Coadsorption behavior and mechanism of ciprofloxacin and Cu(II) on graphene hydrogel wetted surface

Intensive livestock husbandry and the expanding medical industry produce large-scale heavy metal-antibiotic complex wastewater, and gaining insight into the adsorption process is important for understanding environmental behavior of pollutants and developing adsorbents. Graphene hydrogels (GHs) feature a wetted surface that well simulates practical adsorption interfaces, and they have great potential for eliminating antibiotics (ciprofloxacin, ca. 330 mg/L) along with heavy metals (copper(II), ca. 30 mg/L). The presence of Cu(II) improves ciprofloxacin adsorption insignificantly via bridging effect, while high concentrations of Cu(II) compete with ciprofloxacin for adsorption sites. Additionally, ciprofloxacin likely binds Cu(II) and forms a GH-CIP-Cu(II) ternary complex to enhance Cu(II) adsorption. Water confined on the adsorption surface of GH, which can either boost adsorption by forming a hydrogen bonding network or weaken adsorption by shielding, is distinctive from bulk water. This paper provides a new perspective on the coadsorption process and indicates the good performance of GH in complex pollutant adsorption.