| Triclosan(TCS)is a spectrum antibacterial agent,which is widely used in people’s daily necessities,mainly including toothpaste,soap,textiles and the toys of children.In recent years,with the increase of daily necessities,and the related scientific research shows that the presence of triclosan in surface water is the formation of more toxic by-products such as dioxin and endocrine disruptor chemicals.A large amount of long-term use of TCS will affect human health through the food chain.Therefore,it is important to study the removal technology of TCS in the water environment.The combination of photocatalytic technology to degrade organic pollutants in the environment is becoming more and more popular.So,it is of great significance to develop a photocatalyst with visible light response on order to make better use of solar energy.Firstly,a novel n-n heterojunction photocatalyst(Bi709I3/Bi507I)was formed by in situ calcination of Bi709I3.It was obvious that the morphology had changed in the calcination process from the original sheet structure to the bone-stick-like structure,but still maintained a spherical 3-dimensional structure.At the same time,two kinds of lattice fringes were identified from the HR-TEM in sample Bi7O9I3-450 which effectively proved the formation of the Bi709I3/Bi507I heterojunction.This composite photocatalyst could effectively remove TCS from the water.Its photocatalytic efficiency was significantly improved compared with the pure Bi7O9I3.This was attributed to the internal electric field in the composite catalyst which facilitated the transport and migration of photo-generated carriers.The degradation mechanism of TCS was analyzed,and the electron reduction and·O2-species and singlet oxygen oxidation played essential role in the TCS degradation by radical scavenger experiment.Finally,the eleven degradation products were identified by the HPLC-MS method,and the two major reaction pathways were deduced.Secondly,a new composite catalyst Bi7O9I3/Bi was prepared by in situ reduction method.Compared with the Bi7O9I3,the degradation effect of the Bi7O9I3/Bi on triclosan was significantly improved.This is mainly due to the deposition of elemental Bi onto the surface of pure Bi7O9I3,which effectively promotes the separation and migration of photogenerated electron-hole pairs,thereby greatly improving its photocatalytic performance.The free radical trapping experiment and electron spin resonance(ESR)method were used to analyze the degradation mechanism of triclosan.The photogenerate electrons(e-)and superoxide radicals(·O2-)were the main active groups in the chlorine production process.Finally,the effects of inorgantic anions and cations on the photocatalytic degradation of TCS by Bi7O9I3/Bi were studied.The inorganic anions of Cl-,SO42-and NO3-inhibited the reaction due to its surface adsorption and competitive reaction with reactive groups in the system.However,HCO3-promotes the reaction at low concentrations and inhibits photocatalytic degradation of TCS at high concentrations.Moreover,the inorganic cations of Na+ and K+presented suppression effect to the degradation reaction,which could be the effect of Cl-co-present in the solution.But there has an interesting phenomenon,Ca2+ and Mg2+ promote photocatalytic degradation at high concentrations,because the enhancement of degradation by addition of Ca2+and Mg2+is due to increase of charge separation by accepting the conduction band electron. |
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