Chromoionophore integrated hexagonal mesopore silica monolith as reusable two-in-one solid-state sensor for the sequential optical recognition of ultra-trace Co2+ and Fe3+ ions

The study envisages a novel, two-in-one, pH-based, discriminative solid-state dual colorimetric sensor for the selective and sequential sensing and recovery of industrially/environmentally relevant Co2+ and Fe3+ ions. The proposed solid-state optical sensor embraces a direct and uniform dispersion of 4 '-phenyl-2,2 ',6 ',2 ''-terpyridine (PTPy) - a heterocyclic chromoionophore, onto the hexagonal array of honeycomb structured mesoporous silica monolith. The surface morphology, microstructural pattern, phase transition properties, elemental composition and pore features of the sensor material are examined using FE-SEM-EDAX, HR-TEM-SAED, p-XRD, XPS, FT-IR, TGA and BET/BJH analysis. The silica monolith reveals a high surface area and voluminous porosity that ensures a homogeneous dispersion of the chromoionophoric molecules, thus enabling ultra-fast sensing kinetics through easy ion diffusion to the chelating sites. The solid-state colorimetric sensor exhibits a linear response range in the concentration range of 0-100 mu g/L, with 0.5 and 0.3 mu g/L as detection limits for Co2+ and Fe3+, respectively. The proposed optical sensor is loaded with intelligent pH-based selective ion-sensing, easy operation, excellent aqueous compatibility, high chemical/thermal stability, brilliant ion-selectivity and sensitivity. The solid-state sensor exhibits good reusability for several cycles. It can serve as an efficient, low-cost sensor kit for continuous real-time environmental monitoring and an ion-concentrator for industrial applications' resource recovery.