Preparation And Photocatalysis/photoelectrocatalysis Performance Study Of Nitride Carbon-based Composites

Energy and environmental issues have always been the focus of attention in all around worldwide.The development and utilization of renewable energy solar energy is regarded as one of the effective ways to solve these problems in the future.Solar energy having been stored in the form of chemical energy?such as photocatalytic splitting of water to make hydrogen?by means of artificial light synthesis has attracted the attention of researchers all over the world.The light-harvesting efficiency of the photocatalytic material determines the upper limit of solar energy conversion utilization efficiency.Therefore,the development of new semiconductor materials with appropriate structural systems has always been the hot and difficult point in this field.Graphite-phase carbon nitride?g-C₃N₄?is a unique non-metallic polymer semiconductor,its band structure is very suitable for photocatalytic split of water in the two key half-reaction steps of hydrogen and oxygen production.It's also having merits of simple synthetic methods,good thermal stability,lower toxicity.Therefore,it's generally regarded as a promising non-metal based photocatalyst for many photocatalytic applications.However,during the bulk g-C₃N₄ photocatalytic reaction,further enhancement of photocatalytic activity was hindered due to its low specific surface area?caused by stacking?and rapid recombination of photogenerated electron-hole pairs.This thesis based on the shortcomings of the bulk g-C₃N₄,a series of composite photocatalysts were designed by different modification methods.The main contents of this paper is as follows:?1?In this part,the highly efficient and robust heterogeneous photocatalytic hydrogen evolution system was established for the first time by using In situ phosphating nickel ions on the iron-doped graphite carbon nitride.As a typical“transition metal–metalloid”binary alloy,Ni₂P increase electrical conductivity of the hybrid photocatalyst,as well as accelerate the surface reaction.Meanwhile,the synergistic effect of the iron ion and nickel phosphide has good absorption ability of visible light and can reduce the recombination of electrons and holes within the catalyst.Among all the photocatalysts employed,the optimal composite shows the highest H₂ evolution rate of 397?mol h^-1 g^-1 under visible light irradiation,the photocatalyst also shows excellent circulation stability.?2?In this part,carbon layer coated black TiO_2-x/g-C₃N₄ nanosheets(C@TiO_2-x/CNNS)heterojunction photocatalysts were successfully prepared via a polydopamine dopamine carbonization route for the first time.It was found that the hydrogen evolution rate over C@TiO_2-x/CNNS was 537.2?mol h^-1 g^-1 under visible light irradiation and obvious decrease in catalytic activity can be observed after three recycles.The formation of carbon layer on the surface of TiO_2-x can effectively protect Ti³⁺and oxygen vacancies?Ovs?from oxidation by air and dissolved O₂,which can serve as charge carrier traps to inhibit the recombination of light-excited electrons-holes.C@TiO_2-x/CNNS showed a highly conductivity,rapidly effective electron-hole separation and lower transmission resistance comprehensive consideration of the advantages of carbon layer and hetero-junction,which are of great benefit to the improvement of photocatalytic performance.?3?In this work,CoPi decorated type II heterojunction which is composed of one dimensional ZnO NRAs coated with two dimensional g-C₃N₄ nanosheets photoanode was successfully prepared via a simple and effective method.The structure and properties of the prepared photoanodes were characterized by many methods.Highly performance can be attributed to increased visible light trapping by heterojunction of CNNS/ZnO NRAs and efficient separation of photogenerated electrons and holes and fast rectifying electron transport through 1D ZnO NRAs to the counter electrode.Light stability experiment proved bi-functional CoPi can not only accelerate the oxidation of water but also as a shelter effectively inhibiting the photo-corrosion of CNNS/ZnO NRAs and provides a faster holes transfer channel.?4?In this chapter,we use a conductive carbon cloth as the substrate,the prepared triple metal-free conducting polymers were designed as 3D layered independent unit structure.Moreover the recyclable PDA@CNNS-PANI@CC photocatalyst retain⁷8.57%of the activity after 3-cycle reuse.The introduction of PDA enhances the synergy of the ternary system and accelerates the separation of photo-generated carriers without destroying the original structure of CNNS-PANI.The excellent adhesion avoids the secondary pollution of the environment.