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Hierarchical CsAlTi-BEA zeolites, due to the presence of a high concentration of Lewis acid sites formed by tetrahedrally coordinated Ti4+ ions in the zeolite structure and the neutralization of Brønsted acid sites by Cs+ cations, exhibit high catalytic activity in the tandem reaction of cyclic carbonate formation from styrene in the presence of tert-butyl hydroperoxide under CO2 pressure. The conversion of styrene into epoxide and further into carbonate increases with the content of titanium in the samples, while the selectivity for the cyclic carbonate increases with the content of cesium. [ABSTRACT FROM AUTHOR]

A set of Sn- and Zr-BEA zeolites was obtained using Gemini-type surfactants as SDA and hierarchical BEA nanosheets as seeds. The prepared catalysts were tested in the Baeyer–Villiger oxidation of cyclic ketones with hydrogen peroxide resulting into commercially valuable monomers. The highest conversion of cyclohexanone (70.7%) and selectivity towards the desired ε-caprolactone (> 99%) were achieved over mesoporous Sn-BEA_np_75 possessing the highest concentration of Lewis acid sites and comparatively low fraction of extra framework Sn4 + species. [ABSTRACT FROM AUTHOR]

Titanium dioxide (anatase) powders mechanochemically modified with carbon and/or thiourea were obtained. X-ray powder diffraction, scanning electron microscopy with an integrated system for electron microprobe analysis, transmission electron microscopy, Brunauer–Emmett–Teller surface area analysis, X-ray photoelectron spectroscopy, infrared and ultraviolet–visible spectroscopies were applied for the powders characterization. Mechanochemical modification with thiourea and/or carbon with carbon and/or thiourea led to a decrease of the particle size from 21 to 13 nm and formation of oblong rice-like particles. The presence of a hysteresis loop in the nitrogen ad(de)sorption isotherms for the synthesized samples proved their mesoporous structure. The features of the XPS spectra in all samples can be attributed to the fine-structure peculiarities associated with titanium, oxygen, and carbon atoms and, in the case of modification with thiourea, additionally, to sulfur and nitrogen. Photocatalytic activity of the samples was investigated in the photodestruction of Safranine T and Rifampicinum. The modified samples showed higher photocatalytic activity in both reactions compared to unmodified anatase under UV irradiation and demonstrated activity under visible light. The reusability of the powders was investigated. [ABSTRACT FROM AUTHOR]

Carbon-modified TiO2 using a sol–gel method (TiO2/CSG) and mechanochemical treatment (TiO2/CMC) was obtained. X-ray powder diffraction (XRD), scanning electron microscopy with an integrated system for electron microprobe analysis (SEM, EDX), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), Infrared (IR) and Ultraviolet–visible (UV–Vis) spectroscopy were applied for the powders characterization. The presence of a hysteresis loop in the nitrogen ad(de)sorption isotherms for the synthesized samples proved their mesoporous structure. XRD analysis revealed the anatase and rutile phase in TiO2SG with a size of 10 and 7 nm, respectively, and only anatase phase (15–16 nm) for all TiO2/CSG samples modified by a sol–gel method was observed. Carbon additives to TiO2 did not lead to significant shifts in the peaks of bond energies of Ti 2p, O 1s and C 1s levels. The powders TiO2/CSG had additional bands in IR-spectra which are characteristic bonds of carbon with oxygen unlike the TiO2/CMC samples. It was found that modification of titanium dioxide with carbon by a sol–gel method leads to the band gap narrowing. Photocatalytic activity of the synthesized samples was investigated in H2 photoproduction and Rifampicinum (RF) photodestruction. The TiO2/CSG samples showed higher photocatalytic activity in both reactions compared to TiO2/CMC. The correlation between the RF photocatalytic degradation degree and RF adsorption was demonstrated. The reusability of the powders in RF photodegradation was checked. [ABSTRACT FROM AUTHOR]

It is known that titanium dioxide as photocatalyst has significant drawback - limited absorption spectrum in the ultraviolet region makes it impossible to use solar energy. To expands the absorption spectrum of TiO2, the doping of impurities (metal, non-metal, etc.) were used. They affected the electronic structure and spectral characteristics of TiO2. The aim of our work was to investigate the influence of tin impurities on spectral characteristics of titanium dioxide using experimental and theoretical methods. The TiO2 powders modified by different amount of tin (Sn/TiO2) were synthesized by sol-gel method. The samples were characterized by SEM, EDX, FT-IR and UV-VIS spectroscopy. It has been found that Sn/TiO2 consists of fragmented agglomerates in the range of 5–10 μm. EDX spectroscopy proved that powders include TiO2 and Sn elements. Modification of titanium dioxide with tin led to band gap narrowing of samples, which explains by insertion of Sn atoms into crystal lattice of titanium dioxide, because Ti4+ and Sn4+ ions radii are close. The band gap values increased with increasing of tin content. The work also analyzes the vibrational spectra of Sn/TiO2 both experimentally and theoretically. In order to interpret the results obtained, quantum chemical calculations on the spatial and electronic structures of cluster models of titanium dioxide (anatase) with inserted tin atoms using the density functional theory B3LYP method and the basis set 6-31G (d, p) were carried out and the corresponding FT-IR spectra have been simulated. By comparing the experimental and theoretical results, the influence has been analyzed of the number and arrangement of impurity tin atoms in clusters on the observed IR spectra of the samples. This makes it possible to forgive the most probable structural motives of titanium dioxide particles doped with tin atoms, as well as to establish the fact of the presence of tin atoms in the samples. Based on the comparison of the IR spectra of samples with different numbers of tin atoms, it is possible to quantify their composition. [ABSTRACT FROM AUTHOR]

Nanoscale composite materials based on titanium dioxide with different content of sulphur are obtained by the sol–gel method. The samples were analysed using SEM–EDS microscopy, transmission electron microscopy (TEM), x-ray diffraction analysis (XRD), x-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflection spectra (DRUV), room temperature FT–IR spectroscopy, and BET method. X-ray powder diffraction reveals the phase of anatase in all composites and appearance of the rutile phase for the samples with sulphur. As established, doping with sulphur leads to a decrease in the crystallite sizes from 14.6 to 9.9 nm. Analysis of nitrogen sorption– desorption isotherms for the synthesized samples shows the presence of a hysteresis loop, which is the evidence for mesoporous structure of the powders. The composite samples manifest a bathochromic shift as compared with the absorption band of pure TiO2. As found, the modification of titanium dioxide with sulphur leads to band gap narrowing of the composites. Nanocomposite samples show photocatalytic activity in the destruction of safranin T under visible irradiation. It can be attributed to the appearance of absorption in the visible region, narrowing of band gap, participation of sulphur in the inhibition of electron–hole recombination, prolongation of charges lifetime, increasing efficiency of interfacial charge separation, and change in textural characteristics. [ABSTRACT FROM AUTHOR]

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Nanoscale composite materials based on cerium, barium titanate and titanium dioxide were synthesized by thermal hydrolysis. The obtained individual TiO2, BaTiO3 and as-synthesized Ce/xBaTiO3/TiO2 semiconductive nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, transmission electron microscopy, nitrogen adsorption–desorption, UV–vis diffuse reflectance spectroscopy, and Fourier transform infrared spectroscopy. The structural investigations revealed that all prepared powders were nanocrystalline with an average crystallite size within the range of 5–17 nm. Analysis of nitrogen adsorption–desorption isotherms for the synthesized nanocomposites showed the presence of a hysteresis loop, which is evidence for the mesoporous structure of the powders. The photocatalytic degradation of the model pollutants (Safranine T and Rhodamine B) was carried out under UV irradiation. Ce/xBaTiO3/TiO2 nanocomposites showed higher photocatalytic activity compared to pure TiO2 and BaTiO3 as well as BaTiO3/TiO2. An increase of the amount of BaTiO3 in Ce/xBaTiO3/TiO2 samples by more than 12% reduces the photocatalytic activity of nanocomposites while doping of BaTiO3/TiO2 samples with cerium increases their photoactivity. [ABSTRACT FROM AUTHOR]

Conditions and peculiarities of matrix and bulk synthesis of carbon nanoporous adsorbents, methods of activation of carbons to produce highly porous samples for application in various fields (adsorption, catalysis, producing the supercapacitors etc.) were analyzed. The available data on the functionalization of nanoporous carbons, particularly through the doping with heteroatoms (N, P, B, etc.) were summarized. [ABSTRACT FROM AUTHOR]

Carbon-modified TiO2 using a sol–gel method (TiO2/CSG) and mechanochemical treatment (TiO2/CMC) was obtained. X-ray powder diffraction (XRD), scanning electron microscopy with an integrated system for electron microprobe analysis (SEM, EDX), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), Infrared (IR) and Ultraviolet–visible (UV–Vis) spectroscopy were applied for the powders characterization. The presence of a hysteresis loop in the nitrogen ad(de)sorption isotherms for the synthesized samples proved their mesoporous structure. XRD analysis revealed the anatase and rutile phase in TiO2SG with a size of 10 and 7 nm, respectively, and only anatase phase (15–16 nm) for all TiO2/CSG samples modified by a sol–gel method was observed. Carbon additives to TiO2 did not lead to significant shifts in the peaks of bond energies of Ti 2p, O 1s and C 1s levels. The powders TiO2/CSG had additional bands in IR-spectra which are characteristic bonds of carbon with oxygen unlike the TiO2/CMC samples. It was found that modification of titanium dioxide with carbon by a sol–gel method leads to the band gap narrowing. Photocatalytic activity of the synthesized samples was investigated in H2 photoproduction and Rifampicinum (RF) photodestruction. The TiO2/CSG samples showed higher photocatalytic activity in both reactions compared to TiO2/CMC. The correlation between the RF photocatalytic degradation degree and RF adsorption was demonstrated. The reusability of the powders in RF photodegradation was checked. [ABSTRACT FROM AUTHOR]