Preparation Of Cu₂O/Bi₂WO₆ Composites And Photocatalytic Degradation Mechanism Of Short Chain Fatty Acid For Production Of Hydrogen And Alkanes

Novel highly efficient and visible-light-driven photocatalysts is of great importance for photocatalysis research.Hydrogen and alkanes are as carrier for clean energy.Clean fuel production by photocatalytic process is a good solution to solve serious environmental pollution and energy crisis.Photocatalytic production of alkanes and hydrogen gas from shot chain fatty acid solution over composites has been investigated under UV irradiation.Cu₂O and Bi₂WO₆ are selected as bases,a binary Cu₂O-based and two kinds of ternary Bi₂WO₆-based materials have been prepared.By constructing a heterojunction structure of composites,it is beneficial to increase the visible-light-response region and separation and transfer efficiency of photogenerated electrons with holes.The surface structure,morphology,light absorption spectra,chemical elements,separation efficiency of electron-hole pairs of the as-prepared photocatalysts have been characterized using XRD,FESEM,UV-Vis DRS,XPS,PL,EIS and so on.Short chain fatty acids are chosen as electron donors,studies its photocatalytic performance for production of H₂ and alkanes has been studied as well.The specific work is as the following:（1）Cu₂O with different morphologies were prepared by changing the type of surfactants.Different short chain fatty acids were used as sacrificial agents for photocatalytic degradation.Results show that the photocatalytic types of gaseous products are different with different short chain fatty acids as electron donors.According to the gaseous products,the possible photocatalytic reaction pathways for formic acid,acetic acid,propionic acid and butyric acid can be inferred,respectively.Novel heterojunction Cu₂O/BiPO₄ photocatalysts hav been prepared by a two-step hydrothermal method.The heterojunction structure can be formed through Cu₂O nanoparticles loaded on the primary BiPO₄ nanorods.Under high pressure mercury lamp irradiation,Cu₂O/BiPO₄ heterojunction photocatalyst obviously exhibited much higher photocatalytic activity than that of the pure BiPO₄.The 9%Cu₂O/BiPO₄composites showed the best photocatalytic performance.PL results and radicals capture experiments revealed that formation of heterojunction between Cu₂O and BiPO₄ induced the excellent separation and transportation of the photogenerated charges.Then,we propose a possible reaction mechanism for the excellent photocatalytic activity of Cu₂O/BiPO₄composites.（2）Bi₂WO₆ catalyst was synthesized by a simple hydrothermal method.We synthesized different morphology of the catalyst by controlling the pH of precursor solution.For example,nest-like Bi₂WO₆ under pH=1-2 and sheet-like Bi₂WO₆ under pH=7-9,respectively.Then,the growth mechanism of Bi₂WO₆ was put forward by XRD and SEM analysis.A new ternary Cu₂O/Bi₂WO₆-TiO₂ photocatalysts were prepared by a two-step hydrothermal method.Cu₂O nanoparticles closely loaded on the sphere Bi₂WO₆/TiO₂.The photocatalytic materials prossess stronger visible-light absorption.Radicals-capture experiments show that both.OH and h⁺are as the main active species.PL result shows that the recombination of photogenerated carriers was significantly inhibited.The improvement of photocatalytic activity could be due to the ternary heterogeneous structure,leading to more effective separation and fast transfer of the photogenerated carrier.Finally,a possible mechanism over ternary heterogeneous catalyst was proposed.（3）Photocatalytic reaction of two or three mixed short-chain fatty acids with different proportions results showed that the production of gas was significantly higher than that of a single short-chain fatty acid as a sacrificial agent.The active substances in the photocatalytic reaction liquid analysized by HPLC were?OH,?CH₃,?CH₂CH₃ and?CH₂CH₂CH₃.According to the photocatalytic reaction of gaseous products,liquid intermediates and free active radicals species,a general degradation pathway for photocatalytic degradation of mixed short-chain fatty acids was proposed.