Bimodal meso-/macro-porous polymer monolith decorated chromophoric ion-receptor as dualistic solid-state optical sensor for the ultrafast and selective recovery of cobalt ions

Abstract

We propose a facile solid-state colorimetric approach towards the selective optical recognition of Co(II), using a chromoionophoric molecular ion-receptor i.e., (E)-2-(4-(diethylamino)-2-hydroxybenzylidene)-N-phenylhydrazine-1-carbothioamide (DEHPC) uniformly decorated on a bimodal meso-/macro-porous polymer monolith. The surface morphology and structural features of the polymer monolith template and its probe impregnated sensor material are characterized using HR-TEM, FE-SEM, EDAX, SAED, p-XRD, XPS, FT-IR, BET/BJH analysis. The proposed optical sensor displays a series of visual color transitions from pale yellow to dark green, with incremental concentrations of Co(II), with response kinetics of ≤1.5 min. For the authentic ion-sensing process, physicochemical parameters such as solution pH, receptor concentration, sensor dosage, matrix inference, linear response range, temperature, and ion sensitivity are optimized. The Co(II) sensing performance of the solid-state sensor is validated using certified materials that are used as electrode materials in Li-ion batteries. The sensor exhibits a linear response in the concentration range of 0-400 ppb of Co(II), with a detection and quantification limit of 0.2 and 0.6 ppb, respectively. The probe anchored polymer monolithic sensor is befitting for real-time continuous monitoring of both environmental and industrial water samples. In addition, the solid-state monolithic sensor material not only acts as a colorimetric (naked-eye) sensor but also acts as an effective ion-concentrator. The proposed solid-state sensing methodology is eco-benign, economical, reusable, data reliable, and reproducible, with an RSD value of ≤1.86%.