Synthesis And Visible Light Photocatalytic Performance Of Bi₁₂O₁₇Cl₂ Composite Semiconductor Materials

Semiconductor photocatalysis can make use of“green”and cheap solar light to convert solar energy into chemical energy and electrical energy.Under suitable conditions,low-density solar light can be used to degrade and mineralize various pollutants in water and air through semiconductor photocatalysis.There are various advantages in the photocatalytic process such as mild reaction conditions,simple and controllable process,no toxic intermediates and secondary pollution.It is of great concern to solve environmental pollution and energy shortage by semiconductor photocatalysis which shows good application prospects in these two fields.Among many research materials,bismuth halide?BiOX?,especially bismuth halide with rich oxygen semiconductor materials,have attracted wide attention because of their special morphologies and excellent photocatalytic properties.In order to expa nd the spectral absorption range and improve the separation efficiency of photogenerated carriers to improve the photocatalytic performance in the visible light irradiation,people often choose method of doping with metal ions or nonmetal,forming solid solution and constructing heterogeneous structure to modify them.It is an effective way to construct a heterogeneous structure with a narrow-band-gap semiconductor material,which can solve these two problems above-mentioned at the same time,also can combine with the properties of two intrinsic components.In addition,the introduction of metal particles with plasmon resonance in the composite system can effectively improve the spectral absorption of the photocatalyst and avoid the recombination of photogenerated carriers.Based on the above considerations,we designed and synthesized two different types of composite photocatalysts,like the binary composite photocatalyst WO₃/Bi₁₂O₁₇Cl₂ and ternary composite photocatalyst Ag/WO₃/Bi₁₂O₁₇Cl₂,also systematically studied on their compositions,structures,morphologies,optical properties and the photocatalytic performance for the degradation of various organic pollutants under visible light irradiation.The main studies are as follows:1?The WO₃/Bi₁₂O₁₇Cl₂ heterojunction composite photocatalysts with different proportions of WO₃ were prepared by one-pot solvothermal method,and their composition,microstructure,morphology,optical properties and the separation efficiency of photogenerated carries were analyzed by a series of characterize techniques such as X ray diffraction?XRD?,ultraviolet-visible diffuse reflectance spectra?UV-Vis DRS?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,high resolution transmission electron microscope?HRTEM?,energy dispersive spectrometer?EDS?,X ray photoelectron spectroscopy?XPS?,nitrogen adsorption-desorption isotherm curve,pore size distribution,raman spectrum,photoluminescence?PL?spectrum.The TEM,HRTEM and XPS results proved that two components,WO₃ and Bi₁₂O₁₇Cl₂,existed and heterojunction structure formed at the same time.Besides,the introduction of WO₃ nanoparticles did not destroy the original three-dimensional flower shape of the Bi₁₂O₁₇Cl₂ nanoflakes.The photocatalytic degradation of rhodamine B?RhB?and tetracycline hydrochloride?TC?test results under visible light irradiation show that,compared to pure WO₃ and Bi₁₂O₁₇Cl₂,the photocatalytic properties of WBx series composite photocatalytic materials have greatly improved and enhanced,which is closely corresponded to the good micromorphology,the increase of specific surface area,the enhanced visible light absorption and well-matched band structure of two semiconductor materials.On the one hand,the absorption wavelength of composites extended,enhancing the absorption of visible light,which is beneficial to produce more photo generated electrons and holes;on the other hand,the heterostructures can effectively dispersed photogenerated electrons and holes pairs through the interface,so as to improve their photocatalytic performance.Moreover,the additive proportion of two components also has a great influence on the photocatalytic performance.The results show that the excellent photocatalytic performance of the composites is that when the content of WO₃ is 0.5 wt%under the same experimental conditions.In addition,we also carried on the active species capture experiments and electron spin resonance?ESR?to prove that hole?h⁺?and superoxide free radicals??O₂^-?played a major role in photocatalytic degradation of pollutants,and the mechanism of photocatalytic degradation of heterojunctions is proposed.The synthesized composite photocatalysts are easy to recycle,and its structure and properties are basically unchanged after repeated use for5 runs,which confirmed the good stability and reutilization of the prepared photocatalysts.2?Based on the 0.5%WO₃/Bi₁₂O₁₇Cl₂?WB0.5?composite material with the best photocatalytic activity as discussed above,a simple and rapid microwave-assisted method was adopted to introduce noble metal Ag nanopartical to the WB0.5 system,constructing the ternary composite photocatalyst Ag/WO₃/Bi₁₂O₁₇Cl₂.The microstructure,micromorphology,optical properties,optical properties and the separation of photogenerated electrons and holes of the samples with different microwave reaction time or different proportion of Ag were studied by a series of characterization techniques.According to the analysis of the scanning electron microscope?SEM?images,we can find that there was a huge difference between the samples with different microwave reaction time or different Ag contents.The most obvious features was the amount of Ag particles supported on the surface of Bi₁₂O₁₇Cl₂ are quite different,but the introduction of Ag did not destroy the original morphology of Bi₁₂O₁₇Cl₂nanoflakes.The photocatalytic results of Ag/WB0.5 composites by the degradation of target pollutants such as RhB,methyl orange?MO?and TC under visible light suggested that the photocatalytic activity of samples containing Ag possesses the better degradation efficiency than that of sample without Ag?WB0.5?,and 3%Ag/WB0.5-5min is the best candidate among all the samples,mainly because the plasma effect of Ag was access to disperse the photogenerated electrons and holes,so as to enhance the quantum effect of the photocatalyst.In addition,the active species capture and electron spin resonance?ESR?experiments proved the main role of h⁺and?O₂^-in the photocatalytic degradation process.Accordingly,the photocatalytic mechanism of the ternary composite system is proposed.In addition,the reutilization experiment of 3%Ag/WB0.5-5min shows that the ternary composites are easy to recycle,and its structure and properties are basically unchanged after repeated use for5 runs,which confirmed the good structural stability and reutilization.But when it comes to the reutilization experiment of RhB dissolved in saline solution,the latter shows better photocatalytic effect and better stability.This phenomenon suggests that the photocatalytic degradation or transformation of the ternary plasma resonance system can also be applied to the salt water system.