Adsorption of tetracycline by hydrochar derived from co-hydrothermal carbonization of polyvinyl chloride and garden waste: Adsorption characteristics and enhancement mechanism

The environmental risk posed by tetracycline (TC) in aquatic environments cannot be overlooked, and hydrochar has shown promising potential for adsorbing and removing TC. This study utilized polyvinyl chloride (PVC) and garden waste (GW) as feedstock, preparing hydrochar through co-hydrothermal carbonization (co-HTC), aiming to investigate its adsorption performance for TC. The results demonstrated that the equilibrium adsorption amount of hydrochar produced via co-HTC (HPG) for TC was increased by 28.11% and 406.03% compared to hydrochar derived from PVC and GW, respectively. The HTC temperature and reaction time were positively correlated with the TC adsorption amount of HPG, but the increase was limited beyond 220 °C and 4 h, while the PVC blending ratio had a minor effect on TC adsorption. Subsequently, the adsorption characteristics of HPG for TC were systematically investigated to clarify the effects of adsorption conditions, environmental factors, and regeneration cycles on the adsorption performance of HPG; and further through the properties characterization of HPG and hydrochar prepared from the individual feedstock, the potential mechanism enhancing TC adsorption in co-HTC was explored. HPG adsorbed TC through the interaction between surface carbonyl groups and TC's π-electrons, while PVC produced carbonyl compounds through dechlorination and intramolecular dehydration during co-HTC. GW facilitated the dechlorination process of PVC and provided a substrate for the linkage of carbonyl compounds. This study revealed the adsorption performance and mechanism of hydrochar derived from co-HTC of PVC/GW for TC, offering insights for utilizing hydrochar from organic waste for antibiotic pollution control.