Preparation And Performance Characterization Of Cu₂（OH）PO₄-based Photocatalysts

Environment pollution and energy crisis are two of the most serious problems.Semiconductor photocatalytic technology has been considered as a kind of high efficiency and low energy consumption technology for environmental remediation.Up to date,many kinds of semiconductor photocatalysts have been prepared,but still have some disadvantages including poor utilization of solar energy and low stability,which significantly restrain their practical application.Therefore,it is indispensable and highly desirable to develop the efficient visible-light responsive photocatalysts with a broad range of visible-light response,superior photocatalytic activity and easily recycling characteristics.Copper hydroxyphosphate mineral libethenite(Cu2(OH)PO4)with high physical stability and low price,has been found to be a visible-light-driven(VLD)photocatalyst with narrow band-gap(～2.8 e V),but its photocatalytic activity still need to be improved.To further improve its photocatalytic performance,we design and prepare various Cu2(OH)PO4-based photocatalysts by controlling its morphology and /or building semiconductor heterojunction.Using a facile one-step hydrothermal method,various 3D hierarchical superstructures of Cu2(OH)PO4 are synthesized by simply adjusting the p H value(p H = 1,3,5,7,9,10)through adding ammonia or acetic acid.With an increase in p H from 1 to 10,we prepare six kinds of microscopic morphology of Cu2(OH)PO4 such as rod-like,sheaf-like,bundle-like,walnut-like,brick-like and scattered bulk-like hierarchical superstructures,and then we investigate the morphology,crystal phase,Uv-vis absorption and photocatalytic activity of the samples.Cu2(OH)PO4 photocatalysts with different microscopic morphology display excellent visible-light absorption.The uniform walnut-like Cu2(OH)PO4 with a length of ~ 4 μm and width of ~ 6 μm exhibits the most excellent visible-light absorption,and it has a short-wavelength absorption edge at 430 nm.The photocatalytic activity of walnut-like Cu2(OH)PO4 has been measured by the degradation of methylene blue(MB)and tetracycline(TC)solution under visible-light irradiation(λ > 400 nm).The results indicate that walnut-like Cu2(OH)PO4 could degrade 38% MB or 34% TC in 100 minutes under the visible-light irradiation.In addition,the recycling experiments demonstrate that Cu2(OH)PO4 remained photocatalytic stability.Thus,Cu2(OH)PO4 could be used as a stable VLD photocatalyst,but its photocatalytic performance still need to be improved.To further improve the photoabsorption range and photogenerated electron-hole separation efficiency of Cu2(OH)PO4,we design and prepare Cu2(OH)PO4-Cd S heterojunctions.The walnut-like Cu2(OH)PO4 with a length of ~ 4 μm and width of ~ 6 μm are firstly synthesized by a hydrothermal method,and then Cd S nanoparticles with diameters of 50 nm are grown on the surface of Cu2(OH)PO4 by ultrasonic method.Interestingly,after the decoration of Cd S nanoparticles on the surface of Cu2(OH)PO4,Cu2(OH)PO4-Cd S heterojunction displays an intensive and broad visible-light absorption performance,and its short-wavelength absorption edge moves from 430 nm to 525 nm.The photocatalytic activity of Cu2(OH)PO4-Cd S heterojunctions has been measured by the degradation of MB and TC solution under visible-light irradiation(λ > 400 nm).The results indicate that Cu2(OH)PO4-Cd S heterojunctions could degrade 82% MB or 78% TC in 100 minutes under the visible-light irradiation,higher those by single component(Cu2(OH)PO4 or Cd S).In addition,the recycling experiments demonstrate that the heterojunctions remained good photocatalytic stability.Therefore,Cu2(OH)PO4-Cd S could act as a stable and efficient VLD photocatalyst for the purification of wasterwater.