Chromophoric molecular ion-receptor embedded organic-inorganic hybrid monolith as the solid-state optical chemosensor for the selective detection/recovery of ultra-trace uranyl ions

Abstract

The article reports an innovative renewable receptor-imbued organic–inorganic hybrid material as a solid-state chromatic sensor for screening and capturing ultra-trace UO₂²⁺ from environmental samples. The sensor fabrication follows a simple physical immobilization of spirocyclic azomethine-derived ion-receptor (DHDTBX) molecules on tailor-made meso-/macro-pore channels of poly(TMSPMA-co-EGDMA) monolith template. The surface profile and morphological characteristics of the organic–inorganic hybrid monoliths of poly(TMSPMA-co-EGDMA) and DHDTBX@poly(TMSPMA-co-EGDMA) materials are characterized by scanning/transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, infrared spectroscopy, diffuse reflectance spectroscopy, thermogravimetry, and surface area/pore volume analysis. The monolithic template’s voluminous surface area and spacious porosity enhance receptor integration efficiency with constrained spatial orientation, offering exclusive UO₂²⁺ selectivity and maximizing the response kinetics (≤60 s). The optimization of physicochemical parameters reveals that the sensor exhibits maximum response for UO₂²⁺ in the pH range of 6.0–8.0 with 0.125mmol g⁻¹ of receptor loading and a sensor dosage of 4.0–5.0 mg. The sensor proffers a target-specific color transition from initial ivory to dark beige for UO₂²⁺, with signal linearity in the UO₂²⁺ concentration range of 1.0–150 μg L^-1, with a detection and quantification limit of 0.15 and 0.53 μg L^-1 for UO₂²⁺, respectively. The sensor is reusable for upto nine cycles with excellent data reproducibility/reliability and structural stability. The real-time practical utility of the sensor material has been tested with various water samples, revealing a recovery of ≥98.26 % and an RSD of ≤2.1 %. The proposed solid-state optical sensor paves the way for a simple and economically feasible approach for UO₂²⁺ sensing and preconcentration.