Study On Interfacial Charge Transfer Dynamics Of Semiconductor Heterojunction And Photocatalytic Performance Under Visible Light

The excessive consumption of fossil fuels has not only changed the planet’s climate today but has also led to energy shortages.The demand for clean and renewable energy for sustainable development has driven the development of new energy sources and technologies.Photocatalysis,which uses sunlight to convert CO₂ and H₂O into CO,CH₄,H₂ and other energetic substances,has received much attention because of its green and sustainable advantages.As researchers continue to explore,it is found that shortcomings such as the compounding of photogenerated carriers and the small absorption range of visible light in semiconductor photocatalysts seriously hinder further improvement of photocatalytic performance.So far,researches have proposed a number of strategies for increasing the catalytic effectiveness of photocatalysts,with the construction of heterojunctions being one of the most straightforward and successful.It can improve visible light utilization,electron and hole separation,and the redox ability of semiconductor catalysts.Therefore,in this paper,we have constructed semiconductor heterojunctions with distinct components to broaden the optical light response range of a single semiconductor and to facilitate the separation and transfer of electron-hole pairs to enhance photocatalytic performance from the perspective of band matching and electronic structure.The main research contents are as follows:1.Two-dimensional metal-organic framework loaded with CsPbBr₃ with different aspect ratios for photocatalytic CO₂ reduction.In this chapter,we systematically study the effect of the change of aspect ratio on the photocatalytic performance using two-dimensional Ni based metal-organic framework as a cocatalyst and CsPbBr₃ as a model semiconductor.As a result,CO production has been increased by 1.8,2.5,and 4.1-fold for CsPbBr₃ nanocubes,nanorods,and nanowires,respectively,which has been shown to be positively correlated with the aspect ratio of CsPbBr₃.The increased energy difference at the interface between the conduction band of CsPbBr₃ and NMF with elongation of CsPbBr₃,which produces an enlarged driving force for promoted interfacial electron transfer and superior charge separation properties,is attributed to the aspect ratio dependent photocatalytic improvement.2.Engineering an interfacial facet of BiOBr/ZnIn₂S₄ S-scheme heterojunction for improved photocatalytic hydrogen evolution by modulating the internal electric field.In this chapter,the facet engineering is performed with the growth of ZnIn₂S₄ on（010）and（001）facet-dominated BiOBr nanosheets to fabricate ZnIn₂S₄/BiOBr-（010）and ZnIn₂S₄/BiOBr-（001）S-scheme heterojunctions,respectively.The creation of a stronger built-in electric field with more significant band bending in the space charge region near the interface is enabled by a higher Fermi level difference between BiOBr-（001）and ZnIn₂S₄.As a result,the directional migration and recombination of pointless photoexcited electrons in the conduction band of BiOBr and holes in the valence band of ZnIn₂S₄ with weak redox ability is greatly accelerated,resulting in more efficient spatial separation of powerful conduction band electrons of ZnIn₂S₄ and valence band holes of BiOBr.Taking use of these advantages,the ZnIn₂S₄/BiOBr-（001）outperforms the ZnIn₂S₄/BiOBr-（010）and mono-component equivalents in photocatalytic H₂ evolution.3.Synergistic effects of multiple light reflection,spatial charge,hierarchical pores and oxygen vacancies in photocatalytic CO₂ reduction of BiOBr/Bi₂S₃ nanoarray heterojunctions.In this chapter,we synthesized a BiOBr/Bi₂S₃ Type II heterojunction photocatalyst composed of BiOBr nanoplates and meshed Bi₂S₃ nanoarrays.As a results,the heterojunction photocatalyst has the following advantages:（1）The vertically aligned Bi₂S₃ nanowalls enable the light absorption range of the heterojunction to beyond 1000 nm,and the formed mesh pores improves the light absorption due to multiple light reflection and scattering;（2）the intimate contact between Bi₂S₃ and BiOBr improves the separation ability of electrons and holes;（3）the pores and oxygen vacancies on the surface of BiOBr enhance the adsorption and activation of CO₂,and decrease the barrier of the rate-determining step in CO₂-to-CO reduction.Due to the above advantages of BiOBr/Bi₂S₃-34 heterojunction,under broad-spectrum illumination,the CO generation rate is 103.5μmol g^-1_cat h^-1,which is higher than that of the reported BiOBr-based photocatalysts.