Selective photoelectrocatalytic oxidation of glycerol by nanotube, nanobelt and nanosponge structured TiO2 on Ti plates

Photoelectrocatalytic (PEC) oxidation of glycerol to commercially valuable compounds was carried out using nanotube, nanobelt and nanosponge TiO2 on Ti plates prepared by anodic oxidation method. The plates were characterized by XRD, SEM and electrochemical methods (photocurrent profiles and EIS). Glycerol oxidation experiments were carried out under environmentally friendly conditions using air/water as oxidant and water as solvent under UVA irradiation. Glyceraldehyde, 1,3-dihydroxyacetone, formic acid and CO2 were determined as glycerol products. The effects of photoanode morphology, TiO2 crystallinity, applied potential, pH, solution mixing speed, electrolyte type (and concentration) and gas atmosphere on the glycerol oxidation activity and product selectivity were investigated in detail. In addition, the hole trap effect of methanol was also investigated. Optimum conditions were achieved with anatase phase nanotube structured TiO2 photoanodes in the presence of 20 mM Na2SO4, by applying 1.5 V bias, and 400 rpm solution mixing speed at pH 7 in air atmosphere. Electrocatalytic and photocatalytic experiments were performed in order to compare them, and in the first case no activity was observed, while in the second case it was low. The disappointing results obtained by using the single methods demonstrated the presence of a synergistic effect in the PEC experiments. Moreover, the electrode prepared by simple thermal oxidation of the Ti plate showed no activity in the PEC tests, unlike the structures in which TiO2 nanotubes, nanosponges and nanobelts were present which showed significant activity due to the high specific surface area and their other morphological and structural characteristics.