Nitrite ions are shown to have significant influence on the selectivity of the photocatalytic oxidation of methane to methanol. An almost complete inhibition of undesired CO2 has been achieved with BiVO4 in the presence of a low concentration of nitrite, which might act both as a UV filter and as a hydroxyl radical scavenger.
Bismuth-based photocatalysts, Bi2WO6, BiVO4, and coupled Bi2WO6/TiO2–P25, have been synthesized by a facile hydrothermal method, characterized, and evaluated for the first time for the selective photooxidation of methane to methanol. Several conditions were used in order to better comprehend the reaction mechanism. The obtained BiVO4 is, among the others, the most promising photocatalyst for this reaction, displaying higher CH3OH selectivity and being more stable than the others. When Bi2WO6 was coupled with TiO2, the methane conversion increased; however, overoxidation of CH4 to CO2 predominates. A similar effect is observed when electron scavengers such as O2 or Fe3+ were introduced in the photoreactor as a result of the formation of highly oxidant radicals.