In situ polyacrylamide grafted biochar for heavy metal remediation and alleviation of phytotoxicity

Abstract

Biochar exhibits notable potential for heavy metal remediation owing to economic feasibility and environmental compatibility, but pristine coconut shell biochar remains constrained by limited immobilization capability, insufficient stability, as well as narrow applicability. Polyacrylamide grafted coconut shell biochar (PAM-BC) was synthesized via in situ polymerization to overcome previous limitations. PAM-BC exhibited effective adsorption performance in aqueous solutions, with maximum capacities reaching 151.3 mg/g for Cd²⁺ and 174.1 mg/g for Pb²⁺. In a soil-plant system, PAM-BC significantly decreased bioavailable fractions of Cd²⁺ and Pb²⁺ by 56.1%/76.1%, respectively. The reduction effectively inhibited migration and accumulation of heavy metals in plant roots, stems, as well as leaves. Concurrently, the microbial community was optimized through the enrichment of beneficial functional bacteria as well as the suppression of harmful populations. The remediation performance is attributed to the unique architecture. A three dimensional network was constructed by the extension of flexible PAM chains into rigid pores, and the biochar skeleton was preserved. Abundant -NH₂ and -COOH groups facilitated stable chelation with Cd²⁺ and Pb²⁺, achieving dual enhancement via physical entrapment as well as chemical fixation. Consequently, a viable pathway for biochar functionalization is proposed, and the potential of PAM-BC for heavy metal remediation across diverse scenarios is demonstrated.