A green and energy-efficient photocatalytic process for the accelerated synthesis of lactic acid esters using functionalized quantum dots

Abstract

Sulphonate-grafted-titania (SO₃H–TiO₂) quantum dot catalyzed photochemical process offered an energy-efficient, accelerated, and safe approach to synthesize lactic acid esters at ambient temperature conditions. This low-temperature route, conceived in line with green ideas, involves the preparation of a metal oxide-based framework followed by surface grafting using sulphonate groups. These sulphonate grafts, which are characterized using spectroscopy and electron microscopy, decrease the propensity for acid absorption by the bare quantum dot material, which also credits enormous photo-action for lactic acid transformation into lactates. Mechanistically sulphonate species get energized by capturing an electron excited by titania under UV irradiation, consequently stimulating the adsorbed lactic acid molecules. The excess reagent methanol works alongside as a hole-scavenger and was excited to form methoxide ion combining to activate lactic acid-producing desired ester. After a parametric sway, a significant 91 percent methyl lactate yield was obtained at the optimized catalytic catalyst dose of 0.05 g ml⁻¹ and the initial feed ratio of 1 : 10 (lactic acid to alcohol) culminating in no major structural alteration even after many catalytic cycles. Reaction data were modeled using second-order kinetics and the forward rate constant was found to be 9.2 × 10⁻³ L mol min⁻¹. This developed method demonstrated that one can fabulously succeed the traditional homogeneous, thermal heterogeneous, and enzymatic approaches that require high energy, time, and solvent requirements.