Effects of metal ions and pH on ofloxacin sorption to cassava residue-derived biochar

In this study, the impacts of various cations, cation strength and pH on ofloxacin (OFL) adsorption to cassava residue-derived biochars were determined. The associated adsorption mechanisms are discussed. The biochars were prepared at pyrolysis temperatures ranging from 350 °C to 750 °C, and labeled as CW350, CW450, CW550, CW650 and CW750. The Freundlich model provided the best fit to describe the adsorption capacity of OFL and the Freundlich coefficient (logK_f) increased with increasing pyrolysis temperature. The inclusion of Zn^{2 +} or Al^{3 +} increased OFL sorption capacities of five biochars, while Cu^{2 +} reduced sorption to CW450 and CW550. No significant impacts on OFL sorption were observed in the presence of K⁺ and Ca^{2 +}. The concentration of Ca^{2 +} affected the adsorption capacity of CW550, but had no significant impact on other biochars. The pH of OFL solution, ranging from 3 to 9, had no significant changes on OFL adsorption by all the tested biochars. Results of FTIR spectra and zeta potential indicated that electrostatic interactions, cationic exchange, metal bridging and micropore filling could be the main sorption mechanism between OFL and biochars. These studies indicated that cassava residue can be converted into biochars that are effective adsorbents for removing OFL from aqueous solution.