Effective adsorptive removal of tetracycline from aqueous solution by Zn-BTC@SBC derived from sludge:Experimental study and density functional theory (DFT) calculations

Overuse of tetracycline (TC) has caused serious damage to aquatic environment. Developing sustainable and efficient removal technologies for TC is of great significance to eliminate its ecological risks. In this study, a novel zinc metal organic framework porous biochar composite (Zn-BTC@SBC) derived from sludge was the first time synthesized and employed for adsorptive removal of TC from water. The adsorption process of TC followed the Elovich and Temkin model and the maximum capacity of Zn-BTC@SBC to adsorb TC was 125.9 mg/g. Characterization analysis demonstrated that the greater adsorption capacity of Zn-BTC@SBC was ascribed to its larger surface area, pore volume and abundant oxygen-containing functional groups. The fitting results showed that both chemisorption and physical adsorption predominated the adsorption process of TC on Zn-BTC@SBC. Further material characterization (FTIR and XPS) and density functional theory (DFT) calculations at the molecular level suggested that the good adsorption performance of Zn-BTC@SBC on TC might be due to chemisorption dominated by oxygen-containing functional groups, which included π-π conjugation, H-bonding and electrostatic interaction. And it was a spontaneous, endothermic and randomness increasing reaction. Both ion species/strength and solution pH significantly affected the adsorption capacity of Zn-BTC@SBC for TC. The natural water samples with complex composition (lake and river water) still showed 71.27–76.37 % of TC adsorbed. The used Zn-BTC@SBC was capable of maintaining its stable adsorption capacity by NaOH regeneration. This study demonstrated that Zn-BTC@SBC was a promising practicability in removal of TC and workable approach for sustainable utilization of sludge.