Adsorptive removal of dye and antibiotic from water with functionalized zirconium-based metal organic framework and graphene oxide composite nanomaterial Uio-66-(OH) 2 /GO

Adsorptive removal of hazardous organics from water and fuel with functionalized metal-organic frameworks: Contribution of functional groups

The coordination connection of organic linkers to the metal clusters leads to the formation of metal–organic frameworks (MOFs), where the metal clusters and ligands are spatially entangled in a periodic manner. The immense availability of tuneable ligands of different length and functionalities gives rise to robust molecular porosity ranging from several angstroms to nanometres. Among the large family of MOFs, hafnium (Hf) based MOFs have been demonstrated to be highly promising for practical applications due to their unique and outstanding characteristics such as chemical, thermal, and mechanical stability, and acidic nature. Since the report of UiO-66(Hf) and DUT-51(Hf) in 2012, less than 200 Hf-MOFs (ca. 50 types of structures) have been reported. Besides, tetravalent cerium [Ce(IV)] has been proven to be capable of forming similar topological MOF structures to Zr and Hf since its first discovery in 2015. So far, ca. 40 Ce(IV) MOFs with 60% having UiO-66-type structure have been reported. This review will offer a holistic summary of the chemistry, uniqueness, synthesis, and applications of Hf/Ce(IV)-MOFs with a focus on presenting the development in the Hf/Ce(IV)-clusters, topologies, ligand structures, synthetic strategies, and practical applications of Hf/Ce(IV)-MOFs. In the end, we will present the research outlook for the development of Hf/Ce(IV)-MOFs in the future, including fundamental design of Hf/Ce(IV)-clusters, defect engineering, and various applications including membrane development, diversified types of catalytic reactions, irradiation absorption in nuclear waste treatment, water production and wastewater treatment, etc. We will also present the emerging computational approaches coupled with machine-learning algorithms that can be applied in screening Hf and Ce(IV) based MOF structures and identifying the best-performing MOFs for tailor-made applications in future practice.

The chemistry and applications of hafnium and cerium(IV) metal–organic frameworks

The photocatalytic reduction of CO2 in water using a single integrated system utilizing sunlight is the ultimate goal for artificial photosynthesis. Here, we report the design and multistep synthesis of Zr-MBA-Ru/Re-MOF for photocatalytic CO2 reduction via post-synthetic linker exchange (PSE) followed by metalation on MOF-808. The simultaneous covalent immobilization of the molecular [Ru(bpy)3]2+ photosensitizer and [Re(bpy)CO3Cl] catalyst in the confined space of the MOF resulted in highly efficient CO2-to-CO formation with a maximum production rate of 440 μmol g−1 h−1 in aqueous medium without any sacrificial electron donor (with selectivity >99%, QE = 0.11). In parallel, under sunlight, this assembly also produces 210 μmol g−1 of CO in 6 h in aqueous medium. In addition, a maximum production rate of 180 μmol g−1 h−1 is observed in MeCN/H2O (2 : 1) mixed solvent medium with BNAH and TEOA as the sacrificial electron donor (with CO selectivity 69%, QE = 0.22). The high surface area-based Zr-MOF (MOF-808) is robust and water-tolerant, and its post-synthetically modifiable pore surface allows us to covalently attach the molecular photosensitizer and catalyst in the confined nanospace. Covalent grafting of the [Ru(bpy)3]2+ photosensitizer significantly enhances the lifetime of the photoexcited electrons, and the proximity of the catalytic site shortens the transport distance of charge carriers during the reaction, resulting in an efficient catalytic activity. The reaction intermediates are characterized using in situ diffuse reflectance FT-IR (DRIFT), which is well-supported by DFT calculations, and the catalytic cycle involving the reaction mechanism is established.

Covalent grafting of molecular photosensitizer and catalyst on MOF-808: Effect of pore confinement toward visible light-driven CO2 reduction in water

Recent advances of Zr based metal organic frameworks photocatalysis: Energy production and environmental remediation

Nanostructured Zr(IV) metal organic frameworks (MOFs-808) with high stability are synthesized by using trimesic acid (BTC), a highly electron-deficient and polar molecule, as an organic ligand in order to produce efficient adsorbents for hydrogen gas. The MOFs-808 are characterized by XRD, FT-IR, SEM, TEM, specific surface area measurements and thermogravimetric analysis, and the conditions (e.g., the reactant molar ratio, the amount of solvent, the reaction temperature and the reaction time) for synthesis of MOFs-808 are optimized. The MOF-808 obtained under optimized preparation conditions has higher crystallinity, a larger specific surface area, and relatively high stability both in acidic solution and at temperatures up to 300 °C. The hydrogen storage capacity of the optimized MOF-808 under 4 MPa reaches 7.31 wt% at 77 K, which is close to the ultimate target defined for hydrogen storage. Our results indicate that the presence of the electron-deficient ligand on MOFs-808 favors the adsorption of hydrogen gas.

Optimized synthesis of Zr(IV) metal organic frameworks (MOFs-808) for efficient hydrogen storage

The core–shell structure and penetrated structure of Pd-modified metal organic frameworks MOF-808 series materials (named as Pd@MOF-808) are successfully synthesized using Zr(IV) as centron ion, trimesic acid as ligand and Pd as modifier by simple solution method. The structure control and properties of Pd@MOF-808 are characterized by XRD, FT-IR, TEM, XPS, UV–Vis, specific surface area measurement, thermogravimetric analysis, photocatalytic hydrogen production and hydrogen storage testing. The results show that the synthesized Pd nanoparticles have been successfully introduced into the cavity and channel of MOF-808, and the structure of Pd@MOF-808 series materials could remain stable at 350 °C. Photocatalytic hydrogen production experiments exhibit the highest hydrogen production of Pd@MOF-808-b (236 μmol g−1 h−1). More importantly, the results of the adsorption experiment show that the hydrogen storage capacities of the as-prepared 10 wt% Pd@MOF-808-b could reach 2.61 wt%, 5.04 wt% and 8.20 wt% under 4 MPa at 300 K, 195 K and 77 K, respectively. Furthermore, thermodynamic analysis shows that the maximum hydrogen adsorption enthalpy of Pd@MOF-808-b up to − 1.378 kJ mol−1 indicates excellent potential for hydrogen storage and application.

Synthesis, structure and properties of Pd@MOF-808

Hydrogen storage properties of the novel crosslinked UiO-66-(OH)2

A crosslinkable UIO-66 type MOF material denoted UIO-66-DETA composed of Zr(IV) metal ions and 2,5-diallyl ether terephthalic acid (DETA) was synthesized, and then by initiating double bond crosslinking, a new crosslinking MOF material denoted UIO-66-DETA-CL was obtained. UIO-66-DETA and UIO-66-DETA-CL were characterized by FTIR spectroscopy, PXRD, 1H solid-state NMR spectroscopy, SEM, nitrogen sorption, thermogravimetric analysis and hydrogen storage tests to analyze their structure and properties. The results showed that a crosslinked structure has been formed, and UIO-66-DETA-CL can maintain its structure below 340 °C, compared with UIO-66-DETA; its carbon residual rate is improved, which shows that the crosslinking modification enhances the thermal stability. Meanwhile, the hydrogen uptake capacity of UIO-66-DETA-CL reaches 5.36 wt% at 77 K and 4 MPa. Furthermore, the hydrogen adsorption enthalpy of UIO-66-DETA-CL (ΔHUIO-66-DETA-CL) calculated using the Arrhenius equation reaches −0.889 kJ mol−1, which is significantly improved by crosslinking modification. The crosslinked structure changes the pore size and increases the active adsorption sites in organic ligands. The framework of UIO-66-DETA-CL can provide more polar charges to cause some hydrogen molecules to be negatively charged because of a small HOMO–LUMO gap, and a lower LUMO energy level of UIO-66-DETA-CL enables stronger negative charge acceptability. Therefore, crosslinking modification enhances the material's hydrogen storage capacity. This result provides a new idea for the crosslinking modification of MOFs.

Crosslinking modification of a porous metal–organic framework (UIO-66) and hydrogen storage properties

The invention belongs to the technical field of material chemistry, and in particular, relates to a synthesis method for an internally crosslinked hafnium metal organic skeleton material, wherein themethod comprises the following steps: (1) adding a hafnium metal organic skeleton material into distilled water, mixing evenly, adding a crosslinking agent and a catalyst, carrying out a reaction for30-80 min at the temperature of 40-90 DEG C, then cooling, centrifuging, washing and filtering, to obtain a product, wherein the feed ratio of distilled water to the hafnium metal organic framework material to the crosslinking agent to the catalyst is (10-20 mL) to 0.1 g to (0.3-0.5 g) to (2-10 mL); and (2) adding an activator into the product, and refluxing for 48-72 h at the temperature of 30-50DEG C, to obtain the internally crosslinked hafnium metal organic skeleton material. The synthesis method provided by the invention is highly efficient and environmentally friendly, and the preparedinternally crosslinked hafnium metal organic skeleton material is safe in use and high in hydrogen storage capacity.

Wang Zhuo

Papers

Optimized synthesis of Zr(IV) metal organic frameworks (MOFs-808) for efficient hydrogen storage

Synthesis, structure and properties of Pd@MOF-808

Hydrogen storage properties of the novel crosslinked UiO-66-(OH)2

Crosslinking modification of a porous metal–organic framework (UIO-66) and hydrogen storage properties

Synthesis method for internally crosslinked hafnium metal organic skeleton material