Preparation,Characterization And Photocataiytic Performance Of ZnSnO₃/RGO Composite Aerogel

With the rapid development of social economy and industrial production in China,water pollution has become increasingly serious,which has caused serious interference to human health and production and life.How to effectively control organic wastewater pollution and microbial pollution has become an urgent problem to be solved.Recent studies show that compared with traditional wastewater treatment methods,photocatalytic technology has the advantages of environmental friendliness,energy conservation and mid reaction conditions.Besides,it has the potential of using sunlight and no secondary pollution which has broad prospects in wastewater treatment.It is generally believed that the photocatalytic reaction process is closely related to the microscopic surface structure,such as crystal phase structure,crystallinity,surface area,and cocatalyst.Therefore,the type of material and its controllable preparation are critical to its photocatalytic activity.Emerging environmental purification applications require that reagents not only have high purification efficiency,but also be able to withstand mechanical deformation without causing secondary pollution and performance degradation.To this end,in this study,vacuum freeze-drying method was applied to its hydrogel precursor;by the compound of ZnSn（OH）₆ and graphene oxide（GO）,the synthesis of a series of ZnSnO₃/RGO aerogels（ZGA）with high-efficiency photocatalytic activity was controlled.A series of characterization methods were adopted to characterize the micro-morphology,crystal structure,photoelectric properties and specific surface area of the prepared samples.Using methylene blue（MB）and ciprofloxacin（CIP）wastewater as research objects,the ability of the composite photocatalyst to degrade organic matter under natural light and simulated sunlight was evaluated,and the composite photocatalyst experiments Sterilizing activity of E.coli DH5a was evaluated on the through bacteriostatic experiments.The effects of material preparation conditions,microstructure,specific surface area,and photogenerated carrier transport rate on the photocatalytic performance were explored,and the mechanism of composite photocatalyst degradation of organics and sterilization was proposed.The main research contents of the thesis are as follows:（1）The hydrogel precursor is obtained by vacuum freeze-drying of an aqueous mixture of GO and VC,and an ultra-light,compressible graphene aerogel（GA）can be prepared without stirring.The preparation parameters such as particle size of carbon,GO concentration,dosage of reducing agent and solution pH have different effects on the microstructure and adsorption capacity of GA.When the optimal carbon size,GO concentration,GO/VC ratio and solution pH were 500 mesh,2.5 mg/m L,≤2.5 and natural pH,respectively,the as-formed GA possessed superior adsorption capacity for pump oil.The unique porous structure makes the GA possess excellent elastic which can recover after compression,high adsorption capacity to organic solvents and oils（138–328 times its own weight）,complete removal of Cr（VI）after 5hours’simulated light irradiation and more than 86%of degradation efficiency of Cr（VI）after 5 cycles of degradation,complete removal of the dissolved organic matter（DOM）in the textile industry wastewater,and excellent electrical conductivity.（2）ZnSn（OH）₆ nanocube photocatalyst was prepared by liquid precipitation method.The effects of different pH on the micromorphology,crystal structure,chemical composition,and photocatalytic activity of ZnSn（OH）₆ during the preparation were studied.The experimental results show that:ZnSn（OH）₆nanocube prepared at pH=11.1 have a uniform particle size distribution and good photocatalytic activity,the degradation rate of MB after exposure to natural light for 5 hours is 76.3%,and after 3 hours,the degradation rate of CIP is 64.67%.Subsequently,the ZnSn（OH）₆ nanocube prepared under these conditions were further heat-treated（200℃,24 h）in four different solvents;the effects of heat treatment on the micro-morphology,band structure,specific surface area,electrochemical performance,and photocatalytic activity of ZnSn（OH）₆ were analyzed..The experimental results show that:The H-2 and H-3 photocatalysts after heat treatment in the stock solution and the mixed solution（V water:V ethanol:glacial acetic acid=3:1:1）show excellent photocatalytic performance;under natural light,the degradation rates of MB and CIP were increased to about 100%,the band gap energy was reduced by 0.9 and 0.93 e V,and the light-absorbing edge was red-shifted.Besides,the radical capture experiment showed that the h⁺and·O₂^-are the main active species for the ZnSn（OH）₆ nanocube and H-2,respectively,while all these three·OH,·O₂^-and ¹O₂ are radicals for H-3.（3）Based on the first two work,ZnSnO₃/RGO aerogel（ZGA）photocatalyst was prepared by vacuum freeze-drying of the hydrogel precursor obtained from an aqueous mixture of ZnSn（OH）₆（pH=11.1）and GO.The effects of different composite ratios of ZnSn（OH）₆ and GO on the micromorphology,crystal structure,specific surface area,and photocatalytic performance of ZGA aerogels were studied.The experimental results show that the photocatalytic activity of ZGA-4 aerogel is the strongest when the mass ratio of ZnSn（OH）₆（pH=11.1）to GO is 1:2（ZGA-4）;when the simulated light irradiated for 2 h,the degradation rate of 100 mg/L CIP reaches almost 100%.In addition,ZGA-4 also has good antibacterial activity,and the antibacterial activity of the degraded CIP wastewater on E.coli DH5a is almost completely inactivated.The improvement of the photocatalytic activity of ZGA-4 composites is related to the large specific surface area,wider light absorption range and photogenerated charge separation efficiency induced by composite GO.