Biopolymer-CMTG and m-BPDM Based Hydrogel Composite for Promising Sensing of Zinc, Cadmium, and Mercury in Aqueous Medium

The detection of spectroscopically silent metal ions is challenging due to their electronic configuration (d¹⁰). A practical approach to overcome this issue is the use of complex-based sensing platforms for metal ion detection. However, sensing using these ligand-based complexes occurs only in organic media, hindering their large-scale applications. Therefore, the current study aims to develop a biopolymer-based hydrogel composite for colorimetric sensing in aqueous medium. The meta-benziporphodimethene (m-BPDM)-modified carboxymethyl tamarind gum (CMTG)/polyacrylamide (PAM) hydrogel was developed via in situ incorporation of m-BPDM into hydrogel matrix. Solid-state UV-visible spectroscopy, FTIR, MXRD, and SEM characterized the m-BPDM-modified CMTG-based hydrogel composite. The as-synthesized m-BPDM-modified hydrogel was applied as a sensor for the colorimetric sensing of Zn^+ 2, Hg^+ 2, and Cd^+ 2 metal ions. It demonstrated a color change from pinkish red to dark blue in the aqueous solution of metal salts. The change in color of hydrogel upon contact with the metal solution was also validated by Solid UV-visible spectroscopy. Further, the impact of temperature, the concentration of heavy metal ions, solution pH on sensing time, and sensing of zinc ions in E. coli cells were investigated. The sensor’s performance was also assessed in industrial effluents to check its applicability in real-time applications. The quantitative determination of Zn^+ 2, Hg^+ 2, and Cd^+ 2 from industrial effluents was confirmed using atomic absorption spectroscopy (AAS). This suggests that synthesized hydrogel can be utilized as a sensor for the visual on-site detection of zinc, cadmium, and mercury metal ions in an aqueous medium.