Engineering a sulfadoxine-functionalized NH2-UiO-66(Zr) metal-organic framework via post-synthetic modification for dual-mode spectrophotometric and fluorometric detection of Cd2.

The sustainable development of a metal-organic framework (MOF) composite was performed for the sensing of hazardous cadmium(ii) contamination in water, providing a successful MOF material through post-synthetic modification involving the integration of SDX and GA (SDX-GA@UiO-66). Physicochemical characterization was performed to confirm the formation of the desired composite along with the evaluation of heteroatom integration in the framework to clearly elucidate the pore structure and crystal morphology. Detection was achieved through two complementary optical transduction techniques, UV-vis spectrophotometry and steady-state fluorescence spectroscopy (λ ex = 360 nm, λ em = 440 nm), both arising from chelation-enhanced quenching (CHEQ) of the SDX-GA chromophore upon Cd2+ binding. The covalently immobilized SDX-GA moiety serves as the fluorophore, with Cd2+ coordination at its nitrogen and oxygen donor atoms promoting heavy-atom-assisted intersystem crossing that quenches its emission. The UV-vis channel achieved a linear range of 0.0-0.12 ppm with a calculated LOD of 0.0181 ppm, and the platform provided dual-mode detection with selectivity against fifteen competing cations, achieving >85% signal response compared to the other coexisting metal cations. Additionally, cadmium(ii) recovery was validated at multiple concentration levels using the developed sensor, with recoveries ranging from 97.13-100.77%. DFT analysis was performed on the sensing performance of the fabricated framework to better understand the coordination of cadmium(ii) by the platform in the presence of coexisting ions. This sustainable, reusable MOF-based platform offers a dependable strategy for addressing environmental cadmium contamination and the associated risks of severe cadmium poisoning worldwide.