Chromoionophoric ligand impregnated mesoporous polymeric optical sensors for the colorimetric quantification of Cu2+ in water samples

Abstract

In this work, we demonstrate the use of simple, low-cost, benign, and portable solid-state optical sensor material constructed through direct immobilization of chromoionophoric probe onto a porous polymer monolithic template. The fabricated polymer template depicts superior sensing properties such as a high surface area with uniform porous networks, which is suitable for the homogenous dispersion of chromoionophoric probe onto the voluminous cavity of the polymer template. The surface morphological features and the structural analysis of the polymer template are characterized using p-XRD, TEM, SEM, SAED, EDAX, XPS, and N2 isotherm analysis. The impregnation of the probe, 2-(4-(dimethylamino)benzylidene)-N-phenylhydrazine-1-carbothioamide (DABNC) onto the pore surface of the polymer monolith renders superior sensing performance in capturing ultra-trace concentration of Cu2+ ions, which is inferred from a series of visual color transitions (dull white to sap green). The selective naked-eye color recognition is associated with the formation of stable charge-transfer complexes with the chelating sites of the probe molecules with Cu2+ ions. To ensure the effectiveness of ion-sensing, analytical parameters such as solution pH, probe concentration, sensor dosage, temperature, response kinetics, and ion-selectivity amidst matrix ions are systematically optimized. The range of linear response signal is found to be 0–100 μg/L, with a limit of detection and quantification values of 0.15 and 0.56 μg/L, respectively. The used sensor material can be regenerated to its original state, without any loss of its sensing efficacy, up to six regenerative cycles. The practical applicability of the developed sensor is tested using various real water samples, and the analytical data obtained are reliable and reproducible (RSD ≤1.12%, n = 3).