Highly Selective Solid-State Optical Sensor for Co2+ Enabled by a Chelating Probe-Impregnated Porous Polymer Monolith

This work demonstrates the development of a solid-state optical sensor system with aqueous compatibility for the selective detection and recovery of Co 2+ . The sensor material was prepared by immobilizing the chromoionophoric probe, (Z)-2-((4-butylphenyl)diazenyl)-4-methoxyphenol (BPDM), within a custom-made porous polymer monolith composed of butyl methacrylate (BMA) and trimethylolpropane trimethacrylate (TMPTM), named poly(BMA-co-TMPTM). The developed monolithic framework exhibited a well-defined hierarchical macro-/mesoporous architecture with a uniform pore-size distribution, which was favorable for efficient probe immobilization and the rapid diffusion of analyte ions through the porous network. The poly(BMA-co-TMPTM)BPDM sensor demonstrated optimal sensing efficacy at pH 7.0, with a rapid response time of 50 s. Upon complexation with Co 2+ the sensor material exhibited a distinct color shift from saffron to brick red with a significant absorption peak at 525 nm. An ultra-trace limit of detection (LOD) of 0.21 ppb was achieved, along with a linear analytical response over the 0-100 ppb range. Practical testing of the sensor on environmental water samples showcased an excellent analytical accuracy, with recovery values ranging from 98.0% to 99.3%. The proposed sensor offered a simple, selective, sensitive, and highly reliable approach for ultra-trace detection of Co 2+ , demonstrating its strong potential for practical environmental monitoring and water quality assessment.