Controllable Fabrication Of Surface Oxygen Vacancies And Photocatalytic Properties Of Bismuth Based Materials

With the rapid development of the global economy and the improvement of living standards,food safety concerns which are caused by the environmental pollution have become the focus of public attention,and abuse of antibiotics and consequent antibiotic resistance are especially serious in our country.With more than forty years of efforts,now the semiconductor photocatalysis,which could utilize solar energy,is believed as the most promising technology in terms of organic pollutants treatment due to intrinsic merits.However,the widespread applications of photocatalytic technology are still limited by some key points,such as light absorption efficiency,carrier separation efficiency and carrier utilization.With the development of modern material characterization technology,researcher can now gain deeper insight into the reaction mechanism of photocatalytic process.Most recently,surface oxygen vacancies are found not only to enhance the light absorption and transportation of carriers,but also serve as a "bridge" to promote the activation on target molecules by carriers,as a result,the efficiency of photocatalysis was improved.In recent years,more and more articles reported about the activation of surface oxygen vacancies on the surface of semiconductors and enhancement of their catalytic efficiency.However,most of these papers were focused on the performance difference of the material after introduction of oxygen vacancies,and there were few reports on the concentration controls and the stability of oxygen vacancies on the surface of materials.This research is still in the infancy and faced great challenge,but it is really vital to make better use of oxygen vacancies to improve the photocatalytic performance of the materials.Bi-based material,known as a new kind of visible light photocatalytic materials,has a unique electronic structure and strong redox ability,in addition,the easy control of anisotropic layered structure for Bi-based materials makes it be desired model material in the field of photocatalytic reactions.Most importantly,the weak and long Bi-O chemical bonds in the material make the generation of oxygen vacancies much easier to be controlled by soft chemical method.These characteristics provide a convenient condition for the research of oxygen vacancies and on Bi-based materials.In view of this,this dissertation focuses on the controllable introduction of oxygen vacancies in Bi-based materials and their stability during the photocatalytic process.The detail researches and the conclusions are summarized as follows:Under the conditions of controlling the pH value of the reaction solution,{001}and {010} facets exposed Bi2MoO6 nanosheets were synthesized by a hydrothermal method.On the basis of this,the effects of different exposed facets on the formation of oxygen vacancies on Bi2MoO6 were investigated by theoretical calculations and experiments.The concentration of oxygen vacancies on the {001} facets exposed of Bi2MoO6 were highly controlled by using cetyl trimethyl ammonium bromide as the bromine source.It can be concluded that the Br ion has achieved the effective regulation for the generation and stability of oxygen vacancies.The induced oxygen vacancies could also increase the activation of O2 thus enhancing the activities for NO removal and ciprofloxacin degradation.Based on the research about the effects of Br ion for the oxygen vacancies introduction,the {001} facets exposed Bi2MoO6 with different concetration of oxygen vacancies by adding different halogens were synthesized though a one-step hydrothermal method.By theoretical calculation and experimental methods,the different effects of halogens on the introduction of oxygen vacancies on the {001}facets exposed Bi2MoO6 were investigated.Furthermore,after confirming the maximum effects of Br for the oxygen vacancies,the surface oxygen vacancies have been constructed by second-hydrothermal treatment with Br ions.The difference between "Second treatment" and "One pot" methods for oxygen vacancies generation were compared.In addition,the visible light photocatalytic nitrogen fixation efficiency of the obtained materials was evaluated and it could be proved that the surface oxygen vacancies are more important for both nitrogen fixation and degradation of ciprofloxacin.Water-assisted self-assembly of ultrafine Bo5O7Br nanotubes with a uniform diameter of?5 nm was first realized through a low-temperature wet chemical method.The obtained 5 nm-diameter Bi5O7Br nanotubes are characterized by a large surface area,suitable absorption edge,and sufficient light-switchable surface oxygen vacancies,which deliver state-of-the-art visible light-driven photocatalytic N2 fixation performance with a high NH3 generation rate in water without any organic scavengers or noble co-catalysts.The design of nanostructured BiOBr-based photocatalyst exhibits efficient,stable and sustainable visible light N2 fixation and ciprofloxacin degradation.The carbon doped ultrathin Bi2MoO6 with {001} facets exposed nanosheets was first fabricated by simple solvothermal method.a dual-purpose strategy for enhanced molecular oxygen activation is established by this in-situ carbon homogeneous doping process.The C-doped ultrathin material exhibits an enlarged bandgap straddling the electrochemical potential of O2/·O2-and H2O/·OH9 without any attenuation of light absorption.An internal electric field and shorten carriers-transportation distance are also found in the longitude orientation of the nanosheets,leading to a higher density of effective photogenerated carriers localized on the exposed {001} surface.In addition,the light-controllable surface oxygen vacancies can be found after visible light irradiation as the weaker Bi-O bond in the lattice caused by non-crystallizing and doping.As applied for the NO removal and ciprofloxacin degradation,the reactive rate over the ultrathin C-doped Bi2MoO6 nanosheets was higher than that over the bulk counterparts as a result of the increasing reactive oxygen species.