Sunlight Assisted Photocatalytic Valorization of Lignin Using Recyclable Light Harvesters

The abundant aromatic supply lignin, which is generated from agri-biomass, can be used as a sustainable alternative for several platform chemicals and fuels. The strongly cross-linked and randomly polymerized structure of lignin makes it difficult to valorize. In the current work, we have developed a solar photocatalytic system based on porphyrin that can directly depolymerize lignin and lignin-model compounds. The porphyrin has been evaluated for photophysical characteristics such as singlet oxygen and fluorescence quantum yields. The developed catalyst has been initially utilized for the degradation of lignin model compounds and then directly on lignin. For assessment, the degraded lignin various characterization techniques such as UV-vis spectroscopy, heteronuclear single quantum coherence spectroscopy (HSQC), electron paramagnetic resonance (EPR), mass spectroscopy, and gel permeation chromatography (GPC) were used. Later, a plausible mechanism for the breakdown of lignin/lignin model compounds was inferred after the developed photocatalytic system was investigated under a variety of experimental conditions. The photocatalyst's recovery and recyclability were further evaluated. This solar-assisted photocatalytic valorization of lignin driven by the light harvesters is a smart and sustainable initiative to synergize agri-waste removal and platform chemical generation.