Solid-state naked-eye sensing of Cu(II) from industrial effluents and environmental water samples using probe integrated polymeric sensor materials

Abstract

We report on the fabrication of two eco-friendly and fast-responsive solid-state optical sensors for the reliable sensing of Cu(II) ions from natural and industrial wastewater. The solid-state template constitutes indigenously prepared bimodal macro-/meso-porous channels of a monolithic polymer framework of uniform surface morphology, high surface area, and capacious porosity. For the naked-eye colorimetric detection, two chromoionophoric probes i.e., 4-butyl-N-((1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)carbamothioyl)benzamide (BDICB) and 4-butyl-N-(2-(thiophene-2-carbonyl)hydrazine-1-carbonothioyl)benzamide (BTHCB) that offer exclusive ion-selectivity and sensitivity for Cu(II) are synthesized. The monolithic template exhibits multi-diffusible display sites for the uniform anchoring of the probe molecules that act as naked-eye colorimetric ion sensors. The structural and surface profile of the monolithic sensor materials are studied using HR-TEM, FE-SEM, EDAX, SAED, p-XRD, XPS, FT-IR, and BET/BJH analysis. The probe-anchored monolithic materials reciprocate a brilliant visual color shift from an initial colorless state to apple green and greyish black, respectively, for BDICB and BTHCB anchored sensor materials, with varying concentrations of Cu(II), with a response time of ≤1 min. Besides, the sensor fabrication pursues a simple direct encapsulation of probe molecules onto the polymer monolith. The proposed solid-state sensors are certified using simulated and real samples that reflect a reliable detection limit of 0.11 & 0.14 ppb and a quantification limit of 0.38 & 0.45 ppb for Cu(II) ions, respectively, using BDICB & BTHCB anchored polymer monolith sensors. The proposed solid-state colorimetric ion-sensors exhibit dual functionality in serving as a viable ion-sensing tool and concentrator for recovering ultra-trace concentrations of Cu(II) ions.