Carbothermally synthesized, lignin biochar-based, embedded and surface deposited nano zero-valent iron composites: Comparative material characterization, selective gas adsorption and nitroaromatics remediation

Biochar (BC) with nanoscale zero-valent iron (nZVI) incorporation offers advantageous materials for water purification. While the most common approach for nZVI incorporation is the deposition on -a carrier surface, embedding in -a support matrix has also been reported. However, the behavior of the embedded material in contaminant removal has not been adequately studied -nor the characteristics and the remediation capabilities of the two materials have been compared. Present study focuses on preparing and extensively characterizing two materials: nZVI embedded in (Lig-e-nZVI) and surface deposited on (Lig-s-nZVI) lignin BC followed by a comparative study of remedial action for two nitroaromatics, p-nitroaniline (pNA) and p-nitrophenol (pNP). The synthesis of Lig-e-nZVI and Lig-s-nZVI involved simultaneous and subsequent pyrolysis of lignin and carbothermal reduction of the iron salt, respectively. Lig-e-nZVI showed enhanced porosity. XRD confirmed the formation of Fe⁰. HR-TEM images proved the core-shell structure of nZVI, and an interlayer spacing of 0.36 nm of the shell verified that the Fe⁰ particles were encapsulated with graphene while an iron carbide inner layer was also observed, thinner in Lig-e-nZVI and thicker in Lig-s-nZVI. A band gap energy of 2.54 eV suggested photocatalytic activity for both materials. Best fitted Sips isotherms showed 23.1 and 13.1 mg g⁻¹ capacities for Lig-s-nZVI in pNP and pNA adsorption respectively. Highest stability was portrayed by Lig-e-nZVI over 4 regeneration cycles. The physicochemical features of the developed materials further enabled selective gas adsorption. Findings provide new insights into physicochemical characteristics and remedial actions of differently synthesized nZVI-BC composites.