Cu-Doped 2D-Bi₂MoO₆ Nanoribbon/rGO Photocatalysts for Selective Ethanol Production by Photocatalytic CO₂ Reduction

Hydrothermally produced Cu-doped two-dimensional (2D) Bi2MoO6 nanoribbon/rGO composite is explored as the photocatalyst for selective reduction of CO2 to ethanol. In particular, the role of Cu doping of rGO-supported Bi2MoO6 on C2 product selectivity is investigated. Long nanoribbon-type pristine 2D-Bi2MoO6, 2D-Bi2MoO6 nanoribbon/rGO, and that doped with varying weight percentages of copper (Cu) are synthesized and characterized by XRD, FTIR, UV–vis spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, SEM, TEM, EDX, EIS, and BET analyses. Among all the photocatalysts, the optimum 2 wt % Cu-doped two-dimensional (2D) Bi2MoO6 nanoribbon/rGO photocatalyst exhibiting an enhanced absorption edge of visible light at 730 nm, the smallest band gap of 2.02 eV, the lowest rate of electron–hole pair recombination, and improved charge transport offers the highest photocatalytic activity (133.10 μmol gcat.–1 h–1) and 100% selective ethanol production. Absence of either Cu doping or rGO leads to formation of a mixture of methanol and ethanol. rGO separates photoexcited electrons and holes and establishes an electron-rich interface on the rGO-Cu junction of the 2%Cu-doped (2D) Bi2MoO6 nanoribbon/rGO photocatalyst, facilitating high CO2 adsorption. Cu serves as a trap to catch more electrons. Electrons from Mo and Bi atoms (of Bi2MoO6) are drawn to the C 2p (of rGO) and Cu 3d orbitals. Cu doping enhances the thickened electron cloud (drawn from Mo and Bi) on the surface junction of C(rGO)-Cu, which facilitates more CO2 adsorption and reduction. The Mo–C–Cu/Mo–O–Cu bridge formed upon Cu doping effectively reduces the transport distance of photogenerated electrons with the lowest recombination rate to stabilize intermediate radicals such as ·CO and facilitates the transfer of abundant photogenerated electrons to the CO2 tapping sites for selective ethanol formation. The optimum doping of 2% Cu in the (2D) Bi2MoO6 nanoribbon/rGO photocatalyst enhances the yield of selective ethanol production by 2.26 times compared with that of (2D) Bi2MoO6 nanoribbon/rGO.