Effective and selective C-C bond cleavage of lignin Model by tuning metal composition of giant keplerate polyoxometalate photocatalyst

Abstract

Plastic is the most common material around the world and still, no one utilizes it. The need for renewable energy has been challenged for a long time and photocatalysis is denoted as a potentially promising approach to mine free energy and valorize chemical fuels from plastic waste. However, the development of an effective and selective photocatalyst is still challenging for plastic transformation under ambient conditions. We herein report a mild photocatalytic strategy for C-C bond cleavage of lignin-models. We use green and efficient Giant Keplerate polyoxometalate (POM) photocatalyst whose redox potential can be easily tuned by changing its metal compositions, and finally find out what factor enhances the catalyst’s activity or selectivity on chemical bond cleavage. Identifications by NMR techniques and HS-GCMS analysis indicate that $Mo_{132}$ Giant Keplerate POM shows certain interactions with lignin, water, and polar solvent. Moreover, analysis of redox potentials and mechanistic investigations reveal that photogenerated holes of $Mo_{132}$ can trigger C-C bond cleavage of lignin models efficiently by homolytic ligand to metal charge transfer reaction. This study sheds light on further reuse or recycle of plastic wastes regarding proper consideration of homogeneity behavior, solvent effect, and redox potentials in a given reaction environment.