Selective Photocatalytic Upgrading of Polylactic Acid under Mild Conditions at Interface-Engineered MoS₂/BiOCl Heterojunction

Abstract

To address the critical challenges of inefficient charge separation and uncontrollable selectivity in plastic photocatalytic upcycling, a MoS₂/BiOCl heterojunction was designed. The precisely engineered interface created a built-in electric field that enhanced charge separation and optimized the oxidation pathway. Specifically, the moderate oxidation potential of MoS₂ prevents polylactic acid (PLA) mineralization, while the negative conduction band of BiOCl facilitates hydroxyl radicals (·OH) generation via oxygen reduction. The hole and ·OH establish a synergistic dehydrogenation pathway, significantly boosting both reaction rate and product selectivity. The band structure modulation induced by the interface engineering reduces the free energy change for the lactic acid in the key dehydrogenation step from +0.29 eV to –0.13 eV, turning an endergonic into a spontaneous process. Under aqueous conditions at 20 °C, the optimized catalyst exhibits 93% selectivity for pyruvic acid formation at a remarkable rate of 3.46 mmol·h^-1·g_cat.^-1, outperforming BiOCl and MoS₂ by up to 31.5-fold and 2.4-fold, respectively, ranking it among the forefront of reported non-noble-metal photocatalysts. This system achieves a 77.6% carbon conversion, while the apparent quantum efficiency is 0.23% under 420 nm irradiation. This work presents a strategy for high-selectivity in plastic upcycling under mild conditions, enabling green and precise waste conversion.

Keywords

Plastics photocatalytic conversion / PLA conversion / BiOCl / Interface engineering / Pyruvic acid production

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