Enhanced photoreduction of Cr(vi) and photooxidation of NO over TiO2−x mesoporous single crystals

Abstract

Managing air and water pollution is among the greatest challenges and a major issue for human civilizations in the 21^st century. Semiconductors such as TiO₂ are regarded as one of the most promising catalysts that can be used to realize the simultaneous and efficient treatment of multi-component wastewater and NO selective oxidation. However, the granular TiO₂ always contains too many phase interfaces, which are harmful to the transfer of photo-excited electrons. Reduced TiO₂ mesoporous single crystals (TiO_2−x MSCs) with capacity of photoreduction and photooxidation were successfully synthesized by a facile hydrothermal treatment. The formation of Ti³⁺ impurity levels contribute to a narrowed band gap and enhanced visible light adsorption of TiO_2−x. In addition, the mesoporous single crystal structure would provide a long-range order channel for the transfer of photo-generated electrons, which leads to the efficient photoreduction and photooxidation capacity of TiO_2−x MSCs. The results revealed that Ti³⁺-MSCs exhibit outstanding photocatalytic decontamination performance in simultaneous photo-degradation of phenol and removal of Cr(VI) owing to high photo-generated charge separation rate and the synergistic effect of phenol and Cr(VI). In addition, in the absence of any noble metal, the as-prepared reduced Ti³⁺-MSCs still show high selectivity of NO₂ in the NO_x photo-oxidation process, owing to the extended wide-spectrum absorption of Ti³⁺-MSCs and the high-active holes on Ti³⁺-MSCs under solar light irradiation.