Design Of Several Novel Materials And Application In Photocatalytic Area

In recent years,photocatalysis as a potential method was applied to solve energy shortage and environmental pollution,therefore,photocatalytic mechanism,development of new photocatalysts,optimization of experimental conditions and so on have been studied extensively.The application of photocatalysis is mainly concentrated on the following areas:(1)photocatalytic degration organic dyes for water treatment;(2)photocatalytic CO2 reduction to mitigate the greenhouse effect;(3)photocatalytic H2 evolution;(4)photocatalytic organic synthesis and so on.In view of photocatalytic process,the key is to design and prepare photocatalytic semiconductors.An ideal photocatalyst should possess the properties of adsorption of light,efficient separation of photo-induced carriers,suitable conductor band(CB)/valence band(CB)for surface chemical reaction,etc.To achieve the photocatalytic material with aforementioned features,scientists have made lots of efforts to the preparation of photocatalysts,such as doping,loading noble metals,construction of heterojunctions and solid solution.Based on applications of photocatalysis in photocatalytic degration organic dyes and photocatalytic hydrogen evolution,in this paper,novel photocatalysts were developed,the photocatalytic activities were investigated,as well as photocatalytic reaction machnism was studied systematically.Detailed content of this paper is divided into four chapters as follow:In the first chapter,background on energy and environmental issues are introduced at first.Then,a brief review of photocatalysis including photocatalytic process,applications,machnisms,the influence factors of photocatalytic process and the design of photocatalysts,etc.Subsequently,summarizations of the researches in the dissertation are provided.In chapter 2,a three-component system,Ag2Mo2O7@AgBr-Ag hybrid photocatalyst,has been successfully prepared through an in situ ion exchange reaction between Ag2Mo2O7 rods and Br-,followed by visible-light irradiation.Using as-prepared samples as photocatalysts,the visible-light photocatalytic activity for degrading organic dyes including methylene blue(MB)and Rhodamine B(RhB)is examined systematically.Among Ag2Mo2O7,Ag2Mo2O7/Ag,Ag2Mo2O7@AgBr,AgBr-Ag and Ag2Mo2O7@AgBr-Ag,the three-component Ag2Mo2O7@AgBr-Ag heterostructured photocatalyst is demonstrated to be superior to others for dye photodegradation.The enhancement in visible-light absorption and photocatalytic activity is ascribed to the synergistic effects originating from the surface plasmon resonance(SPR)of Ag nanoparticles(NPs)and the cascade energy transfer for the effective separation of photogenerated carriers.Radical-trapping experiments demonstrate that holes(h+)are the major reactive species accounting for the degradation of MB and RhB molecules.Furthermore,the five cycle tests indicate that the three-component hybrid photocatalyst Ag2Mo2O7@AgBr-Ag is highly stable and can be used repeatedly.Therefore,Ag2Mo2O7@AgBr-Ag ternary heterostructure may be a promising candidate used as a visible-light photocatalyst for degrading organic contaminants in the near future.In chapter 3,final metal sulfides Zn0.5Cd0.5S(ZnCdS-CH)are synthesized by coprecipitation process followed by hydrothermal treatment.The morphological,structural and optical performances have been investigated extensively via diverse analytical techniques.The ZnCdS-CH solid solution without noble metal loading is employed in photocatalytic H2 evolution under visible light irradiation(??420 nm)and achieves a superior activity rate of 0.971 mmol/h,which exceeds those of co-precipitated Zn0.5Cd0.5S(ZnCdS-C)samples by more than 13 times.Moreover,in the recycle test,ZnCdS-CH photocatalyst shows a stable photocatalytic activity for H2 evolution under long-term visible-light irradiation.Characterization analyses demonstrate that the excellent photocatalytic H2-evolution performance of ZnCdS-CH sample arises predominantly from the two-step processing procedure of coprecipitation followed by hydrothermal treatment at 200 °C,which makes it possess hexagonal(wurtzite)structure,well dispersity,enhanced crystallinity,appropriate band gap,more negative conduction band,as well as large amount of surface defect states.This finding is of great significance for designing a facile,reproducible and inexpensive method to excavate the potential of ZnxCd1-xS ternary metal sulfides in the field of H2 evolution by water splitting.In chapter 4,we developed a series of brand new UiO-66-NH2-based composites by solvothermal treatment and subsequent calcination.The characterizations demonstrate the intimate lattice-level contacts between UiO-66-NH2 photocatalysts and NiO nanoparticles.Through optimizing each component,even without noble metal loading,the U6N-NiO-2 sample(the weight ratio of NiO to U6N-NiO-2 is calculated theoretically to be ca.10 wt%)with 15 mg Eosin Y as sensitizer brings about a boosting H2 generation rate of 2561.32 ?mol/h/g under visible light irradiation and using TEOA as sacrificial reagents,whose corresponding quantum efficiency is 6.4%at 420 nm.The above H2 evolution activity is 5 times higher than that of UiO-66-NH2 photocatalyst(denoted as U6N)and exceeds than that of U6N-NiO-2 without sensitizer by more than 23 times.It is demonstrated that the high efficiency originates from the visible-light generated electrons of Eosin Y and UiO-66-NH2,the efficient separation of carriers by the cascaded band structure and more negative CB of NiO,as well as the well dispersion of NiO nanoparticles on the octahedral skeleton.It is believed that this study will provide a new insight for the improvement of visible-light photocatalytic rate over MOFs-based material.