Engineering oxygen vacancy in (001)-dominated TiO2 for enhanced CH4 photocatalytic conversion

• (001)-dominated ultrathin TiO 2 nanosheets (NSs) with oxygen vacancy were prepared. • The TiO 2 NSs were used for CH 4 photocatalytic conversion with H 2 O 2 as the necessary oxidant. • Oxygen vacancy largely lowered the reaction energy of CH 4 →CH 3 *+ H *. • The highest C1 products yield was 5.95 mmol g −1 h −1 with selectivity of 99.03%. • The yield is comparable to the record using binary/ternary catalysts with metals. Photooxidation of methane to high valued C1 liquid products with both high yield and selectivity against overoxidation has been a huge challenge. In this work, (001)-dominated ultra-thin TiO 2 nanosheets with plenty of oxygen vacancies (O v ) were mass produced by simple hydrothermal and annealing treatments, and used for photocatalytic oxidation of CH 4 into C1 products (mainly HCHO, CH 3 OOH and HCOOH) with H 2 O 2 as the necessary oxidant. For the optimal catalyst with the largest O v ratio, the highest C1 products yield of 5.95 mmol g −1 h −1 was achieved within 2 h, accompanied by a high C1 selectivity of 99.03%, comparable to the current yield record over precious-metal based binary/ternary catalyst. In-situ electron spin resonance, in-situ Fourier Transform Infrared Spectroscopy and mass spectra combined with density functional theory calculations were used for comprehensive clarification of the underlying reaction mechanism. O v on TiO 2 -(001) face largely lowered the energy required for C H bond cleavage of CH 4 , which was the rate-determinate reaction during CH 4 photooxidation. Then formed *CH 3 went through distinct reaction routes of Ti-OOH+Ti-CH 3 →Ti–OCH 3 +Ti-OH→HCHO, thus achieving high yield and selectivity for the main primary product of HCHO (65.7%).