Tailoring ethylenediamine functionalization on magnetic Zr-based metal-organic frameworks towards enhanced phosphate and tetracycline adsorption by synergy of Fe3O4 and amino functional groups

The development of efficient adsorbent for removing excessive nutrients (e.g. phosphorous – P) and antibiotics (e.g. tetracycline hydrochloride – TC) from livestock wastewater is necessary but challenging in practical application. In this study, magnetic Zr-based metal-organic frameworks (Fe3O4/UiO-66) with interfacial Fe-O-Zr bonds were synthesized and then modified with ethylenediamine (EDA) functional groups. The resultant optimized composite, namely Fe3O4/UiO-66-N2, showed promising removal of P and TC from both single and binary solution systems. It exhibited the maximum P and TC adsorption capacities of 90.0 mg P/g and 72.3 mg/g in the single component solution, respectively. In the binary solution with an initial P concentration of 5 mg P/L, the coexistence of TC posed a slight inhibition effect on the P adsorption over Fe3O4/UiO-66-N2. However, the TC adsorption was increased by raising the initial P concentration in solution from 5 mg P/L to 20 mg P/L. The Fe3O4 nanoparticles and EDA functional groups were suggested jointly improving the adsorption capacities of P and TC, with the synergy factors of 1.1 and 1.8, respectively. The effects of reaction time, water medium, initial pH and coexisting ions on the adsorption were investigated in detail. The mechanisms governing the adsorption of phosphate included electrostatic attraction, hydrogen bonding, ligand exchange and complexation. Those contributing to the adsorption of TC included Lewis acid-base interaction and π-π electron-donor-acceptor interaction, in addition to electrostatic attraction, hydrogen bonding and complexation. This work designed novel functionalized magnetic MOF composite adsorbents targeting at efficient and simultaneous removal of P and TC from water, under the synergistic effect of the Fe3O4 nanoparticles and surface functional groups.