Micro- and nano-plastics play different roles in oxytetracycline adsorption on natural zeolite: Additional adsorbent and competitive adsorbate

Micro- and nano-plastics (MPs and NPs) as well as antibiotics are typical new pollutants in the aquatic environment. Here, to clarify the effect of interactions between the two pollutants on their removal from aquatic ecosystems, we systematically investigated the adsorption mechanism of oxytetracycline (OTC) onto natural zeolite (NZ) in the presence of MPs/NPs. MPs can act as adsorbents to synergize with NZ to remove OTC, whereas NPs act as adsorbates and adsorption competitor. Scanning electron microscopy results showed that NPs were loaded on the surface of NZ, whereas MPs were not. X-ray photoelectron spectroscopy results suggested that the binding energy of C1s spectrum changed, and the percentage of functional groups also decreased. The adsorption of OTC coexisting with MPs on NZ fitted better to the Langmuir and pseudo-second-order kinetic equations, while for NPs, the Freundlich and pseudo-first-order models fit better. pH greatly affected the adsorption performance, and the ionic strength also significantly affected the adsorption performance of OTC on NZ. It is speculated that NZ successfully adsorbed OTC mainly through electrostatic attraction, hydrogen bonds, and π–π bonds. During adsorption, MPs and NPs serve as additional adsorbents and competitive adsorbates. The present work provides a mechanistic understanding of new pollutant removal in a system where microplastics and antibiotics both occur.