Preparation of magnetic porous biochar through hydrothermal pretreatment combined with K2FeO4 activation to improve tetracycline removal

Modification is a key way to enhance the adsorption of tetracycline (TC) by biochar (BC), while how to optimize and identify the most suitable modification methods still need further exploration. In this study, hydrothermal pretreatment combined with K 2 FeO 4 activation were applied to prepare the magnetic porous biochar (H-Fe-BC) derived from a typical biomass (tea waste), with the physicochemical properties of the obtained samples as well as the behaviors and mechanisms toward TC adsorption were systematically investigated. Results showed that, compared with K 2 FeO 4 activated biochar (Fe-BC) and pristine BC, the H-Fe-BC was characterized with enhanced surface area, pore volume, and carbon structure defects, as well as different element compositions, magnetic components and surface functional groups. Elovich, Two-compartment first-order, and Langmuir models can describe well the adsorption process for TC. The maximum adsorption capacity for TC on H-Fe-BC was 229.3 mg g −1 , which was 1.7 times and 4.7 times than those of Fe-BC and BC, respectively. The environmental factors such as pHs and co-existing ions exhibited no obvious influence on TC adsorption. The adsorption mechanisms including the pore-filling, π-π interactions, surface complexation, electrostatic interactions and hydrogen bonding were responsible for the enhanced TC adsorption. The results indicate that combined hydrothermal pretreatment and K 2 FeO 4 activation of BC can be used as a feasible modification technology for aquatic contaminant removal. • Magnetic porous biochar was prepared through hydrothermal pretreatment combined with K 2 FeO 4 activation. • The physicochemical properties of biochar relied heavily on the modification methods. • The theoretical maximum adsorption capacity for tetracycline on biochar reached 229.3 mg g −1 . • Pore-filling, π-π interactions, and surface complexation were the main adsorption mechanisms.