Alkylammonium lead chloride perovskites: Synthesis, characterization and catalytic activity for conversion of lignin into value added products

Abstract

Lignin is the utmost abundant source of renewable aromatics hence its depolymerization into functionalized aromatics is attractive but challenging as well. A lot of interest is diverting to photocatalysis as a promising sustainable approach to depolymerizing lignin. In the present studies, photocatalytic lignin depolymerization has been investigated under UV-light irradiation using i-propylamine lead chloride perovskites (AS1-AS3) as catalysts. These catalysts were characterized by Powder X-ray Diffraction, Scanning Electron Microscopy, Ultraviolet–Visible, Photoluminescence, and Fourier Transform Infra-Red Spectroscopic techniques to evaluate crystallite size, surface morphology, band gaps, and quantum yields. Depolymerization of lignin was monitored by taking UV spectra and catalytic pathways were studied through various kinetic models. The depolymerization extent was monitored for different catalyst doses (0.05g–0.1 g), lignin concentration (50ppm–200 ppm), and temperatures (25–100 °C). More than 50% depolymerization rate was obtained for each catalyst using 100 ppm lignin concentration. AS3 has shown maximum efficiency in depolymerizing lignin. Pseudo-first order and modified Freundlich were found to be best-fitted kinetic models for experimental data of lignin depolymerization. The activation energy (Ea) for the depolymerization reaction was calculated to be 6.8 kJ/mol which is extraordinarily less than conventional depolymerization of lignin exhibiting significant catalytic competencies of synthesized catalysts. One of the products (L-AS3) of lignin depolymerization activity carried out at room temperature was characterized through GCMS analysis which indicated the breakdown of the polymeric structure of lignin into small monomeric functionalities. 2-methoxy-4-methylphenol (9%), benzene (4%), cyclohexene (16%), phenol (6%), catechol (12%) and 2-methoxy-5-propenyl phenol (10%) were detected by GCMS analysis of lignin depolymerization product.