Converting formaldehyde in methanol with MoO₂ under irradiation: A pollution-free strategy for cleaning air

Direct photocatalytic reduction of toxic formaldehyde (HCHO) in value-added chemicals and fuels is promising because that not only abates the environmental pollution, but also solves the energy shortage. Herein, self-supported MoO₂ and MoO₃ nanoparticles growing on Mo meshes were comparatively applied to the photocatalytic conversion of HCHO. Under UV-visble lights, MoO₂ reduces HCHO in methanol (CH₃OH) while MoO₃ oxidizes HCHO in carbon oxide and water. Their contrary photocatalytic capacities were revealed. Compared with MoO₃, the lower work function of MoO₂ enables an electron-rich interface, realizing a complete reduction of 30 ppm HCHO to CH₃OH in 30 min. Theoretical calculations clarify that a large number of delocalized electrons on MoO₂ attracts HCHO molecule and activates its CO bond, facilitating subsequent hydrogenation and reduction of HCHO to CH₃OH. As for MoO₃, the wider bandgap and higher potential of valence band govern the photocatalytic oxidation of HCHO.