Starch-g-tetrapolymer hydrogel via in situ attached monomers for removals of Bi(III) and/or Hg(II) and dye(s): RSM-based optimization

Response surface methodology (i.e., RSM)-optimized starch-g-[2-acrylamido-2-methylpropane sulfonic acid (AMPS)-co-[2-(N-(3-(hydroxymethyl)amino)-3-oxopropyl)acrylamido)-2-methylpropane sulfonic acid] (NHMA-OAMPS)-co-[2-(3-(N-(hydroxymethyl)acrylamido)propanamido)-2-methylpropane sulfonic acid (NHMAPMPS)]co-N-(hydroxymethyl)acrylamide (NHMA)] (i.e., starch-g-tetrapolymer) was synthesized via grafting of starch and in situ strategic protrusion of NHMAOAMPS and NHMAPMPS, using optimum ingredients and temperature. This interpenetrating tetrapolymer-hydrogel bearing extraordinary physicochemical properties and recyclability was applied for unary and/or binary removal(s) of Bi(III)-Hg(II) and brilliant green-crystal violet. The N-H-activated in situ allocation of monomers, grafting of starch, thermal stabilities, surface properties, swellability, sustainability, adsorption capacities, and superadsorption were apprehended via microstructural analyses of unadsorbed and/or adsorbed starch-g-tetrapolymer(s) through FTIR-H-1-/C-13-NMR-UV-vis, TGA-DSC, XRD, SEMEDX, DLS, and % gel-content-pH(PZC)-% graft-ratio. The chemisorption data for metal ions best fitted with Langmuir and combined Langmuir-Freundlich isotherm models for unary and binary adsorption, respectively. The unary/binary adsorption capacities were 1005.41/959.25 and 1087.79/758.56 mg g(-1) for Bi(III) and Hg (II), respectively, at 293 K, 0.02 g, and within 500-1000 ppm.