Natural enzyme mimetics with high catalytic activity at nearly neutral pH values are highly desired for their applications in biological systems. Herein for the first time a stable MOF, namely MOF-808, has been shown to possess high intrinsic peroxidase-like catalytic activity under acidic, neutral, and alkaline conditions. As a novel peroxidase mimetic, MOF-808 can effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine when HO serves as oxidant, accompanied by a significant color variation in the solution. The catalytic activity and the color variation were greatly dependent on HO concentration, and thus MOF-808 can be applied to the colorimetric sensing of HO. The HO detection limit is 4.5 μM, and the linear range is 10 μM to 15 mM. In view of the significant inhibition effect produced by ascorbic acid, a facile and sensitive approach for colorimetric sensing of ascorbic acid was successfully established. The AA detection limit is 15 μM, and the linear range is 30-1030 μM. Further investigation found that the catalytic activity of MOF-808 could be mainly ascribed to the Zr-OH(OH) groups. Such active Zr-OH(OH) groups can be effectively shielded by gluconic acid, and subsequently the catalytic activity of MOF-808 was significantly suppressed. With these findings, a facile and selective colorimetric assay for glucose sensing has been successfully explored via combination of the glucose oxidation with the TMB oxidation. The glucose detection limit is 5.7 μM, and the linear range is 5.7-1700 μM. MOF-808 is one of the best colorimetric biosensors among the peroxidase mimics reported for HO, AA, and glucose detection.

The restriction of sulfur content in fuels has become increasingly stringent as a result of the growing environmental concerns. Although several MOF-derived materials like POM@MOF composites have shown the ability to catalyze oxidative desulfurization (ODS), their catalytic activities inevitably obstructed by the encapsulated catalytic sites like POM due to the blockage of cavities. Therefore, MOFs with intrinsic and accessible catalytic sites are highly desirable for their applications in ultradeep ODS. Herein, four representative Zr-based MOFs (Zr-MOFs), namely, UiO-66, UiO-67, NU-1000, and MOF-808, were assessed for catalytic ODS. These MOFs were confirmed that they have peroxidase-like activity and can catalyze ODS with H2O2 as oxidant. Among them, MOF-808 showed the highest catalytic activity and it can fully desulfurize dibenzothiophene (DBT) in a model gasoline with a S concentration of 1000 ppm under 40 °C within 5 min. An extremely low apparent Arrhenius activation energy (22.0 KJ·mol–1) and an extraordinarily high TOF value (42.7 h–1) were obtained, ranking MOF-808 among the best catalysts for the catalytic DBT oxidation. Further studies confirmed that the excellent catalytic activity is mainly responsible for the high concentration of the accessible Zr-OH­(H2O) catalytic sites decorated in MOF-808. The superoxide radicals (•O2 –) and hydroxyl radicals (•OH) were identified and were proved to involve in the DBT oxidation. Besides, the effects of Brönsted and lewis acidity to the catalytic efficiency were also discussed. Based on the experimental results, a plausible mechanism concerning on Zr-OH­(H2O) groups promoting the H2O2 decomposion in to both •O2 – and •OH was first proposed. Moreover, MOF-808 can be facilely reused for at least eight runs without significant loss of its catalytic activity. By the integration of facile synthesis, high catalytic efficiency, and good stability, MOF-808 thus represents a new benchmark catalyst for catalytic oxidative desulfurization.