Heterostructured compositions of semiconducting photocatalysts can substantially enhance the separation of photogenerated charges due to their improved interphase transfer by heterojunction. In this study, Bi2WO6/ TiO2-N heterostructures were successfully prepared via the hydrothermal method using visible light-active TiO2-N nanoparticles of anatase phase as the starting material and solutions of Bi(NO3)3 and Na2WO4 as the precursors of Bi2WO6. A ratio between components was varied in a wide range to find the optimum for enhanced activity and stability of the heterostructure. The mechanism of Bi2WO6 nucleation at the presence of TiO2-N nanoparticles was studied using XRD, high-resolution TEM, EDX, and XRF analyses, whereas the electrochemical impedance spectroscopy was employed to explain the synergistic effect of composite system. The optimized Bi2WO6/TiO2-N composition containing 21 wt% of Bi2WO6 was further decorated with Fe species (0.1 wt%) to boost the visible-light activity. Photocatalytic ability of designed multicomponent Fe/Bi2WO6/TiO2-N photo-catalyst was evaluated in the degradation of acetone and formaldehyde vapor under blue light. In all cases, Fe-decorated Bi2WO6/TiO2-N heterostructure exhibited higher photocatalytic performance and provided much faster air purification compared to single-component TiO2-N photocatalyst that confirms a strong potential of its application for visible light-driven degradation of organic micropollutants in air.

While recent studies have demonstrated the high potential of nanophosphors based on the monoclinic Y2O3:Eu3+ (m-Y2O3:Eu3+) for various luminescent applications, the influence of europium concentration on their structural and luminescent properties remains unexplored. In this work, a series of monoclinic Y2O3:Eu3+ nanophosphors with a particle size of similar to 18 nm and Eu concentrations of 1.5-30 mol% were synthesized for the first time using the laser vaporization method. It was found that the phase composition and morphology of nanoparticles does not depend on the europium content. From a spectroscopic point of view, the optimal Eu concentration for particles of this size is 12 mol%. At this concentration, the PL absolute quantum yield reaches 53 % without additional heat treatment, while CIE color coordinates are (0.65, 0.33). A prototype of pc-LED was fabricated by coating m-Y2O3:Eu3+ nanophosphor on a UV (395 nm) LED chip. The obtained pc-LED spectrum demonstrates that m-Y2O3:Eu3+ is a potential red-emitting phosphor for UV-pumped pc-LEDs, in particular for plant growth LED technology.

La tungstates possessing a high protonic conductivity (~10–4 S/cm at 600 °C) are state-of-the-art materials for hydrogen separation membranes. A promising approach in design of new materials for this application is creation of triple-conductive materials on their basis. The current work aims at studying structural, textural and transport properties of La27W5O55.5–δ and the composite of La27W5O55.5–δ with NiO and CuO obtained via the mechanical activation and sintered either in a furnace or by radiation thermal sintering using electron beam. The oxide material obtained is distorted double fluorite, while the composites consist of LaNi0.8W0.2O3–δ, NiO and CuO phases. As compared to the oxide sintered in furnace, the electron beam sintered La27W5O55.5–δ demonstrates a lower occupancy of 24f sites by W, higher La:W ratio and larger grain size. Extended defects including grain boundaries are observed in TEM images. La27W5O55.5–δ possesses moderate oxygen transport properties (oxygen tracer diffusion coefficient ~10–10 cm2/s at 800 °C). Thermogravimetric analysis demonstrates that the materials exhibit the hydration behavior typical of proton conductors. The oxygen mobility is demonstrated to decline in the composites, which can be caused by a lower oxygen mobility of the LaNi0.8W0.2O3–δ phase compared to the La27W5O55.5–δ one and the diffusion hindered by nanoparticles of NiO and CuO. Reduction followed by reoxidation of the composites leads to increasing oxygen diffusivity, which can be related to partial unblocking of fast diffusion pathways.

The influence of the composition of photocatalysts represented by the combination of nitrogen-doped anatase-type titanium dioxide and monoclinic bismuth vanadate is studied. Structural features, composition, surface morphology, optical and electrochemical characteristics of the samples are studied by high-resolution electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen porosimetry, UV-Vis spectroscopy diffuse reflectance spectroscopy, and by using electrochemical techniques of photocurrent characterization. Catalytic tests of synthesized photocatalysts in reactions of benzene and acetone vapor oxidation in a flow reactor at 40 °C under LED blue light are conducted. The photoactivity of the samples was estimated by the steady-state rate of accumulation of CO2 as the final oxidation product. As a result, we determine the phase composition of the prepared catalysts and the limiting amount of supported bismuth vanadate beyond which the resulting structure shows features affecting the structure of the resulting obtained composite and its photocatalytic activity. The reported data are practically important, since they expand the area of effective application of photocatalysts inducing chemical transformations under visible light irradiation.

В работе изучено влияние состава фотокатализаторов, представленных композицией азот-допированного диоксида титана типа анатаз и моноклинного ванадата висмута. Исследованы структурные особенности, состав и состояние поверхности, оптические и электрохимические характеристики образцов с помощью методов электронной микроскопии высокого разрешения, рентгеновской дифракции, рентгеновской фотоэлектронной спектроскопии, азотной порометрии, УФ-Вид спектроскопии диффузного отражения и электрохимической регистрации фототоковых характеристик. Проведены каталитические испытания синтезированных фотокатализаторов в тестовых реакциях окисления паров бензола и ацетона в проточном реакторе при температуре 40°С под синим светом от светодиодного источника оптического излучения. Фотоактивность образцов была оценена по стационарной скорости накопления конечного продукта окисления – СО2. На основании полученных данных были определены фазовый состав синтезированных катализаторов и численные границы количества наносимого ванадата висмута, за пределами которых формирование его структуры протекает с особенностями, влияющими на строение получаемого композита и его фотокаталитическую активность. Полученные результаты имеют практическую значимость, поскольку способствуют расширению зоны эффективного применения фотокатализаторов, проводящих химические превращения под действием видимого излучения.

A series of supported Ni phosphide bifunctional hydroisomerization catalysts (Ni2P/ZSM-23/Al2O3) was synthesized by means of Ni hypophosphite reduction at different temperatures. The structure and morphology of Ni phosphide phase were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The surface chemical analysis was performed using X-ray photoelectron spectroscopy (XPS). The hydro/dehydrogenation and acid functions of catalysts were characterized by CO chemisorption, NH3-TPD and IR-spectroscopy of adsorbed pyridine (IR-Py). The reduction of supported precursor at the temperature lying in the range of 550–650 ⁰С resulted in high activity and iso-selectivity in n-decane conversion. The reduction of the supported component at 500 ⁰C or re-reduction of ex-situ reduced and passivated catalysts at 450 ⁰C led to the formation of impurities of other Ni phosphides such as NiP and Ni5P4 and had a negative impact on n-decane conversion. Both the Brønsted acidity and Ni2P dispersion of the catalysts declined with increasing Ni2P content which were accompanied by a drop in their activity without loss of iso-selectivity.

Recently, it was shown that ZrO2 catalysts, the activity of which is determined by the number of oxygen vacancies, are promising for dehydrogenation of light alkanes. In this study, environments with different redox properties were used to obtain a series of ZrO2 catalysts with different stoichiometric composition. To this end, samples of tetragonal ZrO2 with the particle size of 8-10 nm were synthesized by laser vaporization in an Ar and He atmosphere with the addition of H-2 or O-2. According to NH3-TPD data, the number of oxygen vacancies decreases in the series ZrO2 (He + H-2) > ZrO2 (Ar + H-2) > ZrO2 (He) > ZrO2 (Ar) similar to ZrO2 (Ar + O-2). The synthesized samples show high conversions of iso-C4H10 and selectivities to iso-C4H8. However, an increase in the number of oxygen vacancies in the samples leads to a less pronounced effect of the catalyst activation during the reaction. Thus, the highest conversion of 52 % and selectivity of 86 % were obtained for the ZrO2 (He + H-2) sample, for which the activation was not observed at all. Therewith, the specific yield of isobutylene for the samples synthesized in hydrogen-containing atmospheres was higher compared to the samples obtained in oxidizing and inert atmospheres over the entire reaction time. Thus, the use of a reducing atmosphere during the synthesis is an efficient method for enhancing the catalytic performance of ZrO2 dehydrogenation catalysts. The results obtained indicate also that the catalytic performance of such catalysts is determined primarily by the number of oxygen vacancies rather than by reducibility of the oxide, which provides a new insight into the design of ZrO2 dehydrogenation catalysts.

The photoluminescent properties of dopant-free t-ZrO 2 nanoparticles, both in their as-synthesized form and after dehydroxylation, were studied in this work. Nanoparticles were prepared via the laser vaporization synthesis in flow argon. In combination with the study of the morphology, structure, thermal, and optical properties of nanoparticles, this made it possible to establish individual contributions of defects related to oxygen, impurities, and OH-groups. At selective excitation of dopant-free t-ZrO 2 nanoparticles, the intrinsic and extrinsic defects were detected. The luminescence spectra indicate that defects are associated with oxygen vacancies and Ti3+ impurities. For the first time, surface OH-groups were identified in t-ZrO 2 nanoparticles. The intense luminescence of OH-groups in ZrO2 nanoparticles manifests itself in the blue-green region of the spectrum with a maximum at 416-438 nm and is most effectively excited in the band with a maximum at 340 nm. This means that when developing luminescent ZrO2-based nanomaterials for optical devices, it is necessary to control the contribution of defects and impurities, as well as the contribution of OH-groups.

В работе была охарактеризована разупорядоченная структура наночастиц металлического кобальта, полученных восстановлением Co3O4 и Co2.95Al0.05O4 in situ при различных температурах. Согласно просвечивающей электронной микроскопии отдельные частицы имеют полосчатый контраст, т.е. состоят из пластинчатых доменов с различной структурой. Основной особенностью рентгеновских дифракционных картин является анизотропное уширение пиков. Анализ методом Ритвельда показал, что модель, представленная гомогенными частицами с гпу и/или гцк структурами дает плохое соответствие с экспериментом. Методом расчета рентгеновских дифракционных картин на основе статистических моделей 1D разупорядоченных кристаллов было показано, что частицы металлического кобальта гетерогенны и состоят из пластинчатых доменов с гпу и гцк структурой. Были определены зависимости параметров дифракционных пиков от толщины доменов двух типов, и построены соответствующие калибровочные графики. Для двух серий металлических частиц были определены фазовый состав и параметры доменной структуры при увеличении температуры.

The disordered structure of metallic cobalt nanoparticles prepared by the in situ Co3O4 and Co2.95Al0.05O4 reduction at different temperatures is characterized. According to the transmission electron microscopy data, individual particles have a stripe contrast indicating that they consist of plate-like domains with different structures. The main feature of the recorded XRD patterns is the anisotropic peak broadening. The Rietveld analysis shows that the model represented by homogeneous particles with hcp and/or fcc structures does not agree well with the experiment. The XRD patterns calculated using statistical models of 1D disordered crystals show that metallic cobalt particles are heterogeneous and consist of plate-like domains with hcp and fcc structures. The dependences of diffraction peak parameters on the thickness of two types of domains are determined; the corresponding calibration graphs are constructed. The phase composition and domain structure parameters are determined as functions of temperature for two series of metallic particles.

The growing demand for luminescent nanomaterials intended for various applications increases the necessity to develop and improve approaches to the creation of highly efficient nanosized phosphors. In current study, an approach to enhancing the efficiency of red luminescence of monoclinic Y2O3:Eu3+ with the particle size of similar to 20 nm by creating the oxygen-enriched environment during the gas-phase synthesis was developed. To investigate the effect of oxygen amount during the synthesis on characteristics of the phosphor, a series of nanostructured Y2O3:Eu3+ with the addition of 0-40 vol% O-2 to the main buffer gas Ar was synthesized by laser vaporization. It is shown that the amount of added O-2 exerts virtually no effect on the phase composition and particle size, but significantly improves the luminescent characteristics of Y2O3:Eu3+. Thus, the addition of 30 vol% O-2 leads to virtually a 20-fold growth in the photoluminescence (PL) intensity caused by D-5(0)-> F-7(0-4) transitions in Eu3+ and an increase in the absolute PL quantum yield from 3% to 53% (lambda(ex) = 395 nm) compared to the sample synthesized without O-2. The addition of oxygen also improves the emission color coordinates from (0.571, 0.320) to (0.630, 0.322) due to the removal of a considerable fraction of oxygen vacancies. The synthesized nanopowders are shown to be highly stable: upon storage under ambient conditions for two years. Quantum yield (QY) of the samples decreases by less than 2%. It is expected that the key features underlying the proposed approach will be useful for various methods used to synthesize oxide nanophosphors.

Aerogel materials attract a growing interest due to their delicate structure and unique textural properties. However, heat treatment of such materials at elevated temperatures inevitably causes the collapse of their structure. Deposition of a carbon coating is known to improve the thermal stability of nanocrystalline oxides due to the formation of a core-shell structure. In this study, calcium aluminate aerogels with a mayenite stoichiometry were covered with a carbon shell, and resorcinol was used as a carbon source. Transmission electron microscopy confirmed the presence of the carbon shell in the samples thermally treated in an argon flow. As revealed by X-ray diffraction analysis, the carbon shell allowed stabilizing the mayenite phase. When the sample was prepared using the highest resorcinol concentration (0.7 mol/mol), calcined in argon at 1100 degrees C and annealed in air at 500 degrees C, its specific surface area value was as high as 72 m2/g, which significantly exceeds that of pure aerogel-prepared calcium aluminate after the same treatment. Thus, covering the finely dispersed calcium aluminates with the carbon shell appears to be an efficient method to stabilize their phase composition and textural characteristics during the calcination at high temperatures required for the mayenite conversion to chemically active forms.

The paper presents an investigation into the physicochemical and catalytic properties of CuBO2 oxides with a delafossite/crednerite-type structure, exploring the dependence on the nature of the B3+ cation (Mn3+, Co3+, Cr3+, Fe3+, and Ga3+). The catalytic properties in CO oxidation were examined in conjunction with structural data, surface composition, the distribution of surface metal states, and the reactivity of oxygen. The selection of synthesis conditions was tailored to yield crystallized CuBO2 particles exhibiting either a delafossite or crednerite structure, depending on the nature of the B3+ cation nature. Thermal stability increases in the following order: CuMnO2 < CuCrO2 ≈ CuFeO2 ≈ CuCoO2 < CuGaO2. Heating of all the studied mixed oxides in the CO + O2 mixture to 250 °C did not cause changes in the phase composition and structural characteristics. The highest catalytic activity near room temperature was observed for CuMnO2 and CuCrO2. A correlation was established between the catalytic activity of CuBO2 and the reactivity of surface oxygen, presumably attributed to the pronounced lability of the redox transitions between the Cu1+/Cu2+ and Bn+/Bm+ pairs. The transformation of the delafossite/crednerite into a spinel structure can cause both deactivation (B = Fe and Co) and significant catalytic activation (B = Mn and Cr) in low-temperature CO oxidation.

Specific features of the mayenite formation from hydroxide precursors with different phase compositions as well as the evolution of the surface morphology during this process were studied. The synthesis temperature was found to have a substantial effect on the phase composition of the obtained Ca-Al hydroxide precursors with Ca:Al = 6:7 stoichiometry. Practically no reaction between calcium hydroxide and aluminum oxyhydroxide was observed at 25 degrees C whereas synthesis at 75 degrees C led to crystallization of a mixed hydroxide katoite Ca3Al2(OH)(12). It was demonstrated that in the latter case the decomposition of the katoite phase at 300 degrees C results in the formation of the mayenite phase with the 3-4 times higher yield than in the former case. When the sample formed from katoite was calcined further at 500 degrees C, the mayenite average crystallite size decreased from 95 to less than 30 nm. This sample featured the highest surface area of 83 m(2)/g with mayenite as the predominating crystalline phase. Katoite appears to be the key intermediate in the production of finely dispersed mayenite by this method. Calcination at 600-900 degrees C leads to gradual mayenite sintering with the decrease of the surface area and appearance of new large pores that can be easily observed in microscopic images.

The photocatalytic activity of 2D/2D/0D heterostructures based on few-layer black phosphorus (FLBP) g-C3N4/FLBP/Co2P in the reaction of photocatalytic hydrogen formation from an aqueous solution of triethanolamine under under visible light irradiation (400 nm) was studied for the first time. An original method for the preparation of the g‑C3N4/FLBP/Co2P composite photocatalyst is proposed, which consists of the solvothermal synthesis of cobalt phosphide Co2P nanoparticles, their immobilization on the surface of FLBP, and subsequent mixing of the FLBP/Co2P heterostructure with g‑C3N4. The synthesized photocatalysts were characterized by physicochemical analytical methods (X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission microscopy, energy-dispersive X-ray spectroscopy). The hydrogen evolution rate in the presence of the g‑C3N4/FLBP/Co2P heterostructure was 0.09 mmol g_cat^ - 1 h–1, which is 25 times higher than the same characteristic for the unmodified g‑C3N4 sample. The obtained numerical values of the photocatalytic activity are at the level of the literature values.

In this work, NiO and NiO–SiO2 are studied using X-ray diffraction and the method of atomic-pair radial distribution. Using X-ray phase analysis, it is determined that the sizes of NiO particles have a coherent-scattering region of more than 100 nm, while the NiO–SiO2 sample has particle sizes of about 2–3 nm. However, full-profile simulation using the Rietveld method does not allow one to describe the effects observed during diffraction: asymmetry of the peaks, the appearance of an additional shoulder of peak 111 in the region of small angles; therefore, the method of atomic-pair radial distribution is used to analyze the structure. When simulating the experimental curve of the atomic-pair radial distribution, 3 different models are used: pure NiO, a mixture of NiO and Ni2SiO4, as well as a modified NiO model with Si embedded into the crystal lattice. The latter model is created based on the assumption of the incorporation of silicon into the NiO structure, as can be evidenced by the X-ray diffraction data. According to the results of simulation of the curve of the atomic-pair radial distribution, it is the latter model that provides the best description of the observed effects: a significantly increased unit-cell parameter in comparison with the sample without the addition of SiO2, as well as decreased cation–oxygen distances in the structure while the distances between cations are increased.

Ternary oxide of silver, copper and manganese (Ag2CuMnO4) with delafossite-type structure demonstrates excellent catalytic activity in the reaction of CO oxidation at room temperature and even below. To prepare delafossite-based catalyst the hydrothermal approach using metal nitrates in alkaline solution with an excess of peroxodisulphate was applied. X-ray diffraction pattern of Ag2CuMnO4 particles was successfully simulated taking into an account crystallite shape anisotropy, particle size distribution, the presence of stacking faults, and the lattice expansion along c axis. As-prepared Ag2CuMnO4 sample was characterized by the presence of Ag1+-, Cu2+- and Mn4+-like surface species predominantly. In situ XRD data revealed the thermal stability of delafossitetype structure in catalytic CO+O2 mixture up to 500 degrees C, while ex situ XPS showed an evident reorganization of Ag2CuMnO4 surface at markedly lower temperatures (200-250 degrees C). Heating in CO+O2 medium at 150-400 degrees C also resulted in significant catalytic activation of Ag2CuMnO4 owing to the Mn enrichment and optimization of manganese and copper electronic exchange. The low-temperature activity of Ag2CuMnO4 catalyst in CO+O2 reaction was proposed to be mainly provided by redox transitions with the participation of Cu1+/Cu2+ and Mn3+/Mn4+ couples, while the catalytic role of silver species is considered as auxiliary only. The innovation point of this work is related to the investigation of the dynamics of surface and bulk structure transformations in connection with the catalytic activation of delafossite particles for the low-temperature oxidation.

Graphitic carbon nitride (g-C3N4) modified with bromine and iodine was synthesized by a novel two-stage technique that included hydrothermal pre-treatment of melamine and its calcination in a mixture with ammonium halide. Prepared photocatalysts were tested by a set of methods including X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermal gravimetric analysis (TGA), low temperature nitrogen adsorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CVA), impedance spectroscopy, and the Mott Schottky method. All the photocatalysts were studied in the photocatalytic hydrogen production from triethanolamine (TEOA) under visible light irradiation (l = 428 nm). The most active photocatalyst was prepared from a mixture of 50% NH4I and 50% melamine. Its catalytic activity (2120 mmol g-1 h-1) was 35 times higher than that of the catalyst synthesized by the simple calcination of melamine. The highest short-circuit current density of 2.7 mA/cm2 was obtained with a sample synthesized from the mixture of 80% NH4Br and 20% melamine.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

In this work, materials based on graphite-like carbon nitride were synthesized by thermal treatment of a mixture of melamine and urea and the effect of synthesis conditions on the photocatalytic activity of the samples was studied. As a cocatalyst, platinum (1 wt. %) was deposited on the surface of the synthesized g‑C3N4 samples. The photocatalysts were characterized by X-ray phase analysis, diffuse reflectance UV-vis spectro-scopy in the UV and visible range, and low-temperature nitrogen adsorption. Photocatalytic activity was determined in the reaction of hydrogen evolution from an aqueous solution of triethanolamine (10 vol. %) under visible light irradiation (λ = 425 nm). The optimal conditions for the synthesis of the photocatalyst 1% Pt/g-C3N4, obtained by calcination of a mixture of melamine and urea (1 : 3), were found, using which the rate of H2 evolution was 5.0 mmol g–1 h–1 with an apparent quantum efficiency of 2.5%. The developed synthetic approach makes it possible to obtain highly active catalysts due to the formation of an intermediate supramolecular melamine-cyanuric acid complex during the synthesis, which, upon further heating, turns into g-C3N4, which is characterized by a high specific surface area exceeding 100 m2 g–1.

In this work, the correlation between structure, composition, surface state, and CO oxidation catalytic activity of the ternary oxide Ag2CuMnO4 was studied. The stepwise surface and structure modification was implemented with the use of pretreatments in different media at various temperatures. It allowed investigating the nature of low-temperature catalytic activity and determining the conditions for the realization of the most efficient route of CO oxidation. The investigation of the interaction of the ternary oxide with carbon monoxide was carried out using TPR-CO, in situ XRD, and ex situ XPS methods. Ex situ XPS was applied to study the evolution of composition and charge state of the ternary oxide components on the surface of particles during the interaction with the reaction CO + O-2 mixture versus the temperature, preventing the contact of the sample with the air. Ex situ XPS data established the presence of prominent charge transfer between copper and manganese within the delafossite structure during the interaction with CO. The results of catalytic measurements revealed that the most active Ag2CuMnO4 state can be achieved by heating in the inert or in the reaction mixture at 250 degrees C. Under these conditions, the enhancement of an interlayer charge transfer occurs at the expense of Cu+ ions accumulation in the linear-coordinated cation layer. The heating above 300 degrees C led to the appearance of tetrahedral Cu+ cations within the "proto-spinel" entities determining the drop in catalytic activity. The data obtained outline the importance of linear and octahedral charge transfer for low-temperature CO oxidation activity.