*2.1. Materials*

Gum tragacanth (GT), (molecular weight = 8.4 <sup>×</sup> 10<sup>5</sup> g mol−1), potassium persulfate (KPS), *N,N*'-methylenebisacrylamide (NMBA), *N,N*-dimethylacrylamide (DMA) were purchased from Sigma-Aldrich (Sigma Aldrich Chemicals Pvt. Ltd., Delhi, India). Graphite powder, H3PO4, KMnO4, H2O2 and concentrated H2SO4 (98 wt %) were obtained from LOBA-Chemie (Loba Chemie Pvt. Ltd., Tarapur, Maharashtra, India). Hg2<sup>+</sup> and Cr6<sup>+</sup> ions solutions were obtained by dissolving mercury chloride (Sigma Aldrich Chemicals Pvt. Ltd., Delhi, India) and potassium chromate (Sigma Aldrich Chemicals Pvt. Ltd., Delhi, India) reagents in distilled water.
