**Bhawna Sharma 1, Sourbh Thakur 1,2,\*, Djalal Trache 3, Hamed Yazdani Nezhad <sup>4</sup> and Vijay Kumar Thakur 5,6,\***


Received: 28 June 2020; Accepted: 12 August 2020; Published: 18 August 2020

**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 *N*,*N*-dimethylacrylamide (DMA) onto the gum tragacanth (GT) was carried out to develop gum tragacanth-cl-*N*,*N*-dimethylacrylamide (GT-cl-poly(DMA)) hydrogel using *N*,*N*'-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-*N*,*N*-dimethylacrylamide (GT-cl-poly(DMA)/RGO) hydrogel composite. The synthesized samples were used for competent adsorption of Hg2<sup>+</sup> and Cr6<sup>+</sup> 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-*N*,*N*-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-*N*,*N*-dimethylacrylamide hydrogel composite. The experiments of adsorption-desorption cycles for Hg2<sup>+</sup> and Cr6<sup>+</sup> ions were carried out to perform the reusability of gum tragacanth-cl-*N,N*-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-*N,N*-dimethylacrylamide hydrogel composite. From these two samples, reduced graphene oxide incorporated gum tragacanth-cl-*N,N*-dimethylacrylamide exhibited high adsorption ability. The Hg2<sup>+</sup> and Cr6<sup>+</sup> ions adsorption by gum tragacanth-cl-*N,N*-dimethylacrylamide and reduced graphene oxide incorporated gum tragacanth-cl-*N,N*-dimethylacrylamide were best suited for pseudo-second-order kinetics and Langmuir isotherm. The reported maximum Hg2<sup>+</sup> and Cr6<sup>+</sup> ions adsorption capacities were 666.6 mg g-1 and 473.9 mg g-1 respectively.

**Keywords:** reduced graphene oxide; gum tragacanth; hydrogel; hydrogel composite; mercury ion; chromium ion; reusability
