Microwave-Assisted Rapid Synthesis of Reduced Graphene Oxide-Based Gum Tragacanth Hydrogel Nanocomposite for Heavy Metal Ions Adsorption

Abstract

Reduced graphene oxide (RGO) was synthesized in this research via Tour's method for the use of filler in the hydrogel matrix. The copolymerization of <i>N</i>,<i>N</i>-dimethylacrylamide (DMA) onto the gum tragacanth (GT) was carried out to develop gum tragacanth-cl-<i>N</i>,<i>N</i>-dimethylacrylamide (GT-cl-poly(DMA)) hydrogel using <i>N</i>,<i>N</i>'-methylenebisacrylamide (NMBA) and potassium persulfate (KPS) as cross-linker and initiator correspondingly. The various GT-cl-poly(DMA) hydrogel synthesis parameters were optimized to achieve maximum swelling of GT-cl-poly(DMA) hydrogel. The optimized GT-cl-poly(DMA) hydrogel was then filled with RGO to form reduced graphene oxide incorporated gum tragacanth-cl-<i>N</i>,<i>N</i>-dimethylacrylamide (GT-cl-poly(DMA)/RGO) hydrogel composite. The synthesized samples were used for competent adsorption of Hg²⁺ and Cr⁶⁺ ions. Fourier transform infrared, X-ray powder diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy were used to characterize the gum tragacanth-cl-<i>N</i>,<i>N</i>-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-<i>N</i>,<i>N</i>-dimethylacrylamide hydrogel composite. The experiments of adsorption-desorption cycles for Hg²⁺ and Cr⁶⁺ ions were carried out to perform the reusability of gum tragacanth-cl-<i>N,N</i>-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-<i>N,N</i>-dimethylacrylamide hydrogel composite. From these two samples, reduced graphene oxide incorporated gum tragacanth-cl-<i>N,N</i>-dimethylacrylamide exhibited high adsorption ability. The Hg²⁺ and Cr⁶⁺ ions adsorption by gum tragacanth-cl-<i>N,N</i>-dimethylacrylamide and reduced graphene oxide incorporated gum tragacanth-cl-<i>N,N</i>-dimethylacrylamide were best suited for pseudo-second-order kinetics and Langmuir isotherm. The reported maximum Hg²⁺ and Cr⁶⁺ ions adsorption capacities were 666.6 mg g^-1 and 473.9 mg g^-1 respectively.