The Nature of the Low-Temperature Crossover of Water in Hard Confinement.

The dynamics of water confined in mesoporous MIP (2-3 nm pores in size) with silica gel (secondary silica; further, the abbreviation SG will be used) and MAP (10-35 nm pores in size) without SG borosilicate glasses have been studied by broadband dielectric spectroscopy (BDS), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC). MIP samples contain secondary silica inside the pores and provide a confinement size of about 2-3 nm, whereas MAP samples are free of secondary silica and provide a confinement size of about 10-35 nm. It is shown by BDS and NMR techniques that water exhibits a dynamic crossover of around 180 K when it is confined in MIP samples. By contrast, water confined in larger pores (MAP) does not exhibit any changes in its relaxation behavior. It is also shown that the crossover temperature depends on the hydration level (the higher the hydration level, the lower the crossover temperature). Below the crossover temperature, we find that water reorientation is isotropic (NMR) and that the temperature-dependent dielectric relaxation strength (BDS) follows the tendency expected for a solid-like material. In contrast, water reorientation is related to long-range diffusion above the crossover temperature, and the dielectric relaxation strength follows the tendency expected for a liquid-like material. Furthermore, the calorimetric results are compatible with crossing a glass transition near 180 K. Finally, the results are discussed within the Gibbs-Thomson model. In this framework, the crossover could be related to ice crystals melting.

Novel Inorganic Membranes Based on Magnetite-Containing Silica Porous Glasses for Ultrafiltration: Structure and Sorption Properties.

Porous glasses (PGs) obtained from sodium borosilicate (NBS) phase-separated glasses via leaching are promising inorganic membranes. Introducing Fe2O3 into NBS glasses imparts ferrimagnetic properties due to magnetite crystallization. Leaching of such glasses leads to the formation of magnetic PGs with interesting electro-surface characteristics. This work aimed to investigate the process of obtaining magnetite-containing PGs from NBS glasses depending on silica content, using XRPD and Raman spectroscopy, studying the PG membranes' structural characteristics and their sorption properties with respect to methylene blue (MB). Obtained PGs were characterized by a polymodal distribution of mesopores and a small number of micropores with specific surface area values of 32-135 m2/g and an average mesopore diameter of 5-41 nm. The kinetic data were analyzed using pseudo-first-order, pseudo-second-order, and intra-particle diffusion equations. The equilibrium isotherms were fitted with Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models. MB adsorption was found to be a complex process. The glass with the highest specific surface area demonstrated the maximum sorption capacity (10.5 mg/g). The pore size of PGs allowed them to be considered potential novel magnetic membranes for ultrafiltration.

Electrokinetic Properties of Mesoporous Vitreous Membranes Doped by Silver-Silver Halides.

Silver/silver halide materials are considered as efficient and highly stable plasmonic photocatalysts for the organic pollutant degradation and hydrogen evolution from water splitting under solar irradiation, and they possess promising antibacterial activity. Ordered mesoporous silica materials including porous glasses are considered as the most promising template for silver-containing structures. In the present work, Ag/AgHal-doped (Hal = Cl, Br) vitreous membranes on a base of the mesoporous glasses were prepared via step-by-step single-stage impregnation procedure. The chemical and phase composition of the modified membranes were identified by the X-ray photoelectron spectroscopy, the X-ray diffraction and the energy-dispersive X-ray spectroscopy. The structure and morphology of inner membrane space were studied by the scanning electron microscopy. Electrokinetic properties of the silver-containing vitreous membranes were determined by the differential method and the streaming potential method. The inner membrane space is modified unevenly with appearance of the clearly defined regions with different silver content. The formation of the Ag/AgCl clusters along with the individual nanoparticles over thickness of the 1-mm membrane with mean pore radius of 23 nm was detected. The modification of the pore space by Ag-containing structures and the type of halogen ion almost do not affect the electrochemical behavior of the mesoporous vitreous membranes.

New Insight into Phase Transitions of Porous Glass-Based Ferroelectric Nanocomposites.

The results of XRD, FTIR and differential scanning calorimetry (DSC) studies of empty porous silica matrices filled with binary mixtures of K1-xAgxNO3 (x = 0.05, 0.10) are reported in comparison with those obtained for bulk salts in the temperature range of structural phase transitions. Scanning electron microscopic data of the studied empty macroporous and microporous glasses confirmed differences in the pore morphology associated with the presence of silica gel. Accordingly, XRD and FTIR samples contain crystalline phase of KNO3 and AgNO3. The results of calorimetric investigation of porous glasses filled with binary mixtures of K1-xAgxNO3 (x = 0.05, 0.10) are presented. The results show that in the K1-xAgxNO3 nanocomposites, anomalies associated with phase transitions were detected. An influence of the mean value of pores sizes on the ferroelectric phase transition temperatures of K1-xAgxNO3 nanocrystals embedded into the porous matrices was determined. The impact of pore space structure on the phase transitions of ferroics nanocomposites was discussed.

Direct laser writing of barriers with controllable permeability in porous glass.

Barriers were produced in porous glass through its local bulk density modification by direct femtosecond writing accompanied by СО2-laser surface thermal densification, to make functional microfluidic elements separated by such physical barriers with different controlled permeability. The separation of multi-component solutions into individual components with different molecule sizes (molecular separation) was performed in this first integrated microfluidic device fabricated in porous glass. Its application in the environmental gas-phase analysis was demonstrated.