Design And Performance Studies Of Multi-heterojunction Photocatalysts

Semiconductor photocatalysis technology is considered to be one of the ideal technologies to solve environmental and energy problems.It has received extensive attention from researchers.This article focuses on the design and synthesis of multi-junction composite photocatalysts.We improved the activity and efficiency of photocatalysts in energy conversion and environmental purification by adjusting the light response range,promoting the separation of electrons and holes,improving the stability of the photocatalyst and using co-catalysts.Also,the mechanism of multi-junction structure in photocatalytic reaction was explored.CdS-NaNbO₃-Mo S_x composite catalysts with rod-like multi-heterojunction structure were prepared by multi-step hydrothermal reaction method and light deposition method.The experimental results showed that under visible light conditions,the optimal ratio of composite photocatalyst had a photolysis water hydrogen production efficiency of 11.9 times that of CdS,and exhibited excellent stability under long-term light irradiation.The multi-heterojunction structure and Cd-S-Mo bond provided abundant and effective photo-generated charge migration pathways.The electrons on the conduction band of CdS could transfer to the conduction band of NaNbO₃ or be captured by Mo S_x.These reasons could effectively inhibit the recombination of electron-hole pairs and improve the activity of photocatalytic hydrogen evolution.CdS and Ni S₂ were generated on the surface of three-dimensional NaNbO₃ in one step by hydrothermal reaction method.A multi-heterojunction CdS-NaNbO₃-Ni S₂ composite photocatalyst was prepared.The experimental results show that under the same conditions,the hydrogen production efficiency of the optimal ratio of composite photocatalyst was 24.7 times that of CdS.The synchronously loaded hydrothermal preparation method made the direct interface structure between the noble-metal-free promoter and the catalyst closer.It was more conducive to the transfer of photo-generated charges between different semiconductors.At the same time,a larger specific surface area provided more reaction contact sites.By controlling the calcination temperature,the precursor was converted into Ti O₂ with different crystal phases.Then the Ti O₂ was modified with two-dimensional Bi OI by hydrothermal in-situ generation method to obtain multi-junction composite photocatalyst with coexistence of homojunction and heterojunction.When the organic antibiotic contaminants ceftriaxone sodium and Cr(?)were degraded separately,the degradation rate of the multi-junction photocatalyst was improved compared with the single homojunction or single heterojunction catalysts.When used for synergistic degradation,the degradation rate of ceftriaxone sodium was slightly reduced,but the degradation rate of Cr(VI)increased by 8.3times.Under the combined action of the multi-junction structure and synergistic degradation,the migration and separation of photogenerated electrons and holes were promoted.And the recombination were greatly inhibited,thereby enhancing the photocatalytic activity.