Porous lignin based poly (acrylic acid)/organo-montmorillonite nanocomposites: Swelling behaviors and rapid removal of Pb (II) ions

Lignin grafted N, N′-methylene-bisacrylamide (LM) was copolymerized with acrylic acid (AA) to fabricate lignin based poly (acrylic acid) (LBPAA) nanocomposites, and organo-montmorillonite (OrgMMT) was uniformly dispersed in LBPAA by ultrasonic method. The water absorbency in KCl solution was 302.9 g/g for LBPAA/OrgMMT (3 wt% OrgMMT, 43.65 wt% LM, and 53.35 wt% poly(acrylic acid) (PAA)), higher than PAA/OrgMMT (104.5736 g/g), and PAA (131.8 g/g). The Pb2+ adsorption for LBPAA/OrgMMT was demonstrated to be pH-dependent and followed Freundlich multilayer adsorption, with the removal following a pseudo-second-order kinetic model. The Pb2+ absorption capacity of LBPAA (PAA 48.50/48.50 LM)/OrgMMT (3 wt%) was 1.0803 mmol·g−1, the highest among the composites. When the mole ratio of Na+ and Pb2+ was less than 0.21, the Pb2+ adsorption capacity of LBPAA/OrgMMT decreased slightly. The negative ΔG0 indicated that the Pb2+ adsorption process for composite hydrogel and PAA was spontaneous. XPS analysis data indicated that Pb2+ ions formed Pb-O bonds by hydroxyl groups and carboxyl groups for efficient lead ion adsorption. This study demonstrates that LBPAA/OrgMMT can be used as a water retention agent with salt tolerance and as an adsorbent for removing Pb2+ ions from industrial waste water.