Photocatalytic H2 production and degradation of aqueous 2-chlorophenol over B/N-graphene-coated Cu0/TiO2: A DFT, experimental and mechanistic investigation

Abstract

Energy and environmental challenges are global concerns that scientists are interested in alleviating. It is on this premise that we prepared boron/nitrogen graphene-coated Cu0/TiO2 (B/N-graphene-coated Cu/TiO2) photocatalyst of varying B:N ratios with dual functionality of H2 production and 2-Chlorophenol (2-CP) degradation. In-situ coating of Cu0 with B/N-graphene is achieved via solvothermal synthesis and calcination under an inert atmosphere. All B/N-graphene-coated Cu/TiO2 exhibit higher photonic efficiencies (5.68%–7.06% at 300 < λ < 400 nm) towards H2 production than bare TiO2 (0.25% at 300 < λ < 400 nm). Varying the B:N ratio in graphene influences the efficiency of H2 generation. A B:N ratio of 0.08 yields the most active composite exhibiting a photonic efficiency of 7.06% towards H2 evolution and a degradation rate of 4.07 × 10−2 min−1 towards 2-chlorophenol (2-CP). Density functional theory (DFT) investigations determine that B-doping (p-type) enhances graphene stability on Cu0 while N-doping (n-type) increases the reduction potential of Cu0 relative to H+ reduction potential. X-ray photoelectron spectroscopy reveals that increasing the B:N ratio increases p-type BC2O while decreasing n-type pyridinic-N in graphene thus altering the interlayer electron density. Isotopic labelling experiments determine water reduction as the main mechanism by which H2 is produced over B/N-graphene-coated Cu/TiO2. The reactive species involved in the degradation of 2-CP are holes (h+), hydroxyl radical (OH•), and O2•-, of which superoxide (O2•-) plays the major role. This work displays B/N -graphene-coated Cu/TiO2 as a potential photocatalyst for large-scale H2 production and 2-CP degradation.