A Compositional Approach to Solution Adaptation in Case-based Reasoning and its Application

Applied Catalysis B:Environmental 170-171(2015)66–73Contents lists available at ScienceDirectApplied Catalysis B:Environmentalj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /a p c a tbA facile approach to further improve the substitution of nitrogen into reduced TiO 2−x with an enhanced photocatalytic activityYi Zhou,Yunchang Liu,Pengwei Liu,Weiyi Zhang,Mingyang Xing ∗,Jinlong Zhang ∗Key Lab for Advanced Materials and Institute of Fine Chemicals,East China University of Science and Technology,Shanghai 200237,Chinaa r t i c l e i n f o Article history:Received 2December 2014Received in revised form 21January 2015Accepted 26January 2015Available online 28January 2015Keywords:Ti 3+doped TiO 2Nitrogen dopedPhotocatalytic activitya b s t r a c tA series of nitrogen/Ti 3+co-doped titanium dioxides (N–TiO 2−x )were successfully synthesized through a calcination–vacuum activation method by using low-cost ammonium hydroxide as the nitrogen source.Interestingly,the nitrogen could be further doped into TiO 2lattice via the substitution of oxygen vacancies after the vacuum activation treatment.The as-prepared catalysts exhibited high visible light activity by improved substitution of nitrogen concentration with no affecting the UV-light photocatalytic activities.The samples were characterized by the XRD,UV–vis DRS,ESR,XPS and TEM analyzes.When the tem-perature of vacuum activation was 300◦C,N–TiO 2−x catalyst showed the highest photocatalytic activity for the degradation of methyl orange (MO)under the visible light irradiation.The increase in the visible-light photocatalytic activity was attributed to the synergistic effect between Ti 3+and nitrogen doping,which contributed to the increase of absorption in the visible light region.It can be claimed that N–TiO 2−x (300◦C-3h)contained the highest concentration of Ti 3+.©2015Elsevier B.V.All rights reserved.1.IntroductionTitanium dioxide has been widely used as a remarkable photo-catalyst owing to its excellent performance in environmental issue and energy problems,for instance,the degradation of organic pol-lutant [1–7],purification of noxious gas [8–11],capability of solar energy storage [12–15].Additionally,it is also one of the most attractive materials due to its low cost,non-toxicity,well stabil-ity in chemical and physical [16,17].The wide band gap of titania (3.0–3.2eV)limits its photocatalytic application in the UV region,however,there is merely approximately 4%of ultraviolet in sunlight energy [18].Numerous reports [19–22]focused on the modification of semiconductor titanium dioxide to enhance its photocatalytic activity have been published.Since Asahi et al.[23]found that nitrogen doped TiO 2was con-ductive to increase the absorption of visible light and photocatalytic activity.Many researches involved in nonmetal doping modifica-tion in TiO 2,which are mainly to extend the working spectrum of titanium dioxide in the visible light region,have been done in recent years [24–26].Especially,nitrogen doped TiO 2is full of great inter-est,our previous work has demonstrated that there are two major∗Corresponding authors.Tel.:+862164252062;fax:+862164252062.E-mail addresses:mingyangxing@ (M.Xing),jlzhjang@ (J.Zhang).kinds of nitrogen species doped in TiO 2[18].One is the nitrogen doped into TiO 2lattice to substitute the oxygen (N1),and the other is the nitrogen species chemically adsorbed on the surface of cata-lyst (N2).The former nitrogen is beneficial,conversely,the latter nitrogen is harmful to the photocatalytic activity of TiO 2under the visible light irradiation.However,it is very difficult to increase the doping concentration of N1while decreasing the concentra-tion of N2in TiO 2,owing to the departing of lattice N1at a high calcination temperature [27].With the increase of calcination tem-perature,the N1decreases while the N2increases.Thus,it is against to the enhancing of visible light activity of N–TiO 2.Therefore,it is very difficult to obtain a high ratio of N1/N2by using traditional methods.Moreover,Ti 3+-self doped TiO 2has demonstrated the increase in absorption in visible light and attracts a great interest in recent years.Sasikala et al.[28]successfully achieved the evidence of sup-porting that Ti 3+and oxygen vacancies facilitated absorption of visible light for TiO 2–SnO 2.After that,Zuo et al.[29]successfully prepared Ti 3+self-doped TiO 2with high stability,strong absorption of visible light and excellent performance in hydrogen production from photocatalysis water splitting through a one-step method.Xing et al.[30]also obtained modified Ti 3+self-doped TiO 2by a low-temperature vacuum activation method instead of conven-tional method,which needs high temperature or uneconomical equipment.The catalysts showed high stability of Ti 3+and oxy-gen vacancies and outstanding photoactivity.Moreover,a simple/10.1016/j.apcatb.2015.01.0360926-3373/©2015Elsevier B.V.All rights reserved.Y.Zhou et al./Applied Catalysis B:Environmental170-171(2015)66–7367one-step solvent-thermal method using low-cost NaBH4as a reduc-tant was also reported that can successfully synthesize a series of Ti3+self-doped TiO2catalysts.The catalysts also exhibited strong visible light absorption and enhanced photocatalytic activity[31].Metal and nonmetal co-doping have obtained great progress in the modification of titanium dioxide material[32,33].Some inves-tigations on the modification of metal and nitrogen co-doped TiO2 have been reported.Hoang et al.[34]proposed a reversible electron transfer between the paramagnetic bulk species of N(N b)and Ti3+ centers forming the diamagnetic bulk species of N b−and Ti4+,and the synergistic effect involving Ti3+and N in TiO2nanowire arrays is responsible for the outstanding performance of water photo-oxidation under visible illumination.Although a great progress regarding the synthesis of Ti3+/nitrogen co-doped TiO2has been achieved,the mechanism of co-doped is still controversial.Herein,it was aimed in the mechanism of nitrogen and Ti3+ co-doped TiO2to enhance the visible light photocatalytic activ-ity,especially the relationship between the formation of oxygen vacancies and the substitution of nitrogen into TiO2.A series of Ti3+and nitrogen co-doped TiO2catalysts have been obtained by using low-cost ammonium hydroxide as the nitrogen source via a calcination–vacuum activation method.The visible-light pho-todegradation of methyl orange of the co-doped TiO2was enhanced accounted for the synergistic effects between Ti3+and N.2.Experimental2.1.Preparation of N,Ti3+co-doped TiO2Titanium sulfate(24g,Ti(SO4)2)was added to the ultrapure water(120mL)and the solution was stirred at room temperature for1h,and then ammonium hydroxide was added dropwise to the above solution.The suspension with a pH value of7.0was obtained by controlling the amount of ammonium hydroxide.After that,the collected solid particles were washed with large amounts of water by vacuumfiltration.The precipitates were dried under vacuum at 60◦C for12h.The as-dried sample was calcined at400◦C for2h (ramping time95min).The obtained nanoparticles of TiO2doped with nitrogen are denoted as N–TiO2.Thefinal powder was activated in a vacuum tube furnace at 200◦C,300◦C,400◦C,500◦C and600◦C for3h,respectively(ramp-ing time95min).Then a series of nitrogen and Ti3+co-doped TiO2 were obtained and denoted as N–TiO2−x(m-3h)(m=100,200,300, 400,500,600◦C represent the vacuumed temperature).N–TiO2 powder was calcined in the air at300◦C for3h(ramping time 95min).And the obtained nanoparticles are denoted as air-N–TiO2.2.2.Preparation of Ti3+self-doped TiO2Using the same experimental method,in order to control the pH value of7.0,ammonium hydroxide was replaced by sodium hydroxide.The nano-particles of TiO2are denoted as TiO2.After vacuum activation treatment at300◦C for3h,the Ti3+self-doped TiO2was successfully prepared and denoted as TiO2−x(300◦C-3h).2.3.CharacterizationAll prepared samples were measured by a Rigaku D/max2550 VB/PC diffractometer(Cu K radiation, =1.5406Å)in the range of 10–80◦(2Â)for X-ray diffraction(XRD)patterns.The dry-pressed disk samples were used to test the UV–vis absorbance spectra of the catalysts using BaSO4,as the reflectance sample via a Scan UV–vis spectrophotometer(Shimadzu,UV-2450)equipped with an integrating sphere assemble.And the spectra of the catalysts were recorded at room temperature in air within the range200–800nm.A Perkin–Elmer PHI5000C ESCA system with Al K␣radiation operated at250W was used to study the surface constitution of the samples.The shift of the binding energy due to relative surface charging was corrected using the N1s level at401eV as an internal standard.The ESR spectra were recorded at room temperature(Varian E-112).The morphologies of catalysts were obtained by transmission electron microscopy(TEM,JEM-1400). Brunauer–Emmett–Teller(BET)surface area measurements were carried out by a Micromeritics ASAP2020instrument.The pore size distribution was collected by the Barrett–Joyner–Halenda(BJH) method.2.4.Photocatalytic activity testsMethyl orange(MO,10mg/L)was degraded as simulative pol-lutant to evaluate the photocatalytic activity of each sample.The photocatalyst sample(0.07g)was added into a100mL quartz photocatalytic reactor with addition of70ml MO solution.The mixture was stirred for30min in the absence of light in order to achieve the adsorption–desorption equilibrium.The visible light source was provided by a500-W tungsten halogen lamp with UV cutofffilters( >420nm).And a300-W high-pressure Hg lamp,whose strongest emission wavelength was365nm,as the UV light source.The photocatalytic system was cooled usingflow-ing water in a quartz cylindrical jacket,and ambient temperature was approximately constant during the photocatalytic reactions. At given intervals,analytical samples were taken from the mixture and immediately centrifuged.The supernatant liquid was analyzed by recording variations in the absorption of the UV–vis spectra for MO by using a Cary100UV–vis spectrometer.3.Results and discussion3.1.Phase structureThe XRD spectra of various samples are shown in Fig.1.For each sample,all peaks can be ascribed to the anatase phase of -pared with pure TiO2,the increase of intensity peak of the N-doped TiO2indicates higher crystallinity(Fig.1a).The vacuum activa-tion cannot change the crystalline structure of TiO2,even at high temperatures(Fig.1b).Moreover,the maximum peak intensity of N–TiO2−x(600◦C-3h)implies the highest crystallinity.The aver-age crystallite sizes are calculated according to the Debye–Scherer equation,as shown in Table1.The result obtained is in line with the report that the nonmetal doping modifications could cause a decrease in particle size[35]. That is,the N-doped TiO2shows a smaller particle size than pure TiO2.The lattice deformation and oxygen vacancies in the anatase crystallites can lead to the decrease of particle size[36].The dop-ing of nitrogen may restrain the growth of crystals.Conversely,the particle size of vacuum activated TiO2is almost changeless in com-parison with the value of pure TiO2.In addition,with the increase of the temperature about vacuum activation,the particle sizes ofTable1Measured structural characteristics of the various samples.Samples Particle size(nm)(101)d-spacing(Å)TiO224.1 3.5N–TiO219.6 3.5TiO2−x(300◦C-3h)25.0 3.5N–TiO2−x(100◦C-3h)20.6 3.5N–TiO2−x(200◦C-3h)19.4 3.5N–TiO2−x(300◦C-3h)19.8 3.5N–TiO2−x(400◦C-3h)20.1 3.5N–TiO2−x(500◦C-3h)21.8 3.5N–TiO2−x(600◦C-3h)30.4 3.568Y.Zhou et al./Applied Catalysis B:Environmental170-171(2015)66–73Fig.1.XRD patterns of(a)TiO2,N-doped TiO2,TiO2−x,N–TiO2−x(b)N-doped TiO2 vacuum activated at different temperatures.N–TiO2−x decrease atfirst,but then are inclined to increase.When the temperature is higher than400◦C,there is a significant increase of particle size and the N–TiO2−x(600◦C-3h)represents the largest size,which means that the high temperature is beneficial to either the crystallization or the growth of the crystal.During the vacuum activation,the generation of Ti3+and oxygen vacancy is beneficial to the substitution of nitrogen into TiO2,which can further decrease the particle size of co-doped catalysts.Furthermore,the value of the“d”space is almost changeless,which elaborates that the dop-ing of either nitrogen or Ti3+cannot change the average unit cell dimension[22].The N–TiO2−x(300◦C-3h)can be recorded by TEM images,shown in Fig.2.The N–TiO2−x samples exhibit a uniform size at the level of the XRD observation and the particle size of the catalyst is about19.8nm.The N2adsorption–desorption isotherms and BJH pore size dis-tribution(PSD)curves of these samples are employed to investigate the pore structure of N–TiO2−x vacuum activated at different tem-peratures(Fig.3).As a result,all of the isotherms are of the Type II according to the IUPAC classification.And the absorption of N2 in the analysis can be ascribed to the inter-aggregated pores which are structured by the neighboring nanoparticles.Additionally,the surface area and the BJH pore size of the N–TiO2−x vacuum activated at different temperatures are all similar with each other.It can be considered that the substitution of nitrogen for oxygen vacancies into the TiO2leads to a higher visible-light photocatalytic activity instead of differences of pore structure.3.2.Optical propertyThe UV–vis diffuse reflectance spectra of different samples are presented in Fig.4.The comparison between N-doped TiO2 and pure TiO2shows that absorption intensity in the rangeofFig.2.TEM images of the N–TiO2−x(300◦C-3h).400–550nm of TiO2obviously increases with nitrogen doping.And the N-doped TiO2also shifts the absorption edge further to the longer wavelength region(∼550nm).It may be attributed to the generation of some nitrogen species or color spots on the surface of the catalyst.Additionally,compared with pure TiO2,the absorp-tion intensity of the vacuum activated TiO2(TiO2−x)also obviously increases in the wide range of400–750nm,which results from the generation of Ti3+and oxygen vacancies.The result is consistent with the reports of Zuo et al.[29]and our previous works[30].Zuo et al.adopted a one-step method to synthesize Ti3+self-doped TiO2. In addition to that,Xing et ed a vacuum activation method for modifying P25to obtain Ti3+self-doped TiO2.Furthermore,with the increase of activation temperature,the absorption intensity in the visible region enhances atfirst,but recedes later.The N–TiO2−x (300◦C-3h)and the N–TiO2−x(600◦C-3h)are the strongest and the weakest,respectively.The synergistic effect involving Ti3+and nitrogen in TiO2results in the significant enhancement of absorp-tion intensity in the visible-light region of catalyst.The result implies that the catalyst calcinated at300◦C possesses the max-imum amount of Ti3+.When vacuum activation temperature is higher than300◦C,the amount of Ti3+doping decreases.3.3.Chemical compositionESR is employed to investigate the generation of the Ti3+and oxygen vacancy on the vacuum activated samples(Fig.5).No sig-nal is shown for the pure TiO2catalyst at g=1.992,while vacuum activated sample(TiO2−x(300◦C-3h))exhibits a stronger signal as the same as the intensity of the feature at a g-value of1.992for paramagnetic Ti3+center has been widely reported[34,37,38].It implies that the generation of Ti3+is attributed to vacuum acti-vation.It proves that the increase of absorption intensity of the catalyst in visible light region is the result of Ti3+-pared with TiO2−x(300◦C-3h),N–TiO2−x gives rise to a stronger ESR signal,which indicates that vacuum activation is beneficial for the substitution of nitrogen for oxygen vacancy in TiO2as well as the generation of Ti3+for the reason of charge balance.It is worth noting that the strongest ESR signal possessed by sample activated at300◦C among different activation temperature.It can be claimed that N–TiO2−x(300◦C-3h)contains the highest Ti3+concentration.Y.Zhou et al./Applied Catalysis B:Environmental170-171(2015)66–7369Fig.3.N2adsorption–desorption isotherms of N–TiO2catalysts vacuum activated at different temperatures.Insert spectra are the BJH pore size distribution curves of corresponding samples.In another word,the highest concentration of Ti3+corresponds to the strongest absorption intensity of catalyst in visible-light region.XPS characterization is used to investigate the composition of N/Ti3+co-doped TiO2catalyst.The peak from N1s is detected in the survey scan from the surface and subsurface of N–TiO2,air-N–TiO2and N–TiO2−x,as shown in Fig.6.There is a broad peak from396.5eV to404.5eV in N–TiO2,which is considered to be the typical peak of N-doped TiO2reported by several papers[23,39,40]. Afterfitting of the curve,two intense peaks at398.7eV and400.5eV are observed for N–TiO2and N–TiO2−x which is consistent with the N1s binding energy region.It implies that there are two states of nitrogen doping in the TiO2.One is nitrogen doping into lattice of TiO2(N1)and the other is chemically adsorbed on the surface of the catalyst(N2),which can be observed at398.7eV and400.5eV, respectively.Herein,the intense peak at398.7eV by reason of anionic N-in O–Ti–N has been reported by other researcher[41]. Moreover,the peak at400.5eV is attributed to the oxidized nitro-gen of Ti–O–N in our previous study[18].It has been reported that the two states of nitrogen doped in TiO2are all regarded as the important factors to affect the photocatalytic activity of TiO2under the visible light illumination[27].Interestingly,a comparison of the curve between N–TiO2and N–TiO2−x shows a stronger peak at398.7eV and a weaker peak at400.5eV can be observed after vacuum activation(Fig.6a).However,the total N atom percentage is almost changeless after being activated in the vacuum for3h (N/Ti ratio changes from0.022to0.023).The results demonstrate that the vacuum activation facilitates the further doping of nitro-gen into the lattice of TiO2.It can be speculated that the increase of the Ti–N(Fig.6a)is attributed to the substitution of nitrogen for oxygen vacancies into the TiO2lattice during the vacuum activation process.In addition,the total nitrogen atom percentage of N–TiO2 and air-N–TiO2is0.86%and0.42%,pared with the N–TiO2,the air-N–TiO2shows an obvious lower total nitrogen atom percentage.It indicates that the nitrogen in the air cannot be doping into the lattice of TiO2by calcination even if nitrogen exists in the air around the surface of samples,which is also be confirmed by several reports[42,43].In addition,compared with the N–TiO2−x,air-N–TiO2shows a weaker peak at398.7eV and a stronger peak at400.5eV(Fig.6b),which demonstrates that the nitrogen atom chemically absorbed on the surface of the catalyst can further replace the oxygen vacancy sites at a high heating temperature in the vacuum pared with the pure TiO2,the total O atom percentage of N–TiO2obviously decreases after nitrogen doping(O/Ti ratio changes from3.20to2.91).It can be inferred that the nitrogen replaces the oxygen atoms into the surface or subsurface lattice of TiO2during the calcination treat-70Y.Zhou et al./Applied Catalysis B:Environmental 170-171(2015)66–73Fig.4.UV–vis diffuse reflectance spectra and the amplification in the visible-light region of various samples (a)TiO 2,N–TiO 2,TiO 2−x ,N–TiO 2−x (b)N-doped TiO 2vac-uum activated at differenttemperatures.Fig.5.ESR spectra of (a)TiO 2,TiO 2−x (300◦C-3h),N–TiO 2−x (300◦C-3h)and (b)different samples vacuum activated at differenttemperature.Fig.6.N1s XPS spectra of N–TiO 2,N–TiO 2−x and air-N–TiO 2.ment in air,which leads to a decrease of O atom percentage in N–TiO 2.To the N–TiO 2,some nitrogen atoms squeeze into the lat-tice interval of TiO 2,firstly in the beginning of the air calcination,as shown in Fig.7.With the increase of calcination temperature in air,the neighbor oxygen atoms are departing from the lattice and the interval nitrogen is substitutions for the sites of oxygen atoms.As a result,the nitrogen successfully achieves the substitution of nitrogen for oxygen atoms (N1).Meanwhile,some other nitrogen atoms are chemically adsorbed on the surface of TiO 2(N2),as the peak of 400.5eV shown in the Fig.6a.After that,the N–TiO 2is put into the vacuum tube furnace to be activated at different temper-atures.During the vacuum activation process,some oxygen atoms are departed from the lattice of TiO 2to form some oxygen vacan-cies due to the negative pressure at a heating temperature (Fig.7).Moreover,the percentage of nitrogen doping into lattice of TiO 2(N1)and chemically adsorbed on the surface of the catalyst (N2)was obtained by the calculation [18].As a result,the percentages of N1in N–TiO 2and N–TiO 2−x are 0.56at%and 0.18at%,respectively.And the amount of N2in N–TiO 2and N–TiO 2−x are 0.17at%and 0.67at%,respectively.Because of the formation of oxygen vacan-cies,the percentage of nitrogen species adsorbed on the surface of TiO 2(N2)is substitutions of these oxygen vacancies to enhance the percentage of the nitrogen doped into the lattice of TiO 2(N1)after the vacuum activation,with the total nitrogen atom percent-age almost changeless.It leads to the increase of peak at 398.7eV after vacuum activation in Fig.6a.In other aspect,the extra elec-tron in nitrogen will transfer to the neighbor Ti 4+to generate Ti 3+to achieve the charge balance,which is consistent with the ESR results that the N–TiO 2−x has a strong Ti 3+signal in Fig.5a.Hence,the vacuum activation method is a useful technology to enhance the substitution of nitrogen into TiO 2,which is expected to be beneficial to the visible-light photocatalytic activity of TiO 2.Y.Zhou et al./Applied Catalysis B:Environmental170-171(2015)66–7371Fig.7.Proposed anatase crystal(101)surface structural model of TiO2,N–TiO2and N–TiO2−x,and a schematic diagram of the substitution of nitrogen for oxygen vacancies during the vacuum activation.3.4.Photocatalytic activity of N–TiO2−xThe photocatalytic activity of the Ti3+and nitrogen co-dopedsamples is evaluated by the degradation of organic pollutants(MO)under visible light irradiation( >425nm).Fig.8a shows the rel-ative changes of MO concentrations with irradiation time.And allthe catalysts show a very low and similar adsorption for methylorange(MO)in the dark(Fig.9).Compared with the pure TiO2,either N–TiO2or N–TiO2−x shows a higher photo degradation ratefor MO under visible light illumination.After a simple vacuum acti-vation,the TiO2−x gives a higher photocatalytic activity owing tothe generation of Ti3+.To the N–TiO2,it can be considered thatthe nitrogen replaces the oxygen atoms in TiO2.As a result,theband gap of TiO2is reduced after nitrogen doping,leading toanFig.8.(a)Visible light photocatalytic activities of TiO2,N–TiO2,N–TiO2−x and(b) N–TiO2catalysts vacuum activated at different temperatures.efficient visible light photocatalytic activity[23,30].Furthermore, the catalysts show the higher photocatalytic activity after vacuum activation,resulting from the synergistic effect between Ti3+and nitrogen into TiO2lattice.As can be seen in XPS spectra(Fig.6a), there is an obvious increase of the nitrogen of N1and a decrease of the nitrogen of N2after vacuum activation.That is,the ratio of N1/N2significantly increases after vacuum activation,which is beneficial to the enhancing of visible-light activity of TiO2[18].The enhancing nitrogen doping into TiO2lattice after vacuum activa-tion shows an increase of absorption in visible light region,and an enhancing visible light photocatalytic activity(Fig.8b)shows the degradation of MO for the nitrogen doped TiO2after vacuum activa-tion at different temperatures under visible light illumination.It can be seen that with the increase of vacuum activation temperature, photocatalytic activityfirstly increases and then decreases.Under the optimized treating condition,the catalyst N–TiO2−x(300◦C-3h)exhibits the highest photocatalytic activity.On the contrary, the sample N–TiO2−x(600◦C-3h)shows almost no activity owing to the bigger particle size and lower Ti3+concentration.When vac-uum activation temperature increases,the particle sizes increase and the generation of Ti3+decreases(Fig.5b).As a result,the corre-sponding photocatalytic activity is reduced[27,44].Because of the large particle size,the recombination rate of the photo-produced carriers in the bulk of TiO2increases significantly,which results in the decrease of photocatalytic activity.Fig.10shows the changes of the relative concentrations of MO under the UV light pared with pure TiO2,nitrogen doped TiO2exhibits higher activity under UV light illumination. That is because the introduction of nitrogen doping level into the bandgap of TiO2facilitates the separation of electrons andholes.Fig.9.The adsorption capacity for methyl orange(MO)on different samples in the dark.72Y.Zhou et al./Applied Catalysis B:Environmental170-171(2015)66–73Fig.10.(a)Ultraviolet light photocatalytic activities of TiO2,N–TiO2,N–TiO2−x and (b)N–TiO2catalysts vacuum activated at different temperatures.At the same time,the UV-light photoactivity of the samples after vacuum activation is almost changeless.Ti3+self-doping and the further doping of nitrogen cannot introduce carrier recombination centers,therefore,it is different from other metal doping[45,46]. Fig.10b shows the changes of the relative concentrations of MO with irradiation time for N–TiO2after vacuum activation at differ-ent temperatures.The result exhibits that photocatalytic activity of the samples increases smoothly.With the increase of vacuum acti-vation temperature,there is a phenomenon that the photocatalytic activity of the catalysts increases under ultraviolet illumination, which is similar to the trend of catalytic crystalline,and it reaches the maximum at600◦C(Fig.1b).It indicates that high crystalline contributes to high photoactivity in that the decrease of lattice defects in the bulk of TiO2,which is beneficial to the separation of electrons and holes under the circumstance that there is a large number of carries produced under the UV light irradiation.The donor level induced by nitrogen doping upon the VB exists inside the bandgap of TiO2,where electrons are generated under the irradiation of visible light(Fig.11).Meanwhile,Ti3+self-doping introduces an impurity level under the CB which can trap the photo-induced electrons.At the same time,it can reduce oxygen and produce a superoxide radical which promotes the separation of charge carrier,while holes left in the VB accelerate the generation of free OH radicals.The band gap is narrowed by the existence of N doping level and the Ti3+impurity level,which can enhance photo-catalytic activity of TiO2.The N doping can improve the absorption of visible light,and the Ti3+doping can enhance the separation efficiency of photo-generate electrons and holes.It is well worth mentioned that the nitrogen could be further doped into TiO2lat-tice by the substitution of oxygen vacancies during the vacuum activation process,which can further improve the concentration of doping levels inside the bandgap of TiO2.Hence,the synergistic effect between Ti3+and nitrogen is responsible for the high visible light and UV light photocatalytic activity of TiO2.Fig.11.Proposed structural model of energy states that exist between the VB and CB of N–TiO2−x,and a schematic diagram of the charge separation and photocatalytic activity of the photocatalyst.4.ConclusionsIn summary,the N–TiO2−x is successfully prepared by using the calcination–vacuum activation method.The vacuum activa-tion technology is confirmed that it can improve the substitution of nitrogen for oxygen vacancies into the TiO2and decrease the chemically adsorbed nitrogen species,which leads to a higher visible-light photocatalytic activity than the pure TiO2and the N–TiO2.A Ti3+impurity level is introduced by the vacuum acti-vation treatment.And plenty of nitrogen is doped into the lattice of TiO2.The N–TiO2−x catalysts have high photocatalytic activities for the degradation of methyl orange under the visible-light and the UV-light irradiation.The synergistic effect between Ti3+and nitrogen doping is responsible for the high visible light activity of N–TiO2−x(300◦C-3h),and the high crystallinity is the reason for the high UV light activity of N–TiO2−x(600◦C-3h). 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小学下册英语第四单元综合卷[有答案]英语试题一、综合题(本题有50小题，每小题1分，共100分.每小题不选、错误，均不给分)1 What do we call a person who plays the guitar?A. PianistB. GuitaristC. DrummerD. Violinist2 The country known for its maple syrup is ________ (以枫糖浆闻名的国家是________).3 How many legs does a spider have?A. 6B. 8C. 10D. 12答案:B4 A substance that can donate protons in a reaction is called a _______.5 The bat flies at _____.6 The __________ (历史的回顾性) fosters reflection.7 I like to watch ______ (体育) events on TV.8 I love to ______ (与朋友一起) enjoy new experiences.9 The first modern Olympic Games were held in ________ (1896).10 A solution that contains a high concentration of ions is called a ______ solution.11 Carta was signed in _______. (1215年) The Magn12 We built a castle with our ____. (玩具名称)13 The boiling point of water is __________ (100度) Celsius at sea level.14 The chemical formula for glucose is ______.15 They are wearing _____ (sunglasses/hats) at the beach.16 The chemical formula for ammonia is __________.17 The _____ (小猫) loves to play with balls of yarn.18 A _______ is a special type of mixture with tiny particles that never settle.19 What is the name of the activity where you throw a ball into a hoop?A. BasketballB. FootballC. SoccerD. Baseball答案: A20 __________ are used in electrical circuits to control current flow.21 What is the largest mammal in the ocean?A. SharkB. DolphinC. WhaleD. Seal答案: C22 I like to go ______ (滑雪) during winter vacations.23 Which of these is a type of tree?A. RoseC. DaisyD. Tulip24 The first man to dive into the Mariana Trench was _______. (维尔德)25 She loves to _______ (sing) in the shower.26 What is the opposite of 'new'?A. UsedB. OldC. FreshD. Recent答案:B27 I can _____ my bed every morning. (make)28 The ______ is a talented actress.29 What is the capital city of Brazil?A. São PauloB. Rio de JaneiroC. BrasíliaD. Salvador答案:C30 A _______ can change colors throughout the seasons.31 The area where an oceanic plate meets a continental plate is called a ______.32 The classroom is ________ and clean.33 What instrument has keys and is played by pressing?A. GuitarB. ViolinD. Flute答案:C34 What is the largest continent?A. AfricaB. AsiaC. EuropeD. North America答案:B35 The ________ (藤) climbs up the wall.36 The boat is ___ (sailing) on the water.37 I can ________ (ride) a skateboard.38 The _______ in the garden are blooming beautifully.39 My favorite toy is a stuffed ______.40 My favorite toy is a ______ (机器人). It can talk and ______ (跳舞).41 We have a ______ (特别的) event this weekend.42 __________ are known to migrate long distances during winter.43 The boy is watching a ________.44 What is the name of the famous American holiday celebrated in December?A. ThanksgivingB. ChristmasC. New Year's DayD. Halloween答案:B45 The __________ is known for its diverse wildlife. (大堡礁)46 What is the name of the famous American actress known for "Gravity"?A. Sandra BullockB. Cate BlanchettC. Jennifer LawrenceD. Emma Stone答案：A47 His favorite game is ________.48 The __________ was a period of exploration and colonization. (大航海时代)49 The fish are ______ (swimming) in the pond.50 What is the capital of China?A. BeijingB. ShanghaiC. GuangzhouD. Shenzhen51 The __________ can provide critical insights into the impacts of climate change.52 What is the name of the famous American national park located in California?A. YellowstoneB. YosemiteC. Grand CanyonD. Zion答案：B53 What is the name of the process by which seeds grow into plants?A. GerminationB. PollinationC. FertilizationD. Propagation答案:A54 What is 15 divided by 3?A. 3B. 4C. 5D. 6答案:C55 A ______ is a substance that can exist in multiple states.56 The chemical formula for -ethoxybutanoic acid is ______.57 How many continents are there?A. 5B. 6C. 7D. 858 What do we call the process of liquid turning into vapor?A. CondensationB. FreezingC. EvaporationD. Sublimation答案:C59 A __________ (科学探索) expands our understanding of the natural world.60 Chemical reactions involve the breaking and forming of ________.61 Comets are often described as "dirty snowballs" made of ice and ______.62 A homogeneous mixture is uniform in _____.63 What do we call the first woman to fly solo across the Atlantic Ocean?A. Amelia EarhartB. Bessie ColemanC. Harriet QuimbyD. Jacqueline Cochran答案:A64 In a chemical equation, reactants are found on the ______.65 What do we call the primary source of energy for living organisms?A. WaterB. SunlightC. AirD. Food答案:B66 What is the main ingredient in mayonnaise?A. OilB. VinegarC. MustardD. Sugar67 He is _____ (playing/doing) video games.68 ts can be grown ______ (室内). Some pla69 My mom enjoys gardening and growing __________ (植物).70 Tokyo is the capital of __________.71 She is a friendly ________.72 What do you call the study of living things?A. BiologyB. ChemistryC. PhysicsD. Geography答案: A73 He is my _____ (好友) from childhood.74 Planting flowers can attract ______ (蜜蜂) to your garden.75 A __________ is a substance made up of only one type of atom.76 The ancient Romans celebrated festivals to honor their _____.77 What is the name of the famous detective created by Arthur Conan Doyle?A. Hercule PoirotB. Sam SpadeC. Sherlock HolmesD. Philip Marlowe答案: C78 What do we call a scientist who studies chemistry?A. ChemistB. BiochemistC. PhysicistD. Pharmacologist79 The _______ (The American Revolution) established the US as an independent nation.80 The flowers are ________ (多彩).81 The singer has a ______ (beautiful) voice.82 The ______ teaches us about different countries.83 What is the opposite of up?A. DownB. LeftC. RightD. Forward84 The study of matter and its changes is called _______. (化学)85 She is a _____ (护士) who helps deliver babies.86 Chemical reactions can be influenced by temperature and _____.87 __________ are found in many types of detergents.88 What do we call the part of the brain that controls balance?A. CerebrumB. CerebellumC. BrainstemD. Hypothalamus答案:B89 What is the main ingredient in bread?A. FlourB. SugarC. RiceD. Salt90 What do we call the process of water turning into vapor?A. CondensationB. EvaporationC. PrecipitationD. Sublimation答案:B91 The _______ of an atom is determined by the number of protons.92 I like to ______ (参与) in student council meetings.93 I saw a ________ hopping along the path.94 Which planet is known for its rings?A. MarsB. VenusC. SaturnD. Jupiter答案: C. Saturn95 Planting bulbs can lead to beautiful ______ (花朵) in spring.96 A hamster is a small ______.97 The __________ is a region known for its social movements.98 A crab can pinch with its ________________ (钳子).99 A _____ (植物分类) can help identify different species. 100 The kitten is ___ (pouncing) on a toy.。

高二英语科研项目实施单选题40题(带答案)1.In the scientific research project, we need to collect data _____.A.accuratelyB.exactlyC.preciselyD.correctly答案：A。

“accurately”强调准确地，在科研项目中收集数据需要准确无误。

“exactly”表示确切地、完全地；“precisely”精确地，和“accurately”意思较为接近但在科研收集数据的场景下，“accurately”更常用；“correctly”正确地，通常用于方法等正确，不太符合收集数据的语境。

2.When presenting the research results, we should express our ideas _____.A.clearlyB.obviouslyC.apparentlyD.visibly答案：A。

“clearly”清晰地，在展示研究结果时要表达清晰。

“obviously”明显地；“apparently”显然地；“visibly”看得见地，后三个选项不太符合表达想法的语境。

3.The scientific research project requires ______ teamwork.A.cohesiveB.unitedC.cooperativeD.joined答案：C。

“cooperative”合作的，科研项目需要合作的团队合作。

“cohesive”有结合力的；“united”联合的；“joined”连接的，这三个选项不太符合团队合作的语境。

4.We must analyze the data ______ to draw accurate conclusions.A.thoroughlypletelyC.entirelyD.wholely答案：A。

“thoroughly”彻底地，分析数据需要彻底才能得出准确结论。

济宁2024年10版小学五年级上册英语第五单元寒假试卷考试时间：80分钟（总分:120）A卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、听力题：My sister is a ______. She loves to share recipes.2、Which season comes after winter?a. Springb. Summerc. Falld. Autumn答案:A3、填空题：I saw a ________ in the tree branches.4、What is the opposite of 'fast'?A. QuickB. SlowC. SpeedyD. Rapid答案:B5、填空题：I like to wear my ______.6、听力题：A solution with a high concentration of solute is called _______.7、What is the first letter of the alphabet?A. AB. BC. CD. DThe chemical symbol for europium is _____.9、听力题：The rain is ______ on the roof. (falling)10、听力题：A base can neutralize an _______.11、What do we call the act of studying the past?A. ArchaeologyB. HistoryC. AnthropologyD. Paleontology12、填空题：The ancient city of ________ is known for its ruins and history.13、填空题：The chemical formula for table sugar is __________ (C12H22O11).14、Which country is known for pyramids?A. MexicoB. ChinaC. EgyptD. Greece答案:C. Egypt15、填空题：I learned how to ride my new ____ this summer. (玩具名称)16、听力题：Fossils provide evidence of ______ life on Earth.17、听力题：The __________ is a long area of land that is surrounded by water on three sides.18、填空题：The parrot's ability to mimic sounds makes it a popular ________________ (宠物).19、听力题：The ______ helps with the sense of touch.20、填空题：The _____ (果仁) is a part of some plants.The chemical symbol for radon is _____.22、填空题：He is a _____ (作曲家) who creates wonderful music.23、填空题：My dad gave me a toy _____ for my birthday.24、填空题：I like to smell the ________.25、填空题：The ancient Greeks competed in athletic contests at the ________.26、填空题：Understanding the environmental needs of plants can lead to more effective ______. (了解植物的环境需求可以促进更有效的园艺。

最新理论试题及答案英语一、选择题（每题1分，共10分）1. The word "phenomenon" is most closely related to which of the following concepts?A. EventB. FactC. TheoryD. Hypothesis答案：C2. In the context of scientific research, what does the term "hypothesis" refer to?A. A proven factB. A testable statementC. A final conclusionD. An unverifiable assumption答案：B3. Which of the following is NOT a characteristic of scientific theories?A. They are based on empirical evidence.B. They are subject to change.C. They are always universally applicable.D. They are supported by a body of evidence.答案：C4. The scientific method typically involves which of the following steps?A. Observation, hypothesis, experimentation, conclusionB. Hypothesis, observation, conclusion, experimentationC. Experimentation, hypothesis, observation, conclusionD. Conclusion, hypothesis, observation, experimentation答案：A5. What is the role of experimentation in the scientific process?A. To confirm a hypothesisB. To disprove a hypothesisC. To provide evidence for or against a hypothesisD. To replace the need for a hypothesis答案：C6. The term "paradigm shift" in the philosophy of science refers to:A. A minor change in scientific theoryB. A significant change in the dominant scientific viewC. The process of scientific discoveryD. The end of scientific inquiry答案：B7. Which of the following is an example of inductive reasoning?A. Observing a pattern and making a general ruleB. Drawing a specific conclusion from a general ruleC. Making a prediction based on a hypothesisD. Testing a hypothesis through experimentation答案：A8. Deductive reasoning is characterized by:A. Starting with a specific observation and drawing a general conclusionB. Starting with a general rule and applying it to a specific caseC. Making assumptions without evidenceD. Relying on intuition rather than logic答案：B9. In scientific research, what is the purpose of a control group?A. To provide a baseline for comparisonB. To test an alternative hypothesisC. To increase the number of participantsD. To confirm the results of previous studies答案：A10. The principle of falsifiability, introduced by Karl Popper, suggests that:A. Scientific theories must be proven trueB. Scientific theories must be able to withstand attempts at being disprovenC. Scientific theories are never wrongD. Scientific theories are always based on personal beliefs答案：B二、填空题（每题1分，共5分）1. The scientific method is a systematic approach to__________ knowledge through observation, experimentation, and __________.答案：gaining; logical reasoning2. A scientific law is a statement that describes a__________ pattern observed in nature, while a scientific theory explains the __________ behind these patterns.答案：recurring; underlying principles3. The process of peer review in scientific publishing is important because it helps to ensure the __________ and__________ of research findings.答案：validity; reliability4. In the context of scientific inquiry, an __________ is a tentative explanation for an aspect of the natural world that is based on a limited range of __________.答案：hypothesis; observations5. The term "empirical" refers to knowledge that is based on __________ and observation, rather than on theory or__________.答案：experimentation; speculation三、简答题（每题5分，共10分）1. Explain the difference between a scientific theory and a scientific law.答案：A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experimentation. It is a broad framework that can encompass multiple laws and observations. A scientific law, on the other hand, is a concise verbal or mathematical statement that describes a general pattern observed in nature. Laws summarize specific phenomena, while theories explain the broader principles behind those phenomena.2. What is the significance of the falsifiability criterionin the philosophy of science?答案：The falsifiability criterion, proposed byphilosopher of science Karl Popper, is significant because it provides a way to distinguish between scientific and non-scientific theories. For a theory to be considered scientific, it must be testable and potentially refutable by empirical evidence. This criterion ensures that scientific theories are open。

Abstract一、在摘要中直接提出论文主题的句型和句式1、In this paper,we present a… approach to…本文提出了一种针对…的…方法。

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3、We propose a new… model and…algorithm that enables us to…我们提出一种新的…模型和…算法，它让我们能够…4、We present a…model that enables…我们提出了一种…模型，它使我们能够…5、This paper demonstrates the ability of …to perform robust and accurate…本文证明了…进行…可靠准确的…的能力。

6、In this paper we report results of a…approach to…本文报导了…的…方法的实验结果。

7、This paper demonstrates that…can effectively…with very high accuracy.本文证明，…能够有效地准确地…8、The purpose/goal/intention/objective/object/emphasis/aim of this paper is…本文的目的是…9、The primary/chief/overall/main object of this study is to survey…本研究的首要目标是考察…10、The chief aim of this paper/research/study/experiment/the present work is…本文的主要目标是…11 、The emphasis of this study lies in …我们的研究重点是…12、The work presented in this paper focuses on…本文所述工作重点放在…13、Our goal has been to provide…我们的目标是提供…14、The main objective of our investigation has been to obtain some knowledge of …我们的研究目标是获取有关…的知识。