Selective photo-reduction of CO2 to methanol using Cu-doped 1D-Bi2S3/rGO nanocomposites under visible light irradiation

Abstract

A novel Cu-doped one dimensional (1D) Bi₂S₃ rod-shaped nanocapsule/rGO composite is explored as a photocatalyst for selective reduction of CO₂ to methanol. In particular, the effects of Cu doping of rGO supported Bi₂S₃ on band gap tuning and on product selectivity are investigated. Bi₂S₃ rod-shaped nanocapsules and 0.5, 1, and 2 weight percent Cu-doped Bi₂S₃/rGO are synthesised through a hydrothermal approach. The photocatalysts are characterized by XRD, FTIR, UV-Vis spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, and SEM, TEM and EDX analysis. It is revealed that Cu-doped Bi₂S₃/rGO for all different compositions offers selective and enhanced production of methanol compared to undoped Bi₂S₃/rGO, pristine Bi₂S₃, and Cu-doped Bi₂S₃ which produce formic acid along with methanol. The optimum 1 weight percent Cu-doped Bi₂S₃/rGO photocatalyst, exhibiting the smallest band gap and the lowest rate of recombination of electron–hole pairs, offers the highest photocatalytic activity of 719 μmol g_cat.⁻¹ h⁻¹. DFT studies corroborate the experimental finding of a drastic reduction of the band gap (1.36 eV) of Cu-doped Bi₂S₃/graphene and unveil that Cu 3d–C 2p hybridization as well as enhancement of Bi 6p–C 2p hybridization in the presence of copper significantly increases the overall DOS of the system at the Fermi level, resulting in enhancement of electronic conductivity and charge transfer; further deformation in the graphene sheets due to the presence of Cu-Bi₂S₃ creates CO₂ trapping sites for its efficient adsorption and selective photoreduction.