A Comparative Study on the Structure and Catalytic Performance of UiO-66 Supported Pt Nanocatalysts Prepared by NaBH4 and H2 Reduction: Light-Off, Durability and Mechanism for CO Oxidation

Highly Sensitive and Selective Detection of Uranyl Ions Based on a Tb3+-Functionalized MOF via Competitive Host-Guest Coordination

Owing to the rapid development of the nuclear industry, uranium has become a global environmental contaminant due to its radiotoxicity and chemotoxicity, posing significant threats to human health and ecological safety. Although various instrumental and chemical analytical methods have been developed for uranyl ion detection in aquatic environments, searching for new sensors with high stability, sensitivity, and selectivity remains a challenge. In this study, a luminescent Zr-based metal-organic framework (MOF), designated as Tb@UiO-66-(COOH)2, was successfully synthesized utilizing a postsynthetic exchange (PSE) method along with Tb3+ ion doping for uranyl ion detection. Interestingly, the presence of UO22+ ions causes a replacement of guest ions (Tb3+) in the sensor via a competitive host-guest interaction, leading to significant luminescence quenching. The attenuation of the luminescence intensity of Tb@UiO-66-(COOH)2 exhibits an excellent linear relationship with UO22+ ion concentrations within a wide range of 0-2.52 μM. Notably, Tb@UiO-66-(COOH)2 demonstrates an unprecedentedly high detection sensitivity (Ksv = 2.16 × 105 M-1) and an extremely low limit of detection (LOD) down to 8.03 nM (1.91 ppb) in deionized water. More importantly, Tb@UiO-66-(COOH)2 can achieve high selectivity and efficient detection performance, even in the presence of significant excesses of competing ions. The values of Ksv were determined to be 2.10 × 105 M-1 in Xie'ao Lake water and 3.05 × 105 M-1 in seawater; the values of LOD were determined to be 8.26 nM (1.96 ppb) in Xie'ao Lake water and 5.68 nM (1.35 ppb) in seawater. To the best of our knowledge, this is the first instance of introducing a competitive host-guest coordination strategy into a MOF-based chemical sensor to achieve high-performance uranyl ion detection. Hence, the present work offers a novel idea for building functional MOFs for uranyl ion detection in aqueous solutions.

Regulating the defects of MIL-101(Cr) for the efficient and simultaneous determination of eleven plant growth regulators in fresh fruit juice

This work presents an efficient sorbent for plant growth regulators (PGRs) by regulating the defects of a metal-organic framework MIL-101(Cr). Using the regulated MIL-101(Cr), we developed a simple and effective method for the simultaneous determination of eleven PGRs in fresh fruit juice. The extraction conditions were optimized by an orthogonal array design. Under optimal conditions, the method showed a satisfactory limit of detection (0.1-1.2 ng/g), recovery rates (83.4-110.2 %), and precision (2.9-18.0 % for intra-day and 2.7-10.8 % for inter-day), as well as a greatly suppressed matrix effect. Notably, regulating the defects significantly enhanced the desorption of PGRs on MIL-101(Cr). The sorbent didn't need to be destroyed to release the adsorbed PGRs and could be reused at least 6 times. Furthermore, the defects of MIL-101(Cr) and interactions between the sorbent and PGRs were studied by TGA, ATR-IR, XPS, NH3-TPD and UV-Vis DRS.

Active site identification and CO oxidation in UiO-66-XX thin films

Metal-organic frameworks (MOFs) offer an intrinsically porous and chemically tunable platform for gas adsorption, separation, and catalysis. We investigate thin film derivatives of the well-studied Zr-O based MOF powders to understand their adsorption properties and reactivity with their adaption to thin films, involving diverse functionality with the incorporation of different linker groups and the inclusion of embedded metal nanoparticles: UiO-66, UiO-66-NH₂, and Pt@UiO-66-NH₂. Using transflectance IR spectroscopy, we determine the active sites in each film upon consideration of the acid-base properties of the adsorption sites and guest species, and perform metal-based catalysis with CO oxidation of a Pt@UiO-66-NH₂film. Our study shows how surface science characterization techniques can be used to characterize the reactivity and the chemical and electronic structure of MOFs.

Fluoro-Bridged Clusters in Rare-Earth Metal-Organic Frameworks

The modulator 2-fluorobenzoic acid (2-fba) is widely used to prepare RE clusters in metal-organic frameworks (MOFs). In contrast to known RE MOF structures containing hydroxide bridging groups, we report for the first time the possible presence of fluoro bridging groups in RE MOFs. In this report we discuss the synthesis of a holmium-UiO-66 analogue as well as a novel holmium MOF, where evidence of fluorinated clusters is observed. The mechanism of fluorine extraction from 2-fba is discussed as well as the implications that these results have for previously reported RE MOF structures.

Ultrasensitive Electrochemical Sensor for Luteolin Based on Zirconium Metal-Organic Framework UiO-66/Reduced Graphene Oxide Composite Modified Glass Carbon Electrode

Luteolin is a kind of natural flavonoid with many bioactivities purified from a variety of natural herbs, fruits and vegetables. Electrochemical sensing has become an outstanding technology for the detection of luteolin in low concentration due to its fast response, easy operation and low cost. In this study, electroreduced graphene oxide (ErGO) and UiO-66 were successively modified onto a glassy carbon electrode (UiO-66/ErGO/GCE) and applied to the detection of luteolin. A combination of UiO-66 and ErGO showed the highest promotion in the oxidation peak current for luteolin compared with those of a single component. The factors affecting the electrochemical behavior of UiO-66/ErGO/GCE were evaluated and optimized including pH, accumulation potential, accumulation time and scan rate. Under optimum conditions, UiO-66/ErGO/GCE showed satisfactory linearity (from 0.001 μM to 20 μM), reproducibility and storage stability. The detection limit of UiO-66/ErGO/GCE reached 0.75 nM of luteolin and was suitable for testing real samples. Stable detection could be provided at least eight times by one modified electrode, which guaranteed the practicability of the proposed sensor. The fabricated UiO-66/ErGO/GCE showed a rapid electrochemical response and low consumption of materials in the detection of luteolin. It also showed satisfactory accuracy for real samples with good recovery. In conclusion, the modification using MOFs and graphene materials made the electrode advanced property in electrochemical sensing of natural active compounds.