Preparation of high-efficient phosphoric acid modified biochar toward ciprofloxacin removal from wastewater

The adsorption of modified biochar can effectively solve antibiotic contamination in water. Nevertheless, few studies have been reported on quantitatively resolving the contribution of each functional group to the adsorption of antibiotics on biochar at the microscopic level, and most modification methods are costly and complex to implement. Therefore, this study successfully synthesized H₃PO₄-modified biochar (PCH) through a one-step process for the removal of ciprofloxacin (CIP) from water. After H₃PO₄ activation, The specific surface area of the PCH rised to 316.1 m²/g, the pore volume reached 0.45 cm³/g The Langmuir isothermal model was used to obtain a better match for the adsorption data, the maximum adsorption capacity of biochar at 25°C was 572.8 mg/g, and the adsorption was a self-initiated process of heat absorption. Cotton husk biochar has a higher adsorption capacity compared to commercial activated carbon and biochar prepared from other agricultural precursors, and cost analysis shows that PCH (3.98 $/ kg) is much less expensive than commercial activated carbon (259.5 $/kg). Furthermore, the main mechanisms of CIP adsorption on PCH are pore filling, electrostatic forces, hydrogen bonding and π-π conjugation. Importantly, DFT calculations showed that O-P groups rather than C-P-O groups could serve as the main sites for CIP adsorption. In conclusion, this study provides new insights into the adsorption of antibiotics on phosphoric acid-modified biochar, and it promotes the application of biochar in the remediation of antibiotic wastewater.