Photocatalytic oxidation of glucose and cellulose to valuable chemicals and hydrogen

Abstract

Utilization of biomass is promising in the process of shifting from fossil fuels usage and evolving technologies implementation. Also, through the mild conditions required for the heterogeneous photocatalysis of cellulose and glucose, various products including organic acids, sugar alcohols, oligosaccharides, and H₂ can be produced. The photocatalytic conversion of glucose was studied under aerobic (atm P), anaerobic (vacuum), inert (Ar) atmosphere and varying irradiation. TiO₂ was the main photocatalyst with Fe₂O₃, Pt, and g-C₃N₄ as co-catalysts. The Fe₂O₃ containing catalysts increased glucose conversion compared to bare TiO₂, Pt containing catalysts increased H₂ production, and g-C₃N₄ containing catalysts showed poor overall performance. A photoreactor with internal irradiation was designed and developed to monitor and control multiple conditions of the photocatalytic testing and achieve simultaneous gas and liquid products analysis. While the analysis of sugars was conducted mainly via HPLC, study of these molecules and development of sugar mixtures analysis was conducted additionally via Raman spectroscopy, providing a quick, cost effective and non destructive alternative. Characterisation of the synthesized catalysts was conducted via multiple analytical techniques, defining the crystal phases, optical behaviour, morphology, and participating phases. Fe₂O₃ increased the visible light absorption of the catalysts, while preserving the properties of TiO₂. High dispersion of the Fe₂O₃ phase was achieved upon addition in low percentages. The Pt/TiO₂ catalysts also showed high dispersion of the metal on the support, while preserving the surface area of TiO₂. The Fe₂O₃/g-C₃N₄-TiO₂ catalysts showed poor homogeneity across the material. Cellulose was characterised regarding the particle size, morphology, and crystalline index. Pre-treatment of cellulose was conducted through ball milling, promoting interaction with the catalyst, which was investigated through multiple techniques. Results of cellulose photocatalytic testing showed H₂ evolution and production of various liquid products. Using the developed photoreactor both gas and liquid products were successfully recorded through chromatographic analysis.