ABSTRACT
Hydrogen adsorption ability is a key parameter characterizing advanced porous materials. Herein, the influence of platinum catalyst on the interaction of Cu-BTC with hydrogen is thoroughly investigated using volumetric measurements, calorimetric titration, XRD, and IR- and EPR spectroscopy. The first hydrogen adsorption by the Cu-BTC + Pt/C composite leads to an irreversible chemical reaction related to the formation of structural defects during synthesis. This process results in a partial reduction of Cu2+ to Cu0 and is accompanied by a decrease in the specific surface area and the appearance of additional mesopores. The following hydrogen adsorption-desorption cycles are completely reversible and reproducible. Besides, the Pt-containing material maintains a positive trend in excess adsorption up to ultra-high pressures in contrast with pristine Cu-BTC. Above 300-400 bars, it demonstrates a significant superiority in hydrogen capacity over the catalyst-free MOF. The possible nature of such a peculiar phenomenon is suggested.
ABSTRACT
We analyze the origins of the luminescence in germania-silica fibers with high germanium concentration (about 30 mol.% GeO2) in the region of 1-2 µm with a laser pump at the wavelength 532 nm. We show that such fibers demonstrate the high level of luminescence which unlikely allows the observation of photon triplets, generated in a third-order spontaneous parametric downconversion process in such fibers. The only efficient approach to the luminescence reduction is the hydrogen saturation of fiber samples; however, even in this case, the level of residual luminescence is still too high for three-photon registration.
