Enhanced capture of Pb2+ by phosphoric acid-activated coffee ground biochar coupling with secondary pyrolysis: A multi-pathway mechanism

With the growing popularity of coffee culture, discard coffee grounds, as a renewable resource, can be converted into biochar through pyrolysis and used to remediate heavy metal-contaminated wastewater. However, original biochar adsorbents mainly remove lead (Pb 2+ ) through physical processes, resulting in low adsorption capacity, poor selectivity, and potential secondary lead leaching. We designed a functional coffee grounds biochar (PBCx) via pyrolysis-H₃PO₄ activation-secondary pyrolysis coupling technology. The optimal PBC3 absorbent possesses abundant microporous structure and a high specific surface area (102 m 2 /g), exhibiting an adsorption capacity of 166 mg/g for Pb 2+ , significantly higher than unactivated biochar (BC) under the same conditions. Mechanism studies confirmed that the superior adsorption performance stems from functional group anchoring of PBC3, resulting in highly stable phosphate and carbonate mineral phases, and the lone pair electron coordination of P O and C O groups. This research provides a high-value and environmentally friendly pathway for the resource utilization of waste coffee grounds, while also offering a novel strategy for the industrial application of heavy metal adsorption.