Hydrothermal stability of Zn2(BTC)(OH)(H2O)•1.67H2O is its unique property, since almost all zinc carboxylates are unstable even in the presence of water in traces. We showed that the reason for high chemical stability towards water lay in the presence π-π interaction between aromatic rings and in the fact that inorganic chains are stabilized by strong hydrogen-bonds between coordinated water in ZnO4(OH)(H2O) units and free water molecules located between the vertices of octahedra. The adsorption and desorption processes were monitored by in situ NMR and IR spectroscopy.
COBISS.SI-ID: 5277722
We have examined the influence of the solvent on the crystallization mechanism in the system Mg-benzene-1,3,5-tricarboxylates. Four new magnesium-1,3,5benzenetricarboxylate MOF materials (NICSn; n = 3 – 6) were synthesized solvothermally in the presence of solvents with different EtOH/H2O ratios. With NMR and other characterisation techniques we showed that the crystallization process of Mg-1,3,5-benzentricarboxylate system strongly depends on the solvent composition and that dimensionality of their structures can be tuned by changing EtOH/water ratios in the reaction mixture. We have showed by DFT calculations and systematic altering of the EtOH/H2O ratio, time and temperature, crystallization, that solvothermal reaction between Mg-precursors and BTC ligand in EtOH/water mixture represents a complex and sensitive thermodynamic process.
COBISS.SI-ID: 5290522
Structural dynamics of Ca(BDC)(DMF)(H2O) with rhombic-shaped channels upon heating and hydration were elucidated by using complementary methods of diffraction (XRD) and spectroscopy (FTIR, MAS NMR, EXAFS, XANES). During heating the framework underwent structural changes in two steps. First change at 150 °C includes breaking of Ca-O bonds with H2O and DMF molecules. In this step DMF is removed from the surface or near the surface of the crystals. The affected parts of the crystals are transformed to a new nonporous CaBDC(400) phase which prevents the diffusion of DMF from the cores of the crystals. Second transition at 400 °C led to the complete transformation to CaBDC(400). This phase is reversibly transformed to pseudo 3-dimensional framework Ca(BDC)(H2O)3 upon exposure to humid environment. The proposed mechanisms of structural transformations includes breaking of the bonds between Ca2+ and carboxylate groups, rotating of BDC ligand and recoordination of COO- groups to Ca2+ centers. The crystal-to-crystal transformations are driven by the tendencies to change the bonding modes between COO- and Ca2+ with the change of Ca2+ coordination number. Thus the decrease of Ca2+ coordination number, which is usually a consequence of activation, does not lead to the expansion or contraction of the pores, but it leads to pronounced structural rearrangement. Such behavior can explain the lack of porosity in CaMOF systems.
COBISS.SI-ID: 36628485
Iron-functionalized silica nanoparticles with interparticle porosity (FeKIL-2) do act as a highly efficient adsorbent and catalyst for the oxidation of toluene in the gas phase. By using UV/Vis, FTIR, and Mössbauer spectroscopic techniques, we proved that the enhanced activity of the catalyst is attributed to iron incorporated into the silica matrix, which depends on the iron content. The iron content with Fe/Si≤0.01 leads to the formation of stable Fe3+ ions in the silica matrix, which ensures easier oxygen release from the catalyst (Fe3+/Fe2+ redox cycles). The increase in the iron content with Fe/Si)0.01 leads to the formation of oligonuclear iron complexes. The material thus introduces a promising, environmentally friendly, cost-effective, and highly efficient catalyst with combined adsorption and catalytic properties for the removal of low-concentration VOC from polluted air.
COBISS.SI-ID: 5150746
The authors of the chapter gave an overview of metal-modified catalysts for the use in advanced oxidation methods for air and water purification. They included an overview of the state-of-the-art research in the field of synthesis of these materials, their structural characterization and performance tests in oxidation processes of degradation of organic compounds.
COBISS.SI-ID: 5339418