Photocatalytic depolymerization of rice husk over TiO2 with H2O2

• Rice husk was photocatalytically depolymerized over TiO2 in H2O2 aqueous solution.
• 172 organic species were identified in the extracts from the reaction mixture.
• Alkanes, phthalates and ketones are the most three abundant group components.
• Lignin–wax and hemicellulose–wax interlinkages are proposed to be new structures.
• The mechanisms for the formation of several identified species were proposed.

Photocatalytic depolymerization (PCDP) of rice husk (RH) over TiO2 in H2O2 aqueous solution under ultraviolet irradiation was investigated. The reaction mixture was fractionated into different extracts by filtration and subsequent sequential extraction with different organic solvents. In total, 172 organic compounds were identified in the extracts with GC/MS. The compounds can be classified into alkanes, alkenes, arenes, non-substituted alkanols, substituted alkanols, alkenols, phenols, alkanals, alkenals, benzaldehydes, ketones, carboxylic acids, alkanoates, phthalates, nitrogen-containing organic compounds, sulfur-containing organic compounds and other species. Alkanes are the most abundant in the group components. They resulted from the degradation of waxes in RH. Aldehydes and ketones were also detected with high relative contents, most of which were derived from cellulose, hemicellulose and waxes. Phthalates and arenes resulted from lignin degradation. Lignin–wax and hemicellulose–wax interlinkages are proposed to be new structures. According to the species identified in the extracts, the mechanisms for photocatalytic oxidation of benzene ring-containing compounds are proposed. The PCDP of RH provides an alternative way to obtain value-added chemicals from biomass with low energy consumption and under eco-friendly conditions.