Microwave-assisted synthesis of Sterculia gum- graft-poly(acrylamide-co-vinyl acetate) hydrogel for remarkable removal of crystal violet from aqueous solution

This study aimed to synthesize novel Sterculia gum-graft-poly(acrylamide-co-vinyl acetate) hydrogel abbreviated as SG-g-(PAAm-co-PVAc) hydrogel by microwave-assisted free radical reaction to remove crystal violet (CV) dye from aqueous media. The graft copolymerization reaction of acrylamide (AAm) and vinyl acetate (VAc) onto sterculia gum (SG) was optimized by varying the concentration of SG, monomers AAm, VAc, initiator, crosslinker and studying the effect of these conditions on the swelling ratio (g/g) and hydrogel integrity. The hydrogel was characterized by scanning electron microscopy (SEM), infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller analysi (BET) and differential thermal analysis (DTA) methods to confirm synthesis. SEM demonstrated uneven heterogeneous morphology with irregular pores and craters. Inclusion of monomer units into hydrogel was confirmed by FTIR. The maximum swelling ability of fabricated hydrogel was 1263% at optimized concentrations at pH 9.2. SG-g-(PAAm-co-PVAc) hydrogel (having pH_PZC of 4.09) showed a good adsorption ability for CV dye. The maximum removal of CV dye (64.385 ± 1.044 mg/g) was achieved at temperature of 30 °C, pH 9.2 and at hydrogel dose level of 20 mg. The experimental data fit closely with pseudo-first-order and Temkin models. The enhanced CV dye adsorption was driven by electrostatic attractions, hydrogen bonding, and π–π stacking. Thermodynamically, the studied process was spontaneous and exothermic. Reusability experiments demonstrated the hydrogel's stability over five adsorption–desorption cycles. Overall, the study reveals adsorptive properties of novel SG-g-(PAAm-co-PVAc) hydrogel as a promising adsorbent for sustainable CV dye treatment from water.