A Zr metal–organic framework based on tetrakis(4-carboxyphenyl) silane and factors affecting the hydrothermal stability of Zr-MOFs

Abstract

A new (4,8)-connected Zr-MOF porous zirconium metal-organic framework (Zr-MOF) with flu topology, Zr6(μ3-O)4(μ3-OH)4(TCPS)2(H2O)4(OH)4 (, TCPS = tetrakis(4-carboxyphenyl) silane) with a BET specific area of 1402 m(2) g(-1) has been constructed and fully characterized. is stable in air and acid media but unstable in water and basic media, and thermally stable up to 200 °C. The new MOF is a wide band gap semiconductor with Eg = 3.95 eV. The excitation of at 260 nm gives a ligand-based emission peak at 435 nm. After solvent exchange processes and activation at 200 °C, this MOF exhibits high storage capacities for H2, CH4 and CO2. We summarized the hydrothermal stability data of Zr-MOFs, calculated the NBO (natural bond orbital) charges of the coordinating oxygen atoms of the corresponding carboxylate ligands and analyzed the influencing factors. Besides the known reasons of hydrothermal stabilities of Zr-MOFs, we demonstrated that NBO charges of coordinating atoms of the ligands can be used to explain the hydrothermal stabilities of Zr-MOFs.

A Robust Infinite Zirconium Phenolate Building Unit to Enhance the Chemical Stability of Zr MOFs

“…3). [6] Indeed, using highly charged cations has led to various carboxylate-based MOFs showing remarkable stability.N otably,Z r IV -based MOFs,b uilt up either from Zr 6 oxo/hydroxo clusters (UiO-66s,P CN-222,…) [7][8][9][10][11][12][13][14][15][16] or Zr oxide chains (MIL-140s), [17,18] fall into this category.I na ddition, the use of azolate derivatives has also yielded chemically stable MOFs,e specially M II imidazolates (ZIF-8,…) [19] and pyrazolates. [20][21][22][23][24] As aconsequence,itmight be expected that combining highly charged metal cations with high pK a functional groups should offer frameworks with even higher chemical stability.N evertheless,t he pronounced oxophilic character of M n (n !…”

Highly Stable Mesoporous Zirconium Porphyrinic Frameworks with Distinct Flexibility

“…The durability of NUPF-1a gainst acid is outstanding, and to the best of our knowledge,N UPF-1 is one of the rare MOFs that could resist concentrated HCl. [24] Even in aqua regia, the crystalline structure of NUPF-1 could be maintained for 24 h( Figure S9b), further demonstrating its remarkable acid resistance. Thermogravimetric (TG) analysis( Figure S10a in the Supporting Information) and PXRD studies ( Figure S10b) revealed that NUPF-1 wass table up to~450 8C, demonstrating its high thermals tability.M oreover,N UPF-1 retainedi ts crystallinity after exposure to 12.5 tons cm À2 of uniaxial pressure( Figure S11i nt he Supporting Information), suggesting that it possesses excellent mechanical stability.The unusualstructural stability of NUPF-1 laid the foundation for further exploration of its applications.…”

“…After the crystals of NUPF‐1 were immersed into common organic solvents, boiling water, HCl (pH 1, 2, 3; 1 m and concentrated), and NaOH solutions (pH 9 and 10) for three days, all the samples except those in pH 10 solutions retained their crystallinity and morphology, as shown by powder XRD and optical images (Figure and Figure S9a in the Supporting Information). The durability of NUPF‐1 against acid is outstanding, and to the best of our knowledge, NUPF‐1 is one of the rare MOFs that could resist concentrated HCl . Even in aqua regia, the crystalline structure of NUPF‐1 could be maintained for 24 h (Figure S9b), further demonstrating its remarkable acid resistance.…”

Metal-Organic Frameworks Applied for Water Purification

“…The stability can greatly impedes their practical applications because during the degradation of the MOF a dramatic drop of the surface area is observed and hence, detrimental for the removal of impurities from water via adsorption. A strong metal-ligand coordination is an indication that the MOF will be able to prevent the coordination of water molecules and thus preventing the degradation of these materials [17]. Therefore, the metal nodes coordination in the frameworks plays a key role to stabilize MOFs in water.…”