Preparation, Characterization And Photocatalytic Properties Of TiO₂-based Porous Microspheres

TiO₂porous microspheres with submicron size have important application value inphotochemical solar energy conversion and utilization. The size of the porous microspheresin submicrometer level is comparable to the wavelength of near ultraviolet and visiblephotons, thus it may display interesting light trapping via multiple scattering at air-solidinterface. The porosity of the microspheres ensures the sub-micron powder materials havesimilar specific surface area with the nano-powder, which is beneficial to the conduct of theinterface photochemical process. We prepared TiO₂-based porous microspheres by ultrasonicspray pyrolysis method provided a one-step, continuous and low cost process. How toenhance the photocatalytic activity of TiO₂was investigated by doped and composite method.Moreover, TiO₂porous microspheres were applied in self-cleaning cement. The contents ofthe paper are listed as follow:1In order to improve the sunlight utilization of TiO₂. The visible light responseNb-doped TiO₂porous microspheres were prepared. Due to the multiple scattering ofmicrospheres and Nb-doping, the spectral absorption of TiO₂was extended into visiblespectrum, and the absorption onset was red-shifted for about88nm at a doping level of5%compared to pristine TiO₂microspheres. Under solar or visible irradiation, Nb-doped TiO₂microspheres showed higher photocatalytic activity for methylene blue degradation comparedwith TiO₂microspheres, which could be ascribed to the extended light absorption range andthe suppression of electron-hole pair recombination.2In order to enhance charge separation of TiO₂. TiO₂/Graphene compositemicrospheres（TiO₂-GR） were prepared using Degussa P25and Graphene oxide （GO） asprecursors. With the increasing of graphene content, the surface area of TiO₂-GR increasedand the absorption intensity of TiO₂-GR in the visible light region increased. The PLintensities of TiO₂-GR are lower than that of TiO₂and gradually decrease with the increasingof GR content, which suggests the introducing of Graphene enhances charge separation ofTiO₂. Under solar irradiation, TiO₂-GR microspheres showed higher photocatalytic activityfor methylene blue degradation compared with TiO₂microspheres, which could be ascribedto the suppression of electron-hole pair recombination.3Heterostructured TiO₂/WO₃porous microspheres with W/Ti molar ratio of2,4, and10%（TW-2, TW-4, TW-10, respectively） were prepared using Degussa P25and ammoniumtungstate as precursors. Crystal phase evolution of WO₃from amorphous to orthorhombicwas observed with the increase of its content. TiO₂/WO₃heterostructured microspheres displayed higher photocatalytic activity towards acetaldehyde degradation than pure TiO₂dueto the enhanced charge separation by TiO₂/WO₃heterojunction, but only the TW-2microspheres with amorphous WO₃phase displayed faster generation of CO2and freehydroxyl radicals than TiO₂（TW-0） micropheres. Photochromism was observed on the TW-4and TW-10microspheres due to electron accumulation in orthorhombic WO₃, but notobserved on the TW-2with amorphous WO₃. These observations suggests that electronaccumulation in WO₃is detrimental to the photocatalytic activity of TiO₂4TiO₂porous microspheres were applied in self-cleaning cement. The change of watercontact angle under after applying oleic acid to the film surface, the change of the absorptionintensity of Resazurin dye and the acetaldehyde mineralization are chosen as model reactionto evaluate the photocatalytic activities of the present samples. Under UV light irradiation,cement film did not show photocatalytic activity, TiO₂microspheres-cement film showedhigher photocatalytic activity compared with TiO₂particles-cement film, which could beascribed to the enhancing of the sunlight utilization and the increasing of the amount of TiO₂participated in the reaction in cement internal and surface by the introducing of TiO₂porousmicrospheres.