Design,Synthesis,Electronic Structure Regulation And Performance Research Of Silver/Cadmium Based Semiconductors Photocatalytic Materials

With the fast-growing and rapid economic development of society,the demand for energy is increasing day by day.Meanwhile,the environmental pollution brought by economic activities had an increasingly serious impact on the human living environment.Therefore,lacking of renewable energy and facing with horrible surroundings have become restrictive factors for the sustainable development of human society.How to solve these two challenges by means of a safe,pollution-free and an efficient way is a hot topic for scientists who pay attention to these fields at present.Semiconductor photocatalysis technology is undoubtedly the most effective means to solve the issue because of its eco-friendly and free of contaminations.The dissertation concentrates on silver-based and cadmium-based semiconductors photocatalyst,using doping strategies and heterostructure construction principles of semiconductor to artificially modulate surface electronic structure and interface charge transfer of semiconductors.Aiming at solve the above problems fundamentally,such as the narrow scope of spectral absorption,strong recombination rate of photogenerated electron-hole pairs,and poor endurance and so on.Researches showed that advances have been acquired in the reduction of nitrobenzene and decomposition of water through the modified doping semiconductor materials and heterojunction photocatalyst with reasonable structure design.The main research contents are summarized as follows.（1）A series of non-stoichiometric ratio Ag Nb_1-xTa_xO₃ solid solutions were prepared by solid-phase calcination method.By exploring the doping type,doping site and doping concentration of Ta in AgNbO₃ for crystal phase structure,band energy position,and work function,the following conclusions were drawn.Doped metal heteroatoms with less electronegativity,similar ion radius and charge states into semiconductor will lower the lattice constant and work function,but raised carrier mobility.In the reaction of convert p-nitrophenol to p-aminophenol,the selective adsorption of nitrobenzene by the in-situ formed metal Ag and AgNb_1-xTa_xO₃ solid solution,as well as the enhanced reduction capacity of AgTaO₃ were the main reasons for the improved performance of the solid solutions.Unfortunately,the light absorption of AgTaO₃ is poor.（2）In order to broaden the light absorption capacity of AgTaO₃,the chapter will load the photosensitivity CdS QDs on the AgTaO₃.Experimental results showed that the triple composite CdS QDs/Ag@AgTaO₃ showed excellent photocatalytic activity for p-nitrophenol pollutants eliminate with different molar concentration,and the photocatalytic activity was 10 times higher than Ag/AgTaO₃ under visible light.In addition,it remained efficient after 10 test cycles.The photosensitivity of CdS QDs,as well as the multi-electron transfer and multi-active site synergistic catalysis of the heterojunction structure further improve the photocatalytic performance of AgTaO₃.（3）Based on the experimental investigation in last chapter,it was found that CdS QDs photocatalysts had an excellent light absorbability and strong reducing capability.However,it often exhibited unsatisfactory photocatalytic activities due to the lack of active sites and the high photocarrier recombination rate.In order to meet this challenge,the single atom Ni loaded and doped CdS QDs was designed and synthesized.Experimental observations and theoretical calculation showed that the active sites of Ni atoms and the impurity energy levels synergistically enhance the performance of Ni/CdS QDs for photocatalytic water splitting.Without the co-catalyst,the H₂ production was close to 54 mmol/g during 5 h under visible light,and the apparent quantum efficiency（AQY）reached 52.71%.（4）Compared with CdS QDs,bulk CdS also has a suitable optical band gap（2.4eV）,a negative conduction band potential,and the surface is rich in a large number of active sites.However,the rapid recombination of photogenerated electrons and holes,as well as severe photocorrosion hindered its further research.In order to solve the problem fundamentally,a zinc defect ZnS/CdS heterojunction with intimately interface contact and a new I-S charge transfer mode was synthesized.The results showed that zinc defects not only effectively improved the optical absorption performance of ZnS,but also changed the charge transfer mode of ZnS and CdS.The I-S charge transfer mode could accelerate the electron transfer in kinetics,blocke the accumulation of photogenerated holes in the valence band of CdS simultaneously,and inhibite the anode photocorrosion of CdS effectively.（5）Based on the above studies,it was found that cadmium-based quantum dots photocatalysts have an excellent optical property and photocatalytic water splitting performance.Therefore,CdTe QDs/NaTaO₃ composites modified by bifunctional molecule were synthesized in this chapter.The experimental results showed that the crystal grain sizes of Cd Te QDs decreased and the light absorption curves blue shifted with shortened the preparation time of quantum dots,however,the performance of photocatalytic water splitting performance improved.Photocurrent and ABPE tests showed that the controllable energy level caused by quantum confinement effect had an important effect on the dynamics of photogenerated charge transfer.Meanwhile,the length of carbon chain in the ligand also had an influence on the dynamics of interfacial electron transfer.