Insight into adsorption of combined antibiotic-heavy metal contaminants on graphene oxide in water

This paper performed a comparative study on the adsorption of typical antibiotics (tetracycline and sulfadiazine) and heavy metals (Cu(II) and Zn(II)) onto graphene oxides (GO), a promising nano-adsorbent, from both experimental and theoretical viewpoints. Effects of solution chemistry parameters were studied. Interfacial interactions and geometries among contaminants and GO were clarified using experimental and computational tools. Interaction strength of contaminants towards GO followed the order of Cu(II) > Zn(II)≫tetracycline > sulfadiazine (coordination of heavy metal-GO in sp3 regions; π-π stacking of antibiotic-GO in sp2 and H-bonding in sp3 regions). In the combined contaminants, heavy metals demonstrated enhancement effect for the adsorption capacities (Qe) for antibiotics, but antibiotics displayed slight promotion to Qe for heavy metals. Through coordination, the combined contaminants formed complexes, which preferred to be adsorbed onto GO’s sp3 regions with heavy metals acting like “bridges” and facing towards GO, instead of antibiotics directly interacting with GO. Coexisting salt ions, especially Ca2+, inhibited the adsorption. Humic acid provided more sites for heavy metal uptake but competed with antibiotics for adsorption. After six adsorption-release cycles, re-adsorption capacities still kept high, implying the feasibility of GO on such sort of combined contaminants removal.