EFFECT OF THE LIGNIN FUNCTIONALIZATION ON THE MORPHOLOGY AND ADSORPTION POTENTIAL OF THE LIGNIN-BASED MICROSPHERES

Abstract

The morphological properties and adsorption potential of lignin-based porous microspheres (LgMS) for heavy metals ions were investigated. LgMS were produced via suspension copolymerization of unmodified or acryloyl modified kraft lignin with amine (polyethylene imine - PEI) or acrylate (trimethylolpropanetriacrylate - TMPTA) functional polymers. Structural and morphological characterization of LgMS was performed using FTIR, BET, and SEM techniques. Copolymerization of the unmodified lignin and PEI, using epoxy chloropropane cross-linker, provided highly porous LgMS, with 800 ± 80 μm diameter, 7.68 m2g−1 surface area and 7.7 mmol g−1 of terminal amino groups. The LgMS produced by copolymerization of the acryloyl functionalized lignin and TMPTA provided a decrease in LgMS diameter (253 ± 42 μm), while surface area and porosity increase, 69.4 m2 g-1and 59%, respectively. The effect of acryloyl functionalization of kraft lignin on the LgMS adsorption capacity for Ni2+ ions was also studied in a comparative study. The results showed that final adsorption performances of LgMS were affected by the key factors including lignin functionality and the LgMS synthesis condition. Lower adsorption capacity of 22.6 mg g-1 for Ni2+ was observed for acryloyl LgMS due to lower affinity for formation electrostatic interactions of Ni2+ ions with phenol/hydroxyl groups responsible for adsorption. Opposite was found for amino LgMS where 49.4 mg g-1was achieved. However, this study indicated that removal of heavy metal ions from wastewater can be realized through the application of eco-friendly lignin-based porous microspheres.