*3.11. Adsorption-Desorption Study*

For an ideal adsorbent, ability for regeneration without considerable loss of removal percentage is of paramount importance. The five cycles of adsorption-desorption and their effects on percentage adsorption are presented in Figure 11. The Hg2<sup>+</sup> ions adsorption percentages were 83.4% (1st cycle), 80.9% (2nd cycle), 78.4% (3rd cycle), 75% (4th cycle), 73.6% (5th cycle) and 94.1% (1st cycle), 92.7% (2nd cycle), 89.8% (3rd cycle), 87.9% (4th cycle), 85.5% (5th cycle) for GT-cl-poly(DMA) hydrogel and GT-cl-poly(DMA)/RGO hydrogel composite respectively (Figure 11a). For Cr6<sup>+</sup>, GT-cl-poly(DMA) and GT-cl-poly(DMA)/RGO exhibited 77.2% (1st cycle), 74.7% (2nd cycle), 71% (3rd cycle), 68.4% (4th cycle), 66.3% (5th cycle) and 82.3% (1st cycle), 80.1% (2nd cycle), 78.5% (3rd cycle), 76.9% (4th cycle), 73.1% (5th cycle) respectively (Figure 11b). Hence, the synthesized GT-cl-poly(DMA) hydrogel and GT-cl-poly(DMA)/RGO hydrogel composite can be effectively reused for up to five cycles, which leads to reduction in cost.

**Figure 11.** Recycling ability of gum tragacanth-cl-*N,N*-dimethylacrylamide (GT-cl-poly(DMA)) hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-*N,N*-dimethylacrylamide (GT-cl-poly(DMA)/RGO) hydrogel composite for the removal of (**a**) Hg2<sup>+</sup> and (**b**) Cr6<sup>+</sup> metal ions up to five cycles.
