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

Abstract

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.