Preparation And Gas-phase Photocatalytic Properities Of Dispersed Heterojunction Microspheres Photocatalysts Based On Titanium Dioxide By Spray Pyrolysis Method

Photocatalytic technology has been one of the ideal green means to solve the problem of energy shortages and environmental pollution in future,however,the low solar energy conversion efficiency has become the biggest bottleneck in its application.Efficiency in terms of sunlight capture,separation of photogenerated charge and charge utilization rate via surface redox reaction are the most important three factors to determine the utilization rate of solar energy conversion efficiency of the photocatalyst.Studies show that,when two semiconductor material with matched energy band structure form type ? heterojunction,the directional transfer of photoinduced carriers at the interface between two semiconductors improves the photo-generated charge separation efficiency.However,single heterojunction is difficult to simultaneously satisfy the above three factors.This thesis intends to assemble dispersed heterojunction microspheres photocatalyst based on titanium dioxide to promote the multi-electron transfer process and broaden the range of visible light response of the titanium dioxide,thereby,improve the photocatalytic redox capability of photocatalyst.By employing platinum loaded ultrathin WO3 nanosheet and titanium dioxide?P25?nanoparticles as building blocks,porous multi-heterojunction of platinum/tungsten oxide/titanium dioxide is assembled by spray pyrolysis technique.Studies show that,such multi-heterojunction platinum/tungsten oxide/titanium dioxide with preferred contact mode can effectively improve the separation efficiency of photogenerated electrons and holes and thus inhibit their recombination.Therefore,the multi-heterojunctions exhibit superior photocatalytic activity to single-heterojunction against degradation of volatile organic pollutants,whose reaction rate is 1.52 times and 2.86 times higher than tungsten oxide/titanium dioxide and platinum/titanium dioxide,respectively.Even only 0.04 wt%loading of platinum on the tungsten trioxide nanosheet can still improve the photocatalytic activity of titanium dioxide,due to the high crystallinity of the ultrathin tungsten trioxide nanosheet.Porous phosphotungstic acid surface-modified porous microspheres were fabricated from P25 nanoparticles and phosphotungstic acid?PW12?aqueous solution by spray pyrolysis method.The study shows that an ultrathin interface is formed between PW12 and TiO₂ when the amount of PW12 is lower than 5 wt%.Such ultrathin interface is beneficial to upshift of the Fermi level of titanium dioxide,promote migration of the photo-generated electrons from bluk to the surface of titanium dioxide and induce a multi-electron transfer process on the surface of titanium dioxide.Further,the surface modification of titanium dioxide by phosphotungstic acid enriches the density of surface hydroxyl on titanium dioxide,thereby improving the adsorption capacity of carbon dioxide molecules onto the surface of titanium dioxide.Photocatalytic test via photo-reduction of carbon dioxide displays that a loading amount of 5 wt%of phosphorous on titanium dioxide suface can produce methane with an evolution rate as high as 5?l/g/h,which benefits from the multi-electron transfer process and improved adsorption capability of carbon dioxide.Gold/?anatase phase-TiO₂?B??multi-heterojunction porous microspheres were assembled by spray pyrolysis method by using oxygen-deficient type B phase titanium dioxide nanoparticles and chloroauric acid solution as precursor.Interestingly,growth of anatase phase-TiO₂?B?heterojunction and gold deposition on titanium dioxide surface were synchronously implemented.Effect of spray temperature and the loading amount of gold on the activity of photocatalytic oxidation of carbon monoxide was explored.The research shows that the spray pyrolysis at low temperature is beneficial to the uniform dispersion of Au nanoparticles on the surface of titanium dioxide.Oxygen defects in titanium dioxide nanoparticles and gold plasma absorption significantly broaden the visible light response range of titanium dioxide,besides synergistically inhibition of recombination of photogenerated carrier by anatase phase-TiO₂?B?heterojunction and Au/titanium dioxide heterojunction.The visible-light-activity over as-obtained multi-heterojunction photocatalyst towards photooxidation of carbon monoxide can be 1.67 times higher than TiO₂?B?with oxygen defects.