In Situ Allocation of a Monomer in Pectin-g-TerpolymerHydrogels and Effect of Comonomer Compositions on Superadsorptionof Metal Ions/Dyes

摘要

Pectin-g-(sodium acrylate-co-3-(N-isopropylacrylamido) sodium propanoate-co-N-isopropylacrylamide) interpenetrating polymer networks (PANIPNs) were synthesized through systematic multistage optimization of equilibrium swelling ratio by response surface methodology for individual and/or synergistic removal(s) of cationic safranine (SF), anionic methyl orange, and M(II/III), such as Hg(II), Cd(II), and Cr(III). The relative effects of copolymer compositions on ligand-selective adsorption, strong/weak H-bonds, thermal stabilities, crystallinity, surface properties, swelling abilities, cross-link densities, network parameters, hydrophilic–hydrophobic characteristics, and adsorption capacities (ACs) were measured through extensive microstructural analyses of adsorbed and/or unadsorbed PANIPN41 and PANIPN21 bearing sodium acrylate and N-isopropylacrylamide (SA/NIPAm) in 4:1 and 2:1 ratios, respectively, using Fourier transform infrared, ¹H and ¹³C NMR, X-ray photoelectron spectroscopy, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy, along with measuring lower critical solution temperature, % gel content (% GC), % −COOH, and pHPZC. Extensive UV–vismeasurements were carried out at varying copolymer compositions, initialpH (pHi), and dyes, interpreted consideringmonomer–dimer and azonium–ammonium equilibrium of dye,dye–dye complexation, ligand-selective PANIPNs–dye adductformation, π–π stacking interactions, and orientationeffect of dyes. Thermodynamically feasible chemisorption processesshowed the maximum ACs of 127.61, 96.78, 103.36, and 99.41 mg g^–1 for SF, Hg(II), Cd(II), and Cr(III), respectively,under optimum conditions.