Room-temperature photocatalytic conversion of CH4 into liquid oxygenates with O2/H2O provides an appealing route for sustainable chemical industry, which, however, suffers from poor efficiency due to the undesired carrier kinetics and low yield of reactive oxygen species of the currently available photocatalysts. Here, we report an effective surface engineering strategy where concurrent constructions of oxygen vacancies and phosphate sites on TiO2 nanosheets address the above challenge. The surface oxygen vacancies and phosphates are respective acceptors of photogenerated electrons and holes for promoted separation and migration of charge carriers. Moreover, in addition to the facilitated activation of O2 to •OH by electrons at oxygen vacancies, the surface phosphates also facilely adsorb H2O via hydrogen bonds and thus effectively transfer holes to H2O for enhanced •OH production, thereby boosting CH4 conversion. As a result, compared with TiO2 sheets with only oxygen vacancies, a 2.8 times improvement in liquid oxygenate production with near-unity selectivity is achieved by virtue of the synergy of surface oxygen vacancies and phosphate sites, together with an unprecedent quantum efficiency of 19.8% under 365 nm irradiation.
Keywords: H2O oxidation; O2 reduction; oxygen vacancy; phosphate; photocatalytic CH4 conversion.