For the first time, guar gum-g-(acrylic acid-co-acrylamide-co-3-acrylamido propanoic acid) (GGAAAMAPA), a smart environment-friendly and sustainable interpenetrating polymer network hydrogel having unprecedented thermomechanical/physicochemical properties and excellent recyclability, has been synthesized by the grafting of guar gum (GG) and in situ adjunct allocation of 3-acrylamido propanoic acid (APA) during solution polymerization of acrylic acid (AA) and acrylamide (AM), using N,N′-methylenebisacrylamide (MBA) and potassium persulfate (PPS)–sodium bisulfite (SBS) as a crosslinker and a redox pair of initiators, respectively, through systematic multistage optimization of the constituents and the temperature of the reaction, for a comprehensive understanding of the individual/synergistic superadsorption mechanism during recycling of hazardous dyes, like 2,8-dimethyl-3,7-diamino-phenazine (i.e. safranine, SF), 3,7-bis(dimethylamino)-phenothiazin-5-ium chloride (i.e. methylene blue, MB) and sodium 4{[4(dimethylamino)phenyl]diazenyl}benzene-1-sulfonate (i.e. methyl orange, MO), along with the adsorptive exclusion of metal ions, i.e. M(II), like Pb(II), Cd(II) and Cu(II). The unambiguous in situ addition of APA, the grafting of GG into the AA-co-AM-co-APA (AAAMAPA) matrix and the superadsorption mechanism have been systematically determined by extensive analyses of FTIR, ¹H-/¹³C-NMR, O 1s-/N 1s-/C 1s-/Pb 4f_7/2,5/2-/Cd 3d_5/2,3/2- and Cu 2p_3/2,1/2-XPS, TGA, DSC, XRD, FESEM, EDX, and storage/loss moduli and supported by computational measurements via density functional theory (DFT), along with the measurements of %gel content (%GC), pH at point of zero charge (pH_PZC), %graft ratio (%GR) and network parameters of hydrogels. The prevalence of ionic (I) and variegated interactions, like monodentate (M), bidentate bridging (BB) and bidentate chelating (BC), between GGAAAMAPA and M(II), has also been rationalized by FTIR and fitting of kinetics data to the pseudosecond order model and by the measurement of activation energies of adsorption. The individual/interactive effects of cationic and/or anionic dyes have been rationally determined via extensive UV-Vis analyses at 1 : 1, 1 : 2 and 2 : 1 mole ratios of dyes and pH_i = 2/9, interpreted through the appearance of the metachromic effect, dye-aggregates, π–π stacking interaction, diprotonated MO etc. The BET and Langmuir isotherms have fitted the best to MB and SF/Cd(II)/Cu(II)/Pb(II), respectively. Thermodynamically spontaneous chemisorption processes have shown the maximum adsorption capacities (ACs) of 27.06, 39.35, 40.55, 39.42, and 41.98 mg g⁻¹ for MB, SF, Cd(II), Cu(II) and Pb(II), respectively, at 303 K, adsorbent dose = 0.025 g and initial concentration of dyes/M(II) = 30 ppm.

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 polymers (i.e. pectin, PC), using a crosslinker (i.e. N,N′-methylenebisacrylamide, MBA) and a redox pair of initiators (i.e. potassium persulfate, PPS and sodium bisulfite, SBS), through systematic incorporation and successive optimization of different initial compositions and temperatures, for the 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). The rational appearance of several physicochemical changes in IPNS networks, both loaded and/or unloaded, has systematically been characterized by FTIR, NMR, XPS, TGA, DTG, DSC, XRD, SEM, EDX, and rheological studies, along with measuring the lower critical solution temperature (LCST), gel content, % of –COOH, % graft ratio (%GR), pH_PZC and network parameters of IPNS. Mere or interactive effects of structurally/chemically dissimilar dyes have comprehensively been interpreted via analyzing the 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 the intraparticle diffusion model. The 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, under optimum conditions.

Herein, gum ghatti-g-(N-isopropylacrylamide-co-3-(N-isopropylacrylamido) propanoic acid-co-sodium acrylate) (GTINIAMSA), a novel interpenetrating terpolymer network hydrogel with unprecedented thermomechanical and physicochemical properties and excellent recyclability, was synthesized via the grafting of gum ghatti (GTI) and the in situ strategic protrusion of 3-(N-isopropylacrylamido) propanoic acid (NIPAMPA) during the solution polymerization of sodium acrylate (SA) and N-isopropylacrylamide (NIPAm) using N,N′-methylenebisacrylamide (MBA) and potassium persulfate (PPS)/sodium bisulfite (SBS) as a cross-linker and redox pair of initiators, respectively, through the systematic multistage optimization of the constituents and the reaction temperature for a comprehensive understanding of the superadsorption mechanism of hazardous metal ions, i.e. M(II/III), like Cd(II), Pb(II), Bi(III) and Sb(III). The unorthodox in situ attachment of NIPAMPA, grafting of GTI into NIPAm-co-NIPAMPA-co-SA (NIAMSA) matrix and the superadsorption mechanism were systematically investigated via extensive unloaded and/or loaded microstructural analyses by FTIR, ¹H-/¹³C-NMR, C 1s-/O 1s-/Cd 3d_5/2,3/2-/Pb 4f_7/2,5/2-/Bi 4f_7/2,5/2-/Sb 3d_3/2-XPS, TGA, XRD, FESEM and EDX, along with the measurements of the %gel content (% GC), pH at point of zero charge (pH_PZC), % graft ratio (% GR) and network parameters of the hydrogels. The prevalence of ionic (I) and variegated coordinative interactions, such as monodentate (M), bidentate bridging (BB) and bidentate chelation (BC), between GTINIAMSA and M(II/III) were also investigated by FTIR and the fitting of kinetics data to a pseudo-second-order model as well as by the measurements of the activation energies of adsorption. The equilibrium adsorption data of M(II/III) were fitted excellently to the Langmuir isotherm model. The thermodynamically spontaneous chemisorption processes showed the excellent maximum adsorption capacities (ACs) of 1477.83, 1568.81, 1582.38 and 1518.09 mg g⁻¹ for Cd(II), Pb(II), Bi(III), and Sb(III), respectively, at 303 K with an adsorbent dose of 0.02 g and initial concentration of M(II/III) = 500–800 ppm.

Grafting of guar gum (GG) and in situ strategic attachment of acrylamidosodiumpropanoate (ASP) via solution polymerization of acrylamide (AM) and sodium acrylate (SA) resulted in the synthesis of a sustainable GG-g-(AM-co-SA-co-ASP)/GGAMSAASP interpenetrating polymer network (IPN)-based smart superadsorbent with excellent physicochemical properties and reusability, through systematic optimization by response surface methodology (RSM) for removal of methyl violet (MV) and/or Hg(II). The relative effects of SA/AM ratios, in situ allocation of ASP, grafting of GG into the AMSAASP terpolymer, ligand-selective superadsorption mechanism, and relative microstructural changes in individually/synergistically-adsorbed MV–/Hg(II)–/Hg(II)–MV–GGAMSAASPs were determined by extensive analyses using Fourier transform infrared (FTIR), proton nuclear magnetic resonance, ultraviolet–visible (UV–vis), and O 1s-/N 1s-/C 1s-/Hg 4f_7/2,5/2-X-ray photoelectron spectroscopies, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, field emission scanning electron microscopy, and energy-dispersive spectroscopy and were supported by % gel content, pH_PZC, and % graft ratio. The ionic/covalent-bonding, monodentate, bidentate bridging, and bidentate chelating coordination between GGAMSAASPs and Hg(II), and MV⁺–Hg(II) bonding were rationalized by FTIR, UV–vis, fitment of kinetics data to the pseudo-second-order model, and thermodynamic parameters. The maximum adsorption capacities of 49.12 and 53.28 mg g^–1 were determined for Hg(II) and MV, respectively, under optimized conditions.