Controllable Synthesis Of Hollow Mesoporous Anatase Nanomaterials And The Application In Photocatalysis

It is an inevitable trend to develop clean and renewable energy, since globalenergy crisis and environmental problems have affected our human life largely.Considering into solar energy, a kind of exhaustless energy in our nature, a lot ofresearch groups have devote themselves to converting solar energy to availableenergy for human, such as solar cells, photoelectrochemical cell and so on.Particularly, photocatalysis field based on inexpensive and efficient TiO2semiconductor metal oxide, including water splitting, imitation of photosynthesisand sewage treatment, has received widespread attention.However, the photocatalytic performance of TiO2materials in practicalapplications is limited with many factors: the forbidden band gap, the band position,the pore diameter, specific surface area, water solubility, crystallinity, etc. Then,numbers of research work has been done to improve the photocatalytic activity ofTiO2over the past decades. Generally, photocatalytic reactions usually occur in theaqueous solution, so it is very important to ensure that the reactant molecules canreach the active site of the surface about the TiO2molecules. In order to solve thisproblem, we can remove the center of the colloid TiO2nanoparticle,with uniformshell and pore structure remained, which can provide more active sites on unit area,reduce the diffusion resistance, improve the passing rate, becoming a hollowmesoporous nanoparticles. Another factor affecting the photocatalytic activity ofTiO2nanostructures is crystallinity. Although the band gap of rutile TiO2has lower(3.0eV)than that of anatase, anatase TiO2with high reduction potential and lowrecombination rate of electron-hole is considered to be the crystalline phase whichhas a high catalytic activity under UV irradiation. Anatase TiO2also can excite moreelectronic and prolong the life of electronic under UV, which can improvephotocatalytic activity of the whole TiO2nanoparticles.As a stronghold, we have successfully prepared hollow mesoporous anatase nanospheres with high specific surface area and high crystallinity. Firstly, a uniformTiO2lay was coated on the surface of SiO2nanospheres to form core-shellSiO2@TiO2composites. After selective removal of SiO2hard template, an acidexchange process for protonation was executed. Finally, the hollow mesoporousanatase nanospheres were obtained through crystallization process. The hollowmesoporous anatase nanomaterials exhibit high specific surface area and highcrystallinity. Additionally, the nanoscale crystallinity and uniform porous diameter inTiO2shell was controllable by adjusting crystallization temperature. Thephotocatalytic activity for degrading Rhodamine B under ultraviolet light wasimproved largely，and the degradation rate is obviously faster than P25.Furthermore, we decorated the hollow mesoporous anatase nanospheres withheavy metal nanoparticles to improve the responsivity for visible light. In thissituation, we synthesized yolk-shell mesoporous anatase Au@TiO2nanomaterials,and the photocatalytic activity under visible light was examined. Similar to aboveconclusion, the yolk-shell mesoporous anatase Au@TiO2nanomaterials also exhibithigh specific surface area and high crystallinity. Additionally, the nanoscalecrystallinity and uniform porous diameter in TiO2shell was also controllable byadjusting crystallization temperature. It is notable that the Au nanoparticles did notaggregate because of high temperature crystallization process, owing to the confineof TiO2shell. These characteristic make sure that the Au@TiO2nanomaterialsexhibited excellent photocatalytic activity under visible light.