Photocatalytic Degradation Of Organic Wastewater Pollutant By Sn-Contained Layered Double Hydroxides

With the rapid development of industrialization,the discharge of organic pollutants is increasing,which bring great threat to ecological environment.Therefore,the effective treatment of organic wastewater has aroused people's great attention.The traditional semiconductor materials have a certain photocatalytic performance,but they have serious disadvantages such as low visible light utilization,low quantum yield,and poor stability,which limite the practical application of materials.In this paper,based on the special structure of layered double hydroxides?LDHs?,we successfully introduce Sn into brucite type layers,obtaining ZnSn-LDHs photocatalytic material;and on the other side,the ZnSn-LDHs is modified by transition metal oxide CeO₂ through wet impregnation method,then,the sample is further calcined to get CeO₂/ZnO/SnO₂ composite oxides.Meanwhile,the prepared materials are tested by photocatalytic degradation reaction of representative organic compounds?such as 4-chlorophenol,Methylene blue,Methyl orange,Rhodamine B?for their performance,the photocatalytic reaction paths are deduced by HPLC-MS,GC-MS and density functional theory?DFT?.To sum up,the main research contents and conclusions of this paper are as follows:?1?ZnSn-LDHs,ZnAl-LDHs and SnO₂/ZnAl-LDHs are synthesized by co-precipitation and wet impregnation method.The obtained LDHs solids are thoroughly characterized by powder X-ray diffraction?XRD?,Fourier transform infrared spectrometer?FTIR?,Brunauer Emmett Teller?BET?surface area analysis,etc.And their photocatalytic activities are evaluated by degradation of 4-chlorophenol?4-CP?under visible light.The results indicate that ZnSn-LDHs with narrow band gap and high specific surface area,display rather high photocatalytic activity,the degradation rate and removal amount of 4-CP was about 92.4% and 34.6 mg/g,respectively.What's more,the studies on photocatalytic degradation mechanism show the main intermediate products are hydrochinone and 4-chloropyrocatechol.?2?High photocatalytic activities of CeO₂/ZnO/SnO₂ composite oxides are obtained by roasting ZnSn-LDHs modified with different amount of CeO₂ at different temperatures.XRD,SEM and UV-Vis DRS are applied to characterize the composite oxides,and the densities of states of samples are analyzed by DFT.The effect of CeO₂ amount and calcined temperature on photocatalytic properties of materials are explored using mixed-dye of MO and MB?CMO:CMB=1:1?as the degradation object.It can be concluded that with increasing of CeO₂ content and calcined temperature,the removal efficiency of MO and MB are increased.When CeO₂ content is 20% and calcination temperature is 700 ?,the composite oxides present highest photocatalytic activity and the degradation rate of MO and MB are all more than 95%.In addition,based on the experimental results and theoretical calculations,the possible degradation pathways of MO and MB in mixed-dye are speculated.?3?CeO₂/ZnO/SnO₂ composite oxide with CeO₂ content of 20% and calcination temperature of 700 ? is further used for the degradation of mixed-dye of RhB and MB?CRhB:CMB=3:1?.And the effect of catalyst amount,initial pH value,reaction temperature and other factors on the photocatalytic properties of materials are discussed in detail.The crystal form,morphology and optical performanc of samples are characterized by XRD,TEM and UV-Vis DRS.It is found that the optimal experimental conditions are 30 mg of CeO₂/ZnO/SnO₂,pH 6.09,reaction temperature 35 ?,CRhB=12 mg/L,CMB=4 mg/L,illumination time 420 min.CeO₂/ZnO/SnO₂ show high photocatalytic activity under the optimal experimental conditions,and removal efficiency of RhB and MB are all more than 98%.Moreover,on basis of FED calculation results of RhB and MB molecules,the possible photocatalytic processes for RhB and MB decomposed by CeO₂/ZnO/SnO₂ are also investigated.