High-Performance 3d Microporous Biochar for the Efficient Capture of Cd2+ Via Multi-Pathway Mechanism

Abstract

Cadmium ions (Cd2+) with 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 involved mechanism is mainly coordination, in which generated large H+ is unfavorable for Cd2+ removal, resulting in poor adsorption capacity. Here, coffee grounds by calcining were prepared into functional biochar modified by phosphoric acid and mercaptoacetic acid (PAC-SH) as a high-performance absorbent for removal of Cd2+ from contaminated water. PAC-SH-140 possessed three-dimensional (3D) microporous structure and large specific surface area (781 m²/g). The adsorption capacity of PAC-SH-140 for Cd2+ was 208 mg/g, which is 2.8 times higher than that of PAC (75 mg/g). Besides complexation, cation-p coordination and electrostatic interaction, Cd2+ could also be reduced to Cd0 under the action of sulfoxide. The adsorption capacity of PAC-SH-140 was improved via these multi-pathway mechanism. For the first time, the interference of H+ was weakened in the adsorption process to enhance the adsorption behavior. The adsorption capacity achieved a significant breakthrough (328 mg/g, up by 57%), providing a 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 circumstances.

Keywords: Coffee grounds, Sulfhydryl modification, Cadmium ions, Heavy metals