Synthesis and Characterization of Modified Lignin Flocculants for Congo Red and Methylene Blue Removal

This study focused on synthesizing lignin-based flocculants through grafting sulfonic acid (SA) and [2-(methacryloyloxy)ethyl] trimethylammonium chloride (METAC) using potassium persulfate as the initiator. The resulting flocculants were characterized by particle size, thermal stability, surface morphology, and functional groups. Their dye removal performance was tested with Congo red and methylene blue across various pH levels. FTIR analysis confirmed successful grafting of METAC and SA onto the lignin backbone in lignin-METAC, lignin-SA, and lignin-METAC-SA. Particle size analysis revealed an increase only in ligninMETAC-SA. Modifications led to increased folding and the emergence of raised structures on the flocculants. Thermal analysis showed that, compared to unmodified lignin (degradation at 384°C), all modified lignins exhibited higher maximum degradation temperatures (400– 500°C). Modifying lignin improved dye removal efficiency, with lignin-SA demonstrating the highest performance for both dyes. All flocculants performed better against methylene blue at all pH levels, notably lignin-SA (82.9%) and lignin-METAC-SA (82.3%) at pH 10. Higher Congo red removal (46–69%) occurred in more acidic conditions (pH 4). These findings underscore the potential of grafted lignin-based flocculants for dye wastewater treatment.