Ag.g-C3N4复合光催化材料的光物理及光催化性能

g-C3N4基光催化剂的合成及性能优化的研究g-C3N4基光催化剂的合成及性能优化的研究近年来，光催化技术因为其在环境污染治理、能源转化和有机合成等方面的巨大潜力，受到了广泛的关注。

在这些应用中，g-C3N4基光催化剂因其可见光响应和较高的光催化活性而备受瞩目。

g-C3N4是一种类似于石墨烯的二维材料，由碳、氮元素组成。

由于其具有较高的可见光吸收能力和良好的电子传导性，因此成为制备光催化剂的有力候选材料。

然而，纯g-C3N4的光催化活性较低，主要原因是其带隙能量较大，不利于可见光的吸收。

因此，针对g-C3N4的合成和性能优化成为了当前研究的热点之一。

目前，研究者们通过一系列方法来合成g-C3N4光催化剂，并改善其光催化性能。

一种常见的方法是通过热聚合的方式制备g-C3N4。

通常，蓝薯、尿素等富含氮元素的有机物被选择为前身，经过简单的热处理即可得到g-C3N4材料。

此外，研究者们还探索了其他合成方法，如溶剂热法、微波辐射法和气相沉积法等。

这些方法在改善光催化性能方面发挥了积极的作用。

为了进一步提高g-C3N4光催化剂的性能，研究者们采用了多种方法对其进行改性。

一种常见的方法是通过掺杂其他元素来引入缺陷或能带调制。

例如，研究者们通过掺杂金属等元素，有效降低了g-C3N4的带隙能量，并增强了其可见光吸收能力。

此外，还有研究表明，通过改变g-C3N4的形貌和结构，也可以显著改善其光催化性能。

如采用纳米多孔结构、片状结构等形貌设计，可以增加催化剂的比表面积和光响应能力。

除了合成和形貌结构的改进，提高光催化性能还需要研究者们合理设计反应体系。

例如，在选择催化剂和底物的组合时，需要考虑其能级匹配和反应活性。

此外，还需要优化催化条件，如光照强度、反应温度、pH值等，以提高催化效率。

同时，研究者们也在不断探索新的催化机制，以深入理解g-C3N4光催化剂的工作原理。

综上所述，g-C3N4基光催化剂的合成及性能优化的研究是一个复杂而富有挑战性的领域。

[Article]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin .2014,30(4),729-737April Received:December 9,2013;Revised:February 24,2014;Published on Web:February 24,2014.∗Corresponding author.Email:wyfwyf53540708@;Tel:+86-139********.The project was supported by the National Natural Science Foundation of China (21206105,21176168).国家自然科学基金(21206105,21176168)资助项目©Editorial office of Acta Physico -Chimica Sinicadoi:10.3866/PKU.WHXB 201402243Ag/Ag 3PO 4/g-C 3N 4复合光催化剂的合成与再生及其可见光下的光催化性能刘建新王韵芳*王雅文樊彩梅(太原理工大学洁净化工研究所,太原030024)摘要:研究了用离子交换沉淀法制备的Ag/Ag 3PO 4/g-C 3N 4的可见光光催化性能及再生方法.通过X 射线衍射(XRD)、场发射扫描电子显微镜(FESEM)、紫外-可见(UV-Vis)吸收光谱及X 射线光电子能谱(XPS)对其进行了结构特性分析.XRD 结果显示再生后催化剂的结构未发生改变.FESEM 及UV-Vis 分析结果说明催化剂由Ag 3PO 4与g-C 3N 4复合而成.XPS 分析结果表明催化剂表面出现少量的银单质.利用可见光(λ>420nm)照射下的苯酚降解实验评价了样品的光催化活性,并通过活性物种及能带结构的分析对催化剂的光催化机理进行了推测.研究表明,Ag/Ag 3PO 4/g-C 3N 4的光催化活性明显高于纯Ag 3PO 4及纯g-C 3N 4,主要原因归结为单质银、Ag 3PO 4及g-C 3N 4的协同效应.经过氧化氢和磷酸氢铵钠(NaNH 4HPO 4)的再生可完全恢复催化剂的活性,这表明该绿色环保的再生方法可实现Ag/Ag 3PO 4/g-C 3N 4催化剂在环境中的实际应用.关键词:磷酸银;g-C 3N 4;金属银;催化剂再生;苯酚;光催化中图分类号:O644;O649Synthesis,Regeneration and Photocatalytic Activity under Visible-LightIrradiation of Ag/Ag 3PO 4/g-C 3N 4Hybrid PhotocatalystsLIU Jian-XinWANG Yun-Fang *WANG Ya-WenFAN Cai-Mei(Institute of Clean Technique for Chemical Engineering,Taiyuan University of Technology,Taiyuan 030024,P .R.China )Abstract:Ag/Ag 3PO 4/g-C 3N 4(g denotes graphitic)was synthesized via an anion-exchange precipitation method,and its photocatalytic activity under visible light and regeneration with H 2O 2and NaNH 4HPO 4were investigated.The structural characteristics were analyzed using X-ray diffraction (XRD),field-emission scanning electron microscopy (FESEM),ultraviolet-visible (UV-Vis)absorption spectroscopy,and X-ray photoelectron spectroscopy (XPS).The XRD results showed that the structure of the regenerated catalyst was unchanged.The FESEM and UV-Vis absorption spectroscopy results showed that the Ag/Ag 3PO 4/g-C 3N 4catalyst was composed of Ag 3PO 4and g-C 3N 4.XPS showed that a small amount of Ag particles were present on the catalyst surface.The photocatalytic activity was evaluated using phenol degradation under visible light (λ>420nm)and the photocatalytic mechanism was discussed based on the active species during the photocatalytic process and the band structure.Experimental studies showed that the photocatalytic activity of the as-prepared Ag/Ag 3PO 4/g-C 3N 4was higher than those of pure Ag 3PO 4and g-C 3N 4.The high photocatalytic performance of the Ag/Ag 3PO 4/g-C 3N 4composite can be attributed to the synergistic effect of Ag 3PO 4,g-C 3N 4,and a small amount of Ag 0.Regeneration using H 2O 2and NaNH 4HPO 4∙4H 2O fully restored the photoactivity of the catalyst,showing that this green regeneration method could make Ag/Ag 3PO 4/g-C 3N 4an environmentally friendly catalyst for practical applications.729Acta Phys.-Chim.Sin.2014V ol.301IntroductionThe quest for solar-energy utilization has led to the search for functional semiconductor photocatalysts that can directly split water and photodegrade organic pollutants.Accordingly, exploring novel functional materials,such as development of new monomer photocatalysts,graphene-based composite pho-tocatalysts,metal core/semiconductor shell nanocomposites, have become research focus.1-12Ye et al.13reported Ag3PO4as a new type of photocatalyst that exhibits extremely high photo-oxidative capabilities for O2evolution from water and for de-composing organic dyes under visible-light irradiation.The quantum efficiency of Ag3PO4is significantly higher than that of currently known visible light photocatalysts,such as g-C3N4, N-doped TiO2,and BiVO4.14-16Ag3PO4photocorrodes and decomposes to weakly active Ag during photocatalysis,and trace amount of silver as an electron scavenger can improve quantum efficiency and photocatalytic activity.Unfortunately,the photolysis of a large amount of Ag3PO4results in catalyst deactivation,and excess elemental silver affects catalyst contact with sunlight,thereby seriously hampering the practical application of Ag3PO4in photocataly-sis.To solve this problem,many composite photocatalysts, such as AgX(Br,I)/Ag3PO4,17,18TiO2/Ag3PO4,19Ag/Ag3PO4/g-C3N4,20and Ag3PO4/SnO2,21have been developed,and very good results have been achieved.Interestingly,Wang et al.22pro-posed a solution to the problem of recycling Ag from the photo-corrosion and decomposition of Ag3PO4using H2O2as a clean oxidant.However,their method cannot fully restore the catalyt-ic activity of Ag3PO4,and Ag3PO4is lost during the degradation process because Ag3PO4is slightly soluble in aqueous solution, which affects the utilization of the precious metal silver.This study aimed to completely restore activity of photocat-alysts and to avoid the loss of Ag3PO4during catalyst prepara-tion and regeneration.To this end,insoluble g-C3N4was used with Ag3PO4for the chemisorption between g-C3N4and Ag3PO4 to prevent the dissolution of silver phosphate.H2O2and alka-line NaNH4HPO4were used to regenerate the used Ag/Ag3PO4/ g-C3N4hybrid composite photocatalysts that were recycled af-ter the photocatalytic degradation reactions.2Materials and methods2.1Preparation of fresh pure Ag3PO4,pure g-C3N4,and Ag/Ag3PO4/g-C3N4All the reagents were purchased from Sinopharm and used without further purification.Pure Ag3PO4was prepared by the ion-exchange method.About0.39g of AgNO3was dispersed in distilled water(30mL),and an aqueous solution of NaNH4HPO4∙4H2O(15.6mL0.05mol∙L-1)was added.After vigorous stirring for1h,the yellow precipitate was collected by centrifugation,rinsed with distilled water three times,and dried at150°C for4h to obtain Ag3PO4.Pure g-C3N4was pre-pared by heating urea to400°C for0.5h to obtain melamine, and then heating was continued at575°C for2h.To prepare Ag/Ag3PO4/g-C3N4hybrid photocatalysts,the as-prepared g-C3N4power(0.1g)was dispersed in30mL of distilled water under ultrasonication for30min.About0.39g of AgNO3was added to ensure the molar ratio of Ag3PO4to g-C3N4is1:3, which is the optimum ratio,and the mixture was stirred at room temperature.NaNH4HPO4∙4H2O(15.6mL0.05mol∙L-1) was then added dropwise with continuous stirring for1h.The obtained solid product was centrifuged,washed,and dried at 150°C for4h.2.2Catalyst regenerationAfter phenol photodegradation in an aqueous solution under visible-light irradiation,the photocatalyst Ag/Ag3PO4/g-C3N4 was centrifuged,washed three times with distilled water,and dried at150°C for4h.In a typical regeneration reaction,the used photocatalyst was dispersed in NaNH4HPO4aqueous solu-tion(20mL)after each use.Then,H2O2(15%)was added drop-wise to the above suspension until the end of reaction(no bub-ble release).The products were subsequently collected by cen-trifugation,washed three times with distilled water,and dried at150°C for4h.2.3Characterisation of photocatalystsThe crystalline phases of the samples were examined by an X-ray diffraction(XRD)instrument(Rigaku,D/max-2500)us-ing Cu Kαradiation(λ=0.15406nm)within the2θrange from 10°to80°.The accelerating voltage and applied current were 40kV and30mA,respectively,and the scan rate was8(°)∙min-1.Morphological analysis and product compositions were investigated by field-emission scanning electron microscopy (FESEM,Japan JSM-7001F).The light absorption properties of the samples were recorded on an ultraviolet-visible(UV-Vis)spectrophotometer.Elemental compositions were detected by X-ray photoelectron spectroscopy(XPS,Thermo,ESCAL-AB250Xi).The shift in binding energy caused by relative sur-face charges was referenced to the C1s peak of the surface ad-ventitious carbon.2.4Photocatalytic activityThe photocatalytic activities of Ag/Ag3PO4/g-C3N4and re-Ag/Ag3PO4/g-C3N4(regenerated composite photocatalyst)were evaluated by the photocatalytic degradation of phenol in an aqueous solution under visible-light irradiation.For photocata-lytic phenol degradation,0.07g of the as-prepared photocata-lysts was mixed with100mL of15mg∙L-1phenol solution. During photocatalysis,the samples were periodically with-drawn(sampling time of30min),centrifuged to separate the photocatalyst powder from the solution,and subjected to absor-Key Words:Silver phosphate;g-C3N4;Metallic silver;Catalyst regeneration;Phenol;Photocatalysis730LIU Jian-Xin et al.:Synthesis,Regeneration and Photocatalytic Activity under Visible-Light of Ag/Ag3PO4/g-C3N4 No.4bance measurements.The photocatalytic activity of the com-posites was compared with those of the pure g-C3N4and pureAg3PO4powders under the same experimental conditions.Theregenerated photocatalysts were used to repeat the same degra-dation experiment for three cycles to determine their photosta-bility.3Results and discussion3.1Catalyst characterisationX-ray photoelectron spectroscopy was carried out to deter-mine the chemical composition of Ag3PO4,Ag/Ag3PO4/g-C3N4,and re-Ag/Ag3PO4/g-C3N4,as well as the valence states of vari-ous species present therein.The binding energies obtained inthe XPS analysis were corrected for specimen charging by ref-erencing C1s to284.60eV.Photoelectron peaks of Ag,O,P,N,and C were clearly observed in the Ag/Ag3PO4/g-C3N4andre-Ag/Ag3PO4/g-C3N4hybrids,as shown in Fig.1(A),whichconfirmed the presence of Ag,O,P,N,and C in the compos-ites.The comparison of O1s spectra in Fig.1(B)revealed thatthe O1s peak was fitted using XPS PEAK software to separatelattice oxygen and adsorbed oxygen located at530.62and532.80eV,respectively.The presence of adsorbed oxygen canimprove photocatalytic efficiency.25For Ag3PO4,the binding en-ergies of Ag3d5/2and Ag3d3/2peaks were located at367.7and373.7eV,respectively,consistent with the presence of Ag+onthe pared with Ag3PO4,the binding ener-gies of Ag3d5/2and Ag3d3/2in the other samples shifted to368.2and374.2eV,26,27respectively,as shown in Fig.1(C).Thisresult indicated that Ag0particles existed on the photocatalystsurface.Given the electron-rich structure of C3N4units,theycan transfer their electron density to Ag3PO4by overlappingwith the p z orbitals of heterocyclic nitrogens during the prepara-tion of the catalyst,which have the exact symmetry of the high-est unoccupied p-type orbital in the Huckel model.23,24Conse-quently,Ag0particles are generated in the preparation of Ag/Ag3PO4/g-C3N4hybrid photocatalyst.However,the content ofAg0particles is too low to be detected by XRD(Fig.2)in thebulk phase of Ag/Ag3PO4/g-C3N4hybrid photocatalyst becauseC3N4is merely excited during the reaction of AgNO3and NaNH4HPO4∙4H2O.The positions of binding energies of the Ag3d5/2and Ag3d3/2peaks of re-Ag/Ag3PO4/g-C3N4were the same as those of Ag/Ag3PO4/g-C3N4,and the XRD of re-Ag/ Ag3PO4/g-C3N4had no diffraction peaks of Ag0,indicating that the electron transfer process from g-C3N4to Ag3PO4occurred during catalyst regeneration,which was the same as the elec-tron transfer process that occurred during catalyst preparation. The intensity of Ag in the re-Ag/Ag3PO4/g-C3N4much lower than that in the original Ag/Ag3PO4/g-C3N4should attribute to the oxidation of hydrogen peroxide.During the catalyst regen-eration process,hydrogen peroxide as an oxidant to convert Ag0to Ag+.Therefore,the content of Ag0on the surface of the cata-lyst is decreased,and the intensity of Ag in the re-Ag/Ag3PO4/g-C3N4is much lower than that in the original Ag/Ag3PO4/g-C3N4.However,there are a small portion of the metallic silver which was wrapped by colloid group produced during catalyst regen-eration still on the surface of catalyst,avoiding the oxidation in-duced by hydrogen peroxide.After drying the catalyst,the met-al silver wrapped in the colloid group was exposed on the sur-face of the catalyst.As a result,a small amount of Ag0still ex-ists on the surface of the catalyst after regeneration.The XRD patterns of Ag/Ag3PO4/g-C3N4hybrid photocata-lysts exhibited coexistence of g-C3N4and Ag3PO4(JCPDS No. 02-0931)phases.27,28The diffraction peak at38.07°(JCPDS No. 04-0783)assigned to Ag0was found in the XRD patterns of the first used Ag/Ag3PO4/g-C3N4after one recycling run,29indicat-ing that severe photocorrosion of Ag3PO4occurred during pho-todegradation reaction.However the diffraction peaks of Ag disappeared in the XRD patterns of the re-Ag/Ag3PO4/g-C3N4, Fig.1XPS spectra of the photocatalysts(A)survey XPS spectra;(B)O1s spectra;(C)Ag3d spectra.(a)Ag3PO4;(b)Ag/Ag3PO4/g-C3N4;(c)re-Ag/Ag3PO4/g-C3N4731Acta Phys.-Chim.Sin .2014V ol.30and the diffraction peaks of re-Ag/Ag 3PO 4/g-C 3N 4had no signif-icant difference from that of the fresh one except that the main diffraction peaks of re-Ag/Ag 3PO 4/g-C 3N 4at 33.26°are little higher than peaks of Ag/Ag 3PO 4/g-C 3N 4,which means that the crystallization of composite photocatalyst has been improved after photocatalyst regeneration.Thus,Ag 0derived from light corrosion process transformed to Ag 3PO 4during photocatalyst regeneration.Therefore,the method of photocatalyst regenera-tion using NaNH 4HPO 4and H 2O 2(15%)effectively regenerated the composite photocatalyst.Fig.3shows the SEM images of Ag 3PO 4,re-Ag 3PO 4,Ag/Ag 3PO 4/g-C 3N 4,re-Ag/Ag 3PO 4/g-C 3N 4,and g-C 3N 4.Fig.3(A,B)reveals that both Ag 3PO 4and re-Ag 3PO 4particles had irregular spherical morphologies and non-uniform diameters.The mean size of Ag 3PO 4was estimated to be 100-500nm.However,the re-Ag 3PO 4particles obtained by photocatalyst regeneration were more regular in shape and homogeneous in distribution (Fig.3(B)).This finding was due to the rearrangement of Ag 3PO 4particles rebuilt from Ag during regeneration,with colloid coagulation and violent gas release.This variation in shape and distribution can be attributed to diffusion-limited aggregation and/or reaction-limited aggre-gation.30Fig.3(E)shows that g-C 3N 4had an irregular layered structure.The SEM images of Ag/Ag 3PO 4/g-C 3N 4and re-Ag/Ag 3PO 4/g-C 3N 4demonstrated a close connection between g-C 3N 4and Ag 3PO 4semiconductors (Fig.3(C,D)).No obvious sign of the presence of silver was observed because Ag was microscale.Importantly,all of them had the dimensionality,unique absorption edges,and morphologies of the original g-C 3N 4and Ag 3PO 4semiconductors.31Considering the different morphologies between Ag 3PO 4and re-Ag 3PO 4,the regeneration process markedly affected the morphology of re-Ag/Ag 3PO 4/g-C 3N pared with fresh Ag/Ag 3PO 4/g-C 3N 4,the layered structures of re-Ag/Ag 3PO 4/g-C 3N 4were more structured,and the distributions of Ag 3PO 4particles in the g-C 3N 4were more homogeneous.The UV-Vis diffuse reflectance measurements of pure g-C 3N 4,pure Ag 3PO 4,Ag/Ag 3PO 4/g-C 3N 4,and re-Ag/Ag 3PO 4/g-C 3N 4are shown in Fig.4(A).The absorption bands of Ag/Ag 3PO 4/g-C 3N 4and re-Ag/Ag 3PO 4/g-C 3N 4were almost identical in UV-Vis diffuse reflectance.This result further illustrated that this method of regenerating phosphorylation silver catalyst can restore the catalytic performance of the composite photocata-lyst.g-C 3N 4and Ag 3PO 4are direct-transition semiconductors.32,33Thus,the plot of (αh ν)1/2versus h νyielded the band gaps of pure g-C 3N 4,pure Ag 3PO 4,Ag/Ag 3PO 4/g-C 3N 4,and re-Ag/Ag 3PO 4/Fig.2XRD patterns of the photocatalysts(a)Ag/Ag 3PO 4/g-C 3N 4;(b)used-Ag/Ag 3PO 4/g-C 3N 4;(c)re-Ag/Ag 3PO 4/g-C 3N 4.A:Ag 3PO 4,C:g-C 3N4Fig.3SEM images of the photocatalysts(A)Ag 3PO 4;(B)re-Ag 3PO 4;(C)Ag/Ag 3PO 4/g-C 3N 4;(D)re-Ag/Ag 3PO 4/g-C 3N 4;(E)g-C 3N 4732LIU Jian-Xin et al .:Synthesis,Regeneration and Photocatalytic Activity under Visible-Light of Ag/Ag 3PO 4/g-C 3N 4No.4g-C 3N 4,as shown in Fig.4(B).Here,αand νare the adsorption coefficient and light frequency,respectively.The conduction band (CB)and valence band (VB)potentials of Ag 3PO 4and g-C 3N 4were determined to explain the mecha-nism of action of the synthesized photocatalysts.For a semi-conductor,CB and VB were calculated according to the follow-ing empirical equation:E CB =χ−E e −0.5E g E VB =E CB +E gwhere E CB and E VB are the CB and VB edge potentials,respec-tively;χis the electronegativity of the semiconductor,which is the geometric mean of the electronegativity of the constituent atoms;E e is the energy of free electrons on the hydrogen scale (about 4.5eV);and E g is the band-gap energy of the semicon-ductor.The calculated values of the CB and VB potentials of Ag 3PO 4and g-C 3N 4are listed in Table 1.3.2Photocatalytic performanceThe photocatalytic activities of as-prepared samples were evaluated by phenol degradation under visible light (>420nm).A phenol-photolysis test was also conducted for the same dura-tion under visible-light irradiation in the absence of catalyst.The blank test confirmed that phenol cannot be degraded with-in 120min under visible-light irradiation,indicating that phe-nol was a stable molecule and photolysis can be ignored.The photocatalytic efficiency of Ag/Ag 3PO 4/g-C 3N 4hybrid photocat-alysts was higher than those of pure g-C 3N 4and Ag 3PO 4as shown in Fig.5,which was calculated according to the absor-bance of solution at 270nm assigned to phenol.The cause of the photoactivity of Ag 3PO 4with 60min visible-light irradia-tion seemingly even better than that at 120min illumination is that some by-products had been generated during the photode-gration by pure Ag 3PO 4and the absorption of phenol at 270nm treated as the basis for calculating degradation rate is no longer applicable for system including a variety of materials.So,for the photodegration by pure Ag 3PO 4,the reduction of absorption of phenol at 270nm does not mean degradation of phenol.A more detailed demonstration was shown in Fig.6(A,B).During the photodegradation by pure Ag 3PO 4,the absorption peak at 244nm (the absorbance of 5mg of benzoquinone was deter-mined in all temporal absorption spectral patterns)that was rep-resentative of benzoquinone was observed in the absorption spectra.29And the irregular fluctuations of absorption of benzo-quinone and phenol during the whole photodegradation caused the absorption of phenol with 60min visible-light irradiation even lower than that at 120min illumination.Furthermore,the color of solution of phenol became pale yellow from colorless during the photodegration by pure Ag 3PO 4(the possible inter-mediates of degradation process of phenol are colorless except benzoquinone that is pale yellow solution),which is the further evidence of the existence of benzoquinone.Therefor phenol was not degraded and merely mutually transformed with benzo-quinone which was more toxic than phenol in aqueous solu-tion.However,during the same photodegradation of Ag/Ag 3PO 4/g-C 3N 4hybrid photocatalysts,the absorption peak of phenol was weakened,and no absorption peak of additional substances was observed in the absorption spectra of phenol.The same trend was found in the temporal absorption spectral patterns of phenol during photodegradation using re-Ag/Ag 3PO 4/g-C 3N 4and re-Ag 3PO 4,as shown in Fig.6(C,D),respec-Fig.4UV -Vis spectra and band gaps of as-synthesized samples(A)UV-Vis spectra;(B)band gaps.(a)Ag 3PO 4;(b)Ag/Ag 3PO 4/g-C 3N 4;(c)re-Ag/Ag 3PO 4/g-C 3N 4;(d)g-C 3N 4Table 1Calculation results of the CB and VB potentials ofAg 3PO 4and g-C 3N 4Ag 3PO 4g-C 3N 4χ5.964.55E g /eV 1.92.5E CB /eV 0.51-1.20E VB /eV 2.411.30Fig.5Photocatalytic degradation of phenol as a function of irradiation time under visible-light irradiation(a)phenol photolysis;(b)g-C 3N 4;(c)Ag 3PO 4;(d)Ag/Ag 3PO 4/g-C 3N 4733Acta Phys.-Chim.Sin.2014V ol.30tively.Conclusively,the Ag/Ag3PO4/g-C3N4hybrid photocatalysts effectively degraded phenol and possessed more excellent pho-tocatalytic properties than pure Ag3PO4and g-C3N4photocata-lysts.And the method of catalyst regeneration completely re-stored the activity of Ag/Ag3PO4/g-C3N4hybrid photocatalysts.3.3Recycling of Ag/Ag3PO4/g-C3N4and re-Ag/Ag3PO4/g-C3N4Fig.7shows cycling runs for the photocatalytic degradation of phenol in the presence of used Ag/Ag3PO4/g-C3N4without any regeneration process and re-Ag/Ag3PO4/g-C3N4regenerated after each photodegradation experiment in aqueous solution un-der visible-light irradiation.For Ag/Ag3PO4/g-C3N4hybrid pho-tocatalysts without regeneration,the rate of phenol degradation under visible-light irradiation significantly decreased in three successive experimental runs.However,under the same condi-tions,the ultimate degradation rate of phenol under visible-light irradiation for re-Ag/Ag3PO4/g-C3N4nearly had no difference from fresh Ag/Ag3PO4/g-C3N4hybrid photocatalysts.This re-sult indicated that the photocatalyst regeneration method using H2O2and NaNH4HPO4effectively restored photocatalytic activ-ity.More importantly,the method can be used continuously without restrictions.3.4Mechanism of Ag3PO4regeneration from AgAg3PO4is known to facilitate easy photolysis.When Ag3PO4 was used as a photocatalyst without a sacrificial reagent,13 Ag3PO4photocorroded and decomposed to weakly active Ag during photodegradation.A small amount of silver as an elec-tron-capture agent contributed to photocatalytic activity.35How-ever,as the reaction proceeded,the increase in silver content hindered contact between Ag3PO4and illumination.Conse-quently,photocatalytic activity gradually deteriorated,thereby limiting the practical application of Ag3PO4as a recyclable highly efficient photocatalyst.In the case of pure Ag3PO4and Ag/Ag3PO4/g-C3N4,the yellow catalysts were observed to dark-en when the photocatalytic reaction was completed.This phe-nomenon confirmed that Ag+in Ag/Ag3PO4/g-C3N4and Ag3PO4 decomposed to Ag0.The redox potential of the Ag+/Ag pair is0.80V,whereas in the presence of a mass of PO43-ions,the redox potential of Ag species markedly decreased to0.45V(Ag3PO4/Ag).36The H2O2/ OH-pair has a redox potential of0.867V in alkalinecondi-Fig.6Temporal absorption spectra of phenol dye during thephotodegradation process(A)Ag/Ag3PO4/g-C3N4;(B)Ag3PO4;(C)re-Ag/Ag3PO4/g-C3N4;(D)re-Ag3PO4Fig.7Cycling runs for the photocatalytic degradation of phenolunder visible-light irradiation(a)Ag/Ag3PO4/g-C3N4;(b)re-Ag/Ag3PO4/g-C3N4734LIU Jian-Xin et al .:Synthesis,Regeneration and Photocatalytic Activity under Visible-Light of Ag/Ag 3PO 4/g-C 3N 4No.4tions,which is higher than that of Ag 3PO 4/Ag.More important-ly,H 2O 2can oxidize Ag without contaminating the system with any impurity.17Thus,hydrogen peroxide as a clear oxidant can oxidized Ag 0to Ag +.The acid environment of their aqueous so-lution can dissolve Ag 3PO 4,and the decomposition rate of H 2O 2was fast.Thus,the weakly alkaline NaNH 4HPO 4was chosen asthe PO 43-source to prevent the loss of Ag 3PO 4.Once H 2O 2was added dropwise to the beaker with NaNH 4HPO 4aqueous solution and the precipitate of used pho-tocatalyst (used-Ag 3PO 4or used-Ag/Ag 3PO 4/g-C 3N 4)during re-generation,severe outgassing was observed and the boundaries between solution and precipitate disappeared.For Ag/Ag 3PO 4/g-C 3N 4,the used-Ag/Ag 3PO 4/g-C 3N 4transformed to g-C 3N 4/Ag 3PO 4/Ag 2O (colloid),and colloid coagulation occurred with g-C 3N 4/Ag 3PO 4/Ag 2O (colloid)and NaNH 4HPO 4.At the same time,electrons of g-C 3N 4transferred to Ag 3PO 4similar to the transfer that occurred during preparation,and the final product Ag/Ag 3PO 4/g-C 3N 4containing only a minimal content of silver was obtained.The reaction process of Ag 3PO 4also applied to pure Ag 3PO 4,which followed the reaction below:4Ag+4H 2O 2=2Ag 2O (colloid)+4H 2O+O 2(1)3Ag 2O+2PO 43-+6H +=2Ag 3PO 4+3H 2O (2)After the easy regeneration reaction using H 2O 2with NaNH 4HPO 4,the color of Ag/Ag 3PO 4/g-C 3N 4returned from black to pale yellow,the majority of Ag 0disappeared and be-came Ag 3PO 4,and the activity of the composite photocatalyst was restored.Although there is the appearance of chromatic ab-erration between Ag/Ag 3PO 4/g-C 3N 4and re-Ag/Ag 3PO 4/g-C 3N 4as shown in Fig.8for the changes of crystal form and morphol-ogy of the photocatalyst during the colloid coagulation,no ob-vious change was observed in photocatalytic activity.It can be concluded that the catalyst regeneration method used using H 2O 2and NaNH 4HPO 4is effective.3.5Detection of reactive oxygen speciesDuring photocatalytic oxidation,a series of reactive oxygen species,such as h +,∙OH,or O 2-●,are supposed to be involved.To examine the role of these reactive species,the effects ofsome radical scavengers and N 2purging on phenol photodegra-dation were investigated to propose a reaction pathway.The ex-periment on identifying reactive oxygen species was similar to the photodegradation experiment.Different quantities of scav-engers were introduced into the phenol solution prior to cata-lyst addition.In this study,tert-butanol (TB)was added to the reaction system as an ∙OH scavenger,and ammonium oxalate (AO)was introduced as a scavenger of h +.N 2purging was thenadopted to quench O 2-●.37-39Fig.9shows that in the presence of scavengers or when N 2purging was conducted,phenol photodegradation was inhibited in varying degrees compared with no scavenger under the same conditions,indicating that all reactive oxygen species act-ed together for phenol degradation.This finding suggested that phenol photodegradation by Ag/Ag 3PO 4/g-C 3N 4hybrid photo-catalysts was a collaborative process of all reactive oxygen spe-cies.This process differed from methyl orange (MO)photodeg-radation under the same conditions,wherein dissolved O 2had no effect on photodegradation under visible-light irradiation.35This experimental result proved that Ag/Ag 3PO 4/g-C 3N 4hy-brid photocatalysts produced a variety of active substancesthatFig.8Schematic diagram for the processes of the photodegradation,regeneration,and recycling of Ag/Ag 3PO 4/g-C 3N4Fig.9Effects of different scavengers on the degradation of phenol in the presence of Ag/Ag 3PO 4/g-C 3N 4photocatalystsunder visible-light irradiation(a)ammonium oxalate;(b)tert -butanol;(c)N 2purging;(d)no scavenger735Acta Phys.-Chim.Sin.2014V ol.30jointly played an important role in phenol photodegradation un-der visible-light irradiation.3.6Mechanism of improved photocatalysisThe photocatalytic activity of catalysts depends on many fac-tors affecting photocatalysts,such as efficient charge separa-tion,surface property,morphology,optical property,and size.Meanwhile,the properties and characteristics of target organicpollutants affect photodegradation efficiency.41-46In our case,the photodegradation capability of both pure Ag3PO4and pureg-C3N4was insufficient for complete phenol degradation,be-cause this process generated other byproducts or had very lowdegradation efficiency.However,the photocatalysis resultsshowed the excellent photoactivity of the Ag/Ag3PO4/g-C3N4composite samples on phenol degradation,indicating that thecombination of g-C3N4and Ag3PO4was feasible and practical.Based on the above results and current literature,20,22,31,35a mechanism was proposed to explain the enhanced photocatalyt-ic activity of Ag/Ag3PO4/g-C3N4photocatalysts for phenol un-der visible-light irradiation.The energy band edge position be-tween g-C3N4and Ag3PO4and the corresponding enhancement of redox ability were found to improve the photocatalytic abili-ty of Ag/Ag3PO4/g-C3N4photocatalysts for phenol.In general,a more positive VB top corresponded to stronger oxidation abili-ty,and a more negative CB bottom corresponded to stronger re-duction ability.17In the process of photocatalytic reaction by Ag/Ag3PO4/g-C3N4photocatalysts under visible-light irradiation, both Ag3PO4and g-C3N4were excited,and the photogenerated electrons and holes were in their CB and VB,respectively.The electrons in the CB of g-C3N4with a more negative potential displayed strong reduction power,whereas holes in the VB of Ag3PO4showed strong oxidation ability.In more detail,the CB edge potential of g-C3N4(E CB=-1.2eV vs NHE(normal hydro-gen electrode))was more negative than E0(O2/O2-●)(-0.286eV vs NHE)and E0(O2/H2O2)(+0.286eV vs NHE).This finding in-dicated that e-can directly reduce the adsorbed O2molecules into O2-●radicals and H2O2.Moreover,the VB edge potentials of Ag3PO4(E VB=+2.51eV vs NHE)were more positive than E0 (∙OH/H2O)(+2.27eV vs NHE),which demonstrated that the h+of Ag3PO4can provide sufficient potential to oxidise H2O to∙OH.The Ag/Ag3PO4/g-C3N4photocatalysts can simultaneous-ly produce a variety of active substances that cooperatively act on the organic substance,consistent with the finding of the ex-perimental detection of reactive species.Then,all active sub-stances simultaneously reacted with phenol,which differed from the interpretation of some previous studies that organic pollutants react with only one active substance at the same time.40The exclusive use of pure Ag3PO4or pure g-C3N4was unable to generate sufficient active substance because of the lack of redox ability.Additional,according to the Z-scheme principle,the photogenerated electrons moved from the CB bot-tom of Ag3PO4(0.51eV)to Ag0and then continued to shift to the VB top of g-C3N4(1.5eV),recombing with the holes there as shown in Fig.10.47Conclusively,the photocatalytic ability of Ag/Ag3PO4/g-C3N4that can complete phenol degradation was due to the synergistic effects among Ag3PO4nanoparticles and the g-C3N4sheet.Some special properties of g-C3N4and Ag3PO4also affected the activity of the composite photocatalyst.The electronic con-ductivity of g-C3N4with a graphite-like structure accelerated the combination of e-and oxygen,reduced the recombination of electrons and holes,and enhanced the quantum efficiency of Ag/Ag3PO4/g-C3N4photocatalysts.For pure Ag3PO4,the ability to dissolve in water led to loss of photocatalytic performance. Given the chemical adsorption between g-C3N4and Ag3PO4, the insoluble g-C3N4sheet can protect Ag3PO4from dissolution in aqueous solution.4ConclusionsFor application of semiconductor in the field of photocataly-sis,photocatalytic activity and recyclable use of photocatalyst were the most critical factors.In this paper,Ag/Ag3PO4/g-C3N4 hybrid photocatalysts containing traces of silver were easily synthesized,which exhibited great higher photocatalytic activi-ty than pure Ag3PO4or pure g-C3N4for phenol photodegrada-tion under visible-light irradiation(>420nm).And H2O2and NaNH4HPO4were adopted to regenerate Ag3PO4from weak photocatalytically active Ag as a recyclable highly efficient photocatalyst,which almost completely restored the catalytic activity.More importantly,the method of synthesis and regen-eration of Ag/Ag3PO4/g-C3N4hybrid photocatalysts was green, simple,and repeatable.References(1)Fujishima,A.;Honda,K.Nature1972,238(5358),37.doi:10.1038/238037a0(2)Hagfeldt,A.;Grätzel,M.Chem.Rev.1995,95(1),49.doi:10.1021/cr00033a003(3)Chen,W.;Dong,X.F.;Chen,Z.S.;Chen,S.Z.;Lin,W.M.Acta Phys.-Chim.Sin.2009,25(6),1107.[陈威,董新法,陈之善,陈胜洲,林维明.物理化学学报,2009,25(6),1107.] Fig.10Schematic diagram of possible reaction mechanism over Ag/Ag3PO4/g-C3N4hybrid photocatalyst undervisible-light irradiation736。

g-C3N4光催化氧化还原性能调控及其环境催化性能增强g-C3N4（石墨相氮化碳）是一种新型的二维材料，具有片状结构和较高的光吸收能力，因此在光催化氧化还原性能调控和环境催化性能增强方面具有巨大的潜力。

本文将重点探讨g-C3N4的调控与增强，并分析其在环境催化中的应用。

首先，我们来看g-C3N4的光催化氧化还原性能调控。

光催化氧化还原反应是指在光照下，通过光生载流子的产生和迁移，将底物氧化或还原的反应过程。

g-C3N4作为一种光催化材料，其光催化性能主要受到其能带结构和表面缺陷的影响。

g-C3N4的能带结构中，价带和导带之间的带隙决定了光催化的吸光能力和载流子传输能力。

研究表明，通过控制g-C3N4的合成条件，可以调控其能带结构中的带隙大小和分布，进而调节其光催化性能。

例如，通过控制氮化温度和氮热处理条件，可以提高g-C3N4的带隙大小，使其对可见光的吸收能力增强。

此外，纳米结构和复合材料的调控也可以有效改善g-C3N4的光催化性能。

例如，将g-C3N4与其他半导体纳米材料复合，可以使其能隙气凝胶变窄，光吸收范围增广，从而提高光催化活性。

除了能带结构调控外，表面缺陷也是影响g-C3N4光催化性能的重要因素。

表面缺陷通常是指氮缺陷、碳缺陷和碳氮缺陷等，它们可以促进光生载流子的产生和迁移，提高光催化反应的效率。

因此，通过控制合成条件和引入适量的缺陷，可以增强g-C3N4的光催化活性。

例如，一些研究通过在g-C3N4的合成过程中引入硫、磷等掺杂原子，有效提高了其光催化氧化还原性能。

除了光催化氧化还原性能调控外，g-C3N4还具有良好的环境催化性能，特别适用于污水处理和空气净化等领域。

一方面，g-C3N4作为一种可见光响应的材料，可以通过光氧化、光还原或光催化降解等反应途径，将有机污染物转化为低毒或无毒的无机物。

另一方面，g-C3N4还具有一定的光催化氧化性能，可以将气体污染物如一氧化碳、二氧化氮等转化为无害物质。

g-C3N4光催化氧化还原性能调控及其环境催化性能增强g-C3N4是一种新型的低成本、可再生的光催化材料，具有广泛的应用潜力。

然而，其光催化性能的低效率和缺乏环境催化性能限制了其在实际应用中的广泛应用。

因此，调控g-C3N4的光催化氧化还原性能以及增强其环境催化性能成为当前研究的热点。

首先，通过调控g-C3N4的结构和形貌，可以改变其光催化性能。

研究表明，g-C3N4的结构具有影响其光催化性能的重要作用。

例如，调控g-C3N4的间隙结构和表面形貌可以提高其电子传输速率和光吸收能力，从而提高光催化活性。

此外，通过引入杂原子和掺杂材料可以调控g-C3N4的能带结构和能隙大小，进一步优化其光催化性能。

因此，通过调控g-C3N4的结构和形貌可以有效提高其光催化氧化还原性能。

其次，通过调控g-C3N4的表面性质，可以增强其环境催化性能。

g-C3N4的表面性质直接影响其各种催化反应的速率和选择性。

例如，通过在g-C3N4表面修饰共价有机框架材料可以增加其特定催化反应的催化活性和选择性。

此外，利用介孔材料包裹g-C3N4可以增加其比表面积，提高催化反应的效率。

另外，通过调控g-C3N4的表面酸碱性和氧化还原性质，可以调节其对污染物的吸附和催化活性，进一步提高其环境催化性能。

最后，通过复合材料的构建，也可以增强g-C3N4的光催化氧化还原性能和环境催化性能。

g-C3N4与其他材料的复合可以通过协同作用提高其光催化活性和稳定性。

例如，将g-C3N4与纳米金属复合可以增强其光催化还原性能；将其与二氧化钛复合可以提高其环境催化性能。

此外，通过调控复合材料的结构和组成，还可以实现对光催化氧化还原性能和环境催化性能的更精确调控。

综上所述，通过调控g-C3N4的光催化氧化还原性能以及增强其环境催化性能可以有效提高其应用潜力。

未来的研究可以进一步探索g-C3N4在其他领域中的应用，并进一步优化其性能，以实现更大的环境益处综上所述，调控g-C3N4的表面性质和构建复合材料是提高其光催化氧化还原性能和环境催化性能的有效方法。

Preparation and Properties of g-C3N4/RGO/AgI
Composite Photocatalyst
作者： 赵馨睿[1]
作者机构： [1]西安科技大学地质与环境学院,陕西西安710054
出版物刊名： 大庆师范学院学报
页码： 51-56页
年卷期： 2019年 第3期
主题词： 光催化;石墨相氮化碳;碘化银;石墨烯
摘要：采用热聚合法制备石墨相氮化碳(g-C3N4),超声法制备还原氧化石墨烯/石墨相氮化碳(RGO/g-C3N4)二元复合光催化剂,再利用共沉淀法在二元复合光催化剂RGO/g-C3N4表面负载AgI,制得g-C3N4/RGO/AgI复合光催化剂。

运用XRD、SEM、FT-IR、UV-Vis和FTIR等手段对材料进行表征,以罗丹明B(RhB)作为目标物,用g-C3N4/RGO/AgI进行光催化降解实验。

结果表明:光照210min后,g-C3N4/RGO/AgI光催化剂对RhB的降解率为96.52%。

相同条件下,RGO/g-C3N4和g-C3N4/AgI对RhB的降解率分别为58.28%和73.80%。

g-
C3N4/RGO/AgI复合光催化剂具有优异的光催化性能。

g-C_3N_4基纳米复合材料的制备及其光催化性能研究五颜六色的饰品、家具早已成为了生活中必不可少的点缀,而印染业大量使用人工有机染料却可能正在毁坏着环境。

近年来,保护环境的号召喊得越来越响亮,如何利用一种对环境友好且高效节能的技术来解决环境污染的问题成为了新世纪科学家们关心的话题。

在上述背景下,半导体光催化技术作为一种绿色无污染的技术,在解决环境污染问题尤其是水污染方面的问题得到了研究者们广泛的关注。

TiO₂作为一种传统的光催化剂,其在能源与环境领域被研究者们研究了很久。

但是TiO₂的缺点也很明显,比如它的带隙较大（大约是3.2eV）只能吸收太阳光中处于紫外光区的光,这一点严重地限制了其对太阳光的使用率。

鉴于此,探索一种使用可见光进行催化的光催化剂成为了光催化研究领域的一大热门方向。

g-C₃N₄是近些年光催化领域研究的一个热门半导体材料,其禁带宽度比TiO₂要小（大约是2.7eV）,对可见光有吸收。

除此之外,g-C₃N₄具有化学稳定性好、制备方法简便、原料来源丰富等优点。

但是g-C₃N₄也有缺点比如:比表面积较小、光生电子和空穴的复合率较高、光催化效率不高等。

构建表面异质结和用金属元素掺杂是改性光催化剂的重要方法,本文从以上两个角度考虑,成功制备出了TiO₂纳米棒/g-C₃N₄纳米片异质结、镧掺杂g-C₃N₄纳米片和钆掺杂g-C₃N₄纳米片。

gC3N4光催化性能的研究进展一、本文概述随着全球能源危机和环境污染问题的日益严重，光催化技术作为一种绿色、环保的能源转化和环境污染治理手段，受到了广泛关注。

g-C3N4，作为一种非金属半导体光催化剂，因其独特的电子结构和良好的化学稳定性，在光催化领域展现出了广阔的应用前景。

本文旨在对g-C3N4光催化性能的研究进展进行全面的概述，从g-C3N4的基本性质出发，探讨其光催化机理，分析影响光催化性能的关键因素，总结当前的研究热点和未来的发展趋势，以期为g-C3N4光催化性能的优化和应用提供有益的参考。

本文将介绍g-C3N4的基本性质，包括其晶体结构、电子结构和光学性质等，为后续的光催化性能研究奠定基础。

接着，从光催化机理出发，阐述g-C3N4在光催化过程中的电子传递和能量转换过程，揭示其光催化活性的本质。

在此基础上，分析影响g-C3N4光催化性能的关键因素，如制备方法、形貌结构、表面性质等，为后续的性能优化提供指导。

然后，本文将重点介绍g-C3N4在光催化领域的应用研究进展，包括光催化分解水制氢、光催化还原二氧化碳、光催化降解有机污染物等方面。

通过综述这些应用领域的研究现状和发展趋势，展示g-C3N4光催化技术的实际应用价值和潜力。

本文将对g-C3N4光催化性能的研究前景进行展望，探讨未来可能的研究方向和挑战。

通过本文的概述，希望能为g-C3N4光催化性能的研究和应用提供有益的参考和启示。

二、gC3N4的基本性质与合成方法gC3N4，也被称为石墨相氮化碳，是一种非金属二维半导体材料，因其独特的电子结构和出色的物理化学性质，近年来在光催化领域引起了广泛关注。

gC3N4具有适中的禁带宽度（约7 eV），能吸收可见光，且其能带结构、电子态密度等性质使其具备成为高效光催化剂的潜力。

在合成gC3N4的方法上，研究者们已经探索出多种途径。

其中，热缩聚法是最常见的一种方法，通过将富含氮的前驱体（如尿素、硫脲、双氰胺等）在高温下进行热解，可以制得gC3N4。

g-C3N4基光催化剂的制备及性能的研究g-C3N4基光催化剂的制备及性能的研究近年来，随着环境污染和能源危机的日益加剧，人们对环境友好和高效能源转化技术的需求与日俱增。

因此，研究开发一种高效的光催化剂成为了科学家们的研究焦点之一。

g-C3N4（石墨相氮化碳）因其良好的光催化性能而备受关注，可以用来降解有害物质、产生氢气或二氧化碳还原等。

g-C3N4基光催化剂的制备方法主要有热处理法、因子法、溶胶-凝胶法、冷冻干燥法等。

其中，热处理法是制备g-C3N4最常见的方法之一。

首先，选择适当和廉价的前驱体（如尿素），通过热聚合反应形成含有大量三氮（C3N4）键的大分子聚合物。

然后，将聚合物在高温条件下进行热分解，生成g-C3N4晶体。

这种方法具有简单、经济的优势，但由于热解条件的限制，得到的g-C3N4往往具有较低的比表面积和较大的颗粒粒径。

研究者们还通过导入不同的掺杂元素，如硫、铁和硼等，来改善g-C3N4的光催化性能。

掺杂能够引入新的能带，扩宽g-C3N4的光响应范围，增强电子和空穴的分离效率。

此外，选择合适的载体材料也可以提高g-C3N4的催化活性。

由于g-C3N4的特殊结构，它在水中的分散性较差。

因此，在制备g-C3N4光催化剂时，通常采用混合材料的形式，例如将g-C3N4与TiO2、ZnO或二氧化硅等载体相结合。

这些载体材料可以提供更大的比表面积和更好的分散性，从而促进光催化剂的光吸收和催化反应效率。

除了制备方法的改进，研究者们还注意到了g-C3N4的光催化机理和提高催化性能的策略。

g-C3N4在光照条件下可以产生电子-空穴对，其中电子和空穴分别参与催化反应中的还原和氧化过程。

因此，提高g-C3N4的分离效率是提高光催化性能的关键。

研究发现，调控杂质浓度和晶体结构可以有效地改善g-C3N4光生载流子的分离效率。

此外，结构修饰和表面修饰也是提高g-C3N4光催化活性的重要途径。

例如，g-C3N4的表面可通过改性和修饰来引入更多的催化活性位点，提高催化剂的催化活性和稳定性。