Tetrapolymer Network Hydrogels via Gum Ghatti-Graftedand N–H/C–H-Activated Allocation of Monomers for Composition-DependentSuperadsorption of Metal Ions

摘要

Herein, gum ghatti (GGTI)-g-[sodium acrylate (SA)-co-3-(N-(4-(4-methyl pentanoate))acrylamido)propanoate (NMPAP)-co-4-(acrylamido)-4-methyl pentanoate (AMP)-co-N-isopropylacrylamide (NIPA)] (i.e., GGTI-g-TetraP), a novel interpenetrating tetrapolymer network-based sustainable hydrogel, possessing extraordinary physicochemical properties and excellent recyclability, has been synthesized via grafting of GGTI and in situ strategic protrusion of NMPAP and AMP during the solution polymerization of SA and NIPA, through systematic multistage optimization of ingredients and temperature, for ligand-selective superadsorption of hazardous metal ions (M(II)), such as Sr(II), Hg(II), and Cu(II). The in situ allocation of NMPAP and AMP via N–H and C–H activations, grafting of GGTI into the SA-co-NMPAP-co-AMP-co-NIPA (TetraP) matrix, the effect of comonomer compositions on ligand-selective adsorption, crystallinity, thermal stabilities, surface properties, swellability, adsorption capacities (ACs), mechanical properties, and the superadsorption mechanism have been apprehended via extensive microstructural analyses of unloaded and/or loaded GGTI-g-TetraP1 and GGTI-g-TetraP2 bearing SA/NIPA in 8:1 and 2:1 ratios, respectively,using Fourier transform infrared (FTIR), ¹H/¹³C/DEPT-135 NMR, X-ray photoelectron spectroscopy (XPS), thermogravimetricanalysis, differential scanning calorimetry, X-ray diffraction, fieldemission scanning electron microscopy, rheological analysis, and energy-dispersiveX-ray spectrometry, along with measuring % gel content, pH at pointof zero charge (pHPZC), and % graft ratio. The thermodynamicallyspontaneous chemisorption has been inferred from FTIR, XPS, fittingof kinetics data to pseudo-second-order model, and activation energies.The chemisorption data have exhibited excellent fitting to the Langmuirisotherm model. For Sr(II), Hg(II), and Cu(II), ACs were 1940.24/1748.36,1759.50/1848.03, and 1903.64/1781.63 mg g^–1, respectively,at 293 K, 0.02 g of GGTI-g-TetraP1/2, and initialconcentration of M(II) = 500–1000 ppm.