Crystallization of aluminum-free zeolite-Beta from viscous gel and incorporation of titanium into its framework were investigated by several spectroscopic techniques. Hydrothermal synthesis was stopped at different times and the gels obtained from the autoclaves were analyzed by liquid-state 29Si NMR spectroscopy. The gels were subsequently dried and inspected by solid-state 29Si NMR, Fourier-transform infrared, and X-ray absorption spectroscopy. NMR spectroscopy distinguished signals from oligomers and from two populations of nanoparticles with different typical dimensions. It also provided information about the composition of the oligomers and nanoparticles, in terms of the relative fractions of Qn units within them. Investigation showed that the synthesis of zeolite Ti-Beta startedwith a quick formation of oligomers. After 20 h of the hydrothermal treatment, oligomers with a high fraction of Q3 units gradually aggregated into primary nanoparticles with a diameter of∼2 nm.During first 20 h, primary nanoparticles began to agglomerate into secondary nanoparticles with a diameter of 5-10 nm. These nanoparticles already had a high fraction of Q4 units and already possessed a zeolitic character.With a further increase in the hydrothermal treatment time, the concentration of secondary nanoparticles increased and they started to gather into zeolitic crystallites. Ti atoms were incorporated into the growing silicate framework at a very early stage of the crystallization process.
COBISS.SI-ID: 1795579
The hydrogen adsorption capacity and heat of adsorption at 77 K have been evaluated for several porous metal terephthalate MOFs (MIL-53(Fe), MIL-125(Ti)and UiO-66(Zr)), as well as in their -NH2 and -(CF3)2 functionalized isoreticular structures. The capacity of hydrogen is basically related to the textural properties of the solids and not to their composition.The heats of adsorption at low coverage are on the whole close to those usually reported for MOFs (6-7 kJ mol-1), except for the UiO-66(Zr) and MIL-53(Fe)-(CF3)2 analogues, whereas the presence of Lewis acid sites and/or aconfinement effect enhances significantly the strength of interaction with hydrogen.
COBISS.SI-ID: 4665370
The Serbian natural zeolite is moderately effective in removing the zinc(II) ions from aqueous solutions. At 298K the sorption capacity varies from 13 to 26% for the initial Zn(II) solution concentration of 100 and 600mgZndm−3, respectively. The sorption isotherm at 298–338K is best represented by the Langmuir model and the sorption kinetics by the pseudo-second-order model. The sorption involves a combination of film diffusion, intra-particle diffusion, and a chemical cation-exchange between the Na+ ions of clinoptilolite and Zn2+ ions. The sorption was found to be endothermic and spontaneous in the 298–338K range. The exhausted sorbent can remove phosphate ions and it exhibits an excellent antibacterial activity towards Acinetobacter junii. By dehydration at about 500 ◦C it transforms to a ZnO-containing product featuring nano-sized wurtzite ZnO particles widespread over the clinoptilolite surface.
COBISS.SI-ID: 4551194