Photocatalytic biorefining green closed-loop: Photocatalytic alkali lignin depolymerization in supramolecular solvent

In lignin depolymerization, we use a lot of organic solvent which is still an environment problem in large scale industrialization. Therefore, we propose the photocatalytic biorefining green closed-loop (PBGC) to realize green and sustainable development. Different from organic solvents, we find that supramolecular solvents can synergistically interact with photocatalysts to influence the final products. The solubility of Alkali lignin (AL) in supramolecular solvent was 150 % higher than in ChCl/1,4 BDO (1:3) due to the AL and solvent have the similar supramolecular structure. Additionally, supramolecular solvent was used at low temperature (60 °C) which overcame the bottleneck of high viscosity provided huge possibility on industrial application. AL was photocatalytic-assisted oxidized by WO 3 /g-C 3 N 4 /h-BN (WCB). The conversion of AL achieves 38.61 wt%, and the yield of vanillic acid is 22.87 % in product. In this process, the β-O-4 bonds within the lignin structure were activated by hydroxyl radicals originating from the supramolecular solvent. The hydroxyl radical was produced from 1,4 BDO in supramolecular solvent. In dark environment, AL interacted with supramolecular solvent aroused the generation of C α aryloxy radical (ArO•). The superoxide radical was produced on the WCB from O 2 which could stabilize the C α ArO• quickly to final products.