High-performance spent coffee grounds-based 3D microporous biochar for the efficient capture of Cd2+ via a multi-pathway mechanism

Cadmium ions (Cd2+), due to their high toxicity, easy migration and recalcitrant degradation, pose a high risk to both ecological security and human health. Various biosorbents have been developed to eliminate Cd2+ from contaminated environmental media. However, the mechanism involved is mainly coordination, in which the large amount of H+ generated is unfavorable for Cd2+ removal, resulting in a poor adsorption capacity. Here, coffee grounds were prepared by calcining into functional biochar modified by phosphoric acid and mercaptoacetic acid (PAC-SH) as a high-performance absorbent for the removal of Cd2+ from contaminated water. PAC-SH-140 possesses a three-dimensional (3D) microporous structure and large specific surface area (781 m2/g). The adsorption capacity of PAC-SH-140 for Cd2+ was 205 mg/g, which is 2.7 times higher than that of PAC (75 mg/g). Besides complexation, cation-π coordination and electrostatic interaction, Cd2+ was also reduced to Cd0 under the action of sulfoxide. The adsorption capacity of PAC-SH-140 was improved via these multi-pathway mechanisms. For the first time, the interference of H+ in the adsorption process was weakened, thereby enhancing the adsorption behavior. The adsorption capacity achieved a significant breakthrough (328 mg/g, up by 60 %), providing new guidance for the industrial application of heavy metal adsorption. These findings may offer a promising strategy for low-cost and friendly remediation of Cd2+ contaminated media.