Synthesis and swelling behavior of metal-chelating superabsorbent hydrogels based on sodium alginate-g-poly(AMPS-co-AA-co-AM) obtained under microwave irradiation

Abstract

A metal-chelating superabsorbent hydrogel based on poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylic acid-co-acrylamide) grafted onto sodium alginate backbone, NaAlg-g-poly(AMPS-co-AA-co-AM) is prepared under microwave irradiation. The Taguchi method is used for the optimization of synthetic parameters of the hydrogel based on water absorbency. The Taguchi L9 (34) orthogonal array is chosen for experimental design. Mass concentrations of crosslinker MBA $$C_{\text{MBA}}$$ initiator KPS $$C_{\text{KPS}}$$ , sodium alginate $$C_{\text{NaAlg}}$$ and mass ratio of monomers $$C_{\text{AM/AA/AMPS}}$$ are chosen as four factors. The analysis of variance of the test results indicates the following optimal conditions: 0.8 g L−1 of MBA, 0.9 g L−1 of KPS, 8 g L−1 of NaAlg and $$R_{\text{AM/AA/AMPS}}$$ equals to 1:1.1:1.1. The maximum water absorbency of the optimized final hydrogel is found to be 822 g g−1. The relative thermal stability of the optimized hydrogel in comparison with sodium alginate is demonstrated via thermogravimetric analysis. The prepared hydrogel is characterized by FTIR spectroscopy and scanning electron microscopy. The influence of the environmental parameters on water absorbency such as the pH and the ionic force is also investigated. The optimized hydrogel is used as adsorbent for hazardous heavy metal ions Pb(II), Cd(II), Ni(II) and Cu(II) and their competitive adsorption is also discussed. Isotherm of adsorption and effect of pH, adsorption dosage and recyclability are investigated. The results show that the maximum adsorption capacities of lead and cadmium ions on the hydrogel are 628.93 and 456.62 mg g−1, respectively. The adsorption is well described by Langmuir isotherm model. The hydrogel is also utilized for the loading of potassium nitrate as an active agrochemical agent and the release of this active agent has also been investigated.