Double network hydrophobic starch based amphoteric hydrogel as an effective adsorbent for both cationic and anionic dyes

[Display omitted] •Hydrophobically associated starch based double network hydrogel was synthesized.•The hydrogel having positive and negative charges exhibited amphoteric property.•The double cross-linked hydrogel possesses low water swelling ability.•The amphoteric hydrogel can remove both the cationic and anionic dyes.•Pseudo second order kinetics model was the best fitted kinetics model. A double-network hydrophobic-hydrogel was successfully synthesized. Here epichlorohydrin (ECH) and N, N-methylene bis-acrylamide act as the crosslinkers for starch and poly(acrylic acid), respectively. The synthesized hydrogel having both positive and negative charge exhibited amphoteric properties and employed for the exclusion of anionic and cationic dyes from waste aqueous solution. The formation of positive charge occurs via reaction of triethylamine with the open up epoxy ring of ECH while carboxylate ion of poly(acrylic acid) gives the negative charge in the hydrogel. The formation of double cross-linking and the presence of quaternized alkyl chains lead towards hydrophobicity with much lower swelling ability. As an adsorbent, the hydrogel was able to remove both cationic dye (methylene blue) and anionic dye (congo red) with adsorption maxima of 133.65 mg/g and 64.73 mg/g, respectively. This study showed that the synthesized hydrogel offers enormous potential as the toxic dye adsorbent for effluent treatment of industrial wastewater.