Structure Design And Functional Studies Of Semiconductor-Based Nano-Photocatalyst System

Photocatalytic reaction is a common approach that can convert solar energy into chemical energy effectively.With its demonstrated capability in both hydrogen generation and organic pollutant photodegradation,photocatalysis becames a promising technology with significant potential in dealing with the energy crisis and environmental pollution.It is thus of great importance to develop highly active semiconductor-based photocatalyst.Generally speaking,the photocatalytic efficiency of semiconductor-based photocatalysists mainly depends on their light absorption range and the separation efficiency of photogenerated carriers.At the same time,the effective contact between photogenerated carriers and reactants also plays a part in photocatalytic activity of semiconductor-based photocatalyst.This thesis focuses on the rational construction of catalytic system aiming at promotion of hydrogen production performance and efficient photodegradation.A series of highly efficient catalytic systems have been constructed in order to study the impact of the transportation properties of photogenerated carriers on the photocatalytic performance,and the internal relations between nanostructured electrodes and their photocatalytic performance.And the introduction of solar-thermal conversion function on TiO₂-based nanoparticle composite film also contributes to the efficient utilization of solar energy and its multifunctional conversion.At last,this thesis also develops a novel method to construct nano-composite structures in order to offer various possible structures for the better exploration and regulation of the semiconductor-based photocatalytic performance.This thesis involves several aspects as follows:1.To explore the impact of the interface structure on the transport properties of photogenerated carriers through the generation of metal-semiconductor hetrojunctions with specific crystal planes,which could provide new approaches to fabricate highly efficient photocatalyst.Here,I construct a Pt/PbS heterojunction using PbS NCs with well-controlled shapes to regulate and explore the impact of the interface structure on the transport properties of photogenerated carriers and the photocatalytic performance.Research results have shown that the photocatalytic activities of Pt/PbS catalyst are strongly related to the contacting facets of PbS at the junction.The Pt/octahedral PbS NCs with PbS?111?facets exposed show the highest photo-induced enhancement of hydrogen evolution reaction activity,which is¹4.38 times higher than the ones with only PbS?100?facets?Pt/cubic PbS NCs?.The DFT results also confirm that the different contacting interfaces of Pt/PbS catalyst result in Schottky junctions with different heights,which block the transport of photogenerated carriers with different extent and further influence the photocatalytic performance.The findings may offer a method to optimize the transport properties of photogenerated carriers,which may improve the photocatalytic performance of the constructed nano-photocatalytic system.2.A visualized characterization method has been developed to study the relationship between the nanostructured surface and the mass transfer process during photocatalysis.Here,electrodes with large-area SiNWs are fabricated by a wet-etching method for hydrogen generation.It is found that the nanostructured surface will promote the effective release of generated hydrogen bubbles on the electrode surface,alleviate the bubble adhesion to a large extent,and then improve the mass transfer process between the electrode and the electrolyte.Besides,changing the etching time is a method to regulate the roughness of the electrode nanostructured surface.This thesis explores the relationship between the electrode with different surface roughness and the behaviors of generated bubbles.Research results have shown that with the increase of the length of SiNWs,the surface of the obtained SiNWs electrode offers more nucleation sites as well as bigger departure diameter for the hydrogen bubbles with improved catalytic efficiency.Such improvement is consistent with the result of electrochemical test.3.Introducing some solar-thermal conversion material into TiO₂-based nanoparticle composite film contributes to the efficient utilization of solar energy and its multifunctional conversion.In this study,a bifunctional membrane TiO₂-Au-AAO was designed and fabricated through multiple filtration processes.SEM,UV-vis,IR were used to characterize the structure morphology and optical adsorption properties of the constructed composite membrane.The photocatalytic property of the fabricated bifunctional membrane is evalued by the photodegradation of RhB solution using simulated solar illumination.The relations betweent the structure and purification efficiency are also analyzed.Research results have shown that such a design enables both TiO₂ NP-based photocatalytic function and Au NP-based solar-driven plasmonic evaporation,which also helps open up a new strategy for maximizing solar energy conversion and utilization.In order to further increase the utilization of solar energy and improve its practicality,a similar method was adopted to fabricate the paper-based composite membrane.Research results have demonstrated that this new design helps integrate the functionality of physical adsorption with photocatalytic performance and photothermal conversion ability.Such design could further increase the efficiency of solar energy utilization and conversion while improving the performance of waste-water treatment.4.As to the construction of highly efficient semiconductor-based nano-photocatalytic system,the fabrication of nano-composite structure may offer more designs to improve the photocatalytic performance and realize its multifunction.This thesis also focuses on a novel method to construct nano-composite structures,which is generated by size segregation of charge stabilized nanoparticles in water/air interface.This thesis primarily uses Au NPs as in the model system to systematically study such self-assembly technology.Experimental results have demonstrated that this method is simple and easy,and it enables the formation of monolayers of Au NPs with single sizes.Besides,the self-assemble membrane can be transferred to various substrate.As to Au NPs solution with mixed sizes?for example,100-nm Au NPs&10-nm Au NPs?,it is found that the self-assembled membrane presented obvious layered structure,in which the top layer contains large NPs and the bottom layer contains small NPs.In addition,combined with UV-vis spectra test and Zeta potential test,this thesis systematically analyzed the mechanism about the vertical segregation during this self-assembly.