Fluorescent ZnO Quantum Dots Embedded in a Zn(II) Metal–Organic Framework for Highly Sensitive and Selective Nitrate Ion Detection

In this study, we developed a fluorescent sensing platform for the detection of nitrate ions using APTMS‐capped ZnO quantum dots (APTMS‐QDs) combined with a metal–organic framework (MOF), forming an APTMS‐QDs@MOF composite. The sensing performance is based on the interactions between the APTMS‐QDs@MOF and nitrate ions. The amine–Zn interaction and electrostatic interaction between negatively charged MOF and positively charged APTMS‐QDs result in the quenching of APTMS‐QDs due to an electron transfer process, along with the formation of the flower‐like morphology of APTMS‐QDs@MOF. When nitrate ions were introduced into the APTMS‐QDs@MOF system, the quenching effect was reduced, resulting in a noticeable recovery of fluorescence. The fluorescence intensity increased proportionally with nitrate ion concentration, indicating good selectivity. The sensor exhibited a good linear response in the concentration range of 0.8–4.0 μM, with a detection limit of 0.295 μM. The sensing mechanism was further studied using scanning electron microscopy (SEM), X‐ray diffraction (XRD), and HR‐TEM. The results revealed that nitrate ions weakened the interactions between the MOF and the APTMS‐QDs, leading to a partial collapse of the MOF structure and recovery of fluorescence. The proposed sensing method was successfully applied to the determination of nitrate ions in environmental water samples, demonstrating its potential for practical environmental monitoring and opening a new pathway for nitrate detection using fluorescent nanocomposites.