Dithiocarbamate functionalized lignin for efficient removal of metallic ions and the usage of the metal-loaded bio-sorbents as potential free radical scavengers

Lignin-based dithiocarbamate (LDTC) was synthesized by anchoring the chelating agent of dithiocarbamate to the ortho sites of phenol hydroxyl groups in the alkaline lignin matrix. The LDTC biomaterial was characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and elemental analysis. Due to the cross-linked polymer matrix, high content of dithiocarbamate groups and excellent complex ability, the LDTC was used as a new bio-adsorbent for the removal of metallic ions from aqueous solution. The influences of pH, LDTC dosage, contact time, and initial metallic ion concentration on adsorption capacity and competitive adsorption of multi metallic ions have been investigated. The regeneration of LDTC was also studied. The results demonstrated that LDTC showed fast adsorption, higher adsorption capacity and feasible regeneration compared to other lignin-based bio-adsorbents even activated carbon. The adsorption kinetics and adsorption isotherms were fitted well by a pseudo second-order model and D–R model, respectively. Moreover, the resultant metal-loaded solid bio-sorbents (LDTC-M) were firstly estimated as free radical scavengers due to the inherent merits of naturally occurring polyphenols which therefore could provide a potential way for value-added usage of the LDTC-M.