Preparation And Photocatalytic Activity Of Zinc Oxide Micro-nano Materials

In recent years,environmental pollution is the primary problem to be solved urgently.The application of semiconductor in photocatalyst is considered as an effective approach to solve environmental pollution,which is studied extensively in the world.ZnO,as one of the photocatalytic materials used to reduce environmental pollution,arouses the wide research attention.ZnO is a typical wide-bandgap direct band gap semiconductor material?Eg=3.37 eV?,and has good biocompatibility and environmental safety.On the other hand,aerogel is a new kind of material with porous network structure,having the advantages of high porosity,large specific surface area and low density.The combination of ZnO and aerogel has promising application prospect.In this dissertation,the influence of morphology of ZnO on the photocatalytic properties of ZnO is investigated firstly.In addition,taking into account the adsorption of ZnO to organics materials can affect the photocatalytic activity,we prepared the ZnO composite aerogel using the aerogels with high adsorption properties as a modified material to improve the ZnO adsorption of organic matter.We also explored the effect of the adsorption properties of photocatalyst on the photocatalytic activity.The hydrothermal method was used to synthesize the spindle zinc oxide microrods.The optimum technological conditions for preparing the ZnO photocatalyst were determined as following:5 mmol zinc acetate dihydrate,5 mL TEA and 3 mL ammonia water.The amount of distilled water was 60 mL and the temperature was120?,the reaction time was 8 h.The efficiency of sample degrading methyl orange solution under ultraviolet light was about 97.91%.The results of XRD and SEM showed that ZnO nanocrystals were all hexagonal wurtzite with spindle shape and good uniformity.The TEMPO-NaBr-NaClO system was used to oxidize the pulp plate to nanofibers?NFC?.The ZnO-cellulose composite aerogel was prepared by constant temperature water bath method and freeze-drying method.By changing the amount of zinc source and surfactant,flake and spherical nano-ZnO were grown on the surface of cellulose skeleton.The stress-strain curve indicates that the modified aerogel has strong mechanical properties and the resilience can reach 63.5%.Based on the thermogravimetric analysis,the thermal stability temperature of the composite aerogel was 270?.The degradation rate of the sample to the MO solution under ultraviolet light can reach 98.8%,and after 5 cycles,the degradation rate can still reach over 90%.ZnO-SiO₂ composite aerogels were synthesized by sol-gel method.The optimum conditions for the synthesis were determined:the molar ratio of Zn?NO₃?₂/H₂O/HCl/NH₃·H₂O/TEOS was 0.2:4:2.4×10^-4:1.8×10^-2:1,the hydrolysis conditions were hydrolysis at 35? for 24 h,the aging temperature was 50?.The molar ratio of surface modifier TMCS to silicon source?TEOS?was one,the modification time was24 h,the hydrophobic angle of the airgel can reach 145°at the modification temperature of 40?.It has excellent hydrophobic property,the specific surface area was 972.1 m²/g,the average pore diameter was 12 nm,with typical aerogel structure characteristics.When the sample was irradiated with ultraviolet light for 90 minutes,the degradation rate of the MO solution reached nearly 100%,and the photocatalytic efficiency was significantly improved.After 5 cycles,the photocatalytic efficiency could still reach over 95%.