Promising photocatalytic degradation of lignin over carbon quantum dots decorated TiO2 nanocomposite in aqueous condition

Abstract

The complex branched structure of lignin offers challenges in its chemical/biological transformation. The recalcitrant nature hampers its effective utilization towards the synthesis of potential chemicals and products through depolymerization. Herein, we demonstrate the effective process for lignin decomposition via photocatalysis using CQDs decorated TiO2 nanohybrid in aqueous conditions. Indeed, the sophisticated analytical determinations, including powder XRD, HR-TEM, and XPS, witnessed the structural characteristics of the as-prepared TiO2/CQDs nanocomposite. The photocatalyst promoted a nearly complete decomposition of commercial alkali lignin up to 99 % with the direct sunlight illumination, yielding a different variety of market-value lignin derivative products like m-anisic acid (3-methoxybenzoic acid) and p-hydroxybenzoic acid (PHBA) with 20 % and 16.25 % selectivity, respectively, through the probable oxidation mechanism. Upon verifying its effectiveness towards the decomposition of kraft lignin, it showed a promising response (80 % conversion) within 6 h of photocatalysis. The recyclability study showed that the photocatalyst has an exceptional photostability.