Study On The Preparation Of Visible Light Responsive Semiconductor Heterojunction Composite Material And Its Photo/Photoelectric Catalytic Water Splitting Performance

In recent decades,energy crisis and environmental deterioration has become more and more serious due to human beings'extreme dependence on fossil fuels.Hydrogen energy,as a kind of high efficiency,clean and renewable energy,which has attracted wide attention and is known as the new energy in the 21st century.As a green and sustainable technology,photocatalytic water splitting is one of the ideal ways to obtain hydrogen energy.At present,researchers are committed to the research and development of high-efficiency photocatalyst,and has made some progress.But there are still a series of problems,such as low solar energy efficiency,low photogenerated electron-hole separation efficiency and et al.Therefore,it is of great significance and value to develop and utilize semiconductors with ideal band structure that can respond to visible light.The construction of semiconductor heterojunction is an effective way to achieve this goal,which can not only integrate the advantages of multi-component semiconductor,but also expand the absorption range of visible light,improve the separation efficiency of photogenerated electron-hole and enhance the redox ability of photocatalyst.Therefore,from the perspective of electronic structure and energy band matching,different semiconductor heterojunctions are constructed in this paper to broaden the light response range of a single semiconductor,improve its light absorption capacity,promote the separation and transfer of photogenerated carriers,and thus enhance the photo/photoelectric catalysis performance.The main work of this paper is as follows:I?In this work,the direct Z-scheme Ta ON/ZCS heterojunction of Cd_0.5Zn_0.5S(ZCS)solid solution nanoparticles modified with porous Ta ON was successfully prepared,and the photocatalytic hydrogen production efficiency using Ta ON/ZCS heterojunction as photocatalyst,Na₂SO₃/Na₂S as hole sacrifice reagent and non-noble metal Ni S as co-catalyst was investigated.The results showed that the maximum photocatalytic hydrogen production rate reached 34.8 mmol h^-1 g^-1 when 0.5 wt%Ni S was loaded on 4 wt%Ta ON/ZCS(T4-ZCS)surface by photodeposition.The high photocatalytic performance was firstly attributed to the composition of direct Z-scheme Ta ON/ZCS heterojunction.Secondly,Ni S was used as a co-catalyst,which acts as an electron collector to reduce protons to hydrogen which adsorbed on its surface.Both sides synergistically promote the effective transfer and separation of photogenerated charge carriers.II?The sol-gel method was used to prepare the black N-doped Ti O_2-xnanoparticles loaded on the carbon framework(N-Ti O_2-x/C,NTC)in one step.In this work,the synthesized NTC material was combined with short Cd_0.5Zn_0.5S(ZCS)nanorods to form a direct Z-scheme NTC/ZCS photocatalyst without using of electron mediator.The free radicals trapping experiment was also carried out through the photocatalytic degradation of Rhodamine B(Rh B)to determine the mechanism of photocatalytic hydrogen production.As a result,the 2 wt%NTC/ZCS exhibited an optimal photocatalytic H₂ production rate which is up to 36.6 mmol h^-1 g^-1 and about5.2 times higher than that of pristine ZCS nanorods.The apparent quantum efficiency(AQE)of the 2 wt%NTC/ZCS heterojunction under 420 nm monochromatic light irradiation was calculated to be 51.2%.III?This work successfully prepared composites of carbon-modified in-phase Mo C-Mo₂C(Mo C-Mo₂C@C,MMC)nanosheets with Cd_0.5Zn_0.5S(ZCS)short nanorods.The loading of MMC nanosheets significantly improved the hydrogen production rate of ZCS nanorods.The results showed that the photocatalytic hydrogen production rate of ZCS was the highest when MMC nanosheets are 1 wt%of ZCS nanorods(1-MMC/ZCS),reaching 68.7 mmol h^-1 g^-1,which is 7.7 times that of pure ZCS nanorods.Under the irradiation of 420 nm monochromatic light,the quantum efficiency of 1-MMC/ZCS was 32.9%.The carbon layer can promote the rapid transfer of photogenerated electrons,and the Mo₂C-Mo C in-phase junction as the active site which both synergistically improve the photocatalytic hydrogen production rate of ZCS.At present,most Mo₂C-based materials are still used in the field of electrocatalysis.IV?Efficient solar-powered water oxidation over the Bi VO₄-based anodes requires coupling photoactive semiconductors to improve the inferior activity and stability.Herein,we studied the photoelectrocatalytic performance of a photoanode formed by doctor-blading porous Ta ON-Bi VO₄ on the surface of the WO₃ layer obtained by spin coating.Compared with the unmodified Ta ON-Bi VO₄ photoanode,the Ta ON-Bi VO₄/WO₃ composite photoanode has a significantly enhanced water oxidation photocurrent density at 1.23 V(vs.RHE).The effects of the forming of particularly porous microstructure and PEC performance of the resulting anodes are explored.The various materials and photoanodes were characterized by XRD,SEM,TEM,XPS and CV,etc.Besides,the formation process and probable transfer mechanism of photoinduced carriers were also discussed.