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Synthetic opals, a composition of homogeneous silica spheres in the mesoscale size range, have attracted the attention of scientists due to their favorable chemical and physical properties. Their chemical inertness and stability, biocompatibility, homogeneity, elevated specific surface area, and ease of functionalization of their surfaces make them a versatile nanotool. In the present study, the Stöber process was used to investigate the effect of parameters, such as reagent concentration and synthesis temperature, on the resulting silica particle size and structure. The optimal conditions for successfully obtaining homogeneous particles in the mesoscale range with high reproducibility were investigated. Several synthesis procedures and their dependence on the reaction temperature were presented to allow the selection of the assumed diameter of silica spheres. The numerous samples obtained were examined for size, homogeneity, structure, and specific surface area. On the basis of specific surface area measurements and nuclear magnetic resonance studies, the internal hierarchical structure of the spherical silica was confirmed as consisting of a solid core and layers of secondary spheres covered by a solid shell. Structural studies (X-ray Spectroscopy, X-ray Absorption Near-Edge Structure, and nuclear magnetic resonance), together with infrared vibrational spectroscopy, showed no dependence of the structure of the obtained mesospheres on the concentration of reagents and the size of the obtained particles. [ABSTRACT FROM AUTHOR]

A new type of oxyfluoride glass-ceramics based on the silicate glassy matrix and the nano-phase of LaF3 was developed for generating the up-conversion luminescence processes. In such material, the low-phonon energy crystals of LaF3 are desirable host for the rare-earth elements. The effect of admixture of 3 mol% of La2F6 on the structural changes of glasses in the Na2O-B2O3-SiO2 system was investigated. The effect of LaF3 additive was studied using 29Si, 11B, and 23Na MAS NMR to learn more about the structural role of modifiers as well as fluorine in the glassy matrix. Glasses with compositions corresponding to different B2O3/Na2O and B2O3/(Na2O + 3La2F6) ratios in the 0.6-1.2 range were obtained by melt quenching. The 29Si MAS NMR spectra indicated that the [SiO4] units are more polymerized when the ratios and the fluorine admixture increase. The 11B NMR spectra revealed the presence of both [BO4] (Q4) and [BO3] (Q³) units. The fraction of Q³ increased with the decreasing sodium content. Glasses with the LaF3 additive showed higher BO3/BO4 ratios. The effect of thermal treatment for glasses with the tendency towards LaF3 crystallization was discussed in terms of structural changes. [ABSTRACT FROM AUTHOR]

Activation of natural sepiolite by means of grinding in a planetary mill followed by wet NaOH activation was studied for the purpose of endowing the product with enhanced basicity for potential catalytic/sorptive applications. Synthesized solids were characterized with X-ray powder diffraction (XRD), N2 adsorption/desorption, scanning electron microscopy (SEM), energy dispersive (EDX), atomic absorption (AAS), Fourier-transform infrared (FTIR) and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Surface basicity was determined by titration with benzoic acid. Grinding changed the pathway of sepiolite phase transformation upon NaOH treatment. The as-received sepiolite evolved to Na-sepiolite (loughlinite) with a micropore system blocked by nanocrystalline Mg(OH)2, while ground samples yielded magnesium silicate hydrate phase (MSH), with well-developed microporous texture. In unmilled sepiolite desilication involved preferential leaching of Si from the center of the structural ribbons, while in ground samples additional loss of Si from ribbon-ribbon corner linkages was observed. In all cases treatment with NaOH led to enhancement of surface basicity. Synthesized materials were tested as catalysts in a base-catalyzed aldol self-condensation of acetone and oxidation of cyclohexanone to ε-caprolactone, as well as CO2 sorbents. Catalytic trends depended not only on samples' basicity, but also on texture and phase composition of the catalysts. Grinding combined with alkali activation proved a simple and effective method for boosting CO2-sorption capacity of sepiolite to the level comparable to amine-functionalized, acid-activated sepiolite sorbents. [ABSTRACT FROM AUTHOR]

• The high LiF-content phosphate glass was obtained. • The fluorophosphate glass has high thermal stability. • The linearity of the thermoluminescence response was confirmed. The set of six fluorophosphate glasses were obtained to measure the effect of composition on their thermal and luminescence properties. It was found that the phosphate network can accept much more lithium fluoride as compared to silica and borate glasses. The differential thermal analysis study shows a significant increase of thermal stability and decrease of the crystallization with higher content of lithium fluoride. Simultaneously, a gradual increase in the intensity of thermoluminescence was observed as well as linearity of the thermoluminescence response. We correlated the observed effects with the structural changes based on fourier-transform infrared spectroscopy and magic angle spinning nuclear magnetic resonance analysis. [ABSTRACT FROM AUTHOR]

This study aims to thoroughly understand the local structure of copper phosphonate groups covalently attached via propyl arms to pores interior of SBA-15 mesoporous silica. The studied sample contains 20% of propyl-POO 2 Cu groups attached to the mesoporous silica matrix as host material. X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) at the copper K-edge were utilized to discern the valence state and geometric arrangement of copper sites within the pores. Various machine learning techniques, including principal component analysis, K-means clustering, and neural networks, were applied to theoretically calculated XANES spectra. This facilitated our quantitative analysis of the experimental spectrum and the extension of the EXAFS equation fit to the second shell. Additional molecular structure analysis was performed based on Raman scattering supported by numerical simulations. Nuclear magnetic resonance aided in analyzing the silicon and phosphorus environment. Results indicate that copper atoms are coordinated by two phosphonate groups, forming a pseudo-bi-trigonal pyramid with surrounding oxygen atoms. These results contribute to a better understanding of the physical properties of the studied nanocomposite material. This, in turn, makes it possible to optimize the molecular structure of materials to optimize their antimicrobial and photonic properties, making them useful in practice. [Display omitted] • Two phosphonic units can coordinate a single copper atom inside SBA-15 silica. • The properties of copper-containing molecules depend on the local copper environment. • Copper's local environment in nanocomposites varies with functional groups' density. • XRS, supported by simulations & AI, enables analysis of nanomaterials' structure. [ABSTRACT FROM AUTHOR]

Abstract: The present investigations are devoted to silicate–phosphate glasses of the NaCaPO4–SiO2–BPO4 system. Glasses belonging to this system are characterized by a glass phase separation phenomenon, i.e. occurrence of spherical amorphous inclusions dispersed in an amorphous matrix, which have been detected by SEM. SEM investigation has also shown that the introduction of boron ions into the structure of silicate–phosphate glasses leads to homogenization of their microstructure. Based on EDX analyses, it has been found that the introduction of boron ions results in an inversion of the matrix and chemical composition of inclusions. Structural investigations (middle infrared spectroscopy – MIR) of the obtained glasses as well as of the corresponding crystalline materials have shown that the glasses studied exhibit a domain composition. The structure of the domains is close to that of the corresponding crystalline phases. Spectroscopic investigations involving spectra decomposition into component bands have made it possible to establish the homogenising effect of boron ions on the structure of silicate–phosphate glasses. 11B MAS NMR research revealed that in the structure of the NaCaPO4–SiO2–BPO4 silicate–phosphate glasses boron ions show coordination numbers of 3 and 4. 29Si MAS NMR studies have shown the total separation of silicate and sodium–calcium–phosphate phases. [Copyright &y& Elsevier]

[Display omitted] • Structural study on modified silicon oxycarbide-based (SiOC) amorphous materials. • Implementation of phosphate ions for enhancing bioperformances. • Use of the aluminium and boron ions as phosphate doping supports. • FTIR and Raman spectroscopy as the essential tools for the examination. • Detection of Si-C bond along with bonds between modifying ions and glass matrix. Vibrational spectroscopy is the most effective, efficient and informative method of structural analysis of amorphous materials with silica matrix and, therefore, an indispensable tool for examining silicon oxycarbide-based amorphous materials (SiOC). The subject of this work is a description of the modification process of SiOC glasses with phosphate ions based on the structural examination including mainly Infrared and Raman Spectroscopy. They were obtained as polymer-derived ceramics based on ladder-like silsesquioxanes synthesised via the sol-gel method. With the high phosphate's volatility, it was decided to introduce the co-doping ions to create [AlPO 4 ] and [BPO 4 ] stable structural units. As a result, several samples from the Si P OC, Si PAl OC and Si PB OC systems were obtained with various quantities of the modifiers. All samples underwent a detailed structural evaluation of both polymer precursors and ceramics after high-temperature treatment with Fourier-transformed infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and magic angle spinning nuclear magnetic resonance (MAS-NMR). Obtained results proved the efficient preparation of desired materials that exhibit structural parameters similar to the unmodified one. They were X-ray-amorphous with no phase separation and crystallisation. Spectroscopic measurements confirmed the presence of the crucial Si-C bond and how modifying ions are incorporated into the SiOC network. It was also possible to characterise the turbostratic free carbon phase. The modification was aimed to improve the bioperformance of the materials in the context of their future application as bioactive coatings on metallic implants. [ABSTRACT FROM AUTHOR]