Chromoionophoric probe imbued porous polymer monolith as a Three-in-One Solid-state Naked-eye sensor for the selective sensing and recovery of Ultra-trace Lead, Mercury, and cadmium ions from Industrial/Environmental samples

This article presents a simple, low-cost, eco-benign, and portable naked-eye solid-state sensor for the selective and sensitive colorimetric detection and recovery of ultra-trace concentrations of Pb(II), Hg(II) and Cd(II) from environmental/industrial sources. For solid-state sensing, an indigenously synthesized polymer monolith, i.e., poly(VAn-EGDMA), in-built with high surface area and interlinked meso-/macro-pore network serves as a template for the voluminous and uniform decoration of chromoionophoric probe molecules, i.e., 2-((1H-benzo[d]imidazol-2-yl)diazenyl)-4-methoxyphenol (IDMP) onto the monolith perforations via. direct immobilization technique. The structural and surface topological properties of poly(VAn-EGDMA) monolith and probe-loaded polymer, i.e., IDMP@poly(VAn-EGDMA) sensor, are characterized through FE-SEM, HR-TEM, EDAX, XPS, p-XRD, SAED, FT-IR, BET and BJH analysis. The IDMP@poly(VAn-EGDMA) sensor forms a selective/stable metal complex through visually imposing enhanced charge transfer color transitions from its original canary yellow to dark denim blue, brownish green and lapis blue for varying concentrations of Pb(II), Hg(II) and Cd(II), respectively. The sensor reusability has been tested by decomplexing the IDMP-Mn+ complex with 0.1 M HCl and repeating the sensor performance consistently for eight consecutive cycles. The IDMP@poly(VAn-EGDMA) sensor exhibits pH-dependent ion-sensing, demonstrating a wide linear response range for Pb(II) (0–200 ppb), Hg(II) (0–150 ppb), and Cd(II) (0–150 ppb), with a detection limit of 0.44, 0.56, and 0.52 ppb, respectively. The three-in-one sensor exhibits pH-dependent sequential selectivity, chemical/thermal stability, and data reliability/reproducibility, thus proving effective for on-spot sensing of various sources of contaminated samples.