Adsorptive catalysis of hierarchical porous heteroatom-doped biomass: from recovered heavy metal to efficient pollutant decontamination

Abstract

Extraction of heavy metals from wastewater serves to meet the global challenges of toxic metal waste remediation and valuable metal recycling. Herein, by utilizing a cheap and abundant biowaste of defatted soybean residues as a N-rich biomass precursor, a heteroatom-doped macroporous carbon biosorbent (denoted CKS) was formed through a one-pot pyrolysis method in the presence of potassium oxalate (activating agent) and calcium sulfate (hard template). Increased surface polarity with high sulfur doping (10.73 at%) results in the as-prepared material having a strong affinity for heavy metals due to soft acid-soft base interactions, and the optimized CKS-800 (pyrolyzed at 800 °C) shows high selectivity toward Cu²⁺ and Ni²⁺ with high distribution coefficients (6.7 × 10⁵ mL g⁻¹ for Cu²⁺ and 9.8 × 10⁴ mL g⁻¹ for Ni²⁺). Detailed isotherm studies demonstrate the excellent adsorption capacities of CKS toward Cu²⁺ (1366.67 mg g⁻¹), Ni²⁺ (1250.21 mg g⁻¹) and Pb²⁺ (619.23 mg g⁻¹). Moreover, the prepared CKS–metals (CKS–M) after metal remediation display superior catalytic capability both for organic pollutant degradation with peroxymonosulfate as an oxidant and catalytic reduction of toxic Cr^VI to nontoxic Cr^III with formic acid as a reducing agent. The synergistic effects of crystalline carbon and heteroatom doping render the low-cost hierarchical CKS biomass an effective adsorptive catalysis material for efficient water remediation and sustainable utilization in homogeneous catalysis, which avoids further disposal and valorizes the metal complex itself in a “circular economy” model for multi-pollutant decontamination.