Modified lignin-based microspheres as a green sorbent for the removal of chromium ions

Abstract

The unique chemical structure of lignin shows the possibility of its application as a basic material for the sorption of various pollutants from water. In this paper, the newly synthesized porous lignin-based material was used to remove Cr(VI) ions. Modified lignin microspheres (LMS) were synthesized by the process of inverse copolymerization of kraft lignin with poly (ethylene-imine), and amino modified iron oxide (magnetite) using epoxy-functionalized cross-linker. The shape of obtained adsorption material was partially spherical to spherical. The functionalization was performed to improve the pollutant removal capacity. Structural and surface characteristics of the LMS microspheres were characterized by Brunauer-Emmett-Teller method (BET), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and point of zero charge pH (pHPZC). The maximum adsorption capacity for oxyanion Cr(VI) was 77.024 mg g-1obtained by Langmuir adsorption isotherm at 35°C. Based on kinetic studies, the adsorption process follows a pseudo second-order model. Thermodynamic parameters have shown that the adsorption process is endothermic and spontaneous. LMS is an environmentally friendly, cost-effective and therefore promising adsorbent for the removal of Cr(VI) with efficient adsorption and reusability.