Minimizing CO2 emissions by photocatalytic CO2 reduction to CH3OH over Li2MnO3/WO3 heterostructures under visible illumination

Abstract

Photocatalytic CO₂ reduction to valuable fuels has proved to be a favourable process to produce renewable energy and reduce CO₂ emissions, which mostly depends on designing effective photocatalysts with the rapid separation rate of charge carriers. In this contribution, mesoporous n-n heterojunction Li₂MnO₃/WO₃ nanocomposites were designed via a simplistic sol-gel process for CO₂ reduction utilizing visible illumination (λ > 420 nm). XRD and TEM measurements confirmed the synthesized Li₂MnO₃/WO₃ nanocomposite is a monoclinic structure, and its particle size is 25 ± 5 nm. The obtained Li₂MnO₃/WO₃ exhibited narrower bandgap energy (1.74 eV), larger surface area (212 m²g^-1), exceedingly visible absorbing, and lower recombination of electron and hole. The yield of CH₃OH was determined about 198, 871, 1140, 1550 and 1570 mmolg^-1 for bare WO₃ and 5%, 10%, 15% and 20% Li₂MnO₃/WO₃ nanocomposites, respectively. These results evidenced that the 15% Li₂MnO₃/WO₃ photocatalyst exhibited the best reduction ability compared to other nanocomposites. The CO₂ reduction over 15% Li₂MnO₃/WO₃ photocatalyst achieved a maximal CO₂ conversion with the substantially boosted CH₃OH, i.e., 1550 mmolg^-1 after 9 h, which was enhanced 7.8 folds great than of WO₃ NPs. Mesoporous Li₂MnO₃/WO₃ nanocomposites, in comparison with bare WO₃ NPs, created more active sites for facilitating CO₂ and had a specific electric field to more effectively separate charge carriers. The Li₂MnO₃/WO₃ photocatalyst has superior photostability during the continuous reduction of CO₂ for 45 h with no remarkable decrease. The possible direct S-scheme mechanism for electron transfer over Li₂MnO₃/WO₃ photocatalyst with the enhanced CO₂ reduction ability was discussed. The present work demonstrates an avenue for building highly effective heterostructure photocatalysts in solar-energy-induced potential applications.

Keywords: CO(2) photoreduction; Heterojunction; Li(2)MnO(3)/WO(3) nanocomposites; S- scheme.