Mesoporous black N-TiO2−x hollow spheres as efficient visible-light-driven photocatalysts

Mesoporous black N-TiO2−x hollow spheres are successfully fabricated through a facile evaporation-induced self-assembly (EISA) process, coupled with an etching procedure and an in-situ solid-state chemical reduction strategy. The resultant black N-TiO2−x hollow spheres with high crystallinity possess a narrow band gap of ∼2.37 eV, a large specific surface area of ∼128 m2 g−1, and a well defined hollow sphere structure, which exhibit excellent visible-light-driven photocatalytic performance for degradation of phenol, reduction of Cr(IV), and hydrogen production. The photocatalytic reaction apparent rate constants (k) of the black N-TiO2−x for phenol degradation and Cr(IV) reduction are ∼5 and 6 times higher than that of pristine TiO2, and hydrogen production rate for N-TiO2−x is ∼160 μmol h−1, which is ∼7 folds higher than that of pristine one. The excellent photocatalytic and photoreduction property can be attributed to the synergy effect of N and Ti3+ codoping narrowing the band gap, the high specific surface area offering more surface active sites, and the mesoporous hollow structure favoring light harvesting and refraction.