Effect of Photo-Ageing Regime on PET Microplastics Surface Chemistry and Cd2+ Adsorption Behaviour: Implications for Sustainable Water Management

Ageing radically alters the physicochemical properties of microplastics, significantly increasing their affinity for environmental pollutants. However, the slow nature of natural degradation necessitates the development of efficient laboratory protocols. This study establishes an accelerated ageing methodology that reflects natural dynamics by comparing Polyethene terephthalate microplastics (PET MPs) exposed to sunlight (3 months) with those exposed to laboratory UV-C radiation (varying lamp numbers and 24–336 h). scanning electron microscopy (SEM) imaging confirmed progressive surface degradation, including increased roughness, micro-cavities, and erosion. Photo-oxidation was evidenced by an increase in the carbonyl index (CI) from 7.43 ± 0.30 to 8.97 ± 0.35 (UV-aged) and 11.45 ± 0.45 (sun-aged). Furthermore, crystallinity significantly decreased from 59.5% to 54.4% and 16.6%, respectively, while the point of zero charge (pHPZC) shifted from near neutral (6.5–7.0) to below 2.0. Notably, high-intensity, short-term UV-C exposure accelerated surface functionalization, enhancing cadmium adsorption capacity (qe = 1.9 mg/g). The laboratory protocol provides rapid reactivation on the surface, serving as a proxy for prolonged sunlight exposure. Consequently, these findings offer a framework for assessing heavy metal uptake and the broader environmental implications of microplastics in aquatic environments. This understanding supports pollutant evaluation and sustainable water management for aquatic ecosystem protection.