Enhanced crystal violet adsorption from aqueous solutions on ozone-aged polyvinyl chloride microplastics

Microplastics (MPs), particularly polyvinyl chloride (PVC), have become a growing environmental concern due to their persistence in aquatic ecosystems and their capacity to interact with co-occurring pollutants. In this study, the effects of ozonation on the physical and chemical properties of PVC MPs, as well as their capacity to adsorb crystal violet (CV) dye, were systematically investigated. Aging was simulated by exposing PVC MPs to ozone in an aqueous medium at a concentration of 1.4 mg/L for 1 h. The results demonstrate that ozonation induced substantial surface and chemical modifications, including a reduction in chlorine-containing groups and a concurrent increase in oxygenated functional groups such as carbonyl and carboxyl moieties. Mild structural degradation and a decrease in particle size were also observed, along with a marked shift in surface charge, as reflected by a decrease in zeta potential from - 12.3 mV to - 26.7 mV. These transformations significantly altered the adsorption behavior of PVC, leading to an increase in CV removal efficiency from 52.62% (pristine PVC) to 76.55% (aged PVC). The adsorption process followed pseudo-first-order kinetics and was best described by the Langmuir isotherm model, with a maximum adsorption capacity (qₘₐₓ) of 5.55 mg/g. The findings indicate that ozonation, although commonly applied in water and wastewater treatment, may inadvertently enhance the pollutant-binding potential of PVC MPs, thereby intensifying their role as mobile vectors of contaminants in aquatic environments.