Adsorption of rhodamine B on polyvinyl chloride, polystyrene, and polyethylene terephthalate microplastics in aqueous environments

Rhodamine B (RhB), widely used as a tracer and colorant, is highly toxic, carcinogenic, and mutagenic to humans and organisms. Microplastics (MPs) could accumulate RhB in the aquatic environment, increasing their potential environmental risks. In this study, the interaction between RhB and MPs (polyvinyl chloride (PVC), polystyrene (PS), and polyethylene terephthalate (PET)) were thoroughly investigated, and the effects of pH, salinity, humic acid, particle size, and temperature were explored. The adsorption capacity of RhB on MPs followed the order PVC > PS > PET. The pH significantly influenced the adsorption of RhB on MPs. The presence of Na+ and humic acid could compete with RhB for adsorption sites. High temperature promoted the adsorption of RhB on PVC but inhibited that of PS and PET. The adsorption process could be well described by the pseudo-second-order model and Langmuir model, indicating that the adsorption was monolayer chemisorption. The adsorption capacity of RhB varies with MPs depended on the specific surface area, crystallinity, glassy state, and functional groups of MPs. Electrostatic interaction was a crucial factor in the adsorption of RhB on MPs. The adsorption of RhB on PVC was affected by halogen bonding and polar interaction. PS and PET could be combined with RhB through π–π interaction. This study explored the adsorption characteristics of diverse MPs to RhB and provided a theoretical basis for assessing its potential environmental risks.