Removal of congo red and methyl violet from water using nano clay filled composite hydrogels of poly acrylic acid and polyethylene glycol

• Composite hydrogels were made from acrylic acid, PEG and nano clay.
• Nano clay fillers were incorporated in situ during polymerization.
• The gels were characterized by FTIR, SEM, DTA–TGA and XRD.
• Swelling, diffusion and dye adsorption of the gels were evaluated.
• Composite hydrogels showed high dye adsorption and removal%.

Superabsorbent hydrogels were synthesized from polyethylene glycol (PEG) and crosslinked polyacrylic acid. Nano clay filled composite hydrogels were also synthesized by incorporating 0.5, 1.0 and 1.5 wt% nano size bentonite filler in the hydrogels. These hydrogels were characterized by FTIR, SEM, XRD, DTA–TGA, swelling and diffusion characteristics. The filled composite hydrogels showing the best result in swelling was further used for adsorption of congo red (CR) and methyl violet (MV) dye from water. The composite hydrogel showed high adsorption and removal% for these dyes for both low (2.5–50 mg/L) and high range (100–600 mg/L) of feed dye concentration. The dye adsorption data were fitted to different kinetics and adsorption isotherm models. The external mass transfer coefficient, diffusion coefficient and thermodynamic parameters of dye adsorption were also determined.