| The problems of energy crisis and chean energy with sustainable supply have became the“challenge”facing to all the countries and how to solve them is becoming one significant and hot topic issue.Conversion solar energy to energy source with superiority of cleanliness,environment friendliness and sustainability by ustilizing the technique of semicondurtor photocatalysis is one cutting-edge method to solve above problems with promising.This technique processes a series of m erits including abuntant raw materials,moderate reaction condition as well as simple preparation process for photocatalysts,and so on.However,the conversion efficiency of new energy by photocatalysis is still to low to satify the practical requirement.The photocatalytic reaction mainly includes three processes:?I?the generation of charge carriers when the energy of the incident light is larger than the band gap of a semiconductor;?II?the recombination and migration of photogenerated electrons and holes;?III?the electrons and holes transferred to the surface participating the redox reactions.During these included three processes,the second one usually plays the vital role,because that the essence of a photocatalytic reaction resulting in low efficiency is the fast recombination of photogenerated electrons and holes.Thus,the decisive factor for improving the performance of a photocatalyst is how to inhibit the recombination of photogenerated charge carriers by valid controlling methods.Among so many ways have been applied to modifiy the performace of a semiconductor material,constructing heterojunction to achieve the high separation of photogenerated electrons and holes is undoubtly to be an effective one.The present paper aimed at developing and constructing a series of high-performance heterojunction for photocatalytic H2 production from water splitting,studying the internal relations among heterojunction interface,photogenerated charge carrier behaviors,and photocatalytic activity.It will provide the theoretical support for designing photocatalysts with high-performace.This paper mainly includes the following five parts:1.Cd S and Ni@Ni O synergetic co-catalysts supported on g-C3N4 for visible-light-driven photocatalytic H2 evolution:we have constructed and prepared the Ni@Ni O/CdS/g-C3N4 omposites photocatalyst for highly efficient photocatalytic H2evolution,which is the results of the synergetic effect between CdS and co-catalyst Ni@Ni O.The experiment results reveal that the target Ni@NiO/CdS/g-C3N4 shows the high photocatalytic H2 evolution rate of 1258.7?mol h-1 g-1,which is 400 times higher than that of pure g-C3N4.Under light irradiation,g-C3N4 and Cd S can be excited to generate electrons and holes,then,the CB-electrons?CB,conduction band?of g-C3N4 can be fastly injected to the CB of Cd S under build-in electric field resulting in the efficient separation of charge carriers.On the other hind,the Ni@NiO can remove the CB-electrons of CdS,further suppressing their recombination.Thus,the maximized separation of photogenerated electron-hole pairs can be achieved under the coeffect of Cd S and Ni@Ni O,resulting in the highly efficient photocatalytic H2 evolution performance.2.Novel architecture of dandelion-like Mo2C/TiO2 composite photocatalysts towards high-performance photocatalytic H2 generation production water reduction:we first synthesized the dandelion-like TiO2 photocatalyst using acetic acid and tetrabutyl titanate via a solvothermal method,during this process acetic acid is not only the reactant but also the mass transfer medium.Then,a well-controlled synthetic strategy is developed to loading Mo2C nanoparticles with highly dispersion on the sureface of Ti O2.A seriers of measurements including photovoltage?SPV?,photoluminescence?PL?,time-resolved photoluminescence?TRPL?,and open circuit potential?OCP?decay profiles are conducted to study the charge carrier dynamics,suggesting that Mo2C well controls the photogenerated charge carrier behaviours in process of photocatalysis.Further,Mo2C has the similar electronic density of state to that of Pt and high electrical conductivity,accelerating the abili ty to trap electrons from TiO2.The photocatalysis results reveal that Mo2C/Ti O2 achieves the ultrahigh photocatalytic H2 generation rate of 39.4 mmol h-1 g-1,which is 25 times higher than that of pristine Ti O2.3.Highly efficient Co P/TiO2“n-n”heterojunction catalyst for photocatalyti H2evolution from water splitting:we have successfully syntnesized this high efficiency Co P/TiO2 photocatalyst and expanded the application of transition metal phosphides in system of photocatalysis.In our system,on the one hand,the CoP acts as the cocatalyst to transfer the CB-electrons of TiO2;on the other hand,CoP combines with Ti O2 to form a typical“I-type”heterojunction,facilitating the separation of photogenerated charges on TiO2.In theory,the CB-electrons and VB-holes all transfer to the CoP,a process which is not favour of photocatalytic reaction.While we know that the transfer rate of holes is much lower than that of electrons,resulting in the production of dislocation for these charges not only in space but also in time.Thus,this dislocation breaks the condition for their recombination,results in the high separation of photogenerated charges on CoP.As compared to pure Ti O 2(720?mol h-1 g-1),the CoP/Ti O2 heterojunction achieves the high photocatalytic H2 genration rate of 8350?mol h-1 g-1.This novel composite photocatalyst open new insight for the much more application of transition metal phosphides in the system of photocatalysis.4.Novel and highly efficient Cu3P/TiO2“p-n”heterojunction nanophotocatalyst for H2 evolution from water splitting:we have synthesized the p-type semiconductor character of Cu3P via a simple method,which is confirmed by the measurement of Mott-Schottky?M-S?plot.Then,we combined it with Ti O2?a typical n-type material?prepared by solvothermal method to form a highly efficient“p-n”junction for photocatalytic H2 evolution from water reduction.Under solar light irradiation,Cu3P/Ti O2 shows the H2 evolution rate as high as 7940?mol h-1 g-1,which is 11times higher than that of pure Ti O2.The discussions based on a seriers of measurements analysis speculate that the build-in electric field formed at the interface of Cu3P and Ti O2 contributes to the high separation of photogenerated charge carriers and inhibites their recombination.5.Well-controlled SrTi O3@Mo2Ccore-shellnanofiberphotocatalyst:boosted photo-generated charge carriers transportation and enhanced catalytic performance for water reduction:the SrTi O3 nanofiber is first obtained by a simple single spinneret electrospinning method;then a layer of Mo2C is coated on the surface of SrTiO3 by another simple way to achieve the target SrTi O3@Mo2C core-shell structure composite.The layer of Mo2C not only boosts the separation of photogenerated electron-hole pairs but also enhance their transportation,minimizing their recombinationm to some extent.Thus Sr Ti O3@Mo2C hybrid achieves drastically enhanced photocatalytic H2 generation rate up to 7.93 mmol h-1 g-1 with respect to the pristine SrTi O3(0.53 mmol h-1 g-1)in a solar-driven reaction system,with an AQE of 29.3%at 313 nm.The charge carrier dynamics based mechanism was further confirmed by analysis of time-resolvedphotoluminescence?TRPL?,surface photovoltage?SPV?,transient photovoltage?TPV?,open circuit potential?OCP?decay curves as well as theelectrochemical impedance spectroscopy?EIS?measurements. |
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