UiO-66-NH2 as a fluorescent probe for cyanide ion (CN-) detection: assessing optimization using box-behnken design, selectivity, sensitivity, and sensing mechanism.

UiO-66-NH2 was selected as the sensing platform because its highly stable Zr6-based framework, intrinsic fluorescence, and accessible amino-functional groups provide a robust and potentially selective platform for cyanide ions (CN-) recognition without requiring additional post-synthetic modification or the incorporation of external fluorophores. The synthesis of UiO-66-NH2 as a fluorescent probe has been successfully carried out using the solvothermal method. Next, UiO-66-NH2 was dispersed into DI water to obtain a UiO-66-NH2 suspension, which was then used for the detection of CN- in water media. This study focuses on the study of selectivity, sensitivity, and detection mechanisms of cyanide ions evaluated using Density Functional Theory (DFT), which included geometry optimization, Molecular Electrostatic Potential (MEP), Frontier Molecular Orbital (FMO), Density of States (DOS), Charge Density Difference (CDD), adsorption energy, and QTAIM analyses. The fluorescence response of UiO-66-NH2 to cyanide ions was optimized using the Box-Behnken design with three main factors, namely pH (3-11), cyanide ion concentration (100-1000 ppm), and UiO-66-NH2 concentration (1-5 mg mL-1), with a total of 15 experiments (n=3). The experimental data were analyzed using analysis of variance (ANOVA) to assess the significance of the independent variables and the suitability of the mathematical model developed using RSM-BBD with the experimental results. The ANOVA test results showed that the quadratic model showed excellent predictive performance, with high R2 values (0.9989), adjusted R2 (0.9970), and predicted R2 (0.9859) in good agreement, indicating model stability and good predictive ability. UiO-66-NH2 exhibits good selectivity for CN- ions, evidenced by a blue luminescence phenomenon observed exclusively with CN- ions and high fluorescence intensity (quantum yield,ΦF=15.421%) compared to the other tested ions; this is further supported by anti-interference test data showing that the presence of interfering ions does not significantly affect CN- ion detection. The LOD value obtained was 0.0079 ppm (0.304 μM), which is lower than the maximum limit of cyanide ions in drinking water (1.9 μM, according to WHO), so it can be said that UiO-66-NH2 has good sensitivity. Computational studies using Density Functional Theory (DFT) provide results that the interaction between UiO-66-NH2 and CN- occurs through hydrogen bonds and weak non-covalent contacts on the Zr-O cluster and -NH2 group. Thus, the fluorescence-enhanced response of UiO-66-NH2 originates from specific CN- binding, electronic redistribution, and enhanced charge transfer within the framework.