Chromatic ion-receptor decorated UiO-66 MOF and porous hybrid polymer monolithic scaffolds as reusable solid-state opto-sensors for selective capturing of ultra-trace Pb2+ from aqueous samples

This work demonstrates a methodological approach to fabricating renewable naked-eye opto-sensors using homogeneously decorated receptor molecules across structurally engineered organic–inorganic hybrid porous materials for the selective detection of ultra-trace Pb²⁺ in environmental and commercial samples. A unique chromoionophoric molecular receptor probe, i.e., (E)-1-(benzo[d]thiazol-2-yldiazenyl)naphthalen-2-ol (BTDN), has been indigenously synthesized for the solid-state sensor fabrication by directly immobilizing the BTDN probe onto structurally engineered microporous UiO-66 metal–organic framework (MOF) and mesoporous/macroporous long-range framework of poly(3-(trimethoxysilyl)propyl methacrylate-co-trimethylolpropane triacrylate), i.e., poly(TMSPMA-co-TMPTA) monolithic scaffolds. The intriguing structural properties of host templates enhanced the probe immobilization efficacy and the resulting colorimetric transitions during Pb²⁺ sensing. The surface topography and structural morphology of the porous scaffolds/templates and sensors have been characterized by scanning/transmission electron microscopy, X-ray photoelectron spectroscopy, surface area/pore volume analysis, X-ray diffraction, infrared spectroscopy, thermogravimetry, and UV–visible diffuse reflectance spectroscopy. The target-specific responsiveness for Pb²⁺ is achieved by optimizing numerous analytical parameters to ensure a reliable/reproducible optical/signal response, with a concentration-dependent color transition from apricot to vivid claret during ultra-trace Pb²⁺ sensing. The BTDN@poly(TMSPMA-co-TMPTA) and BTDN@UiO-66 sensors exhibit a Linear response range of 0.1–200 µg/L for Pb²⁺, with a detection Limit of 0.14 and 0.27 µg/L and a quantification Limit of 0.48 and 0.90 µg/L, respectively. The solid-state sensors are simple, eco-friendly, portable, and mass-scalable for water quality assessments and real-time monitoring and recovery of toxic pollutants from environmental/anthropogenic wastewater samples.

Graphical Abstract