li 2(path-way f),a relatively strong attractive interaction between H 2and the Li atom -corannulene complex is observed.The strongest attraction appeared when the center of mass of the H 2molecule is at a distance of 2.47Åfrom the corresponding Li atom (Figure 5),yielding binding energies of -0.47and -2.06kcal/mol with Li 6-C 20H 10and Li 3-C 20H 10-Li 2,respectively.Figure 5shows the structures of H 2interacting with Li 6-C 20H 10and Li 3-C 20H 10-Li 2at the geometries corresponding to the minima on the potential surface curves of Figure 4.The separation of 2.47Å(Figure 5)corresponds to a distance of 2.10Å,shown in Figure 4,because that is the distance between the closest H atom and the corresponding Li atom;the difference between them is one-half of the calculated bond distance of H 2(0.74Å).To account for weak van der Waals forces that are responsible for the H 2/Li -corannulene complex interactions,we use second-order Moller -Plesset perturbation theory to determine the energy corresponding to such geometries using the 6-31G(d,p)basis set.The calculated MP2/6-31G(d,p)energies (single point calculations)are -1.83and -2.82kcal/mol for the H 2-Li 6-Figure 3.Optimized (B3LYP/6-31G(d,p))conformations of corannulene with six Li atoms.(a)Six Li atoms doped at the concave side,Li 6-C 20H 10.(b)Five Li atoms doped at the concave side and one at the convex side,Li 5-C 20H 10-Li.(c)Three Li atoms doped at the concave side and three at the convex side,Li 3-C 20H 10-Li 3.(d)Four Li atoms doped at the concave side and two at the convex side,Li 4-C 20H 10-Li 2.22536J.Phys.Chem.B,Vol.110,No.45,2006Zhang et al.C 20H 10system and H 2-Li 3-C 20H 10-Li 2,respectively.Recently,we reported binding energies of -0.94and -0.83kcal/mol for the physisorption of H 2on corannulene using MP2(full)/6-31G-(d)for H 2on the concave side and the convex side,respec-tively.33Thus,the H 2-Li interaction is stronger than that between H 2and C based on these binding energies.In the next section,we refine these estimates using optimizations with the MP2method.3.2.2.Li 2-C 20H 10.In this section,we analyze the most favorable hydrogen adsorption sites using Li 2-C 20H 10(Figure 6a),first with two hydrogen molecules on the convex side (Figure 6b)and then with two hydrogen molecules on the convex side and two hydrogen molecules on the concave side (a total of four H 2molecules,Figure 6c).The optimized configurations of these systems at the MP2(FC)/6-31G(d)level have a symmetry plane,and the two H 2molecules adsorbed on the convex side are located on that plane (Figure 6b and c),one molecule is adsorbed over the five-membered ring,and the other over a six-membered ring,and each of the lithium atoms is located over a six-membered ring.For the H 2molecule adsorbed over the five-membered ring,the distance between the closer H atom to hub carbons is in the range of 3.13-3.24Å,while the H 2molecule over the six-membered ring is closer to the pair of hub carbon atoms in the center,with a distance in the range of ∼3.18Å.Two additional H 2molecules adsorbed on the concave side (Figure 6c)adsorb on lithium atoms;the shortest H -Li distance is ∼2.12Å,significantly shorter than the distance between H 2molecules (on the convex side)and carbon atoms.The difference between adsorption distances on the various sites suggests that the Li atoms are the most favorable sites for hydrogen adsorption,which is confirmed by the calculated binding energies.For H 2adsorbed on the convex side (Figure 6b),a binding energy of -0.92kcal/mol-H 2is obtained.On the basis of the similar geometry of these two adsorbed H 2molecules in Figure 6b and c,we assume that the binding energy of these two H 2molecules are the same in the two cases,thus we infer that a binding energy of -1.48kcal/mol-H 2corresponds to the interaction between H 2(on the concave side)and a lithium atom.The energetic difference clearly shows that Li atoms are the favorable adsorption sites for H 2molecules,suggesting a mechanism of enhanced hydrogen adsorption on lithium-atom-doped corannulene systems.Another important feature in the Li-doped complexes of corannulene is the increase of the dipole moment.DFT predicts values of 5.39and 3.86D,respectively,for Li 6-C 20H 10and Li 3-C 20H 10-C 2,whereas the MP2calculation yields 3.47D for the Li 2-C 20H 10complex.The presence of this enhanced dipole in the molecule induces a dipole moment in the H 2molecules,which is taken into account to define the effective force field (Section 2.2)for molecular dynamics simulations discussed in the next section.3.3.Adsorption at Finite Temperatures and Pressures.3.3.1.Arrangement of Adsorbent Molecules.To investigate the available space and collective effects on H 2adsorption,we assume that lithium-doped corannulene molecules arrange in a stack configuration.In this case,we can adjust the interlayer and intermolecular distances (as defined below),performing analyses similar to those reported by other researchers using carbon nanotube bundles and graphite nanofibers.30,44-46Each MD simulation cell contains 16lithium-atom-doped corannulene molecules,with eight molecules in each layer located at the bottom of the cell.In the MD simulations,the dynamics of the adsorbent molecules is not included,thus the adsorbent mol-ecules are kept fixed in their initial positions and their distribution in each layer is determined by two parameters,the interlayer distance,ILD,and the intermolecular distance,IMD.The ILD is defined as the distance between two overlapped molecules and the IMD is the separation between the centers of two parallel molecules,as shown in Figure 7.The values of IMD and ILD were determined from DFT calculations discussed in the nextsection.Figure 4.Potential energy surface of H 2approaching corannulene and lithium-doped corannulene at the level of B3LYP/6-311G(d,p);in each curve,H 2approaches corannulene at:(a)the center five-membered ring at the concave side,(b)the center five-membered ring at the convex side,(c)the center of a six-membered ring at the concave side,(d)the center of a six-membered ring at the convex side,(e)the top Li atom in Li 6-C 20H 10(see Figure 3),(f)the Li atom on the convex side in Li 3-C 20H 10-Li 2(see Figure2).Figure 5.Structures corresponding to the minima in the potential energy scans:(a)Li 6-C 20H 10,(b)Li 3-C 20H 10-Li 2.Figure 6.Optimized configurations of H 2adsorption on Li 2-C 20H 10,with MP2(FC)/6-31G(d):(a)Li 2-C 20H 10;(b)2H 2-(Li 2-C 20H 10);(c)4H 2-(Li 2-C 20H 10).Figure 7.Definition of interlayer distance (ILD)and intermolecular distance (IMD).Adsorption of Molecular H on Lithium-Doped Corannulene J.Phys.Chem.B,Vol.110,No.45,2006225373.3.2.Estimation of the IMD and ILD Parameters.DFT partial optimizations at the level of B3LYP/6-311G(d,p)are performed for the characterization of the ILD and IMD distances in dimers of Li 6-C 20H 10,as shown in Figure 7.To determine the optimum ILD value,only the z coordinates of the dimer are allowed to change,whereas only the x coordinates of the dimer are allowed to change to investigate the optimum IMD value.The results are 11.4Åfor the IMD and 6.5Åfor the ILD.In our MD simulations,the IMD is fixed to 11.0Åfor all the adsorbent systems,and additional values of ILD of 8.0and 10.0Åare used for a simple stack of two different lithium-doped corannulene systems.Such a system is chosen to investigate the potential H 2uptake capacity,assuming thatsubstitution of H with bulky alkyl function groups to the rim carbons or bridging of lithium-atom-doped corannulene mol-ecules might be used to increase the ILD.3.3.3.Hydrogen Adsorption on Lithium-Doped Corannulene.Figure 8shows the predicted H 2uptake at 273and 300K and various ILD for Li 6C 20H 10as a function of H 2pressure.Overall,the MD simulations predict:(1)at all the conditions studied,the H 2uptake is higher than 2wt %;(2)the H 2uptake at a given ILD and temperature is almost linear with the increase of pressure;(3)adsorption decreases as temperature increases;(4)increasing ILD while keeping the same T and P significantly increases the H 2uptake,and the change is especially notorious increasing the ILD from 8.0to 10.0Å.At the estimated equilibrium separation ILD of 6.5Å,the predicted H 2uptake values are 2.75-5.08wt %at 70and 225bar at 273K,whereas at 300K,the values are reduced to 2.38-4.58wt %at 75and 230bar,respectively (Figure 8).Thus,according to the projection,the H 2uptake at an ILD of 6.5Åwould reach 6.5wt %at 300K and 315bar.Parts c -f of Figure 8illustrate that the rate of increase of H 2uptake (i.e.,the slope of the lines in Figure 8)increases as the interlayer distance increases at the same conditions of temper-ature and pressure,yielding significantly enhanced uptake at higher pressures for higher ILD separations.This could be attributed to the distribution of hydrogen molecules between adsorbent molecules,as seen from radial distribution functions (RDFs)between C and H 2,shown in Figure 9.At an ILD of 6.5Å,a relatively sharp peak is observed at a distance between 3.5and 4.5Å,with a shoulder appearing at about 5Å.This fairly sharp peak indicates that the majority of the H 2molecules located between adsorbent molecules are dis-tributed in a relatively thin layer,possibly interacting with the Li atom on top,whereas the shoulder may correspond to the molecules in a second layer located in the intermolecular space.As the ILD increases to 8Å,a broader peak (Figure 9)covers a distance between 4.0and 7Å,which reveals the larger space accessible to hydrogen molecules and the thickening of the adsorption layer.These features are clearly illustrated in Figure 10.At an ILD of 10Å,two broad (overlapping)peaks are evident in Figure 9,centered in ∼4and ∼7Årespectively,corresponding to the formation of two adsorption layers of hydrogen molecules between adsorbent molecules.The formation of two adsorption layers might explain the large increase in H 2uptake when the ILD increases from 8to 10Å.Similar H 2distribution has been found in single-wall and double-wall carbon nanotubes,and especially in GNFs as the VDW gaps increase in these systems.44According toourFigure 8.Calculated hydrogen uptake capacity of Li 6-C 20H 10molecules assembled in stacks.(a)ILD )6.5Å,273K;(b)ILD )6.5Å,300K;(c)ILD )8Å,273K;(d)ILD )8Å,300K;(e)ILD )10Å,273K;(f)ILD )10Å,300K.Figure 9.Radial distribution function of pairs C -H 2for the adsorption of H 2in stacks of the Li 6-C 20H 10complex at 273K:(a)ILD )6.5Å,P )119bar,and H 2uptake of 3.63wt %;(b)ILD )8Å,P )118bar,and H 2uptake of 3.95wt %;(c)ILD )10Å,P )114bar,and H 2uptake of 4.61wt%.Figure 10.Snapshots of Li 6-C 20H 10systems of adsorbent layers with hydrogen adsorbed at ILD )8Å,300K,and 124bar.22538J.Phys.Chem.B,Vol.110,No.45,2006Zhang et al.。

High pressure adsorption of hydrogen,nitrogen,carbon dioxide and methane on the metal–organic framework HKUST-1J.Moellmer a ,A.Moeller a ,F.Dreisbach b ,R.Glaeser a ,c ,R.Staudt d ,⇑aInstitut für Nichtklassische Chemie e.V.,Permoserstr.15,D-04318Leipzig,Germany bRubotherm GmbH,Universitätsstr.142,D-44799Bochum,Germany cInstitute of Chemical Technology,University of Leipzig,Linnéstr.3,D-04103Leipzig,Germany dUniversity of Applied Sciences Offenburg,Badstraße 24,D-77652Offenburg,Germanya r t i c l e i n f o Article history:Received 20April 2010Received in revised form 30August 2010Accepted 19September 2010Available online 25September 2010Keywords:Surface excessAbsolute amount adsorbed High pressure MOFIsosteric heata b s t r a c tHigh pressure adsorption phenomena are discussed for different gases on HKUST-1(Cu 3(BTC)2,commer-cially available product Basolite TM C300).Sorption isotherms for hydrogen,nitrogen,methane and carbon dioxide on HKUST-1were measured in the temperature range of 273–343K and at pressures up to 50MPa.The calculated surface excess adsorption capacities for all four adsorptive are one of the highest reported in the literature for HKUST-1samples.All surface excess data were further calculated from the experimental data by using the helium buoyancy correction.A detailed description was given.Also a procedure to calculate the absolute amount adsorbed from the surface excess amount by using two different models is ing one model,the density and the volume of the adsorbed phase can be calculated.The density of the adsorbed phase q ads corresponds to the liquid density of the adsorptive at its boiling point q liq,BP .In case of hydrogen no excess maximum was found up to 50MPa,so that one model could not be applied.Finally,the isosteric heat of adsorption for each gas was calculated by using the Clausius–Clapeyron equation.Ó2010Elsevier Inc.All rights reserved.1.IntroductionA new group of porous materials was developed in the mid 90ties by Yaghi and co-workers [1–3],the so called metal–organic frameworks or coordination polymers.Such materials consist of metal atoms or metal/oxygen-cluster,which are connected by or-ganic linkers.Several linkers and also motifs have been described to form hundreds of different porous materials [4–9].One of the most important specimens of this class of materials is HKUST-1(also named Cu 3(BTC)2or,as a commercially available product,Basolite TM C300)[10–12].As already mentioned in the Refs.[10,11],HKUST-1consists of Cu–Cu-dimers which are connected by 1,3,5-tricarboxylate linkers to form a 3-dimensional network with micropores in a range of 0.7–0.9nm.Spectroscopic analysis of the commercially available HKUST-1prepared by electrochemical synthesis is given in Ref.[11].During the last decade,the well known material HKUST-1has been widely studied in adsorption processes and adsorptive sepa-rations by several groups.Among those,adsorption applications like purification and separation processes [11,13–17],gas storage,especially hydrogen storage under ambient or cryogenic tempera-tures [18–22]or gas capture in the presence of environmental applications or for vehicle industry [23,24]are of the main interest.To the best of our knowledge,only one recent publication by Senkovska and Kaskel [25]has dealt with high pressure adsorption data of gases (>15MPa at T =298K for methane)on HKUST-1at room temperature up to 20MPa.These authors have reported stor-age capacities for methane in synthetic HKUST-1-samples of about 15.7wt.%at 303K.Thus,we report for the first time high pressure (>20MPa)adsorption data for the MOF-type material HKUST-1.In this study,we measured the sorption capacities of HKUST-1(Basolite TM C300)for the supercritical gases hydrogen,nitrogen,methane and carbon dioxide in a temperature range of 303–343K and pressures up to 50MPa.However,the adsorption of a supercritical gas on a microporous solid up to high pressures has been widely studied [26–41].It is therefore known,that the adsorption isotherm of a supercritical fluid on a microporous material consists of a maximum in the sur-face excess amount at a certain pressure.The experimental surface excess amount should be the starting point for the calculation of the absolute amount adsorbed for an experimentally working sci-entist,because it is not possible to determine the absolute ad-sorbed quantities by experimental techniques.This is of interests,when experimental data have to be compared with results from simulation experiments,where the absolute amount adsorbed1387-1811/$-see front matter Ó2010Elsevier Inc.All rights reserved.doi:10.1016/j.micromeso.2010.09.013⇑Corresponding author.E-mail addresses:moeller@inc.uni-leipzig.de (A.Moeller),dreisbach@rubotherm.de (F.Dreisbach),staudt@inc.uni-leipzig.de ,Reiner.Staudt@fh-offenburg.de (R.Staudt).can be obtained.Therefore,modelsabsolute amount adsorbed from the face excess.The major aim of this work two different models for the calculation sorbed from the surface excess amount. models.On the one hand,we use the adsorbent to calculate the absolutethe other hand,a second model gives us sity of adsorbed phase[38,46–49].The were further compared to each other. can be used to characterize specific phase.Furthermore,the isosteric heat of (hydrogen,nitrogen,methane andusing the Clausius–Clapeyron equation of the isotherms.2.Materials and experimental2.1.MaterialsThe adsorbent HKUST-1was used in cially available material,Basolite TM Aldrich(US).For a more detailedalso Ref.[11].All used gases were obtained from Air Products(US)with variable purity(CO299.995%,N299.995%,CH499.5%,H299.995%and He 99.9992%).Finally,methanol was purchased from Fluka(Germany) with a purity of99.9%.2.2.Low pressure adsorption isotherms2.2.1.Nitrogen physisorption at77KNitrogen adsorption isotherms at77K on HKUST-1were ob-tained by using the commercially available volumetric sorption analyzer BELSORP-miniII from Bel Japan Inc.equipped with a high resolution pressure sensor.2.2.2.Methanol adsorption at298KMethanol adsorption measurements at298K were performed on a magnetic suspension balance(Rubotherm,Germany) equipped with a dosage system for methanol from the vapor phase. Details are shown in Fig.1.Highly accurate pressure transducers (MKS Baratron,US and Newport Omega,US)were used in a range from vacuum up to10kPa and from10kPa up to0.1MPa.Prior to the analysis,all samples were outgassed at423K for 12h under turbomolecular pump vacuum(<1Pa).2.3.High pressure gravimetric adsorption measurementsHigh pressure sorption isotherms of carbon dioxide,nitrogen, methane,hydrogen and helium were recorded in a magnetic sus-pension balance(Rubotherm,Germany[50])that can be operated up to50MPa.In Fig.1,a scheme of the balance including temper-ature and pressure sensors and various gas supplies(additionally, the dosage system for methanol)is shown.Various pressure trans-ducers(Newport Omega,US)were used in a range from vacuum up to50MPa with an accuracy of0.05%.In a typical experiment,a stainless steel sample holder was filled with about1g of HKUST-1and the balance was evacuated for12h at423K and0.3Pa until constant mass was achieved. For measuring the sorption capacity,the gas was dosed into the balance chamber to elevated pressures.Equilibrium was achieved within30min for each gas,which is characterized by constant weight and pressure.The temperature was kept constant with an accuracy of±0.5K for each measurement.Additionally,for each isotherm,a minimum of two measure-ments were carried out with a fresh sample.The high pressure adsorption isotherms presented in the following consist of the en-tirety of all measured values at elevated temperatures.For the determination of the density for all gases,the program FLUIDCAL was used[51–54].3.Results and discussion3.1.Determination of the specific pore volumeGenerally,the textural properties of nanoporous solids such as MOFs,can be investigated by physisorption experiments,e.g.,by nitrogen(77K)or argon(87K)sorption isotherms[42–45].Not only the specific surface area and the pore size distribution are of interest,but also the specific pore volume is an important param-eter,especially for the determination of the absolute amount ad-sorbed from the surface excess amount[45].A detailed analysis of such procedures can be found in Ref.[42]for an In-based MOF with soc topology(soc=square octahedral).In this study,the pore volume was calculated using the adsorp-tion isotherms of three different adsorptive in the temperature range of77–298K up to the saturation pressure P S of each gas.In Fig.2,the isotherms of nitrogen(77K,P S=0.097,152MPa),carbon dioxide(273K,P S=3.4851MPa)and methanol(298K, P S=0.016,981MPa)are shown.All isotherms are type-I isotherms according to the IUPAC classification[55].In the case of the carbon dioxide adsorption isotherm,the surface excess mass at higher pressures(P>0.1MPa)was converted into the absolute amount adsorbed using the procedure described in Ref.[42]and also in Section3.3.The Gurvitch rule(P/P0=0.95)was used to determine the spe-cific pore volume from the isotherms shown in Fig.2[43–45].In the case of nitrogen,the slope of the isotherm can be seen at lower relative pressures as in the case of carbon dioxide and methanol, respectively.Evidently,the interaction for carbon dioxide and methanol with the surface of the porous material is equal.This is Fig. 1.Scheme of a gravimetric magnetic suspension balance(Rubotherm, Germany)equipped with a dosage system of vapor(here for methanol)as an option.J.obvious from the identical slope of the isotherm for both gases in the same relative pressure region(0.001<P/P0<0.1).This is remarkable because carbon dioxide is nonpolar but has a quadru-pol moment and a high polarizability,while methanol is polar with a similar polarizability[56].However,the effective adsorption po-tential of the inner surface of HKUST-1to methanol and carbon dioxide is equal.The calculated specific pore volumes for nitrogen(V Pore= 0.71cm3gÀ1calculated with q N2=0.80,770cm3gÀ1)and methanol (V Pore=0.69cm3gÀ1calculated with q methanol=0.78,624cm3 gÀ1)are in good agreement with each other.However,the pore volume determined from the carbon dioxide high pressure adsorp-3À1sample volume by using the helium buoyancy correction is esti-mated in a wrong way.To avoid this effect,several measurements have to be carried out and compared to each other.Alternatively,a helium buoyancy correction at high temperature can be used,if the adsorbent(surface)at the higher temperature can be assumed to remain unchanged.Secondly,the density of helium is usually lower than the den-sity of the gas to be measured[58].The buoyancy effect is propor-tional to the density of the bulk phase of the adsorptive.The density of helium during buoyancy measurements is in most cases (not for hydrogen)several times lower than the density of other adsorptives,e.g.,Ar,Kr,Xe,N2,O2,CO2or CH4,at the same pres-sure.This behavior can be seen in Fig.3a,where the adsorption iso-therms for hydrogen,methane and nitrogen at303K and also the helium buoyancy measurement up to50MPa are plotted over their corresponding densities.For a buoyancy correction,the surface ex-cess of helium should have to be known over the whole density re-gime of the adsorptive,i.e.,up to q bulk,methane=0.3g cmÀ3for methane(corresponding pressure P0.3,helium=560MPa)and q bulk,nitrogen=0.4g cmÀ3for nitrogen(corresponding pressure P0.4,helium=1075MPa).Since the helium surface excess is known for lower densities only,a direct buoyancy correction is possible only for hydrogen(see Fig.3a).Herein,we used the so called reduced mass X,which wasfirstly described by Staudt et al.[59]in1993,for a better understanding of the buoyancy correction.The reduced mass can be considered as a direct experimental value and is a function of the sample mass, temperature,pressure/density and,of course,of the adsorption capacity[57].Here,the surface excess was obtained by using the reduced mass X corrected by the product of bulk density of thefluid q bulk and the specific adsorbent volume V HeAs(according to Eq.(1)),calcu-lated from helium measurements.m r¼Xþq bulk V He As;ð1ÞFig.2.Nitrogen(77K),carbon dioxide(273K)and methanol(298K)adsorptionisotherms on HKUST-1up to their corresponding saturation pressure.Fig.3a.Surface excess amount of nitrogen,methane,hydrogen and heliumadsorption at303K on HKUST-1as a function of density.Materials138(2011)140–148the surface excess amount for each gas in the above mentioned procedure.3.3.Density of the adsorbed phase and calculation of the absolute amount adsorbedAs already mentioned before,the surface excess mass is the quantity,which can be calculated in a simple way from the re-duced mass(Eq.(1)).However,also the absolute amount adsorbed is of interest.Here,we use two different ways to determine the absolute amount adsorbed from the surface excess data.First,the absolute amount adsorbed m ads can be described as:m ads¼m rþq bulk V ads;ð2Þwhere m r is the surface excess mass,q bulk is the density of the gas phase and V ads is the volume of the adsorbed phase[37,57].The volume of the adsorbed phase is unknown,but can easily be obtained as V ads=m ads/q ads,where q ads is the density of the ad-sorbed phase.Then,Eq.(2)becomes m r¼m adsð1Àq bulk=q adsÞ:ð3ÞWith the assumption,that the adsorbed phase is in a liquid-like state(q ads=q liq)[57],this expression can now be used to determine the absolute amount adsorbed at high pressures(P>0.1MPa),but only forfluids below their critical point.This was already used for the carbon dioxide adsorption isotherm at273K(shown before, see section3.1).Generally,Eq.(2)can also be used to describe the surface excess mass of a supercriticalfluid[26,57,60–62]by substitution of the adsorbed mass with m ads=V ads q ads.Then,Eq.(2)can be written in the following way:m r¼ðq adsÀq bulk V adsÞ:ð4ÞA similar approach was used by Poirier et al.[46].These authors used the Dubinin-Astakhov equation for the calculation of the ad-sorbed mass m ads.Nevertheless,the surface excess isotherm of a microporous material shows a maximum at the point,where the difference be-tween the density of the adsorbed phase q ads and the bulk phase q bulk is maximal[61,62].For higher pressures,the bulk phase ismore compressible than the adsorbed phase and the surface excess decreases.In the same way,the surface excess isotherm decreases as well.The surface excess isotherm at high pressures is mainly influenced by the equation of state of the adsorptive and after the maximum an inflection point of such isotherms(surface excess plotted against pressure and density)is evident[26,27,35].The location of this inflection point depends on the adsorbate/adsor-bent interaction and also on the thermodynamic state of the adsorptive.This can be nicely seen in the high pressure adsorption isotherms reported in Refs.[26,32,35].In this study,the surface excess isotherms of carbon dioxide(T/ T C=1.01(308K),T/T C=1.03(313K),T/T C=1.08(328K),T/T C=1.13 (343K)),methane(T/T C=1.59(303K),T/T C=1.67(318K),T/T C= 1.754(333K))and nitrogen(T/T C=2.40(303K),T/T C=2.52 (318K),T/T C=2.64(333K))show a maximum below50MPa.Here, wefit the experimental surface excess masses against the density of carbon dioxide,methane and nitrogen in the linear range after the maximum of the surface excess by using Eq.(4).In an optimal procedure,thefirst derivative at the inflection point of the surface excess(surface excess plotted against the density)has to befitted. From thisfit,the adsorbed volume V ads and the density of the ad-sorbed phase q ads can be easily obtained.In Table2,all data from thefitting procedure are summarized.Additionally,thefit param-eters of Eq(40,for carbon dioxide,methane and nitrogen data,can also be taken from Figs.4a,4b and4c,respectively.The estimated values of the density of the adsorbed phase,i.e., the intersection of thefit curve with the x-axis,for methane (q ads=0.44–0.45g cmÀ3)are in the range of its liquid density at its boiling point q liq,BP(q liq,BP=0.4226g cmÀ3).According to its phase diagram[51]it is not possible to specify the liquid density at its boiling point for carbon dioxide.Here,the liquid density be-tween its triple point(T p=216.6K)and its critical point (T C=304.1K)was calculated to q liq,Tp=1.18g cmÀ3and q liq,T c=0.54g cmÀ3[51].Nevertheless,an adsorbed density of q ads=1.07–1.08g cmÀ3was calculated by using Eq.(4)for carbon dioxide,which is within its liquid density regime and insignificant lower than the liquid density at its triple point.This indicates strongly the consistency of the model for methane and carbon dioxide and makes also clear that at50MPa(methane)and 30MPa(carbon dioxide)the inflection point of the surface excess isotherm(plotted against the density)is already achieved.However,for nitrogen(q ads=1.16–1.17g cmÀ3)the calculated density of the adsorbed phase is somewhat higher than the liquid density at its boiling point(q liq,BP=0.8085g cmÀ3for nitrogen). The higher values of the density of the adsorbed phase for nitrogenMaterials138(2011)140–148143(estimated byfitting the linear part of the isotherm above the max-imum)indicate,that up to50MPa the inflection point for the sur-face excess isotherm of nitrogen is not achieved(see Fig.4c Consequently,the calculated densities of the adsorbed phase for nitrogen are30%higher than the liquid density at its boiling.Be-cause of that,measurements of nitrogen above50MPa are highly desired.In case of adsorbed carbon dioxide and methane,the calculated adsorbed volume(V ads=0.60–0.75cm3gÀ1for carbon dioxide andads =0.38–0.44cm3gÀ1for methane,respectively)are much high-Table2Carbon dioxide,methane and nitrogen data obtained from surface excess using the Fit with equation4(Details can be also found in Fig.5a and5b).Specific Volume of the adsorbed phase bV ads/(cm3gÀ1)Porefilling factor bV ads/V PoreDensity of the adsorbedphase q ads/(g cmÀ3)Reduced density of theadsorbed phase q ads/q critReducedtemperature T/T critCO2(308K)0.750.95 1.07 2.29 1.01 CO2(313K)0.720.91 1.08 2.31 1.03 CO2(328K)0.670.85 1.07 2.29 1.08 CO2(343K)0.600.76 1.07 2.29 1.13CH4(303K)0.440.630.44 2.71 1.59 CH4(318K)0.410.590.44 2.71 1.67 CH4(333K)0.380.540.45 2.77 1.75Fig.4b.Methane adsorption isotherms in temperature range303–333K on HKUST-Each isotherm wasfitted in the linear range above the maximum of the surface excess with Eq.(4).Fig.4c.Nitrogen adsorption isotherms in temperature range303–333K on HKUST-Each isotherm wasfitted in the linear range above the maximum of the surface excess with Eq.(4).144J.Moellmer et al./Microporous and Mesoporous Materials138(2011)140–148V Pore=0.79cm3gÀ1from carbon dioxide adsorption isotherm at 273K)for carbon dioxide,0.54–0.63for methane and0.26–0.31 for nitrogen were observed.The porefilling factor for carbon diox-ide at308K is near1,because carbon dioxide is only slightly above its critical temperature.The pore volume V P for HKUST-1was cal-culated using the Gurvitch rule(see Section3.1)by using the car-bon dioxide adsorption isotherm at273K.This value of the pore volume V P=0.79cmÀ3gÀ1is the starting value of the adsorbed vol-ume of a supercriticalfluid.With increasing temperature,the cal-culated adsorbed volume decreases,because of the increasing adsorbate–adsorbate interactions.This means also,that in the sat-uration regime of an isotherm,a supercriticalfluidfills the whole micropore volume of the adsorbent,but the estimated values of the pore volume and therefore the porefilling factor seem to be a function of temperature,according to the higher adsorbate–adsorbate interactions.Furthermore,the higher porefilling factors for methane are also due to the fact that methane is near its bulk critical temperature as it is for nitrogen.In case of hydrogen no maximum can be observed up to an adsorptive density of0.03g cmÀ3(and pressures up to50MPa). This can be seen in Fig.4d,while carbon dioxide,methane and nitrogen exhibit a maximum,which are shown in Figs.4a,4b and4c,respectively.This is also due to the fact,that at tempera-tures of303K to333K,hydrogen is far above its critical tempera-ture(T/T C=9.13(303K);T/T C=9.58(318K);T/T C=10.03(333K)). Thus,at these temperatures,a maximum could not be observed until50MPa and it is not possible to calculate the absolute amount adsorbed using Eq.(4).Poirier et al.[47–49]discussed high pres-sure hydrogen adsorption isotherms at lower reduced tempera-tures(between35K(T/T C=1.05)and100K(T/T C=3.01))in the context of adsorbed phase densities of hydrogen on different MOF materials.For all materials,no maximum was found at tem-peratures higher than100K and pressures up to8MPa.By using a modified Dubinin-Astakhov approach,they showed for different in its saturation regime of the isotherm can be assumed to be that of a liquid-like state.With the approach given by Eq.(4),the absolute amount ad-sorbed for hydrogen was calculated by using the liquid density at its boiling point to specify the density of the adsorbed phase.Thus, the adsorbed volume for hydrogen at each temperature was calcu-lated by using the liquid density and by extrapolating the methane data.These data can also be found in supplementary Table2.By adopting the volume of the adsorbed phase,the absolute amount adsorbed was then ing Eq.(4)(model1),the linear range after the maximum of the surface excess mass against the density was shifted into the saturation regime.It is thus clear,that with this approach the lowest value of the absolute amount ad-sorbed can be calculated.Further,a second model was used to calculate the absolute amount adsorbed.By using Eq.(2)and by adopting the specific pore volume(which was obtained from the N2/77K and metha-nol/298K adsorption isotherm to give V Pore=0.7cm3gÀ1),as the volume of the adsorbate(Section3.1).Here,we assume that the to-tal pore volume isfilled with adsorbate.By applying this approach, the resulting absolute amount adsorbed can be understood as the maximum adsorption capacity(total adsorbed amount)or as an overall limiting value.All results,for both models are shown in Figs.5a,5b,5c and5d,respectively,where the absolute amount ad-sorbed are plotted against the pressure.Allfits were done by using the Padèequation.A detailed description of the model can be found in the supplementary datafile.3.4.Determination of the isosteric heat of adsorptionFor all industrial adsorption processes,information about the temperature dependency of adsorption isotherms is necessary. From this dependency,the isosteric heat of adsorption can be cal-Fig.4d.Hydrogen adsorption isotherms in temperature range303–333K onHKUST-1.No surface excess maximum could be obtained until50MPa.J.Moellmer et al./Microporous and Mesoporous Materials138(2011)140–148145range between303and333K using Eq.(4)and V ads)for calculation of the isosteric heat of adsorption.In Fig.6,all estimated values forthe isosteric heat of adsorption are shown as a function of loading. Additionally,the calculated values for all gases are constant over a wide range of loadings(up to10mmol gÀ1),but decrease slightly in case of carbon dioxide and methane.At higher loading the adsorbate–adsorbate interactions become more important and thus,the isosteric heat of adsorption has to increase rapidly.How-ever,up to10mmol gÀ1the maximum adsorption capacities for carbon dioxide,methane and nitrogen are not observed,and no in-crease is found up to10mmol gÀ1.Nevertheless,all calculated isosteric heats of adsorption at zero coverage are higher than the corresponding values of the heat of vaporization of each adsorptive.For carbon dioxide a value of ca.29.2kJ molÀ1at zero loading was determined.This is lower than the value given by Wang et al.[16](ca.35kJ molÀ1)calculated from experimental sorption isosteres for carbon dioxide on HKUST-1samples.Also,a high affinity for methane on HKUST-1was observed.A value of ca.20.7kJ molÀ1at zero loading indicates strong binding between thefluid molecules and the surface area of HKUST-1.Both values, for carbon dioxide and methane,are higher than for several com-mercially activated carbons(16–25kJ molÀ1for carbon dioxide at zero loading and16–20kJ molÀ1for methane at zero loading, respectively)[65].However,not only adsorption measurements can be used to determine the isosteric heats,but indeed also grand canonical Monte Carlo simulations(GCMC)methods are useful for estimation of the heat of adsorption.Walton et al.[66]calculated the isosteric heat for several gases such as carbon monoxide,hydrogen(ca.6.3kJ molÀ1),methane(ca.18.7kJ molÀ1)and nitrogen(ca.13.0kJ molÀ1)on HKUST-1at zero loading at298K.These data are consistent with the calculated values in this study.Further-more,the values of the isosteric heat of adsorption for HKUST-1 are higher than for zeolite–imidazolate frameworks, e.g.ZIF-8, ZIF-69or ZIF-76,and also for MOF-5[70,71]and an In-based Fig.5d.Hydrogen adsorption isotherms in temperature range303–333K HKUST-1(Surface excess vs.absolute amount adsorbed using two different models, plotted lines arefits with Padèequation).soc-MOF[42].The values of the isosteric heat of adsorption ob-tained in this study are shown in Fig.6.Additionally,a detailed comparison with values from other materials could be found in Table3.4.ConclusionPure gas adsorption data of nitrogen,hydrogen,carbon dioxide and methane on the commercially available metal–organic frame-work HKUST-1(Basolite TM C300)were measured at temperatures between303and343K and pressures up to50MPa by using the gravimetric method.Textural informations were obtained from adsorption isotherms of several adsorptives at different tempera-tures and pressures,e.g.,nitrogen adsorption at77K and carbon dioxide adsorption at273K.A detailed description of the effect of buoyancy for high pres-sure data correction was given.The approach was then used to cal-culate the surface excess mass from the experimental data,the reduced mass.The absolute amount adsorbed,given by extrapola-tion of the surface excess isotherm in the linear range after the maximum,can be seen as the lowest limit for the absolute amount adsorbed.From this model,information about the adsorbed vol-ume was received,which was then also used to determine the absolute amount adsorbed.The calculated adsorbed volumes of carbon dioxide,methane and nitrogen decrease with increasing temperature.This is due to the fact,that at higher temperature an increase of adsorbate–adsorbate interactions can be assumed. Another important aspect is the calculation of the density of the adsorbed phase using this model.For carbon dioxide and methane, densities of 1.07–1.08g cmÀ3and0.44g cmÀ3were calculated, which corresponds to the assumption that the adsorbedfluid is in a liquid-like state.In a second model the specific pore volume from nitrogen mea-surement at77K and methanol adsorption at298K (V Pore=0.7cm3gÀ1)was used for calculation of the absolute ad-sorbed amount.The obtained values can be understood as the overall or total adsorption capacities.In summary,both concepts show the lowest and the highest value of the absolute amount adsorbed.Additionally,the isosteric heat of adsorption for hydrogen (6.9kJ molÀ1),nitrogen(12.8kJ molÀ1),methane(20.5kJ molÀ1) and carbon dioxide(33.9kJ molÀ1)was calculated using the Padèequation and applying the Clausius–Clapeyron equation up to its saturation regime of the isotherms.The obtained values are in good agreement with data from the literature calculated by using experimental data and as well for simulation data. AcknowledgementThe authors thank the‘‘Deutsche Forschungsgemeinschaft”DFG-project SPP1362MOF(STA428/17-1)forfinancial support. Appendix A.Supplementary dataSupplementary data associated with this article can be found,in the online version,at doi:10.1016/j.micromeso.2010.09.013. 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不对称自由基反应英文Asymmetric Radical Reactions: An Insight into Their Mechanism and Applications.Introduction.Asymmetric radical reactions have emerged as a powerful tool in organic synthesis, enabling the synthesis of chiral compounds with high enantiomeric purity. These reactions differ significantly from their symmetric counterparts, as they involve the generation and utilization of chiral radicals. These chiral radicals can undergo a range of reactions, including substitution, addition, and cyclization, leading to the formation of enantiomerically enriched products.Mechanism of Asymmetric Radical Reactions.The mechanism of asymmetric radical reactions typically involves three key steps: radical generation, chiralitytransfer, and radical termination.Radical Generation.The first step involves the generation of a radical species. This can be achieved through various methods, such as photolysis, thermal decomposition, or redox reactions. The generated radical can be chiral or achiral, depending on the starting materials and the conditions used.Chirality Transfer.The second step involves the transfer of chirality from a chiral auxiliary or catalyst to the radical species. This chirality transfer can occur through covalent or non-covalent interactions between the catalyst/auxiliary and the radical. The nature of these interactions determines the stereoselectivity of the reaction.Radical Termination.The final step involves the termination of the radicalspecies, leading to the formation of the desired product. This termination can occur through various mechanisms, such as coupling with another radical species, hydrogen atom abstraction, or disproportionation.Applications of Asymmetric Radical Reactions.Asymmetric radical reactions have found widespread applications in various fields of organic synthesis, including the synthesis of natural products, pharmaceuticals, and functional materials.Synthesis of Natural Products.Natural products often possess complex chiral structures, making their synthesis challenging. Asymmetric radical reactions have proven to be effective tools for the synthesis of such chiral natural products. For example, the use of chiral radicals generated from appropriate precursors has enabled the enantioselective synthesis of alkaloids, terpenes, and amino acids.Pharmaceutical Applications.The enantiomers of chiral drugs often differ significantly in their biological activities, making it crucial to control their enantiomeric purity. Asymmetric radical reactions can be used to synthesize enantiomerically enriched chiral drugs with high selectivity. This approach has been successfully applied to the synthesis of various drugs, including anti-inflammatory agents, anticancer agents, and antiviral agents.Functional Materials.Chiral materials possess unique physical and chemical properties that make them useful in various applications, such as displays, sensors, and catalysts. Asymmetricradical reactions can be used to synthesize chiral building blocks for the preparation of such materials. For instance, chiral polymers can be synthesized by utilizing asymmetric radical polymerization reactions, leading to the formation of materials with controlled chirality and tailored properties.Conclusion.Asymmetric radical reactions have emerged as powerful tools for the synthesis of enantiomerically enriched chiral compounds. Their unique mechanism, involving chirality transfer from a chiral catalyst/auxiliary to the radical species, enables high selectivity and enantiopurity in the product. The widespread applications of asymmetric radical reactions in organic synthesis, particularly in the synthesis of natural products, pharmaceuticals, and functional materials, highlight their importance in modern chemistry.Future Perspectives.Despite the significant progress made in the field of asymmetric radical reactions, there are still numerous challenges and opportunities for further exploration.Improving Selectivity and Efficiency.One of the key challenges in asymmetric radical reactions is achieving high selectivity and efficiency. While significant progress has been made in this area, there is still room for improvement. Future research could focus on developing new chiral catalysts/auxiliaries that can promote asymmetric radical reactions with higher selectivity and efficiency.Expanding the Scope of Reactions.Currently, the scope of asymmetric radical reactions is limited by the availability of suitable precursors and the reactivity of the generated radicals. Future research could aim to expand the scope of these reactions by developing new methods for generating radicals with desired functionalities and reactivities.Applications in Sustainable Chemistry.In the context of sustainable chemistry, asymmetric radical reactions offer an attractive alternative to traditional synthetic methods. By utilizing renewableresources and mild reaction conditions, asymmetric radical reactions could contribute to the development of more sustainable synthetic routes for the preparation of chiral compounds.Integration with Other Techniques.The integration of asymmetric radical reactions with other techniques, such as photocatalysis, electrochemistry, and microfluidics, could lead to the development of new and innovative synthetic methods. By combining the advantages of these techniques, it may be possible to achieve even higher selectivity, efficiency, and scalability in asymmetric radical reactions.In conclusion, asymmetric radical reactions have emerged as powerful tools for the synthesis of enantiomerically enriched chiral compounds. While significant progress has been made in this area, there are still numerous opportunities for further exploration and development. Future research in this field could lead tothe discovery of new and innovative synthetic methods with improved selectivity, efficiency, and sustainability.。

生物技术进展 2024 年 第 14 卷 第 1 期 102 ~ 110Current Biotechnology ISSN 2095‑2341进展评述Reviews氢气在医学领域的应用进展刘星宇 ， 赵国利 ， 李雪婧中石化（大连）石油化工研究院有限公司，辽宁 大连 116045摘 要：氢气在能源领域的优势已日渐凸显，其在医学领域同样是一种清洁、高效、经济的治疗手段。

氢医学领域主要包括氢气对疾病的基础研究和临床研究，如氢气的使用方法、剂量、对健康的促进作用、对疾病的治疗效果以及作用机理等。

氢分子可以清除羟基自由基和过氧亚硝酸盐，对氧化应激和炎症相关疾病具有显著的治疗效果，同时其作为一种内源性气体，无毒无害，对人体不会造成不良反应。

通过直接摄入和控制释放等方式，可以实现对脑和神经系统疾病、心血管疾病、糖尿病和癌症等疾病的靶向治疗。

介绍了释放氢气的不同方式及其在医学领域的研究进展，并对氢医学的科学和实践问题进行了展望，以期为氢气在生物医学领域的应用研究提供参考。

关键词：氢气；纳米材料；抗氧化；抗炎DOI ：10.19586/j.2095⁃2341.2023.0097 中图分类号：Q41， R318 文献标志码：AApplication Progress of Hydrogen in Medical FieldLIU Xingyu ， ZHAO Guoli ， LI XuejingSINOPEC （Dalian ） Research Institute of Petroleum and Petrochemical Co. Ltd.， Liaoning Dalian 116045， ChinaAbstract ：Hydrogen has attracted a lot of attention in energy field ， at the same time ， it is also a clean ， efficient and economical technology in medical field . The field of hydrogen medicine mainly includes basic and clinical research on the effects of hydro⁃gen on diseases ， such as the usage methods ， dosage ， health promoting effects ， therapeutic effects on diseases ， and mechanisms of action of hydrogen. Hydrogen can remove hydroxyl radicals and peroxynitrites ，which have significant therapeutic effect for oxi⁃dative stress and inflammation related diseases. At the same time ， as an endogenous gas ， it is non -toxic and harmless ， and will not cause adverse reactions to human body. Targeted treatment of brain and nervous system diseases ， cardiovascular diseases ， di⁃abetes ， cancer and other diseases can be achieved through direct intake and controlled release. The article introduced the differ⁃ent ways of releasing hydrogen gas and its applications in the medical field ， and looked forward to the scientific and practical is⁃sues of hydrogen medicine ， in order to provide reference for the application research of hydrogen in the biomedical field.Key words ：hydrogen ； nanoparticles ； antioxidant ； anti -inflammatory通常观点认为氢气是一种生物惰性分子。

空分分子筛工作流程英文回答：Working Process of Zeolite Molecular Sieve.Zeolite molecular sieve is a highly efficient material used for adsorption and separation in various industries. Its working process involves several steps, starting from the preparation of the zeolite material to the final application in different processes.Firstly, the raw materials required for zeolite synthesis are gathered. These materials typically include silica, alumina, and various alkali metals. The specific composition may vary depending on the desired properties of the molecular sieve. These raw materials are mixed together in a specific ratio and then subjected to a hydrothermal treatment. This treatment involves heating the mixture in an autoclave at a high temperature and pressure for a certain period of time. The hydrothermal treatment promotesthe formation of the desired zeolite structure.Once the zeolite material is synthesized, it is then subjected to a series of post-synthesis treatments. These treatments are aimed at modifying the properties of the zeolite to suit specific applications. For example, the zeolite may undergo ion exchange to replace the alkali metal ions with other cations, such as hydrogen or metal ions. This ion exchange process helps in enhancing the selectivity and adsorption capacity of the molecular sieve.After the post-synthesis treatments, the zeolite molecular sieve is typically activated by calcination. Calcination involves heating the zeolite at a high temperature to remove any residual organic species and water molecules. This step is crucial to ensure thestability and effectiveness of the molecular sieve during its application.Once the zeolite molecular sieve is activated, it can be utilized in various industrial processes. One of the most common applications is in the field of gas separation.The zeolite material can selectively adsorb certain gas molecules, allowing for the separation of different components in a gas mixture. For example, in the petrochemical industry, zeolite molecular sieves are used to separate and purify hydrocarbon gases.Another important application of zeolite molecular sieves is in catalysis. The unique structure of zeolites provides a large surface area and a well-defined pore structure, which makes them excellent catalysts for various chemical reactions. For instance, zeolite catalysts are widely used in the petroleum refining industry for processes such as cracking and isomerization.In conclusion, the working process of zeolite molecular sieve involves the synthesis of the zeolite material, post-synthesis treatments, activation, and application in various industrial processes. Each step is crucial in determining the properties and effectiveness of the molecular sieve. Through its adsorption and separation capabilities, zeolite molecular sieves play a vital role in numerous industries.中文回答：沸石分子筛的工作流程。

摘要摘要氢气作为一种极其重要的能源物质，被广泛应用于化工、航天、医药、交通等各个领域。

由于氢气的易燃易爆性质，一种快速、可靠的氢气传感器就显得十分必要，本论文重点研究了钯基氢气传感器的敏感机理，提出了一种钯纳米粒子吸氢模型，并且基于“裂结”原理推导了氢气传感器响应时间与钯纳米点体积的相关关系，得出了氢气传感器响应时间与钯纳米点体积或者是体积的平方根成正比的结论，并使用matlab计算模拟了二者之间的关系。

随后，基于“裂结”原理制作了相应的氢气传感器，测试了氢气传感器的性能，并结合理论研究基础进行了实验结果的分析。

本工作对快速响应纳米钯基氢气传感器的制备提供了有力的理论依据，具有重要的研究意义。

关键词：氢气传感器，“裂结”原理，响应时间，钯纳米点IABSTRACTABSTRACTHydrogen is widely used in chemistry, aerospace, medical, transportation and other fields as an extremely important energy source. Because hydrogen is very flammable and explosive, a fast and reliable hydrogen sensor is very necessary. In this work, we focus on studying the sensitive mechanism of palladium-based hydrogen sensors and build the model of palladium nanodots with hydrogen absorption. The correlation between the response time of the hydrogen sensor and the volume of palladium nanodots based on the principle of “Break junction” was achieved. We concluded that the value of response time is proportional to the volume (or the square of the volume) of palladium nanodots. In addition, Matlab is used to calculate and simulate this relationship.Subsequently, we made the hydrogen sensor based on the principle of “Break junction”and tested its performance. Finally, we analyzed the experiment results combined with basic theory research. This work provides solid theoretical of fast response nano-palladium based hydrogen sensors and has important significance. Key words: hydrogen sensors, “Break junction”, response time, palladium nanodotsII目录摘要 (I)ABSTRACT (II)目录 (III)第1章引言 (1)第2章氢气传感器的研究进程 (3)2.1 氢气传感器的研究背景 (3)2.2 钯金属中的氢气 (4)2.3 钯纳米结构的制备技术 (7)2.4 钯纳米材料在氢气传感器中的应用 (9)第3章钯纳米粒子中电子传输性质的研究 (12)3.1 金属Pb纳米粒子阵列薄膜不同状态与其电阻的研究 (12)3.1.1 钯金属纳米粒子的金属态 (12)3.1.2 钯金属纳米粒子的量子传导态 (13)3.1.3 钯金属纳米粒子的绝缘态 (14)3.2 钯金属纳米粒子薄膜体系的电子传输性质研究 (14)3.2.1 隧穿模型 (14)3.2.2 ES模型 (17)3.2.3 变程跳跃模型 (18)第4章钯基氢气传感器的响应机理 (22)4.1 钯纳米粒子吸氢机理研究 (22)4.1.1 表面化学吸附 (23)4.1.2 表层渗透 (24)4.2 经典力学理论研究 (28)4.2.1 膨胀动力学理论研究基础 (28)4.2.2 钯的膨胀动力学研究 (30)4.3 Matlab软件计算和讨论 (34)4.3.1 Matlab简介 (34)4.3.2 钯纳米粒子吸氢机理计算与讨论 (36)III4.3.3 响应时间与钯纳米粒子体积大小关系计算 (38)第5章基于性能测试的敏感机理研究 (41)5.1 钯基氢气传感器的制作与测试 (41)5.2 钯基氢气传感器的性能以及敏感机理分析 (43)第6章结束语 (44)6.1 工作归纳总结 (44)6.2 工作展望 (44)参考文献 (45)外文资料原文 (51)外文资料译文 (58)IV第1章引言第1章引言氢气作为最重要的还原气体被广泛应用在化工、航空、医药、石化、交通和能源等各个领域[1-6]。

第28卷第6期2012年12月哈尔滨商业大学学报（自然科学版）Journal of Harbin University of Commerce （Natural Sciences Edition ）Vol．28No．6Dec．2012收稿日期：2012－03－15．作者简介：王少逸（1987－），男，硕士，研究方向：环境影响评价．通讯作者：孟宪林（1961－），男，博士，副教授，研究方向：环境影响评价教学与研究．粉末状活性炭对腐殖酸的吸附研究王少逸，孟宪林（哈尔滨工业大学市政环境工程学院，哈尔滨150090）摘要：通过配制原始炭质量浓度在2．2 2．5mg /L 的Aldrich 腐殖酸（AHA ）溶液，采用活性炭用量阶（1 400mg /L ）进行了吸附试验，实验结果表明，从等温吸附线的拟合结果来看，可以发现两个具有不同斜率的直线区域．这两条线可能代表着以下两类物质，即具有最高亲和力的腐殖酸与具有亲和力较弱的腐殖酸或吸附能力更弱的黄腐酸．前者代表的有机物就是在对微污染物进行吸附处理过程中实际与其产生竞争作用的部分，在采用吸附法处理农药残留物时应给予高度关注．关键词：粉末活性炭；吸附平衡；腐殖酸中图分类号：X703文献标识码：A文章编号：1672－0946（2012）06－0653－04Study on humic acid adsorption by activated carbon powderWANG Shao-yi ，MENG Xian-lin（School of Municipal and Environmental Engineering ，HarbinInstitute of Technology ，Harbin 150090，China ）Abstract ：The adsorption study deals with the adsorption isotherms obtained from solutions of aldrich humic acid （AHA ）with initial carbon concentration between 2．2and 2．5mg /L．For each experiment ，a wide range of masses of activated carbon was selected （1 400mg /L ）．By the application of several models of isothermal equilibrium ，it appeared two straight lines of different slopes．The two lines are probably correspond ，on one hand ，to the adsorp-tion of humic acids with the highest affinity ，and on the other hand ，to the adsorption of hu-mic or fulvic acids with weaker adsorption capacity．The former organic fraction is one that is actually competing during adsorption of micropollutants．Great attention should be paid on these fractions when using adsorption treatment to control pesticide residues．Key words ：activated carbon powder ；adsorption equilibrium ；humic acid农药在使用过程中会不可避免地出现在水资源领域中，这种非正常的存在给水处理工作者提出了一个重要问题．为了对这些污染物进行处理，目前已经开发出多种不同类型的方法［1－3］，包括完全转化型的方法（氧化或生物处理）、非转化型或称为回收型的方法（活性炭或沸石的吸收或吸附，膜处理过程）．迄今为止，以上各处理方法中，在给水处理部门最常实际采用的是吸附处理过程法．从相关研究报告中可以看出，相比于对诸如某种杀虫剂等特异性有机污染物的吸附研究［4－7］，对于自然有机物质方面的吸附进行的研究明显较少．由于有机物质无时无刻不出现在地表水中，而且其含量又比农药大得多，所以在吸附处理过程中，有机物质将不可避免的与后者进行着竞争作用．因此，我们有必要对有机物吸附等温线的相关参数进行了解，并通过这些有机物吸附等温线发现某些假想中的组分［8］，这些组分可能就是真正与某些农药污染物进行竞争的部分［9］．本文借助于碳测量仪器与紫外吸收测量仪器等不同的分析工具，对粉末状活性炭（PAC）对有机物质的吸附平衡进行了人系统研究．1实验内容1．1试剂本实验所用的有机试剂为ALDRICH腐殖酸—AHA．这种有机物表现为具有聚合物和多官能团性质的复杂结构，主要显酸性．根据MONTEIL－RIVERA等人的相关研究［10］，这种腐殖酸的特性类似于从土壤和煤炭中提取的腐殖质的性质，具体内容见表1．表1ALDRICH腐殖酸和从土壤中提取的腐殖酸特性比较表（取自国际腐殖质协会）样品元素组成C H O N S含水量/%总酸度/（mmol·g－1）羧基/（mmol·g－1）酚/（mmol·g－1）羧基/%SAldrich腐殖酸54．744．3836．250．833．8011．36．5ʃ0．24．2ʃ0．12．3ʃ0．39．2从土壤中提取的腐殖酸54．244．0036．074．020．4910．45．9ʃ0．23．6ʃ0．12．3ʃ0．38．0实验中使用的活性炭为NORIT SA/UF粉末状活性炭．其主要特性见表2．表2NORIT SA/UF粉末状活性炭的一般特性（数据由生产商提供）生产商使用商标来源商品形式表观密度/（g·cm－3）比表面积/（m2·g－1）NORIT SA/U F或R O W0．8SU PR A泥炭颗粒0．5331153平均颗粒直径/mm有效尺寸/mm均匀性系数空隙直径（ ）微孔隙体积（＜2nm）中孔隙体积（2 50nm）1．17（1．16）0．87（0．81）1．44（1．44）6．60．5370．537本文使用的粉末状活性炭，先由商品级活性炭（颗粒大小低于50μm）经过研磨和过筛，然后经过超纯水清洗，在100ħ的温度下烘干24h而制成的．1．2实验方法实验使用的ALDRICH腐殖酸（AHA）溶液在MilliQ系统生成的反渗透水（3 10mΩ/cm，TOC=0．1 0．12mg/L）中制备，其目的是避免与其他有机物质产生吸附竞争作用．然后，该溶液由磷酸钠盐（NaH2PO4和Na2HPO4）进行缓冲，缓冲后最终离子强度为1．75．10－3mol/L．溶液的最终pH值调整至7．5 7．8．为了绘制吸附等温线，将不同质量浓度（1 400mg/L）的粉末状活性炭（Norit SA/UF）加入AHA缓冲溶液（DOC质量浓度介于2．1 2．5mg/L 之间）．在配制溶液的过程中，我们根据粉末状活性炭添加量的不同使用了0．250、1、5、10、20、50L的反应瓶．随后进行的第一次取样是为了估计有机物的初始浓度，然后，将计算好不同质量的粉末状活性炭分别加入反应瓶．搅拌过程通过磁力搅拌或机械搅拌进行，保证避光条件，将环境温度恒定在（20ʃ1）ħ．反应接触时间经过确认选择为24h，这一时间长度足以实现完全的反应平衡．试样在提取后通过0．45μm的玻璃纤维膜进行过滤，以保证能够精确测定平衡时的AHA质量浓度．而且，该滤膜事先经过彻底清洗，以防止由新膜造成的DOC测量损失而干扰测定．2结果与讨论2．1溶液状态下SA/UF粉末状活性炭（PAC）对ALDRICH腐殖酸（AHA）吸附平衡研究Aldrich腐殖酸（AHA）全幅度吸附等温线（ms 为1 400mg/L）实验结果通过Freundlich方程和Langmuir方程进行线性化，结果如图1、2所示．通过图1、2可以观察出，采用DOC的测量方法进行的拟合效果不如采用UV254吸收量的测量结果进行的拟合效果，拟合的结果表明符合Freundli-ch的等温吸附线．同时还可以看出：Freundlich模型中存在两个不同的区域：较宽的线性区域与狭窄的区域（对应着Ce的高值即ms的低值）．为此，研究中对这不同ms值（高值和低值）进行了进一步的研究．·456·哈尔滨商业大学学报（自然科学版）第28卷2．2高质量浓度粉末状活性炭（PAC ）吸附Aldrich 腐殖酸（AHA ）的吸附等温线本文采用了高质量浓度粉末状活性炭（PAC （m s 为40 250mg /L ）进行了Aldrich 腐殖酸（AHA ）的吸附等温线的研究．实验数据通过由Freundlich 吸附等温线进行拟合，其结果如图3所示．图3高质量浓度SA /UF PAC 吸附AHA 的Freundlich 形式吸附等温线（m s =40 250mg /L ）对于低质量浓度AHA 溶液状态的吸附平衡（ 0．01UA /L ＜C e （UV ）＜ 0．08UA /L ），我们可以根据Freundlich 吸附等温线得到一条直线．K F 和n 的值如表3所示．表3SA /UF PAC 吸附AHA 的Freundlich 吸附参数（m s =40 250mg /L ）K F n r 216．980．610．952．3低质量浓度粉末状活性炭（PAC ）吸附Aldrich 腐殖酸（AHA ）的吸附等温线在这一部分的研究中，我们将着重关注上述对应于C e 的高值也就是m s 的低值（m s 为1 6mg /L ）的狭窄区域．实验结果由Freundlich 吸附等温线拟合的结果如图4所示．K F 和n 的值如表4所示．K F ，1和n 1：较强吸附部分的Freundlich 常数；K F ，2和n 2：较弱吸附部分的Freundlich 常数·556·第6期王少逸，等：粉末状活性炭对腐殖酸的吸附研究图4低质量浓度SA/UF PAC吸附AHA的Freundlich形式吸附等温线（ms=1 6mg/L）表4低质量浓度SA/UF PAC吸附AHA的Freundlich吸附参数（ms=1 6mg/L）K F，1n1r12KF，2n2r227762．474．160．9916．211．210．99本课题实验结果显示，双参数模式吸附等温线的线性形式对于本研究所使用的AHA溶液不同的初始质量浓度和PAC不同的用量而言，并不是在全部范围内都符合直线形式，这一点同其他相关文献研究所得出的结论相似［11－12］．在本研究的实验条件下（使用AHA溶液），由Freundlich吸附等温线的拟合可以看出两段直线部分：1）较长的直线部分，指示AHA较低质量浓度的平衡状态（ 0．01UA/L＜Ce（UV）＜ 0．20 UA/L），即与PAC的高质量浓度状态相对应；吸附具有吸附能力较弱的腐殖酸或吸附能力更弱的黄腐酸．2）另一较短的直线部分，指示AHA较高质量浓度的平衡状态（ 0．20UA/L＜Ce（UV）＜ 0．22UA/L），即与PAC的低质量浓度状态相对应．这一部分按与AHA溶液质量浓度相关的紫外吸收量计算大约占到原始AHA溶液紫外吸收总量的10%．吸附具有最高亲和力的腐殖酸．从以上分析中可以看出，某一较低比例的溶解性有机物（对于本课题实验结果为紫外吸收量的10%，根据AL MARDINI的实验结果为 20%）可以被看作是通过紫外吸光法测出的溶解性有机物中的强烈吸附组分．从实际的结果可以得出上述的少部分有机物就是在对微污染物进行吸附处理过程中实际与其产生竞争作用的部分．3结论在本研究的实验条件下（使用AHA溶液），由Freundlich吸附等温线的拟合可以看出存在两段直线部分，即较长的直线部分，指示AHA较低质量浓度的平衡状态（ 0．01UA/L＜Ce（UV）＜ 0．20UA/L），与PAC的高质量浓度状态相对应；较短的直线部分，指示AHA较高质量浓度的平衡状态（ 0．20UA/L＜Ce（UV）＜ 0．22UA/L），与PAC的低质量浓度状态相对应．少部分的有机物就是在对微污染物进行吸附处理过程中实际与其产生竞争作用的部分．因此，在采用吸附法处理农药残留物时应给予关注．参考文献：［1］胡大波，刘福强，凌盼盼，等．农药废水的处理技术进展与展望［J］．环境科技，2009，22（5）：63－66．［2］胡振华，于萍，罗运柏．突发性水体敌百虫污染的应急处理研究［J］．环境科学与技术，2012，35（1）：76－79．［3］张英民，李开明，周伟坚，等．高级氧化技术在农药废水处理中的应用［J］．现代化农业，2009，364（11）：27－29．［4］AL MARDINI F，LEGUBE B．Effect of the adsorbate（bro-macil）equilibrium concentration in water on its adsorption onpowdered activated carbon．Part1：Equilibrium parameters［J］．Journal of Hazardous Materials，2009，170（2－3），744－753．［5］何文杰，谭浩强，韩宏大，等．粉末活性炭对水中农药的吸附性能研究［J］．环境工程学报，2010，4（8）：1692－1696．［6］贾丽萍，刘学卿，王新刚，等．粉末活性炭应急处理阿特拉津突发污染原水的研究［J］．工业安全与环保，2012，38（2）：24－73．［7］朱丹，李帆，王茜．活性炭处理敌百虫农药废水的研究［J］．安徽农业科学，2012，40（1）：356－486．［8］HAMDAOUI O，NAFFRECHOUX E．Modeling of adsorption i-sotherms of phenol and chlorophenols onto granular activated car-bon．Part1．Two－parameter models and equations allowing de-termination of thermodynamic parameters［J］．Hazardous Materi-als，2007，147（1－2）：381－394．［9］QI S，SCHIDEMAN L，MARINAS B J，SNOEYINK V L，et al．Simplification of the IAST for activated carbon adsorption of traceorganic compounds from natural water［J］．Water Research，2007，41（2）：440－448．［10］MONTEIL－RIVERA F，BROUWER E B，MASSET S，et al．Combination of X－ray photoelectron and solid－state13C nu-clear magnetic resonance spectroscopy in the structural character-isation of humic acids［J］．Analytica Chimica Acta，2000，424（2）：243－255．［11］Al MARDINI F，LEGUBE B．Effect of the adsorbate（bro-macil）equilibrium concentration in water on its adsorption onpowdered activated carbon．Part3：Competition with natural or-ganic matter［J］．Journal of Hazardous Materials，2010，182（1－3）：10－17．［12］任芝军，马桂林，宫林林，等.预氧化对生物活性炭工艺中硝化的细菌的影响［J］．哈尔滨商业大学学报：自然科学版，2012，28（4）：407－410．·656·哈尔滨商业大学学报（自然科学版）第28卷。

[Article]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin.2014,30(10),1810-1820OctoberReceived:May 13,2014;Revised:August 21,2014;Published on Web:August 22,2014.∗Corresponding author.Email:qc2008@;Tel:+86-591-22866162.The project was supported by the National Natural Science Foundation of China (10676007)and Scientific Research Foundation of Fujian Provincial Education Department,China (JB14222).国家自然科学基金(10676007)和福建省教育厅科研基金(JB14222)资助项目©Editorial office of Acta Physico-Chimica Sinicadoi:10.3866/PKU.WHXB201408221铀酰离子在羟基化α-石英(101)表面的吸附辜家芳1陈文凯2,*(1福州大学至诚学院化学工程系,福州350002;2福州大学化学系,福州350116)摘要:采用周期性密度泛函理论研究羟基化α-石英(101)面的铀酰离子吸附行为.通过对铀酰离子的水合作用考虑水溶剂对结构的短程溶剂化效应,并通过类导体屏蔽模型(COSMO)考虑水溶剂对结构的远程溶剂化效应.吸附能计算结果和电子结构数据均表明水合铀酰离子吸附构型比氢氧化铀酰吸附构型稳定,并且在液相中两种类型的稳定吸附位均为dia-O s1O s2位.两种形式在电子结构上有很大的差异,主要是由于铀与表面作用后成键强弱程度不同,使5f 轨道宽化和略微红移存在差异.在铀酰离子吸附的基础上利用卤素离子改变铀酰离子配位环境可调整体系的带隙.关键词:α-石英(101)面;铀酰;密度泛函理论;溶剂效应中图分类号:O641Adsorption of the Uranyl Ion on the Hydroxylated α-Quartz (101)SurfaceGU Jia-Fang 1CHEN Wen-Kai 2,*(1Department of Chemical Engineering,Zhicheng College,Fuzhou University,Fuzhou 350002,P .R.China ;2Department of Chemistry,Fuzhou University,Fuzhou 350116,P .R.China )Abstract:Uranyl ion adsorption on the hydroxylated α-quartz (101)surface was investigated by first-principles density functional theory calculations.We explicitly considered the first hydration shell of the uranyl ion for short-range solvent effects and used the conductor-like screening model (COSMO)for long-range solvent effects.Both the adsorption energies and electronic structures of the adsorption system indicated that the bidentate hydrated uranyl species were more stable than bidentate hydroxylated species,and bidentate adsorption of the uranyl ion on the bridge site of dia-O s1O s2was the most stable adsorption model in the aqueous state.The large differences in the electronic structures of the two forms were mainly because of the different degree of bonding between uranium and the surface after adsorption,which makes the 5f orbital narrow and causes a red e of halogen ions in the uranyl coordination environment can adjust the band gap of the uranyl adsorption system.Key Words:α-Quartz (101)surface;Uranyl;Density functional theory;Solvent effect1引言商业核电站给人类带来了很多便利的同时也留下核废料的污染隐患.铀酰是核废料中较为稳定的一种离子,研究铀酰离子在多种矿物质表面的吸附行为有助于对核污染点铀的扩散进行评估.同时也有实验表明铀酰卤化合物可以用于光催化氧化大量的有机和无机化学物质.1将铀酰离子负载在稳定的矿物质基底上不仅可以避免回收铀带来的困难,也能很好地发挥铀酰离子的光催化活性.2-4与铀酰水溶液相比,吸附铀酰离子的石英纳米颗粒有更1810辜家芳等:铀酰离子在羟基化α-石英(101)表面的吸附No.10长的激发态寿命.2,3在光照下,吸附铀酰离子的MCM-41分子筛是一种可以将短链烷烃进行降解的高效多相光催化剂.4有大量的实验对地下水中铀酰离子在一些矿物质表面的吸附行为进行研究,5-19理论上也报道了一些关于铀酰离子在固体表面的吸附研究.20-30批量实验从宏观上通过测量吸附后的溶液里铀减少的数量来研究不同的环境条件对铀吸附的影响.5-8但是这些研究没有对所吸附物的种类和结构给予解析.X射线吸收光谱实验(XAS),其中包括X-射线近边结构吸收光谱(XANES)和扩展X 射线精细结构吸收光谱(EXAFS)的运用有助于直接探测吸附构型的结构和吸附金属的氧化价态的研究.7,9-11然而,当表面吸附的化合物不是单一物质,而是由多种吸附构型混合时,通过光谱实验得到的只能是各种吸附结构的平均结构参数.理论上主要是通过第一性原理密度泛函理论研究铀酰离子在高岭土、20-23α-Al2O3、24,25水合金红石结构的TiO2、26,27水合镍金属28和氢氧化铝等表面的吸附.Glezakou和deJong24计算得到U与α-Al2O3表面直接配位形成的铀酰内层双齿配位结构是最稳定的吸附构型.同时通过铀酰离子吸附,由中性的α-Al2O3表面去掉两个H质子的缺陷表面重新从吸附的水合铀酰离子结构获得H原子,而使得铀酰的两个水分子配体转化为氢氧根配体.铀酰离子倾向于吸附在去质子化的高岭土Al(O)表面,而高岭土的Si(O)表面的铀酰吸附作用比较弱.21,22铀酰离子与水合TiO2(110)表面的O t―H作用形成的吸附构型是最稳定的.26,27铀酰离子在水合Ni(111)表面存在两种吸附模式:一种是通过铀酰的配位水分子与水合的Ni(111)表面形成的外层氢键作用;另一种是铀酰的氧与表面的金属Ni 形成强的Ni―O键.28SiO2又称硅石,在自然界中分布很广,如石英、石英砂等.石英是一种理想的吸附剂,它在许多地质环境中是岩石的主要成分.EXAFS实验数据显示,在pH为3.1和6.2条件下,吸附铀酰离子的无定形二氧化硅表面可以测到垂直铀酰轴的平面存在U―O键.12在弱酸性条件下,铀酰离子可以直接与去质子化的硅醇基成键.12,29,30石英表面的分子动力学模拟了含氢氧根离子和碳酸根离子配体的铀酰在羟基化的α-石英(010)表面的吸附行为.29另外分子动力学也模拟了不同低指数的石英表面吸附UO2(OH)20的研究.铀酰除以离子的形式在地下水中迁移,在自然界也很可能沉淀和吸附在矿物表面而使迁移受限制.研究铀酰离子与表面的吸附作用对于解决环境中核污染物扩散问题具有重要的意义.α-石英是天然界最常见的低温石英,其晶体结构为正六面体.水溶液中α-石英(101)表面易发生羟基化,31,32因此本文以羟基化α-石英(101)表面为底物研究铀酰离子与表面的吸附机制,希望能为核污染处理工作提供具有重要意义的理论指导.本课题组33-35之前采用量子化学方法,研究水溶液中铀酰配合物的物理和化学性质,主要包括考虑溶剂化效应分子的几何结构、电子结构、分子光谱和电子光谱.在了解铀酰簇模型的有关性质基础上,我们拟采用密度泛函理论周期平板模型进一步研究铀酰离子结构在羟基化α-石英(101)表面的吸附构型.本论文对铀酰离子考虑水合分子的短程溶剂化作用,同时采用类导体屏蔽模型(COSMO)36考虑水溶剂对结构的长程溶剂化作用.研究了铀酰离子在羟基化α-石英(101)表面的双齿吸附的几何结构、电子结构以及相应的吸附能,并对获得的稳定吸附结构进行卤素配位修饰,研究该负载表面的电子结构特点.2计算方法和表面模型本文应用MS5.5的Dmol3模块程序37,38进行周期性密度泛函计算.计算应用了广义梯度近似(GGA)和PW91泛函相结合的交换相关势,39,40Si、O、H和卤素原子采用全电子双数值基加极化函数(DNP)基组,对铀原子采用内层60个电子冻芯处理,外层32个电子为价电子的有效核赝势(ECP60MWB)基组.DNP基组相当于高斯的6-311G(d)基组,同时还增加了基组重叠误差(BSSE)效应的考虑.41,42液相下的计算采用类导体屏蔽模型(COSMO)考虑溶剂化效应,水的电介常数为78.54.通过对比研究了气相和液相中铀酰离子在羟基化的α-石英(101)表面的吸附结构,探讨了溶剂化效应对该吸附体系的影响.过渡态搜索采用线性同步转变(LST)与二次同步转变(QST)方法,并选用Fine精度计算.结构优化和过渡态以位移、能量和力的收敛为依据,收敛值分别为2.0×10-2Ha∙nm-1、1.0×10-5Ha和5.0×10-2nm.α-石英具有六角对称,其相应的空间点群为P3221.理论研究以α-石英为基底研究水分子吸附机理.31,43-47实验中在α-石英表面的氧易被水羟基化,并只观察到相邻的单一硅醇基(Si―OH),31,32说明羟基化的α-石英(101)表面通常只存在单一硅醇基(Si―OH).关于羟基化石英表面的理论研究也有相关报1811Acta Phys.-Chim.Sin.2014V ol.30道.Goumans等43采用厚度为18的原子层研究羟基化的石英(001)表面.Bandura等31研究发现优化低表面覆盖度下的羟基化的α-石英(101)表面上取3-5个Si3O6层的结构得到的结构参数相差不大.同样我们在选取羟基化α-石英(101)表面时进行了测算,发现取3个和5个Si3O6层的结构得到的结构参数相差不大.因此本文采用Si36O80H16模型(图1),即取3个Si3O6层厚度的2×2超晶包周期平板模型的结构,并对表层Si原子进行羟基化处理,对底层表面O原子用H封闭.真空层厚度取1.2nm,并放开上面两单元Si12O24层,固定底层原子,对底层表面用H封闭主要是用来维持吸附剂的电中性.UO22+铀酰离子本身带两个正电荷,它倾向形成5配位的结构,48,49研究带正电的铀酰离子团UO22+的吸附工作受到体系总电荷不为零的影响.理论研究发现采用去质子化的硅醇基表面21,22或者吸附不带电荷的分子25可以避免体系带电对计算结果的影响.参考其它理论工作者的铀酰离子吸附模型形式,20-30拟采用铀酰离子与去质子化的表面吸附形成双齿吸附和铀酰氢氧配合物与完整表面形成的双齿吸附的形式进行吸附研究,并对铀酰离子周围增加水分子配位以满足铀酰配合物5配位稳定结构的需要.如图1所示,羟基化表面存在Os1和O s2两种类型的羟基氧(Os),双齿吸附位主要有对角关系的桥位dia-Os1O s2、互相平行的para-O s1O s1和para-O s2O s2桥位以及相邻的距离大小不等的short-Os1O s2和long-O s1O s2桥位.在确定最佳吸附模型上的铀酰离子进行卤素离子修饰,离子的负电荷则通过对底层去质子化来使体系总电荷等于零.3结果与讨论3.1几何结构3.1.1非水合和水合铀酰离子在羟基化α-石英(101)表面的吸附构型为研究溶剂化效应对铀酰离子表面吸附的影响,在真空环境下进行气相结构计算,并用COSMO 模型模拟水环境下的计算,对比研究气相和液相下的吸附结构.比较非水合和水合铀酰离子吸附的目的在于考察水分子的短程溶剂化作用对吸附的影响.气相和液相下非水合和水合铀酰离子吸附构型的结构参数列于表1和表2,其对应吸附结构图见图2.通过对比各计算参数发现铀酰离子双齿吸附在该羟基化表面,并且得到两个U＝Oax键的键长相差不到0.005nm(不到U＝Oax键键长的3%).铀酰的U＝O ax键分裂成两个极为接近的值,与铀酰氧和表面的硅醇之间的氢键作用和溶剂化效应有关.图2中,吸附在para-Os1O s1位上的非水合铀酰离子的U＝O ax键长偏长,并且得到弯曲程度大的O＝U＝O轴,其键角大小为105.2°和104.3°,但该位置上的水合铀酰离子仍然保持5配位双齿吸附结构,O＝U＝O 轴仅出现稍微弯曲.非水合铀酰离子吸附构型中O＝U＝O键角大小范围大都出现在160°-172°.通过水合作用得到的吸附结构的键长相对伸长,O＝U＝O键角大,并且吸附表面上的O s―U―O s键角和O s―O s距离也相对较小.dia-O s1O s2位的O s―O s吸附前距离是0.3476nm(图1).而表面经过水合铀酰离子吸附后,该距离在溶液中缩短了0.0404nm(图2).而在液相下dia-Os1O s2位在吸附非水合铀酰离子后,图1羟基化的α-石英(101)的俯视(a)和侧视(b)结构图Fig.1Structures of top(a)and side(b)views for hydroxylated(101)surface ofα-quartz(a)distance unit in nm1812辜家芳等:铀酰离子在羟基化α-石英(101)表面的吸附No.10O s ―O s 距离缩短了0.07-0.13nm.图2中,当铀酰离子不受水分子直接配位的影响时,能够与表面形成较短较强的U ―O s 键.综上分析,作用在非水合铀酰离子吸附构型上的由类导体屏蔽模型提供的远程溶剂化效应不能代替水分子参与直接配位的短程溶剂化效应.考虑水合作用后的水合铀酰离子吸附构型受到长程溶剂化效应作用后结构变化较小.溶剂化效应缩短了吸附表面上的Si ―O 键,增长了含铀的共价键.理论计算结果得到的水合铀酰吸附构型中U 与水分子形成的U ―O water 键与U ―O s 键的键长不同,正好与实验上在多数吸附铀酰离子的表面上测到的两个U ―O 键的数值一致.12,50表3列出了水合铀酰离子吸附构型与非水合铀酰离子吸附构型以及三个水分子的能量差,用于预测水合铀酰离子吸附构型脱水反应能量大小.由表3可见,脱去水合铀酰的水需要很大的能量,进一步说明了液相下,铀酰离子吸附的短程溶剂化效应不可忽略.铀酰离子在矿物质表面吸附受溶液pH 值、铀酰离子浓度等多方面因素的影响.22,51在中性环境下,表面最可能存在水合铀酰离子吸附构型,而实验上得到U ―Si 距离为0.277和0.308nm,12,50只出现在含铀浓度大于1mg ∙g -1情况下的吸附,其它含量的铀酰离子吸附并不存在短的U ―Si 距离.水合铀酰离子吸附构型中U ―Si 的距离范围为0.3189-0.3841nm.而有文献29,30报道包含羟基的铀酰离子理论吸附得到的U ―Si 的平均距离都超过0.4nm.气相和液相中吸附在para-O s1O s1上的水合铀酰离子吸附构型的U ―Si 距离分别为0.3189和0.3389nm,比较接近铀酰离子吸附的石英表面EXAFS 实验数据得到的0.277和0.308nm.12,50吸附在para-O s1O s1上的非水合铀酰离子的U ―Si 距离与EXAFS 实验数据更接近.含氧配体容易与铀酰离子形成配合物,表1气相和液相(aq)下非水合铀酰离子在羟基化的α-石英(101)表面不同桥位上的吸附构型参数Table 1Structure parameters for adsorptions of bare uranyl ion on different bridge sites of hydroxylated α-quartz (101)surface in gas and aqueous (aq)phasesR :bond length;A :bond angle.O ax :the oxygen atom from uranyl ion;O s :the surface oxygen atom from hydroxylated α-quartz (101)surface.Depronated adsorption sites are used to circumvent a charged unitcell.表2气相和液相下水合铀酰离子在羟基化的α-石英(101)表面不同桥位上的吸附构型参数Table 2Structure parameters for adsorptions of hydrated uranyl ion on different bridge sites of hydroxylated α-quartz1813Acta Phys.-Chim.Sin.2014V ol.30当水合铀酰离子与羟基化的α-石英(101)表面形成U ―O s 键时,铀与表层的Si 原子之间的距离必然拉长,因此理论上很难形成强的U ―Si 键,除非铀酰离子的O ＝U ＝O 键在无水状态下发生弯曲使得U ―Si 键易形成(如图2中para-O s1O s1上非水合铀酰离子吸附构型).3.1.2氢氧化铀酰在羟基化α-石英(101)表面的吸附构型图3和表4为优化得到的氢氧化铀酰在羟基化α-石英(101)表面的吸附构型和结构参数.大部分吸附结构保持了5配位结构,并且铀与表面之间的U ―Si 和U ―O s 键明显减弱.吸附结构中U ―OH 键长为0.2135-0.2283nm,U ―O s 和U ―O water 键键长相近.这一构型同样也符合实验上测得的两种U ―O 值.吸附在para-O s1O s1(H,H)(为便于与铀酰和水合铀酰离子吸附构型区分,氢氧化铀酰吸附位后加(H,H),表示吸附位上桥氧的质子)和para-O s2O s2(H,H)的氢氧化铀酰并没有形成最稳定的双齿结构,而倾向与表面硅醇形成氢键作用.长程溶剂化作用同样使U ―O water 发生稍微缩短,并伸长包含铀的各共价键,图2液相下水合和非水合铀酰离子在羟基化的α-石英(101)表面不同桥位上优化后的吸附构型Fig.2Optimized adsorption structures of bare and hydrated uranyl ion on hydroxylated (101)surfaceof α-quartz in aqueous phaseMost elements of the full surface are cut off and shown with only two bridge sites of SiO 4instead.distance unit in nm表3气相和液相下水合铀酰离子吸附构型脱水反应形成非水合铀酰离子吸附构型反应能量Table 3Energies for dehydrating adsorption structuresof hydrated uranyl ion to bare formsathe total energy for dehydrating three water in structure;b the averageenergy for dehydrating one water in structure1814辜家芳等:铀酰离子在羟基化α-石英(101)表面的吸附No.10因此液相中含铀体系的计算也不能忽略长程溶剂化作用.3.2α-石英(101)表面质子转移的可能性水合铀酰离子和氢氧化铀酰在α-石英(101)表面的吸附构型属于同分异构,两结构有可能通过质子转移互相转化.通过Complete LST/QST 过渡态搜索氢氧化铀酰吸附构型和水合铀酰离子吸附构型之间的过渡态,并将结果显示在图4中.研究发现氢氧化铀酰的氢氧离子配位从相邻的表面Si ―OH 上获得质子形成水合铀酰吸附构型是一个能垒低的放热反应.随着反应的进行,表面的SiO ―H 键被拉长,铀酰的U ＝O 键缩短.通过质子转移,铀酰与表面的作用增强.在para-O s1O s1上的质子转移是一个能垒仅为71.76kJ ∙mol -1的吸热过程.因此氢氧化铀酰在α-石英(101)表面的吸附构型很可能转化为水合铀酰离子在表面的吸附构型.羟基化α-石英(101)表面上硅醇间的H 键比较弱,表面去质子很可能在铀酰吸附的过程发生.3.3铀酰吸附能计算吸附能定义为反应前后体系总能量的变化,其符号和大小可以表示发生反应的可能性和程度.吸附能为正值说明该吸附构型的形成属于吸热反应,不易形成,反之吸附能为负值说明吸附构型的形成属于放热反应,较易形成.一般吸附能绝对值大于-40kJ ∙mol -1为化学吸附,小于-40kJ ∙mol -1则为物理吸附.反应式如下:S ur (OH)2+UO 2(OH)2(H 2O)3→S ur (O)2-UO 2(H 2O)3+2H 2O (1)S ur (OH)2+UO 2(OH)2(H 2O)3→S ur (OH)2-UO 2(OH)2(H 2O)+2H 2O (2)其中S ur 表示α-石英表面.反应(1)是吸附物质的氢氧铀酰配合物的氢氧离子配体得到表面的质子,并在图3液相下氢氧化铀酰在羟基化α-石英(101)表面的吸附构型Fig.3Optimized adsorption structures of hydroxylateduranyl on hydroxylated (101)surface ofα-quartz in aqueous phaseMost elements of the full surface are cut off and show with only two bridge sites of SiO 4instead.distance unit in nm表4优化得到的氢氧化铀酰在羟基化α-石英(101)表面吸附构型的结构参数1815Acta Phys.-Chim.Sin.2014V ol.30表面形成水合铀酰离子吸附构型.反应(2)是氢氧铀酰配合物失去两个水分子后与α-石英(101)表面直接作用形成氢氧化铀酰吸附构型.表5中吸附能的大小表明水合铀酰离子吸附构型比氢氧化铀酰吸附构型稳定,并且在液相中两种类型的稳定吸附位均为dia-O s1O s2位.如表5所示,气液两相中,稳定吸附位dia-O s1O s2位上的吸附能大小相差不大,说明溶剂化效应对该稳定吸附位的吸附能大小影响较小且均为化学吸附.其它吸附位的吸附能受溶剂化作用影响明显较大,水溶液的出现会使得大多数的吸附构型由化学吸附转为吸附能小于-40kJ ∙mol -1物理吸附.氢氧化铀酰在short-O s1O s2(H,H)和para-O s2O s2(H,H)位的吸附能出现正值和数值较小的负值,说明这两种吸附发生的可能性很小,更倾向于解离,也进一步表明α-石英(101)表面质子转移的可能性很大,氢氧化铀酰的氢氧离子配位倾向于从相图4液相下羟基化α-石英(101)表面质子转移路径的能量曲线Fig.4Energy profiles for proton transferring mechanism at hydroxylated (101)surface of α-quartz in aqueous phaseAll energies are given in kJ ∙mol -1and the distances are innm.表5气相和液相下水合铀酰离子和氢氧化铀酰吸附能(E a )Table 5Adsorption energies (E a )for hydrated andhydroxylated uranyl surface species1816辜家芳等:铀酰离子在羟基化α-石英(101)表面的吸附No.10邻的表面Si―OH上获得质子形成水合铀酰离子吸附构型.3.4电子结构性质Mulliken电荷布居和态密度分析对理解和掌握铀酰吸附机理具有重要的作用.表6给出铀酰吸附前后构型的Mulliken电荷布居.吸附后,铀的正电荷数目和表面氧(Os1和O s2)的负电荷数目都增加了.这说明发生吸附时铀失电子,与铀成键的其它原子得到电子而羟基化α-石英(101)表面主要通过质子转移得到较多的电子.图5中,铀酰吸附质的带隙很小,而作为绝缘体的石英表面带隙很大.峰位从-10到2eV主要对应于羟基化石英表面的2p轨道.铀酰吸附后,铀5f轨道出现在2到5eV位置.此时体系的能带带隙发生不同的变化.羟基化石英表面得到电子,吸收峰向低能级位置移动.在dia-Os1O s2和short-O s1O s2上的水合铀酰离子吸附构型带隙最小,为1.5eV左右.而氢氧化铀酰吸附构型的带隙普遍比较大.而带隙的大小主要与铀的5f轨道出现的位置有关.当铀失去电表6液相下羟基化α-石英(101)表面,氢氧化铀酰簇和表面双齿吸附构型的Mulliken电荷布居(单位为e)分析Table6Mulliken charge population(unit in e)of the hydroxylatedα-quartz(101)surface,uranyl dihydroxide cluster,图5部分吸附构型液相的分态密度(PDOS)图Fig.5Partial density of state(PDOS)for some adsorptionmodels in aqueous phaseData of band gap(in eV)are displayed.1817Acta Phys.-Chim.Sin.2014V ol.30子,将有更多的5f 空轨道出现在2到5eV 能级位置,进而使得体系的带隙减小.图5中,与吸附前相比dia-O s1O s2和short-O s1O s2吸附位上的铀酰的f 轨道峰出现略微红移和宽化,底物p 轨道峰有明显红移说明U 与底物有明显的成键作用,该位置的吸附作用比较强.而dia-O s1O s2(H,H)和short-O s1O s2(H,H)吸附位上的f 轨道峰变化不明显,说明该位置上的吸附作用比较弱,铀与表面的成键比较弱.态密度分析与前面的吸附能分析结论一致,从电子结构带隙的变化进一步解释了吸附能大小的原由.带隙变化对多相催化剂的性能提高有重要的意义,实验上已证实了表面进行铀酰吸附的体系具有强的光催化性能.2-4铀酰在羟基化石英表面稳定吸附后,从电子结构上看,羟基化石英表面的占据轨道和铀的空f 轨道之间的能级差减小了,即带隙减小,可以有效地提高铀酰的光催化性质.而铀酰的光谱可以通过配位键来调节,34因此铀酰羟基化石英表面同样也可以通过改变铀配位键种类来调控带隙,进而影响铀酰离子的光催化性质.3.5液相中dia-O s1O s2吸附的铀酰卤素配位修饰上述研究发现dia-O s1O s2位是铀酰离子吸附的最稳定化学吸附位.因此取该吸附位进一步研究铀酰离子吸附后的羟基化石英表面体系带隙受配位的影响情况.有孤对电子的卤素离子作为铀酰配体会使得铀酰光谱性质发生不同的变化,通过卤素配位修饰同样可能会对铀酰离子吸附后的石英表面体系的电子结构产生影响.表7中,铀与卤素成键键长分别为U ―F 键约为0.22nm,U ―Cl 键约为0.29nm,U ―Br 键约为0.30nm.S ur (O)2-UO 2Cl 3中有两个U ―Cl 键长为0.3127和0.3172nm,说明结构中的U ―Cl 受配位竞争影响,键能减小.图6为卤素修饰后的dia-O s1O s2铀酰的DOS 图.显然当铀酰的配位发生变化,体系的带隙同样发生不同程度的变化,Cl -和Br -数目增多使体系带隙有减小趋势.而F -数目增多却使得带隙变宽.由此可见铀酰离子吸附体系的带隙可以通过配位键的类型来调节,实验上可以采用此方法来提高铀酰离子的光催化性质.4结论通过周期性密度泛函理论研究了铀酰离子在羟基化α-石英(101)表面的吸附行为.研究发现,液相下铀酰吸附受溶剂化效应的影响很大,结构和吸附能均受到溶剂短程作用和长程作用不同程度的影响.吸附能计算结果和电子结构数据均表明水合表7液相中dia-O s1O s2上吸附模型S ur (O)2-UO 2X n (H 2O)3-n (X=F,Cl,Br;n =1-3)的U ―X 键长Table 7U ―X bond lengths of adsorption models S ur (O)2-UO 2X n (H 2O)3-n (X=F,Cl,Br;n =1-3)on dia-O s1O s2site in aqueousphaseS ur :hydroxylated (101)α-quartzsurface图6液相中dia-O s1O s2上吸附模型S ur (O)2-UO 2X n (H 2O)3-n (X=F,Cl,Br;n =1-3)的DOSsFig.6Density of states (DOSs)for adsorption models S ur (O)2-UO 2X n (H 2O)3-n (X=F,Cl,Br;n =1-3)on dia-O s1O s2inaqueous phaseData of band gap (in eV)are displayed.1818辜家芳等:铀酰离子在羟基化α-石英(101)表面的吸附No.10铀酰离子吸附构型比氢氧化铀酰吸附构型稳定,并且在液相中两种类型的稳定吸附位均为dia-Os1O s2位.当水合铀酰离子与羟基化的α-石英(101)表面形成U―Os键后,理论上很难再形成强的U―Si键,除非铀酰的O＝U＝O键在无水状态下发生弯曲使得U―Si键易形成(如图2中para-O s1O 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Hyperbaric Hydrogen Therapy: A Possible Treatment for CancerAuthor(s): Malcolm Dole, F. Ray Wilson, William P. FifeSource: Science, New Series, Vol. 190, No. 4210 (Oct. 10, 1975), pp. 152-154Published by: American Association for the Advancement of ScienceStable URL: /stable/1740947Accessed: 17/12/2008 01:18Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use.Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at/action/showPublisher?publisherCode=aaas.Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission.JSTOR is a not-for-profit organization founded in 1995 to build trusted digital archives for scholarship. We work with the scholarly community to preserve their work and the materials they rely upon, and to build a common research platform that promotes the discovery and use of these resources. For more information about JSTOR, please contact support@.American Association for the Advancement of Science is collaborating with JSTOR to digitize, preserve andextend access to Science.。