Probe tethered monolithic architectures as facile solid-state chemosensors for the on-site colorimetric recognition of Co(II) in aqueous and industrial samples

Abstract

In this work, we report two novel solid-state opto-chemosensors that proffer exclusive selectivity and excellent sensitivity for the naked-eye detection of ultra-trace Co2+ ions. The opto-chemosensors are concocted using structurally engineered porous silica and polymer monolith templates that are uniformly arranged with a chromoionophoric probe i.e., (Z)-2-mercapto-5-(quinolin-8-yldiazenyl)pyrimidine-4,6-diol (AQTBA). The probe anchored monolithic opto-chemosensors induces sequential color transitions, from yellowish-orange to dark brown, with incremental addition of Co2+ ions. The optimized ground state structure of the AQTBA probe and its AQTBA-Co2+ complex are analyzed using a gaussian 16 program at B3LYP level, with a 6–311+ G (d, p) basis set. The structural and surface morphology of the opto-sensors are characterized using various microscopic, spectroscopic, and diffraction techniques, which discloses a uniform pattern of pore network that proffers rapid ion diffusion kinetics to the probe chelating sites. The proposed monolithic sensors exhibit a high degree of tolerance towards various foreign cations and anions, thus revealing its exclusive selectivity in targeting ultra-trace concentrations of Co2+. The silica and polymer monolithic sensors exhibit a broad linear response range of 0–200 ppb, with a detection limit of 0.35 and 0.07 ppb for Co2+ ions, respectively. The unique features of the proposed sensors are their faster response kinetics (120 s), greater reusability (nine cycles), excellent chemical and thermal durability (pH ≤ 12.0; T ≤ 200 °C), with reliable data reproducibility (recovery ≥99.3 %; RSD ≤2.3 %). The proposed solid-state opto-chemosensors paves way for maximum waste reduction strategy, along with the feasibility for real-time monitoring of environmental and industrial water samples.