Synthesis and characterization of guar gum xanthate derivative super adsorbent hydrogel for the capturing of heavy metal ions from wastewater

Abstract

The Guar Gum Xanthate based hydrogel GGmX-g-poly(AA-co-HEMA) has been successfully synthesized by using the graft copolymerization of two monomers, acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) hydrogel. The synthesis follows the free-radical graft polymerization method. UV-visible spectroscopy (UV), Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Point zero charge (PZC), and field emission scanning electron microscopy (FESEM) were employed for the characterization of the synthesized hydrogel. This hydrogel has shown a high swelling ratio of 430.2 g/g and retention of 75.82% in distilled water which is a notable result. By using GGmX-g-poly(AA-co-HEMA) hydrogel, the maximum percentage of heavy metal ions removal from wastewater was found to be 98.5(±1.5)% and 97.1(±1.5) at optimum pH 6 and 6.5 for Cu2+ and Ni2+ solutions respectively. The Langmuir adsorption isotherm fits best for the adsorption data indicating a monolayer adsorption with maximum adsorption capacity of 423.72 (±26.1) mg/g and 404.85 (±31.4) mg/g for Cu2+ and Ni2+ ions respectively. The pseudo-second-order kinetic model provides the most accurate depiction of adsorption kinetics with rate constant 9.1 × 10−4 (±1.37×10−4)g/(mg.min) for Cu2+ and 8.3 × 10−4 (±1.24×10−4)g/(mg.min) for Ni2+ ions, respectively. The negative ΔG value (-4.75 kJ/mol for Cu2+ and −3.26 kJ/mol for Ni2+ ions) and positive value of ΔH (57.55 (±5.41) kJ/mol for Cu2+ and 40.60(±5.37) kJ/mol for Ni2+ ions) suggested the process to be spontaneous, endothermic, and feasible. It has been found that the hydrogel has excellent regenerative capacity with the % adsorption has been found to be 84.8% for Cu2+ and 82.4% for Ni2+ ions for the fifth cycle.