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.

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.

A series of luminescent binuclear ([dppm{Pt(NNC)}(2)](2+)) and mononuclear ([PPh3Pt(NNC)](+)) complexes containing pincer ligands were synthesized and characterized. Photophysical characteristics of both types of complexes were studied in dichloromethane solution. In the solid phase, the binuclear compounds adopt a syn configuration where the {Pt(NNC)} fragments are held together due to intramolecular Pt-Pt bonding and pi-stacking of the pincer ligand aromatic systems. Analysis of the complexes' molecular structure in solution by multinuclear NMR spectroscopy showed that the stacked intramolecular configuration is retained in fluid media, which is in complete agreement with a considerable red shift of the emission wavelength due to formation of the intramolecular Pt-Pt bond, leading to the transformation of an emissive excited state to (MMLCT)-M-3. It was also found that triethylamine quenches the emission of both types of complexes; the mechanism of quenching is a combination of dynamic and static channels of excited-state deactivation. In the case of binuclear complexes, deprotonation of the dppm methylene bridge by triethylamine also contributes to the chromophore quenching. To explain the observed chemistry of binuclear complex interactions with Et3N, a chemical equilibrium scheme was suggested, which was confirmed by quantitative monitoring of the P-31 signal variations as a function of triethylamine concentration.

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.

(E)-3-Arylidene-4-diazopyrrolidine-2,5-diones previously shown to yield two products in reactions with tetrahydrofuran mediated by rhodium carbenes—tetrahydrofur-2-yl-substituted product of C-H insertion and spirocyclic product of formal C-O insertion. Accidentally, it was noted that the ratio of the two products depends on the catalyst loading, and the phenomenon was investigated in detail. It was found to be of preparative significance: by solely changing the catalyst loading from 0.01 mol% to 10 mol%, one can obtain sound yields of either of the two products. Mechanistic and kinetic interpretation of this new phenomenon has been proposed.

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.

Photocatalytic activity of HB2Nb3O10 perovskite nanosheets (B = Ca, Sr) has been systematically investigated in the reactions of hydrogen production, depending on the method of the photocatalyst preparation: using the pristine nanosheets in the parent suspension without reassembly, filtered nanosheets as well as nanosheets restacked by hydrochloric acid. 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 as well as stability and pH of the reaction suspension. Exfoliation of the niobates into nanosheets allowed obtaining efficient photocatalysts surpassing the initial bulk materials in the activity up to 55 times and providing apparent quantum efficiency up to 20.8% after surface decoration with a Pt cocatalyst. Among the reassembled samples, greater hydrogen evolution activity was exhibited by simply filtered nanosheets that, unlike the HCl-restacked ones, were found to possess much lower specific surface area in a dry state but contain a perceptible amount of tetrabutylammonium cations on the surface. The activity difference, potentially, is associated with the fact that the filtered nanosheets undergo ultrasonic disaggregation before photocatalytic tests much easier than their HCl-restacked counterparts and, thanks to this, have greater active surface in the reaction suspension. In addition, the enhanced activity of the filtered nanosheets may be due to the presence of tetrabutylammonium as an organic modifier on their surface, which is consistent with the high photocatalytic performance of organically modified layered perovskites considered in our previous reports.

Layered perovskite-like niobate CsBa2Nb3O10 has been synthesized in a pure single-phase state for the first time using both nitrates and carbonates of cesium and barium. Unlike its Ca-, Sr- and Pb-containing analogs, the niobate obtained was shown not to undergo substitution of interlayer alkali cations with protons (protonation) upon acid treatments under various conditions. A potential reason for its chemical inactivity may consist in partial disordering of cesium and barium cations between the interlayer space and perovskite slab, hindering the interlayer ion exchange. Optical bandgap energy of CsBa2Nb3O10, being equal to 2.8 eV, potentially allows using visible light (λ < 443 nm) for driving photocatalytic reactions. However, the photocatalytic potential of this niobate towards hydrogen production remains untapped since the activity of the interlayer space in protonation and hydration reactions, as shown earlier, is a fundamentally important factor determining the photocatalytic performance of ion-exchangeable layered perovskite-like oxides.

The stability of platinized n-butylamine-intercalated layered titanate H2La2Ti3O10 during the process of photocatalytic hydrogen production from aqueous methanol under UV irradiation has been thoroughly investigated by means of XRD, CHN, TG, 13C NMR, BET, SEM and GC-MS analysis. It was revealed that n-butylamine completely abandons the interlayer space and transforms into n-butyraldehyde within 3 h of the reaction, while the particle morphology and specific surface area of the photocatalyst are preserved. The resulting solid phase contains carbon in at least two different oxidation states, which are attributed to the intermediate products of methanol oxidation bound to the perovskite matrix. The activity of the photocatalyst formed in this way is stable in time and strongly depends on the medium pH, which is not typical of either the parent H2La2Ti3O10 or TiO2. An approximate linear equation φ ≈ 29−2∙pH holds for the apparent quantum efficiency of hydrogen production in the 220–340 nm range at 1 mol. % methanol concentration. In the acidic medium, the photocatalyst under study outperforms the platinized H2La2Ti3O10 by more than one order of magnitude. The variation in methanol concentration allowed a maximum quantum efficiency of hydrogen production of 44% at 10 mol. % to be reached.

Nowadays, the efficient conversion of plant biomass components (alcohols, carbohydrates, etc.) into more energy-intensive fuels, such as hydrogen, is one of the urgent scientific and technological problems. The present study is the first one focused on the photoinduced hydrogen evolution from aqueous D-glucose and D-xylose using layered perovskite-like oxides HCa2Nb3O10, H2La2Ti3O10, and their organically modified derivatives that have previously proven themselves as highly active photocatalysts. The photocatalytic performance was investigated for the bare compounds and products of their surface modification with a 1 mass. % Pt cocatalyst. The photocatalytic experiments followed an innovative scheme including dark stages as well as the control of the reaction suspension’s pH and composition. The study has revealed that the inorganic−organic derivatives of the layered perovskite-like oxides can provide efficient conversion of carbohydrates into hydrogen fuel, being up to 8.3 times more active than the unmodified materials and reaching apparent quantum efficiency of 8.8%. Based on new and previously obtained data, it was shown that the oxides’ interlayer space functions as an additional reaction zone in the photocatalytic hydrogen production and the contribution of this zone to the overall activity is dependent on the steric characteristics of the sacrificial agent used.

New TiO2/2D mordenite nanocomposites were synthetized from lamellar mordenite by introduction of titanium tetraetoxide (TEOT) into the interlamellar space with further hydrolysis and calcination. Anatase nanoparticles with an average size of 4 nm form pillars separating mordenite layers, creating mesoporosity. The surface area, pore size distribution, and total pore volume of the nanocomposites depend on the media in which the TEOT hydrolysis occurs. Magic angle spinning nuclear magnetic resonance (MAS NMR) on 1H, 23Na, 27Al, and 29Si nuclei was used to study the local structure of synthetized nanocomposites. It was established that in the studied TiO2/2D mordenite nanocomposites, the removal of organic cations during preparation results in a partial collapse of the local mordenite structure. 29Si MAS NMR reveals an important contribution from isolated silanol groups (SiO)3Si–OH, Q3 sites. The obtained TiO2/2D mordenite nanocomposites could be considered as an effective way of immobilization of the TiO2 photocatalyst, which creates opportunity for their application for water purification under flow conditions with a high mass transfer.

Structures of partially and completely protonated Ruddlesden–Popper phases, H0.7Na0.3NdTiO4·0.3H2O and HNdTiO4, have been established by means of neutron and X-ray diffraction analysis and compared among themselves as well as with that of the initial titanate NaNdTiO4. It was shown that while interlayer sodium cations in the partially protonated form are coordinated by nine oxygen atoms, including one related to intercalated water, in the fully protonated compound the ninth oxygen proves to be an axial anion belonging to the opposite slab of titanium-oxygen octahedra. Moreover, the partially protonated titanate was found to significantly differ from the other two in the octahedron distortion pattern. It is characterized by a weakly pronounced elongation of the octahedra towards the Nd-containing interlayer space making Ti4+ cations practically equidistant from both axial oxygen atoms, which is accompanied by a low-frequency shift of the bands relating to the asymmetric stretching mode of axial Ti–O bonds observed in the Raman spectra.

Two series of hybrid inorganic-organic derivatives, obtained via the modification of protonated Ruddlesden–Popper phases H2Ln2Ti3O10 (Ln = La, Nd) with intercalated n-alkylamines and grafted n-alkoxy groups, have been systematically investigated in relation to photocatalytic hydrogen production from a model of 1 mol % aqueous solution of methanol for the first time. Photocatalytic measurements were performed both for bare samples and for their composites with Pt nanoparticles as a cocatalyst using an advanced scheme, including dark stages, monitoring of the volume concentration of the sample in the reaction suspension during the experiment, shifts of its pH and possible exfoliation of layered compounds into nanolayers. It was found that the incorporation of organic components into the interlayer space of the titanates increases their photocatalytic activity up to 117 times compared with that of the initial compounds. Additional platinization of the hybrid samples’ surface allowed for achieving apparent quantum efficiency of hydrogen evolution of more than 40%. It was established that the photocatalytic activity of the hybrid samples correlates with the hydration degree of their interlayer space, which is considered a separate reaction zone in photocatalysis, and that hydrogen indeed generates from the aqueous methanol solution rather than from organic components of the derivatives.

A series of hybrid inorganic–organic niobates HCa2Nb3O10×ROH, containing n-alkoxy groups of primary alcohols (R = Me, Et, Pr, Bu, Hx, and Dc) grafted in the interlayer space, has been studied for the first time in relation to photocatalytic hydrogen generation from a model 1 mol % aqueous solution of methanol under ultraviolet irradiation. Photocatalytic activity was measured both for bare samples and for their composites with Pt nanoparticles as a cocatalyst. The advanced measurement scheme allowed monitoring the volume concentration of a sample in a suspension during the experiment, its pH, and possible exfoliation of layered compounds into nanolayers. In the series of n-alkoxy derivatives, the maximum rate of hydrogen evolution was achieved over a Pt-loaded ethoxy derivative HCa2Nb3O10×EtOH/Pt. Its apparent quantum efficiency of 20.6% in the 220–350 nm range was found not to be caused by changes in the light absorption region or specific surface area upon ethanol grafting. Moreover, the amounts of hydrogen released during the measurements significantly exceeded those of interlayer organic components, indicating that hydrogen is generated from the reaction solution rather than from the hybrid material.

A series of hybrid niobates HCa2Nb3O10×RNH2, containing n-alkylamines (R = Me, Et, Pr, Bu, Hx, Oc) intercalated into the interlayer space, has been thoroughly studied concerning the photocatalytic hydrogen production from a model aqueous solution of methanol for the first time. All the hybrid photocatalysts were synthesized by the conventional ceramic technique followed by protonation and intercalation of n-alkylamines. The products were characterized using XRD, Raman, IR and diffuse reflectance spectroscopy, TGA, CHN-analysis and SEM. Photocatalytic measurements were conducted according to an advanced scheme taking into account possible changes in the photocatalyst concentration because of sedimentation, pH shifts and exfoliation of the samples into nanoplatelets. Special attention was also paid to the feasible improvement of the photocatalytic activity of the samples via their modification with Pt nanoparticles as a cocatalyst. In the series of amine derivatives, the highest rate of hydrogen generation was demonstrated by the Pt-loaded HCa2Nb3O10×BuNH2 reaching apparent quantum efficiency of 13% in the 220-340 nm range. The initial HCa2Nb3O10 showed comparable efficiency of 8.3% that is greater than for other amine derivatives. It was demonstrated that for the investigated samples the photocatalytic activity correlates with their ability of water intercalation.

Eu3+-doped ZrO2 nanostructures in the form of rods, stars, and hollow spheres were prepared by varying hydrothermal conditions. X-ray diffraction, transmission electron microscopy, ultraviolet-visible diffuse reflection spectroscopy, a low-temperature nitrogen adsorption method, Raman spectroscopy and photoluminescence spectra were used to characterize the polymorph modification, surface and optical properties of the Zr0:98Eu0:02O2 nanophosphors. The Eu3+ content in a zirconia monoclinic lattice, remained constant for all types of obtained nanostructures in order to reveal the morphology influence on the efficiency of electronic excitation energy transfer from the host matrix to photoactive centers. The decrease of the average size of the coherent scattering regions in the series rods -> stars -> hollow spheres, is associated with increasing the specific surface area values. At that, in the photoluminescence spectrum, the splitting of the sublevels associated with the monoclinic lattice D-5(0) -> F-7(1) disappears.

A layered perovskite-type oxide intercalated with n-butylamine is reported as an efficient photocatalyst for hydrogen production from aqueous solutions of alcohols for the first time. The hybrid photocatalyst H(2)Nd(2)Ti(3)O(10)xBuNH(2) was synthesized by solid-state ceramic method followed by protonation, intercalation of methylamine and subsequent substitution by n-butylamine. The product was characterized by powder XRD, TGA, STA-MS, DRS, IR, and Raman spectroscopy, CHN analysis, SEM. Intercalation of n-butylamine caused a dramatic increase in photocatalytic activity of H2Nd2Ti3O10 in the reaction of hydrogen evolution from aqueous solutions of methanol, ethanol, and n-butanol under UV radiation. While the non-intercalated Pt-loaded H2Nd2Ti3O10 showed a maximum quantum efficiency of only 2% in the 220-340 nm range, the efficiency for hybrid samples reached 23% under the same conditions and after variation of experimental parameters even 52% efficiency was achieved. This effect may be associated with the significant expansion of the interlayer space, which is considered as a separate reaction zone.

This article is devoted to the investigation of water sorption by the layered perovskite-type titanate K2Nd2Ti3O10 and its intercalated protonated derivatives HxK2−xNd2Ti3O10·yH2O in a humid atmosphere. K2Nd2Ti3O10 was synthesized by the solid-state reaction. Metastable HxK2−xNd2Ti3O10·yH2O compounds were obtained by water flushing. The determination of the samples composition was carried out by XRD and TG analysis. The stability in a humid atmosphere was investigated by a water vapor sorption analyzer. It was found that humid atmosphere has influence only on K2Nd2Ti3O10 while HxK2−xNd2Ti3O10·yH2O phases are stable under experimental conditions. The study of K2Nd2Ti3O10 in humid atmosphere has shown that the intercalation process proceeds with a rate constant kint = 3.2 × 10−6 min−1 at 0–95% RH, and the protonation process takes place at RH more than 80%.

The K2La2Ti3O10 layered oxide was synthesized by high-temperature technique. Ion exchange properties of K2La2Ti3O10·H2O were investigated by continuous potentiometric titration of its suspension in KOH with HCl. The shape of the titration curve indicates that the ion-exchange reaction of interlayer K+ to H+ proceeds at pH 7.5–8.5 at the rate as high as 5% min−1. Samples obtained during the titration experiment at pH 9.8, 4.8, and 1.4 were examined by XRD, TG, ICP-AES, and SEM–EDX. Protonation already occurs at pH > 9.8, while at pH 4.8 a substitution degree of 76% is observed. K2La2Ti3O10 was found to be unstable against K+ leaching, which results in irreversible ion-exchange even when the sample is washed with distilled water. The protonation of the layered oxide significantly suppresses its photocatalytic activity in the reaction of hydrogen production from aqueous isopropanol solution, which correlates with the decreasing amount of intercalated water.