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 0.5 to 4μm with the nanopore size in the range of 3–11 nm.Remarkably,the specific surface area of these nanoporous anatase TiO2 microspheres can be as high as 500m 2g 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(λ ≥ 400 nm),the carbonate-doped TiO2 microspheres can produce 0.2 mmol H2 h1 g1 of photocatalyst,which is significantly higher than those from various other TiO2 photocatalysts.