Systematic Synthesis of Pectin-g-(Sodium Acrylate-co-N-Isopropylacrylamide) Interpenetrating Polymer Network for Mere/Synergistic Superadsorption of Dyes/M(II): Comprehensive Determination of Physicochemical Changes in Loaded Hydrogels
A new interpenetrating polymer network superadsorbent (IPNS) hydrogel, possessing unprecedented physicochemical properties/swellability and excellent recyclability, has been synthesized, via solution polymerization of monomers (i.e. sodium acrylate, SA and N-isopropylacrylamide, NIPA) and natural polymer (i.e. pectin, PC), using crosslinker (i.e. N,N′-methylenebisacrylamide, MBA) and redox pair of initiators (i.e. potassium persulfate, PPS and sodium bisulfite, SBS), through systematic incorporation and successive optimization of different initial compositions and temperature, for eco-/cost-friendly mere/synergistic removal of hazardous cationic dyes (i.e. methyl violet, MV and methylene blue, MB) and/or diphenyl-azo dye (i.e. methyl orange, MO), along with the adsorptive exclusion of toxic bivalent heavy metal ions (M(II)), like Pb(II), Cu(II), Co(II) and Zn(II). Rational appearance of several physicochemical changes in IPNS networks, both loaded and/or unloaded, have systematically been characterized by FTIR, NMR, XPS, TGA, DTG, DSC, XRD, SEM, EDX, rheological studies, along with measuring lower critical solution temperature (LCST), gel content, % of –COOH, % graft ratio (%GR), pHPZC and network parameters of IPNS. Mere or interactive effects, of structurally/chemically dissimilar dyes, have comprehensively been interpreted via analyzing monomer-dimer/dimer-trimer equilibrium, H-/J-aggregate, dye-dye complex, IPNS-dye adducts, hydrophobic interaction of alkylamino groups, orientation effect of dyes (i.e. pyramidal or propeller), azonium-ammonium equilibrium of dye etc., through extensive UV-Vis analyses, during adsorption. In addition to pseudosecond order kinetics, BET and Langmuir isotherms have also been found to be in the best agreement for MB and MV/Cu(II)/Co(II)/Zn(II)/Pb(II), respectively. In all the cases, thermodynamically feasible chemisorption processes have been found to follow intraparticle diffusion model. Maximum adsorption capacities (ACs) of MV, MB, Pb(II), Cu(II), Co(II) and Zn(II) were obtained as 265.49, 137.43, 54.86, 53.86, 51.72 and 50.01 mg g–1, respectively, at optimum conditions.