Porous carbon-based polymer monolithic template implanted with an ion-receptor molecular probe as a solid-state ocular sensor for the selective targeting and capturing of cobalt ions

In this work, we report the fabrication of a solid-state naked-eye sensor for targeting industrially relevant cobalt ions, using a tailor-made bimodal macro-/mesoporous polymer carbon-based monolithic cage-like template with a high surface area and voluminous porosity. The solid-state sensor was fabricated through the homogenous dispersion of a unique chromoionophoric ion receptor (probe), i.e. , 4-((9 H -purin-6-yl)diazenyl)-6-hexylbenzene-1,3-diol (PDHBD), onto a polymer monolith. The ion-receptor-anchored monolithic sensor's structural and surface morphology features were subjected to characterization by surface area analysis, electron microscopic, diffraction, and spectroscopic techniques. The monolith sensor exhibited exclusive selectivity for Co( ii ), with an incremental color transition from pale-orange to deep-red, for Co( ii ) concentrations ranging from 0-500 ppb. The influence of the investigational factors was systematically studied to enhance sensor performance. The monolithic sensor revealed a maximum signal response in the pH range of 7.0-8.0, with response kinetics of ≤3 min, at 40 °C ≤ T ≥ 20 °C, for Co( ii ). The multi-reusable solid-state sensor exhibited a superior detection and quantification limit of 0.3 and 1.0 ppb, respectively, for Co( ii ). The sensor proved its real-time monitoring efficiency in recovering Co( ii ) from environmental and industrial water samples with excellent data reproducibility. The binding mechanism of PDHBD molecules with Co( ii ) for exclusive ion-selectivity was studied using density functional theory. Polymer monolithic solid-state optical sensor offers exclusive selectivity and a faster response for ultra-trace Co( ii ) ions, with excellent reusability and data reproducibility.