Doping high-surface-area mesoporous TiO2 microspheres with carbonate for visible light hydrogen production

First-principles calculations suggest that doping TiO2 with carbonate can effectively reduce the bandgap of TiO2, thus making TiO2 photoactive in the visible region of the solar spectrum. Herein we report a simple "one-pot" solvothermal method for synthesizing brown carbonate-doped TiO2 microspheres. The diameter of the TiO2 microsphere is tunable from similar to 0.5 to 4 mu m with the nanopore size in the range of 3-11 nm. Remarkably, the specific surface area of these nanoporous anatase TiO2 rnicrospheres can be as high as 500 m(2) g(-1). A controllable amount of carbonate could be incorporated into TiO2 through low-temperature post-synthesis annealing, which extends the light absorption of the TiO2 microspheres from the ultraviolet to the visible region of the solar spectrum. Very high photocatalytic activity of these carbonate-doped TiO2 microspheres was demonstrated in the visible light region for both photocatalytic production of hydrogen from water and degradation of methyl orange. Under 3 Sun visible-light illumination (lambda >= 400 nm), the carbonate-doped TiO2 microspheres can produce 0.2 mmol H-2 h(-1) g(-1) of photocatalyst, which is significantly higher than those from various other TiO2 photocatalysts.