Carbonaceous biomass-titania composites with Ti-O-C bonding bridge for efficient photocatalytic reduction of Cr(VI) under narrow visible light

The aim of this study was to develop carbonaceous materials hybridized with anatase TiO2 composed of Activated Carbon-TiO2 (AC-TiO2), Olive Pits-TiO2 (OP-TiO2) and Wood Shaving-TiO2 (WS-TiO2) by ultrasonic-assisted sol-gel process for the photocatalytic Cr(VI) reduction under UV and narrow visible light. The morphology, crystal structure, surface chemistry and optical properties of the as-prepared and bare-TiO2 were investigated by SEM-EDS, XRD, FTIR, BET, UV-DRS, XPS and photo-current measurements. Unlike bare-TiO2, these composite photocatalysts exhibited an enhanced absorption in visible-light. The band gap energies were found to be 3.20 eV, 2.89 eV, 2.81 eV and 2.95 eV for bare-TiO2, AC-TiO2, OP-TiO2 and WS-TiO2, respectively. On the other hand, as-prepared photocatalysts showed significantly improved photocatalytic Cr(VI) reduction performances under UV and visible light illumination compared to bare-TiO2. A total reduction of 10 ppm of Cr (VI) was obtained after 30 min, 50 min and 130 min under visible light (> 420) for AC-TiO2, OP-TiO2 and WS-TiO2, respectively at pH: 3 and in the presence of 10 ppm tartaric acid as hole scavenger, while no reduction was detected for bare-TiO2 under visible light (> 420). The efficient photocatalytic reduction of Cr(VI) under visible light by AC-TiO2, OP-TiO2 and WS-TiO2 was mainly due to (i): the narrow band gap of TiO2 nanoparticle deposited in carbonaceous materials, (ii): self-photo-sensitizer role of carbonaceous materials via Ti-O-C bonds and (iii): the electron transfer from TiO2 to carbonaceous materials.