Adsorption behavior and quantum chemical analysis of surface functionalized polystyrene nano-plastics on gatifloxacin

In this paper, the adsorption of gatifloxacin (GAT) by three types of polystyrene nano-plastics (PSNPs), including 400 nm polystyrene (PS), amino-modified PS (PS-NH₂), and carboxyl-modified PS (PS-COOH) was studied and the adsorption mechanism were assessed. Experimental findings revealed that the equilibrium adsorption capacity of PSNPs to GAT followed the order PS-NH₂ > PS-COOH > PS. The adsorption was regulated by both physical and chemical mechanisms, with intra-particle and external diffusion jointly controlling the adsorption rate. The adsorption process was heterogeneous, spontaneous, and entropy-driven. Sodium chloride (NaCl), alginic acid, copper ions (Cu²⁺), and zinc ions (Zn²⁺) inhibited adsorption, with Cu²⁺ and Zn²⁺ having the strongest effect on PS-NH₂. Theoretical computations indicated that π-π and electrostatic interactions dominated PS adsorption of GAT, while PS-COOH and PS-NH₂ adsorbed GAT through electrostatic interactions, hydrogen bonds, and van der Waals (vdW) forces. The surface electrostatic potential of PS-COOH and PS-NH₂ was considerably higher than that of PS, with the maximum vdW penetration distance of GAT-PS-NH₂ being 1.20 Å. This study's findings provide a theoretical foundation for the migration and synergistic removal of antibiotics, micro-plastics (MPs), and nano-plastics (NPs).