Sulphur vacancy driven phase conversion of MoS2 nanosheets for efficient photoreduction of CO2 under visible light

Abstract

Vacancy-rich systems have immense importance in the field of catalysis due to their active coordination and electron-rich characteristics. Molybdenum disulfide (MoS₂) has attracted much attention due to its promising photocatalytic properties in solar fuel production from water splitting and CO₂ reduction. By creating S vacancies on the basal plane, we have enriched the surface of MoS₂ with more catalytically active sites. Moreover, the S vacancy enables the conversion of the stable 2H phase to catalytically more active 1T′ phases. The presence of S-vacancies makes the 1T′ phase metallic. The surfactant-assisted exfoliation process adopted here also increases inter-lamellar spacing and, hence, increases its light absorption in the visible region. The simultaneous presence of the semiconducting 2H phase and metallic 1T′ phase enhances the separation of photogenerated electron–hole pairs. As a consequence, the exfoliated MoS₂ nanosheet showed excellent photocatalytic activity towards CO₂ reduction with an effective yield of 3.9 μmol g⁻¹ h⁻¹ for formic acid (HCOOH) and 9.9 μmol g⁻¹ h⁻¹ for methanol (CH₃OH) after 14 hours of light irradiation. Through extensive experimental and theoretical studies, we have shown the importance of sulphur vacancies in the system and further established the reduction mechanism from CO₂ to CH₃OH.