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 g_cat.^–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.