Structurally engineered probe infused porous polymer monolith as a solid-state visual sensing platform for Cd²⁺ ions

This work describes an effective optical on-site sensor strategy for quantifying Cd2+ in aqueous samples using a tailor-made physically modified probe-immobilized porous polymer monolithic sensor. The bimodal macro/ mesoporous polymer, namely poly(2-(trifluoromethyl) acrylic acid-co-trimethylolpropane triacrylate) (poly (TFMAA-co-TMPTA)) matrix, was fabricated by simple bulk polymerization, and was uniformly encapsulated with a chromophoric ligand, namely (E)- 5-(quinoline-8-yl-diazenyl)quinoline-8-ol (QDQ) by a direct impregnation process. The designed monolithic template and the concocted sensor were characterized using FE -SEM, EDAX, HR-TEM, SAED, XPS, N2 adsorption isotherms, p-XRD, TGA and FT -IR. The optical sensor benefits from a uniformly interconnected mesostructured polymer template and showcased a superior sensing performance in selectively capturing the ultra-trace amounts of Cd2+. Furthermore, it displayed a dynamic optical property by enabling a distinct progressive visual color change from light orange to brick red due to the selective complexation of the QDQ probe with Cd2+. The solution pH, probe concentration, contact time, temperature, selectivity, and sensitivity were optimized to evaluate the best sensing performance, and the sensor showed a linear response range from 1.5-100 mu g/L, with the lowest detection limit (LOD) of 0.53 mu g/L. The theoretical calculations about the binding mechanism of QDQ probe molecules with Cd2+ were studied using density functional theory (DFT). The newly fabricated solid-state sensor affords a promising tool for detecting trace amounts of Cd2+ in real water and cigarette samples.