**4. Conclusions**

We developed novel reduced graphene oxide incorporated gum tragacanth-cl-*N,N*dimethylacrylamide (GT-cl-poly(DMA)/RGO) hydrogel composite as reusable adsorbent for Hg2<sup>+</sup> and Cr6<sup>+</sup> ions. The reported maximum swelling percentage was 971.9% for reduced graphene oxide incorporated gum tragacanth-cl-*N,N*-dimethylacrylamide hydrogel composite at optimized synthesis conditions (KPS concentration: 10.0 <sup>×</sup> 10−<sup>1</sup> mol L−1, solvent: 11 mL, reaction time: 90 s, microwave power: 20%, DMA concentration: 4.4 <sup>×</sup> 10−<sup>1</sup> mol L<sup>−</sup>1, NMBA concentration: 5.8 <sup>×</sup> 10−<sup>1</sup> mol L−<sup>1</sup> and amount of RGO: 0.020 g). The adsorption efficiencies of 99% and 82% were reported for Hg2<sup>+</sup> and Cr6<sup>+</sup> by using GT-cl-poly(DMA)/RGO hydrogel composite at optimized adsorption conditions (for Hg2+, pH: 5.5, adsorbent dose: 0.035 g, RGO loading: 0.020 g, Hg2<sup>+</sup> concentration: 20 ppm, Hg2<sup>+</sup> volume: 50 mL, time: 270 min, temperature: 25 ◦C and for Cr6<sup>+</sup>, pH: 3.5, adsorbent dose: 0.045 g, RGO loading: 0.020 g, Cr6<sup>+</sup> concentration: 20 ppm, Cr6<sup>+</sup> volume: 50 mL, time: 570 min, temperature: 25 ◦C). The Qmax of Hg2<sup>+</sup> and Cr6<sup>+</sup> onto reduced graphene oxide incorporated gum tragacanth-cl-*N,N*-dimethylacrylamide hydrogel composite were 666.6 mg g−<sup>1</sup> and 473.9 mg g−<sup>1</sup> correspondingly, which were higher than the Qmax of gum tragacanth-cl-*N,N*-dimethylacrylamide hydrogel (Hg2<sup>+</sup> = 625 mg g<sup>−</sup>1, Cr6<sup>+</sup> = 401.6 mg g<sup>−</sup>1). The Hg2<sup>+</sup> and Cr6<sup>+</sup> adsorption were better depicted through pseudo-second-order and Langmuir isotherm. The gum tragacanth-cl-*N,N*-dimethylacrylamide and reduced graphene oxide incorporated gum tragacanth-cl-*N,N*-dimethylacrylamide adsorbents can be effectively reused for up to five cycles for adsorption of Hg2<sup>+</sup> and Cr6<sup>+</sup> ions. Thus, developed adsorbents are highly efficient in heavy metal ion adsorption and can be exploited for environmental remediation application.

**Author Contributions:** Experiments, B.S.; original draft writing, B.S., S.T.; data analysis, B.S., S.T.; writing, review and editing, S.T., V.K.T., D.T., H.Y.N.; supervision, S.T., V.K.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
