In recent decades, layered perovskite-like oxides have been intensively investigated as prominent photocatalysts for water splitting as a method of hydrogen production. In many previous papers, it was shown that deposition of platinum on an oxide sample dramatically increases photocatalytic activity. Nevertheless, little research was conducted to reveal the localisation of platinum in layered oxides; either it is located on the surface or in the interlayer space. In the present work, an attempt to answer this question is made. An HCa2Nb3O10 layered perovskite-like oxide was modified with platinum by photoreduction of H2PtCl6 and then was intercalated with n-alkylamines (R = Me, Bu, Oc). Moreover, another set of samples were prepared by intercalating the amines first into HCa2Nb3O10, followed by Pt deposition. Besides conventional methods for sample characterisation, we measured the kinetics of Pt dissolution during aqua regia etching of the samples, hoping that the rate of platinum dissolution would provide some information about its localisation. It was shown that in HCa2Nb3O10 modified with platinum, less than 20% of the platinum is located on the surface, and that in the case of HCa2Nb3O10 intercalated with amines, an even smaller amount of platinum attaches to the surface. Moreover, Pt in HCa2Nb3O10 intercalated with amines was found to be significantly more stable against aqua regia treatment than in HCa2Nb3O10 decorated with platinum directly.

Hierarchical mesoporous ZSM-5 zeolites were prepared via alkaline desilication and pillaring, and characterized by a combination of XRD, N2 adsorption, 29Si MAS NMR, SEM, and low-field 1D and 2D (T1–T2 correlation) 1H NMR relaxation of confined water. Alkaline treatment resulted in a progressive desilication, increased mesopore volume, and the formation of surface defects, whereas pillaring produced more ordered mesoporosity. The T1–T2 correlation maps revealed distinct relaxation regimes reflecting the strength of the water–surface interactions. The samples with different mesopore organization exhibit very different surface relaxivities and T1/T2: as compared with the parent microporous zeolite, the samples with disordered mesoporosity introduced via the alkaline treatment show higher surface relaxivities but lower T1/T2, whereas the pillared sample, oppositely, exhibits surface relaxivities close to that of the parent sample and essentially higher T1/T2 ratio. The decoupling of T1 and T2 points out on a complex water dynamics in the pillared zeolite with ordered micro- and mesoporosity.

Samarium-doped barium and lanthanum tungstates of the composition Ba(La 1−x Sm x ) 2 WO 7 were obtained by solid-phase synthesis at x = 0.01 and 0.03. X-ray analysis revealed that the samples are single-phase and isostructural with BaLa 2 WO 7 (monoclinic syngony, P112 1 /b), with increasing Sm content leading to only minor changes in the unit cell parameters. Calorimetric studies in the range of 4.2–320 K revealed the low-temperature heat capacity anomalies associated with thermal population of the Stark levels of samarium ions in the CEF structure of the compound. Magnetic properties measurements in the range of 2–400 K allowed identifying the temperature dependence of the effective magnetic moment of paramagnetic Sm 3+ atoms in the diamagnetic matrix BaLa 2 WO 7 and showed paramagnetic behavior of the samples with the presence of a temperature-independent contribution of Van Vleck paramagnetism to the magnetic susceptibility.

Alkaline treatment in 0.2 and 0.4 M NaOH solutions successfully generated controlled mesoporosity into ZSM-5 (Zeolite Socony Mobil-5) zeolite, resulting in average mesopore diameters of approximately 15 and 25 nm, respectively, while preserving the crystalline structure of the zeolite framework. Parent ZSM-5 and its mesoporous derivatives obtained by desilication were used to prepare (Fe species)@(zeolite matrix) composites. The synthesis was carried out by co-precipitating Fe2+/Fe3+ ions onto both parent and desilicated ZSM-5 matrices under oxygen-free conditions. Comprehensive characterization by X-ray diffraction, scanning electron microscopy, N2 adsorption, vibrating-sample magnetometry, 57Fe Mössbauer spectroscopy, and diffuse reflectance UV–Vis spectroscopy revealed that the degree of introduced mesoporosity dramatically influences the size, dispersion, phase composition, and oxidation state of the iron-containing nanospecies. On purely microporous ZSM-5, relatively large (~15 nm) partially oxidized magnetite nanoparticles are formed predominantly on the external surface, exhibiting superparamagnetism at room temperature (Mₛ = 11 emu/g) and a band gap of 2.12 eV. Increasing mesoporosity leads to progressively smaller and more highly dispersed iron(III) oxo/hydroxo clusters with significantly lower blocking temperatures and reduced magnetization (down to 0.7 emu/g for Fe@ZSM-5_0.4). All composites display strong visible-light absorption confirming their potential as magnetically separable visible-light-driven photocatalysts for environmental remediation.

In this work, we investigate advanced photocatalyst Bi3TiNbO9 as promising piezophotocatalyst in terms of the effect of synthesis methods on the surface chemistry, structure, and catalytic performance in process of contaminant removal. Samples were prepared via solid-state reaction (BTNO-900) and molten salt synthesis (BTNO-800), leading to distinct morphologies and defect distributions. SEM imaging revealed that BTNO-900 consists of agglomerated, irregular particles, while BTNO-800 exhibits well-faceted, plate-like grains. Nitrogen adsorption analysis showed that the molten-synthesized sample possesses a significantly higher specific surface area (5.9 m2/g vs. 1.4 m2/g) and slightly larger average pore diameter (2.8 nm vs. 2.6 nm). High-resolution XPS revealed systematic shifts in binding energies for Bi 4f, Ti 2p, Nb 3d, and O 1s peaks in BTNO-900, accompanied by a higher content of adsorbed oxygen species (57% vs. 7.2%), indicating an increased concentration of oxygen vacancies and surface hydroxylation due to the solid-state synthesis route. Catalytic testing demonstrated that BTNO exhibits enhanced piezocatalytic efficiency of Methylene Blue degradation (~78% for both samples), whereas BTNO-800 shows significantly reduced photocatalytic activity (45.6%) compared to BTNO-900 (84.1%), suggesting recombination effects dominate in the more defective material. Synergism of light and mechanical stress results in piezophotocatalytic degradation for both samples (92.4% and 93.4%, relatively). These findings confirm that synthesis-controlled defect engineering is a key parameter for optimizing the photocatalytic behavior of Bi3TiNbO9-based layered oxides and crucial role of its piezocatalytic activity.

Direct light olefin synthesis from bio-syngas hydrogenation is a promising pathway to decarbonize the chemical industry. The present study is devoted to the investigation of co-hydrogenation of carbon oxides in the presence of complex systems with the perovskite structure GdBO3 (B = Fe, Mn, Co). The catalyst samples were synthesized by sol-gel technology and characterized by XRD, XPS, BET and TPR. It was found that the Fe/Mn-containing samples exhibited efficient catalysis of the hydrogenation of simulated bio-syngas to light hydrocarbons. The GdMnO3 catalyst exhibits selectivity for C2–C3 light olefins of up to 37% among C1+ hydrocarbons, with a maximum olefin/paraffin ratio. GdMnO3 also exhibits high conversion of CO and CO2, reaching up to 70–75% at 723 K. However, the GdFeO3 catalyst shows a lower selectivity of (C2−3= = 22%, while it exhibits a higher conversion of CO2, up to 95%, at the same temperature. Herein, we established a catalyst structure–performance relationship as a function of chemical composition. Oxygen mobilities and ratios of surface (Os) to lattice (Ol) oxygen, forms of hydrogen adsorption, formation of -CHx- radicals and their subsequent recombination to olefins are influenced by the nature of the element in the B position. This work provides valuable insights for the rational design of bimetallic catalysts for bio-syngas hydrogenation.

Layered Ruddlesden–Popper titanates HLnTiO4 and H2Ln2Ti3O10 (Ln = La, Nd) have been exfoliated into nanosheets in aqueous tetrabutylammonium hydroxide and systematically investigated as hydrogen evolution photocatalysts. The nanosheets were tested both in as-prepared pristine form and after reassembly by two methods (simple filtration and precipitation by hydrochloric acid). The nanosheet-based samples demonstrated by up to 88 times greater photocatalytic performance in comparison with the bulk precursors and, after modification with a Pt cocatalyst, provided apparent quantum efficiency of hydrogen generation up to 14.2% in 1 mol.% aqueous methanol and 3.15% in pure water. It was established that the form in which the nanosheets are used strongly affects the hydrogen production efficiency: the latter typically decreases when moving from the pristine nanosheets to filtered ones and then to those restacked by hydrochloric acid, which is determined by the difference in their physical–chemical characteristics being influenced by the reassembly approach.

This study investigates the influence of mesoporosity, pre-created by alkali etching in ZSM-5 zeolite, on the characteristics of Fe3+ ion-exchange and subsequent changes in its textural and optical properties. It is shown that the formed hierarchical porosity facilitates the penetration of hydrated iron complexes into the internal channels. This not only increases the degree of exchange, but also leads to the formation of multinuclear FexOy clusters and, possibly, to the partial isomorphic replacement of Al3+ with Fe3+ in the framework. Comprehensive characterization of mesoporous samples (XRD, SEM, N2 adsorption, UV-Vis) confirms the preservation of the microporous crystal structure of MFI on the one hand, and demonstrates a significant change in the distribution of iron-containing species in mesoporous matrices on the other. The introduction of Fe ions significantly reduces the bandgap energy, shifting the absorption edge into the visible range. The results obtained demonstrate that preliminary mesostructuring is an effective approach for creating hierarchically porous Fe zeolites with great potential for photocatalytic applications.

This report focuses on heat capacity and thermodynamic properties of crystalline perovskite-like layered oxides: protonated titanate H2Nd2Ti3O10 and its n-butoxy derivative, designated as H2Nd2Ti3O10 × BuOH, in the temperature range from 5 to 340 K. Isobaric heat capacity of the compounds was measured using precise adiabatic vacuum calorimetry. Standard thermodynamic properties of the oxides were estimated based on the temperature dependencies of the experimental heat capacity. The data obtained allowed us to verify the applicability of the additivity principle for predicting the thermodynamic properties of layered organic–inorganic hybrids. As a result of the experiments, it was established that the principle of additivity is not realized in the case of covalent bonding between the inorganic matrix and organic molecules, which indicates the impossibility of calculating the heat capacity of the hybrid material as the sum of the values for the oxide and organic components, confirming the presence of a covalent bond between them.

This work presents the results of the study of glycerol and water sorption using two complimentary approaches, simultaneous thermal analysis and isothermal sorption calorimetry, on zeolites differing in the framework topology and post modifications (natural clinoptilolite, protonated zeolite ZSM-5 with Si/Al ratio of 50, commercial Na-mordenite with Si/Al ratio of 6.5 then modified by ion exchange for copper ions, or by alkaline etching to develop mesoporosity, and pillared mordenite). For the studied mordenites a correlation between texture and composition and sorption capacity towards glycerol and water was shown. Analysis of glycerol and water desorption suggests the optimal temperature range for catalytic conversion of glycerol via dehydration and carboxylation.

Developing photocatalysts for CO2 reduction with high efficiency and selectivity in a photocatalytic system remains urgent yet challenging. Herein, we report the highly selective photocatalyzed reduction of CO2 to CO by in situ grown ultrafine TiO2 nanoparticles on an ultrathin two-dimensional (2D) porphyrin metal-organic framework (Al-MOF@TiO2). Al-MOF and TiO2 nanoparticles are connected by 4,4-bipyridine (BPY): the nitrogen atom of BPY coordinates with the metal aluminum in Al-MOF and with TiO2 to form the Ti-O-N bond. The ultrathin 2D Al-MOF improved the dispersibility and stability of TiO2 under prolonged light illumination. Additionally, the interfacial Ti-O-N covalent bond promoted charge carrier transfer and separation along with the rapid migration of charge carriers to the surface for the selective reduction of CO2 to CO. The hybrid photocatalyst demonstrated excellent capability in reducing CO2 to CO with a selectivity of 94.1%, producing 1901 mu mol g-1 of CO, which is eight times higher than that obtained using pure Al-MOF. Furthermore, the Al-MOF@TiO2 photocatalyst exhibited superior stability, maintaining its structural integrity in an aqueous reaction system. This work provides an effective strategy for improving the stability and charge separation property of metallic oxide-modified photocatalysts for efficient photocatalytic CO2 reduction.

The search for effective and reliable methods of photosensitization of oxide-based semiconductor materials is of great significance for their use in photocatalytic reactions of hydrogen production and environmental remediation under natural sunlight. The present study is focused on partial substitution of titanium with manganese in the structure of layered perovskite-like titanate Na2La2Ti3O10, which was employed to yield a series of photocatalytically active materials, Na2La2MnxTi3−xO10 (x = 0.002–1.0), as well as their protonated forms H2La2MnxTi3−xO10 and nanosheets. It was established that the manganese cations Mn4+ are embedded in the middle sublayer of oxygen octahedra in the perovskite slabs La2MnxTi3−xO102− and that the maximum achievable manganese content x in the products is ≈0.9. The partial cationic substitution in the perovskite sublattice led to a pronounced contraction of the optical band gap from 3.20 to 1.35 eV (depending on x) and, therefore, allowed the corresponding photocatalysts to utilize not only ultraviolet, but also visible and near-infrared light with wavelengths up to ≈920 nm. The materials obtained were tested as photocatalysts of hydrogen evolution from aqueous methanol, and the greatest activity in this reaction was demonstrated by the samples with low manganese contents (x = 0.002–0.01). However, the materials with greater substitution degrees may be of high interest for use in other photocatalytic processes and, especially, in thermophotocatalysis due to their improved ability to absorb the near-infrared part of solar radiation.

In conditions of depletion of mineral reserves, plant biomass is considered a renewable natural resource that can be photocatalytically processed to produce energy-intensive and environmentally friendly hydrogen fuel. In this regard, the present article focuses on the improvement of photocatalytic activity of the layered perovskite-structured niobate HCa2Nb3O10 in the reactions of hydrogen production from aqueous solutions of typical plant biomass components, glucose and xylose, via its exfoliation into nanosheets followed by their reassembly and modification with a Pt cocatalyst. The reassembled compound obtained was shown to outperform in the activity the initial niobate and reference photocatalyst TiO2 P25 Degussa up to 6.3 and 5.3 times, respectively, providing a hydrogen production rate up to 24.2 mmol h−1g−1 and apparent quantum efficiency up to 10

The layered double hydroxides (LDHs) of transition metals are of great interest as building blocks for the creation of composite photocatalytic materials for hydrogen production, environmental remediation and other applications. However, the synthesis of most LDHs is reported only by the conventional coprecipitation method, which makes it difficult to control the catalyst’s crystallinity. In the present study, ZnCr- and NiCr-LDHs have been successfully prepared using a facile hydrothermal approach. Varying the hydrothermal synthesis conditions allowed us to obtain target products with a controllable crystallite size in the range of 2–26 nm and a specific surface area of 45–83 m2∙g−1. The LDHs synthesized were investigated as photocatalysts of hydrogen generation from aqueous methanol. It was revealed that the photocatalytic activity of ZnCr-LDH samples grows monotonically with the increase in their average crystallite size, while that of NiCr-LDH ones reaches a maximum with intermediate-sized crystallites and then decreases due to the specific surface area reduction. The concentration dependence of the hydrogen evolution activity is generally consistent with the standard Langmuir–Hinshelwood model for heterogeneous catalysis. At a methanol content of 50 mol. %, the rate of hydrogen generation over ZnCr- and NiCr-LDHs reaches 88 and 41 μmol∙h−1∙g−1, respectively. The hydrothermally synthesized LDHs with enhanced crystallinity may be of interest for further fabrication of their nanosheets being promising components of new composite photocatalysts.

The data on molar excess enthalpies, HmE, for the binary mixtures acetic acid + n-butanol, acetic acid + n-butyl acetate and n-butanol + n-butyl acetate at 313.15 K and atmospheric pressure were obtained with use of the C80 isothermal mixing calorimeter (Setaram). The correlation of the data was carried out using the NRTL model and Redlich–Kister equation. A comparative analysis with the literature data on all available binary subsystems of the quaternary system was carried out. Other thermodynamic properties (Cp,mE, SmE, ΔmixSm, GmE and ΔmixGm) of the binary systems were estimated using literature data and well-known formulas of classical thermodynamics.

The effect of strontium substitution in the structure of the complex oxide Gd2SrFe2O7 on the production of light olefins by CO hydrogenation was investigated. Perovskite-type oxides Gd2−xSr1+xFe2O7 (x = 0; 0.1; 0.2; 0.3; 0.4) were synthesized by sol–gel technology and characterized by XRD, Mössbauer spectroscopy, BET specific area, acidity testing, and SEM. The experimental data revealed a correlation between the state of iron atoms, acidity, and catalytic performance. It was found that with an increase in the content of Sr2+ in the perovskite phase, the basicity of the surface and the oxygen diffusion rate increased. This contributed to the CO dissociative adsorption, formation of active carbon, and its further interaction with atomic hydrogen.

Two series of hybrid inorganic–organic materials, prepared via interlayer organic modification of protonated Ruddlesden–Popper phases HLnTiO4 (Ln = La, Nd) with n-alkylamines and n-alkoxy groups of various lengths, have been systematically studied with respect to photocatalytic hydrogen evolution from aqueous methanol under near-ultraviolet irradiation for the first time. Photocatalytic measurements were organized in such a way as to control a wide range of parameters, including the hydrogen generation rate, quantum efficiency of the reaction, potential dark activity of the sample, its actual volume concentration in the suspension, pH of the medium and stability of the photocatalytic material under the operating conditions. The insertion of the organic modifiers into the interlayer space of the titanates allowed obtaining new, more efficient photocatalytic materials, being up to 68 and 29 times superior in the activity in comparison with the initial unmodified compounds HLnTiO4 and a reference photocatalyst TiO2 P25 Degussa, respectively. The hydrogen evolution rate over the samples correlates with the extent of their interlayer hydration, as in the case of the inorganic–organic derivatives of other layered perovskites reported earlier. However, the HLnTiO4-based samples demonstrate increased stability with regard to the photodegradation of the interlayer organic components as compared with related H2Ln2Ti3O10-based hybrid materials.

In this study, geopolymers based on mechanically activated mixtures of fly ash (FA) with SrCO3 (strontianite) and BaCO3 (witherite) were synthesized. NaOH solution was used as an alkaline agent and curing was carried out under ambient conditions. XRD, FTIR spectroscopy, thermogravimetry, and SEM were used to study the geopolymerization process and microstructure. The product of geopolymerization of the milled (FA + SrCO3) and (FA + BaCO3) blends was X-ray amorphous N-A-S-H gel. The beneficial impact of mechanical activation on the compressive strength of geopolymers was most evident during the initial stages of the curing process. The strength of geopolymers based on the (FA + carbonate) blends after 7 d was either less than the corresponding strength of geopolymers based on the 100% FA or, within the measurement accuracy, equal to it. With increasing curing time, the strength development of geopolymers synthesized from (70% FA + 30% carbonate) blends exceeded the strength growth of geopolymers containing less carbonates; after curing for 180 d, these geopolymers showed the highest compressive strength (20–27 MPa). This trend was more pronounced for the geopolymers based on the (FA + SrCO3) blends. The influence of SrCO3 and BaCO3 addition to the FA on the strength of composite geopolymers was explained by dilution and microfiller effects. The geopolymers based on the FA blended with SrCO3 and BaCO3 exhibit potential applications in immobilizing radioactive strontium and producing radiation shielding materials.

Synthesis of layered perovskite-like niobates APb2Nb3O10 (A = Rb, Cs), being promising visible light active photocatalysts, has been conducted by the ceramic method under variable conditions to obtain the samples with the highest possible phase purity. The oxides prepared were shown practically not to undergo protonation and hydration of the interlayer space upon keeping in water. Both phases APb2Nb3O10 were used to yield corresponding protonated hydrated forms HxA1 − xPb2Nb3O10∙yH2O via acid treatment. It was found that the propensity of the samples to the substitution of interlayer cations by protons depends clearly on the A+ cation: while the Rb-containing niobate is capable of complete protonation (x = 1) upon a single treatment with 6 M nitric acid, the Cs-containing counterpart gives a high enough protonation degree (x ≥ 0.9) only after several renewals of the acid solution. The protonated niobates obtained were exposed to an additional water treatment under hydrothermal conditions, which allowed producing new hydrated derivatives with the enhanced thermal stability towards interlayer dehydration as compared with the protonated precursors.