Surface functional groups determine adsorption of pharmaceuticals and personal care products on polypropylene microplastics

The pervasiveness of microplastics (MPs), which can absorb pharmaceuticals and personal care products (PPCPs), has a certain impact on pollutant migration in natural waters. The adsorption behaviors of PPCPs on the aged polypropylene (PP) followed the pseudo-second-order kinetics and Langmuir isotherm, and the adsorption capacity (q(e)) on the aged PP was much higher than that on the fresh PP. The Weber-Morris and Boyd models confirmed that the liquid-film and intra-particle diffusion affected the adsorption of PPCPs on the aged PP while the surface diffusion was a rate-limiting step for the fresh PP. The analysis of SEM-EDS, BET, FT-IR, and XPS further showed that changes in the type and content of the surface functional groups of PP led to differences in adsorption capacity and adsorption interactions. The Dragon-descriptor-based LFER and the quantum-chemical descriptor-based QSAR models reflected the difference in adsorption interaction mechanisms. The examined models showed that the adsorption of the fresh PP toward PPCPs relied on hydrophobic and hydrogen bonding interaction, while for the aged PP electrostatic interaction and hydrogen bonding controlled the adsorption. The findings clarified interactions between PPCPs and MPs and provided a theoretical basis for the assessment of environmental behavior and ecological risk when MPs and PPCPs coexist.

Automated summary

This study found that aged polypropylene has a higher adsorption capacity for pharmaceuticals and personal care products, with adsorption behavior affected by surface diffusion, while fresh polypropylene is influenced by liquid-film and intra-particle diffusion. Analysis of surface functional groups further demonstrated differences in adsorption capacity and interactions.