Effect of chitosan modification on the properties of magnetic porous biochar and its adsorption performance towards tetracycline and Cu2+

Chitosan modification of biochar has received increasing attention. However, the effects of chitosan modification on the properties of biochars, and their adsorption behavior toward antibiotics (e.g., tetracycline, TC) and heavy metals ions (e.g., Cu2+) still need further exploration. In this study, magnetic porous biochar (MPBC) and chitosan-modified magnetic porous biochar (CMPBC) were prepared, with their adsorption processes and mechanisms toward TC and Cu2+ revealed. Results showed that, compared with MPBC, the chitosan-modification process increased the O/N content, the N/O-related functional groups, and the carbon structure defects, but decreased the surface area, pore volume, and the magnetism of biochar. The two-compartment first-order and Elovich models fitted well the adsorption kinetics of TC and Cu2+ on CMPBC. The Langmuir and Dubinin-Radushkevich models described better the adsorption isotherms of TC on CMPBC, whereas the Freundlich and Temkin models fitted well the adsorption behavior of Cu2+ on CMPBC. Chitosan modification promoted the adsorption amount of Cu2+ from 17.32 mg g−1 to 65.87 mg g−1 but inhibited the adsorption capacity of TC from 471.77 mg g−1 to 241.33 mg g−1. The promotion of Cu2+ adsorption was ascribed to the N/O functional groups complexation and elestrostatic interaction, whereas the inhibition of TC adsorption was attributed to the weakening of pore-filling, π–π interaction, and complexation. Furthermore, the presence of coexisting ions furhter decreased the TC adsorption but increased the Cu2+ adsorption. The recyclabilities of CMPBC exhibited good reusability for TC and Cu2+ removal. Therefore, CMPBC was considered as a promising adsorbent with excellent co-adsorption potential for removing TC and Cu2+.