Solar driven photocatalytic glycerol and glucose reforming via noble metals free BiOX (X = Cl, Br, I)-TiO₂ composites

Recent research on the valorization of biomass has received a lot of interest as it allows the obtaining of products with high added value. In this regard, this study explores aerobic and anaerobic heterogeneous photocatalytic partial oxidation under both UV and simulated solar irradiation of glycerol and glucose in aqueous medium using bismuth oxyhalide-based photocatalysts BiOX (X = Cl, Br, I). Moreover, noble metal-free BiOX-TiO₂ (P25) composites were prepared through a simple ball milling procedure. Both the formation of partial oxidation compounds, namely 1,3-dihydroxyacetone, glyceraldehyde and glycolic acid from glycerol and arabinose and formic acid from glucose in solution, and the production of CO₂ and H₂ in the gas phase, were followed. Pure BiOBr and BiOCl proved to be more effective than bare TiO₂ P25 (one of the most used and studied photocatalysts) affording a higher selectivity towards high added value products whilst the composites samples displayed high glycerol conversion values that reached 62 %. Particularly noteworthy was the effectiveness of BiOCl-P25 and BiOBr-P25 samples containing 5 and 7 wt% of BiOCl or BiOBr with respect to P25, in promoting also H₂ formation under simulated sunlight irradiation and without the presence of noble metal species such as Pt. To the best of our knowledge, BiOX-TiO₂ photocatalysts have never been used for the photoreforming of glycerol and glucose.