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

Abstract

Micro / nano plastics will age and produce a variety of functional groups, but there are few studies on the interaction behavior of surface-functionalized nano-plastics with antibiotics. In this paper, 400 nm polystyrene microspheres (PS), amino modified PS-NH₂, carboxyl modified PS-COOH (PSNPs) and gatifloxacin (GAT) were selected as research objects. The adsorption of GAT by PSNPs was comparatively studied by both experimental and theoretical calculations, and the adsorption mechanism of nano-plastics to antibiotics were revealed. The equilibrium adsorption capacity of PSNPs to GAT was PS-NH₂ > PS-COOOH > PS, and adsorption capacity of PS-NH₂ was the largest, which was 236 mg/g. The adsorption kinetics of GAT showed that adsorption was controlled by both physical and chemical mechanisms, and the intra-particle diffusion and external diffusion jointly controlled the adsorption rate. All of Na⁺, alginic acid, Cu²⁺ and Zn²⁺ inhibited the adsorption, and the inhibition effect of Cu²⁺ and Zn²⁺ on PS-NH₂ adsorption of GAT was the most significant., which may be related to the inhibition of hydrogen bond formation by chelates formed by amino functional groups and heavy metals. The theoretical calculation results showed that π-π interaction and electrostatic interaction were the main interactions between PS and GAT, and electrostatic interactions, hydrogen bonds and van der Waals forces (vdW) were the main interactions between PS-COOH, PS-NH₂ and GAT. The surface electrostatic potential of PS-COOH and PS-NH₂ was significantly larger than PS, and the maximum penetration distance of van der Waals was GAT-PS-NH₂ (1.20 Å) > GAT-PS-COOH (1.06 Å) > GAT-PS (0.63 Å). The results provided a theoretical basis for the migration and synergistic removal of antibiotics and micro-nano-plastics.