Hollow structured black TiO2 with thickness-controllable microporous shells for enhanced visible-light-driven photocatalysis

Black TiO2 has attracted great attentions due to its wide application potentials in visible-light photocatalysis, solar-thermal conversion for water evaporation, photothermal therapy and so on because of its controllable band gap using lattice disorder engineering. In this work, we proposed the design of microporous hollow structure in black TiO2 with thickness-controllable nano-shells to further optimize its photocatalytic ability. The hollow shells were produced from the evaporation-induced self-assembly (EISA) followed by NaBH4 reduction, and the shell thicknesses could be adjusted from ~20 to ~145 nm. The prepared microporous hollow shells showed excellent light absorption and enhanced photocatalysis performance with decreased shell thickness. Under visible light irradiation, the photocatalytic efficiency of the 20-nm shells was ~8 times higher than that of the 145-nm shells, revealing the strong promotion effect of the nano-shell design on the photocatalytic activity of hollow black TiO2. This great effect can be attributed to the higher surface area, more catalytic active sites and less diffusing distance in pore channels of the thinner shells. Our work demonstrates a scheme for the porous hollow structural design of black TiO2 with ultrathin nano-shell, and provides significant insights for its applications in higher efficiency of visible-light utilization and photocatalysis.