Enhanced Selective Formic Acid Production by Photocatalytic CO2 Reduction Using a N-Doped rGO/BiVO4 Nanocomposite

Abstract

A nitrogen-doped reduced graphene oxide (rGO)/BiVO4 nanocomposite has been prepared through a hydrothermal route as a photocatalyst for selective photoreduction of CO2 into formic acid. This study specifically examines how N doping of the rGO/BiVO4 nanocomposite governs the selectivity and yield of the C1 product. Two-dimensional nanohexagonal BiVO4, BiVO4 loaded with varying wt % rGO, and rGO/BiVO4 doped with varying wt % N are synthesized and characterized by UV–vis absorption, XRD, PL, XPS, BET, SEM, EDX, TEM, EIS, and Mott–Schottky measurements. Among all the compositions examined, the sample with 1.5 wt % N doping on 2.5 wt % rGO/BiVO4 stood out, with an average particle size of about 6–25 nm, a red-shifted absorption edge at 659.39 nm, a narrowed band gap of 2.06 eV, the least electron–hole recombination, and improved charge-carrier separation and mobility; this sample delivered the highest photocatalytic activity, reaching 593.24 ± 5.15 μmol gcat.–1 h–1 with a 100% selective yield of formic acid. Doping 1.5% nitrogen into the (2.5%)rGO/BiVO4 photocatalyst also raises the number of defect sites available for capturing CO2, boosting the selective yield of photocatalytic CO2 conversion into formic acid, with an AQY of roughly 0.148 ± 0.00064%. Both the experiments and DFT calculations show that N doping narrows the band gap and shifts the VBM toward the CBM through the introduced N-2p orbitals and further predict hybridization among the overlapping N-2p, O-2p, Bi-6p, and V-3d orbitals near the Fermi level. The proposed mechanism indicates that photogenerated electrons migrate from BiVO4 toward the doped N atoms through the rGO network to fill the electron vacancy in the N-2p orbital. Acting as an electron acceptor, rGO separates the photo-excited electron–hole pairs across the junction interface and promotes adsorption of CO2 molecules onto the photocatalyst surface. Doping (2.5%)rGO/BiVO4 with 1.5% N raises the selective formic acid yield 2-fold relative to undoped (2.5%)rGO/BiVO4.