Preparation Of Porous Layer Spherical Bi₂WO₆-based Photocatalyst And Photocatalytic Degradation Of Ethylene Under Visible Light

After the fruits and vegetables are picked,because of the poor storage technology,there is a large amount of fruit and vegetable spoilage each year,resulting in huge economic losses.After harvest the fruits and vegetables remain life activities,through the respiratory metabolism to produce ethylene（also called plant hormone）,which is one of the main cause of vegetable and fruit rot,when the ethylene concentration in the environment exceeds the threshold concentration of the fruits and vegetables,it will accelerate the maturity of the fruit and vegetable.Therefore,reducing or removing ethylene in the storage and transportation environment of fruits and vegetables is an urgent problem to be solved in the field of storage and preservation of fruits and vegetables.Bismuth Tungstate（Bi₂WO₆）is considered to be one of the best photocatalytic active semiconductor catalysts in bismuth oxide,but its rapid recombination of bare carrier and narrow visible light response range limitation of these factors and so on,make the single visible light catalytic activity of Bi₂WO₆ is restrained,therefore,to solve this problem,this experiment starts with controlling the morphology of Bi₂WO₆ and modifieding Bi₂WO₆ to increase its specific surface area,broaden the range of spectral response and inhibitate photosynthetic electron hole recombination,achieveing the goal of enhancing photocatalytic activity.The samples were characterized by XRD,SEM,UV/Vis-DRS,XPS,FT-IR,BET and PL,The ripening hormone ethylene gas was chosen as the target degradation product,and the photocatalytic performance of the sample was evaluated.（1）Using simple hydrothermal method,the effects of synthetic conditions such as hydrothermal temperature,hydrothermal time,pH of precursor and calcination temperature on Bi₂WO₆ photocatalyst and visible light catalytic degradation of ethylene were investigated.Meanwhile,the crystal phase composition,morphological structure and optical properties were characterized.The results showed that,When the reaction conditions were hydrothermal temperature 120℃,hydrothermal time 12h,precursor pH was 0.5,the calcination temperature 450℃,through anisotropic growth and self-assembly Ostwald ripening process,Bi₂WO₆ photocatalyst was composed of two-dimensional nanoparticles self-assembled to form porous layer spherical structure,the average diameter of microspheres is about 3μm,with smaller grain size（22.403nm）.the surface area was the largest,14.7686 m²/g,which increases the contact area of ethylene gas effectively,forbidden band gap was 2.86 eV,visible light response range was wide,and showed excellent photocatalytic performance,within 240 min of visible light catalytic reaction of ethylene degradation rate of 13.69%.（2）The basis of the above part,TiO₂-Bi₂WO₆ composite layer microspheres prepared by simple deposition,the commercial TiO₂（Degussa P25）ornament on three-dimensional spherical structure Bi₂WO₆ microsphere surface,the effects of TiO₂ addition on photocatalytic degradation of ethylene were investigated.Meanwhile,the crystal phase composition,morphology,optical properties and surface chemical structure were characterized,the results showed that,with TiO₂ coating,the growth of Bi₂WO₆photocatalyst was inhibited,the surface oxygen vacancy increased,Ti,Bi,W shared with some oxygen atoms,and formed Ti-O-Bi and Ti-O-W new chemical bond,when TiO₂adding amount was 10%,nano-TiO₂ powder was evenly dispersed on the surface Bi₂WO_6,the grain size was 17.859 nm,the specific surface area of 21.874 m²/g,and the forbidden band gap was reduced to 2.76eV,the absorption threshold was extended to 449.8nm,the PL emission intensity was weakest,Effectively prevent the combination of photoelectric cavity,The degradation rate of ethylene was as high as 20.90%,1.53 times than that of a single Bi₂WO₆ photocatalyst.（3）To further improve the photocatalytic activity of TiO₂-Bi₂WO₆ composite photocatalyst,on the basis of the second part,it was modified with graphene oxide（GO）,The GO coated GO-TiO₂-Bi₂WO₆ composite photocatalyst was prepared.the effects of GO addition on photocatalytic degradation of ethylene were investigated.Meanwhile,the crystal phase composition,morphology,optical properties and surface chemical structure were characterized,the results showed that,The addition of GO reduces the emission intensity of the composite photocatalyst,and C atoms replace the O atoms in the TiO₂ lattice,and the exchange doping of lattice oxygen,forming Ti-C bond.When the addition of GO was 1.5%,the GO was evenly attached to the surface of TiO₂-Bi₂WO₆ microspheres.Meanwhile,the composite photocatalyst has the largest specific surface area（23.619 m²/g）,and the forbidden band gap was reduced to 2.63 eV,GO-TiO₂-Bi₂WO₆ composite photocatalyst has thebest photocatalytic activity,and the photocatalytic reaction rate constant K′was the largest(1.270′10^-3min^-1).within 240 min of visible light catalytic reaction of ethylene degradation rate of 25.04%,1.20 times than that of TiO₂-Bi₂WO₆ composite photocatalyst.