Tailor-made porous polymer and silica monolithic designs as probe anchoring templates for the solid-state naked eye sensing and preconcentration of hexavalent chromium

[Display omitted] •Structurally designed monolithic solid-state optical sensors for Cr6+ sensing and preconcentration.•First of its kind report in using polymer monoliths as solid-state colorimetric chemosensors.•Silica and polymer monolithic templates offered high surface area and porosity for probe anchoring.•Excellent data reliability and reproducibility achieved for trace levels of Cr6+ with super responsive kinetics.•Monolithic solid-state optical sensors are environmentally benign and cost effective. We present a facile approach towards the fabrication of solid state optical sensors for the naked-eye sensing of carcinogenic Cr6+ ions, using porous polymer and silica monoliths, as probe anchoring templates. The monoliths proffer superior structural properties of high surface area and capacious pore size for the uniform and voluminous probe anchoring. The surface morphology and structural features of the monoliths are analyzed using various surface and structural characterization techniques. The solid-state optical sensors are concocted by the transmogrification of monoliths through impregnation of an amphipathic chromoionophore i.e., 1,5-bis-(4-butylphenyl)carbazone (BBPC), as the ion-sensing probe. The sensors offer long-term stability and rapid response kinetics (< 10 min) with superior ion-selectivity for ultra-trace Cr6+ ions. The ascendancy of physicochemical parameters with reference to solution pH, probe concentration, response kinetics, medium temperature, sensor capacity, linear signal response, selectivity, and sensitivity has been optimized. The sensors exhibit a linear signal response for Cr6+ ions in the concentration range of 5–125 ppb and 3–150 ppb, for silica and polymer sensors, respectively. The solid-state sensor systems exhibit excellent data reliability and reproducibility (RSD ≤ 2.85%), with an LD of 1.87 and 0.41 ppb, and an LQ of 6.23 and 1.36 ppb, for silica and polymer sensors, respectively.