Sono-Enhanced Selective Oxidation of Lignin-Based Coniferyl Alcohol in Continuous Flow through a Synergistic Metal Oxide Heterostructure

The selective oxidation of organic substances is today considered one of the greenest strategies to synthesize important starting materials in different technological applications. This study investigates the sono-enhanced selective oxidation of coniferyl alcohol, a lignin-based model compound, under visible light by integrating sonophotocatalysis in a continuous flow system. The process utilizes a CuBi2O4/TiO2 heterostructure as photocatalyst which is prepared by a simple and low-cost method. The heterostructure demonstrates significant improvements in catalytic performance due to its effective charge separation and extended light absorption range with a conversion and selectivity of 92% and 46%, 30%, respectively, for coniferyl aldehyde and ferulic acid after 4 h under visible-light irradiation by using acetonitrile as the solvent. The synergistic combination effects of ultrasonic irradiation and photocatalysis are explored to enhance the efficiency and selectivity of the oxidation reaction with 54% conversion with significant selectivity of ferulic acid measured 65%. Additionally, the continuous flow setup offers advantages in scalability and operational stability, making this method a promising approach for sustainable biomass valorization. The results highlight the potential of combining sonication and photocatalysis to achieve efficient and selective chemical transformations in renewable energy and green chemistry applications, and specially contribute to the sustainable transformation of lignin-based compounds into high-value chemicals, aiding in the utilization of biomass.