Superior photocatalytic dye degradation under visible light by reduced graphene oxide laminated TiO2-B nanowire composite

Abstract

Reduced graphene oxide laminated TiO2-B NW composites [R(GO/TNW)] were grown by high pressure and high temperature hydrothermal method via subsequent solid-state reaction with NaBH4. During the reduction process the TiO2 nanowires retained the pure bronze phase, while gradually the C=C bonds from the graphene oxide increased, the oxygenated functional groups dissipated, while the Ti4+ oxidation states regularly transformed into Ti3+ configuration. The specific surface area and the pore volume of TiO2-B nanowires (TNW) both grossly increased in R(GO/TNW) composites. The optical band gap of TiO2-B NWs (∼2.92 eV) notably reduced in R(GO/TNW) composites (≤ 2.0 eV) in which visible absorption increased due to the synergistic effect of reduced TiO2-B nanowires (RTNW), reduced graphene oxide (RGO) and the Ti3+ defects. A significantly improved visible light dye degradation efficiency (∼96%) with a superior rate constant (∼0.028 min−1) was attained in R(GO/TNW) composite by virtue of higher light absorption due to narrowing of band gap and increased surface area and pore volume, together with increased adsorption due to the π-π stacking interactions between GO and the dye molecules. Defect elicited additional states within the band gap of TiO2-B NWs acted as trapping centers for the photogenerated charge carriers and impeded the recombination process, and thus facilitated enhancing the dye degradation efficiency of the photocatalyst by using those trapped charges. Photo generated holes, electrons, superoxide and hydroxyl radicals are the reactive species controlling the dye degradation process.