Interactive Surface Chemistry of CO2 and NO2 on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

Cataloged from PDF version of article.Interactive surface chemistry of CO2 and NO2 on BaOx/Pt(111) model catalyst surfaces were investigated via X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) techniques with a particular emphasis on the competition between different adsorbates for the catalytic adsorption sites and adsorbate-induced morphological changes. After NO2 adsorption, nitrated BaO x/Pt(111) surfaces do not reveal available adsorption sites for CO2 at 323 K, irrespective of the presence/absence of exposed Pt sites on the surface. Although NO2 adsorption on thick BaO x(>10MLE)/Pt(111) overlayers at 323 K leads to the formation of predominantly nitrate species, NO2 adsorption on the corresponding carbonated surface leads to the formation of coexisting nitrates and nitrites. The presence of carbonates on BaOx/Pt(111) overlayers does not prevent NO2 uptake. Carbonated BaOx(1.5 MLE)/Pt(111) surfaces (with exposed Pt sites) obtained via CO2 adsorption can also further interact with NO2, forming surface nitrate/nitrite species, accompanied by the transformation of surface carbonates into bulk carbonate species. These results suggest that the nitrate formation process requires the presence of two adjacent unoccupied adsorption sites. It is apparent that in the presence of both NO2 and CO2, carbonate species formed on Lewis base (O2-) sites enable the formation of nitrites on Lewis acid (Ba2+) sites. Thermal aging, nitration, and carbonation have a direct impact on the morphology of the two-/three-dimensional (2D/3D) BaO x aggregates on Pt(111). While thermal aging in vacuum leads to the sintering of the BaOx domains, nitration and carbonation results in redispersion and spreading of the BaOx domains on the Pt(111) substrate. © 2013 American Chemical Society.

Direct Evidence for the Instability and Deactivation of Mixed-Oxide Systems: Influence of Surface Segregation and Subsurface Diffusion

Cataloged from PDF version of article.In the current contribution, we provide a direct demonstration of the thermally induced surface structural transformations of an alkaline-earth oxide/transition metal oxide interface that is detrimental to the essential catalytic functionality of such mixed-oxide systems toward particular reactants. The BaO(x)/TiO(2)/Pt(111) surface was chosen as a model interfacial system where the enrichment of the surface elemental composition with Ti atoms and the facile diffusion of Ba atoms into the underlying TiO(2) matrix within 523-873 K leads to the formation of perovskite type surface species (BaTiO(3)/Ba(2)TiO(4)/Ba(x)Ti(y)O(z)). At elevated temperatures (T > 973 K), excessive surface segregation of Ti atoms results in an exclusively TiO(2)/TiO(x)-terminated surface which is almost free of Ba species. Although the freshly prepared BaO(x)/TiO(2)/Pt(111) surface can strongly adsorb ubiquitous catalytic adsorbates such as NO(2) and CO(2), a thermally deactivated surface at T > 973 K practically loses all of its NO(2)/CO(2) adsorption capacity due to the deficiency of surface BaO(x) domains

Role of the Exposed Pt Active Sites and BaO2 Formation in Nox Storage Reduction Systems: A Model Catalyst Study on BaOx/Pt(111)

Cataloged from PDF version of article.BaOx(0.5 MLE - 10 MLE)/Pt(111) (MLE: monolayer equivalent) surfaces were synthesized as model NOx storage reduction (NSR) catalysts. Chemical structure, surface morphology, and the nature of the adsorbed species on BaOx/Pt(111) surfaces were studied via X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED). For theta(BaOx) = 2.5 MLE) were found to be amorphous. Extensive NO2 adsorption on BaOx(10 MLE)/Pt(111) yields predominantly nitrate species that decompose at higher temperatures through the formation of nitrites. Nitrate decomposition occurs on BaOx(10 MLE)/Pt(111) in two successive steps: (1) NO(g) evolution and BaO2 formation at 650 K and (2) NO(g) + O-2(g) evolution at 700 K. O-2(g) treatment of the BaOx(10 MLE)/Pt(111) surface at 873 K facilitates the BaO2 formation and results in the agglomeration of BaOx domains leading to the generation of exposed Pt(111) surface sites. BaO2 formed on BaOx(10 MLE)/Pt(111) is stable even after annealing at 1073 K, whereas on thinner films (theta(BaOx) = 2.5 MLE), BaO2 partially decomposes into BaOx indicating that small BaO2 clusters in close proximity of the exposed Pt(111) sites are prone to decomposition. Nitrate decomposition temperature decreases monotonically from 550 to 375 K with decreasing BaOx coverage within theta(BaOx) = 0.5 to 1.0 MLE. Nitrate decomposition occurs at a rather constant temperature range of 650-700 K for thicker BaOx overlayers (2.5 MLE < theta(BaOx) < 10 MLE). These two distinctly characteristic BaOx-coverage-dependent nitrate decomposition regimes are in very good agreement with the observation of the so-called "surface" and "bulk" barium nitrates previously reported for realistic NSR catalysts, clearly demonstrating the strong dependence of the nitrate thermal stability on the NOx storage domain size

Are Au nanoparticles on oxygen free supports catalytically active?

Gold nanoparticles Au NPs on oxygen free supports were examined using near ambient pressure X ray photoelectron spectroscopy NAP XPS under CO oxidation conditions, and ex situ using scanning electron microscopy SEM and transmission electron microscopy TEM . Our observations demonstrate that Au NPs supported on carbon materials are inactive, regardless of the preparation method. Ozone O3 treatment of carbon supports leads oxygen functionalization of the supports. When subsequently exposed to a CO feed, CO is oxidized by the functionalized sites of the carbon support via a stoichiometric pathway. Microscopy reveals that the reaction with CO does not change the morphology of the Au NPs. In situ XPS reveals that the O3 treatment gives rise to additional Au 4f and O 1s peaks at binding energies of 85.25 85.6 eV and 529.4 530 eV, respectively, which are assigned to the presence of Au oxide. A surface oxide phase is formed during the activation of Au NPs supported on Au foil by O3 treatment. However, this phase decomposes in vacuum and the remaining low coordinative atoms do not have sufficient catalytic properties to oxidize CO, so the size reduction of Au NPs and or oxidation of Au NPs is not sufficient to activate A

Oxygen transport in Pr nickelates: Elucidation of atomic-scale features

Pr2NiO4+δ oxide with a layered Ruddlesden–Popper structure is a promising material for SOFC cathodes and oxygen separation membranes due to a high oxygen mobility provided by the cooperative mechanism of oxygen migration involving both interstitial oxygen species and apical oxygen of the NiO6 octahedra. Doping by Ca improves thermodynamic stability and increases electronic conductivity of Pr2 − xCaxNiO4+δ, but decreases oxygen mobility due to decreasing the oxygen excess and appearing of 1–2 additional slow diffusion channels at x ≥ 0.4, probably, due to hampering of cooperative mechanism of migration. However, atomic-scale features of these materials determining oxygen migration require further studies. In this work characteristics of oxygen diffusion in Pr2 − xCaxNiO4+δ (x = 0–0.6) are compared with results of the surface analysis by X-ray photoelectron spectroscopy and modeling of the interstitial oxygen migration by the plane-wave density functional theory calculations. According to the X-ray photoelectron spectroscopy data, the surface is enriched by Pr for undoped sample and by Ca for doped ones. The O1s peak at ~531 eV corresponding to a weakly bound form of surface oxygen located at Pr cations disappears at ~500 °C. Migration of interstitial oxygen was modeled for a I4/mmm phase of Pr2NiO4+δ. The interstitial oxygen anion repulses the apical one in the NiO6 octahedra pushing it into the tetrahedral site between Pr cations. The calculated activation barrier of this migration is equal to 0.585 eV, which reasonably agrees with the experimental value of 0.83 eV obtained by the oxygen isotope exchange method. At the same time, for the model compound Ca2NiO4+δ, obtained by isomorphic substitution of Pr by Ca in Pr2NiO4+δ, calculations implied formation of the peroxide ion comprised of interstitial and lattice oxygen species not revealed in the case of incomplete substitution (up to PrCaNiO4+δ composition). Hence, calculations in the framework of the plane-wave density functional theory provide a realistic estimation of specificity of oxygen migration features in Pr2NiO4+δ doped by alkaline-earth metals. © 2019 Elsevier B.V.Russian Science Foundation, RSF: 16-13-00112Support by Russian Science Foundation (Project 16-13-00112 ) is gratefully acknowledged

Constructing g-C3N4/Cd1−xZnxS-Based Heterostructures for Efficient Hydrogen Production under Visible Light

Two types of photocatalysts, 1%Pt/Cd1−x Znx S/g-C3 N4 (x = 0.2–0.3) and Cd1−x Znx S/1% Pt/g-C3 N4 (x = 0.2–0.3), were synthesized by varying the deposition order of platinum, and a solid solution of cadmium and zinc sulfides onto the surface of g-C3 N4. The characterization of photo-catalysts showed that, for 1%Pt/Cd1−x Znx S/g-C3 N4, small platinum particles were deposited onto a solid solution of cadmium and zinc sulfides; in the case of Cd1−x Znx S/1%Pt/g-C3 N4, enlarged platinum clusters were located on the surface of graphitic carbon nitride. Based on the structure of the photocatalysts, we assumed that, in the first case, type II heterojunctions and, in the latter case, S-scheme heterojunctions were realized. The activity of the synthesized samples was tested in hydrogen evolution from triethanolamine (TEOA) basic solution under visible light (λ = 450 nm). A remarkable increase in hydrogen evolution rate compared to single-phase platinized 1%Pt/Cd1−x Znx S photocat-alysts was observed only in the case of ternary photocatalysts with platinum located on the g-C3 N4 surface, Cd1−x Znx S/1%Pt/g-C3 N4. Thus, we proved using kinetic experiments and characterization techniques that, for composite photocatalysts based on Cd1−x Znx S and g-C3 N4, the formation of the S-scheme mechanism is more favorable than that for type II heterojunction. The highest activity, 2.5 mmol H2 g−1 h−1, with an apparent quantum efficiency equal to 6.0% at a wavelength of 450 nm was achieved by sample 20% Cd0.8 Zn0.2 S/1% Pt/g-C3 N4. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This work was supported by the Ministry of Science and Higher Education of the Russian Federation within the governmental order for Boreskov Institute of Catalysis (project AAAA-A21-121011390009-1) and was also funded by the Russian Foundation for Basic Research (project No. 20-33-70086). A.S.V. and I.A.W. thank Minobrnauki research project FEUZ-2020-0059 for financial support

КОМПЬЮТЕРНАЯ ТОМОГРАФИЯ В ДИАГНОСТИКЕ И ДИФФЕРЕНЦИАЛЬНОЙ ДИАГНОСТИКЕ ПНЕВМОКОНИОЗА

Introduction. Pneumoconiosis is a disease caused by exposure industrial dust.The aim of the work was to determine the diagnostic effectiveness of radiation research methods in its diagnosis and systematize CT semiotics.Materials and methods. 105 mining and metallurgical workers were surveyed. All patients underwent a clinical and radiological examination.Results. In addition to focal and interstitial changes, nodular changes were detected, and the presence of a cavity was not always a sign of tuberculosis. The sensitivity of CT was 98,94%, the specificity was 90,0%.Conclusion. CT is necessary for all patients with suspected pneumoconiosis. The combination of the disseminated process in the lungs and professional harmfulness is not decisive in making a diagnosis, a comprehensive approach is necessary.Введение. Пневмокониоз — профессиональное заболевание от воздействия промышленной пыли.Цель работы: определить диагностическую эффективность лучевых методов исследования в его диагностике и систематизировать КТ-семиотику.Материалы и методы. Обследовано 105 работников горнодобывающей промышленности и металлургии. Всем пациентам проведено комплексное клинико-лучевое обследование.Результаты. Кроме очаговых и интерстициальных изменений, определялись узловые формы, причем наличие полости не всегда являлось признаком присоединения туберкулеза. Чувствительность КТ составила 98,94%, специфичность — 90,0%.Заключение. Необходимо проведение КТ пациентам при подозрении на пневмокониоз. У пациентов с диссеминацией наличие профессиональной вредности не является определяющим критерием в постановке диагноза, необходим комплексный подход

Бактерицидная эффективность излучения светодиода с длиной волны 272 нм в отношении госпитального штамма Klebsiella pneumoniae

Relevance. Currently, the use of ultraviolet (UV) radiation for the disinfection of objects and the treatment for infectious diseases is considered as a promising alternative to chemical biocides and antibiotics. Shortwave — UV-C and UV-B -light emitting diodes (LED) are a relatively new type of UV radiation sources and potentially able to meet the requirements of current medical technologies. However, their possibilities for the treatment of wounds and infectious diseases have not been practically researched to date, which determines the relevance of experiments aimed at studying the biocidal and therapeutic properties of shortwavelength UV LEDs.Purpose. OF STUDY To evaluate the bactericidal efficacy of 272 nm LED radiation against hospital strains of Klebsiella pneumoniae bacteria characterized by multidrug resistance.Materials and Methods. The studies were carried out with an experimental sample of the LED apparatus for UV irradiation. In the irradiator of the device, 5 LEDs are installed with a maximum radiation at a wavelength of 272 nm and a total electrical power of 10 watts. The UV radiation dose achieved in one irradiation session (12 seconds) at a distance of 10 cm from the irradiator was 8 mJ/cm2 . In the experiments, a hospital strain of the bacterium Klebsiella pneumoniae, isolated from the patient’s blood, was used. The strain was characterized by multidrug resistance. A daily culture suspension of K. pneumoniae with a concentration of 108 CFU/ml in a volume of 100 µl was transferred into a Petri dish with a diameter of 9 cm with meat-peptone agar and evenly distributed over a surface with a diameter of 8 cm. Petri dishes were irradiated from a distance of 10 cm from the irradiator. The change in the dose of UV irradiation from 4 to 80 mJ/cm2 was carried out by varying the exposure time. Studies were carried out in 4 repetitions at each dose. After irradiation, the experimental and control (without irradiation) Petri dishes were placed in a thermostat at 37ºC for 24 hours, then the grown colonies were counted. A total of 60 experiments were carried out.Results. As a result of the research, it was shown that the LED device based on five 272 nm diodes provides deep and prompt disinfection of the surface from hospital strains of K. pneumoniae bacteria characterized by multidrug resistance. A dose of UV radiation of 8 mJ/cm2 reduces surface contamination with K. pneumoniae bacteria by more than a million times (decontamination efficiency over 99.9999%). At doses less than 10 mJ/cm2 , the efficiency of the 272 nm LED device in terms of inactivation of K. pneumoniae bacteria is 3–4 times higher than the bactericidal efficiency of mercury lamps.Conclusion.The prospects of using UV devices based on LEDs with a maximum radiation at a wavelength of 272 nm in systems for the operational disinfection of massively contaminated surfaces, potentially including wound surfaces, have been shown.Актуальность. В настоящее время применение ультрафиолетового (УФ) излучения для дезинфекции объектов и терапии инфекционных заболеваний рассматривается как перспективная альтернатива химическим биоцидным средствам и антибиотикам. Коротковолновые светоизлучающие диоды в спектральном диапазоне 200–280 нм и 280–315 нм являются сравнительно новым типом источников УФ излучения и потенциально способны удовлетворить требованиям актуальных медицинских технологий. Однако их возможности для лечения ран и инфекционных заболеваний на сегодняшний день практически не исследованы, что определяет актуальность экспериментов, направленных на изучение биоцидных и терапевтических свойств коротковолновых УФ светодиодов.Цель исследования. Оценить бактерицидную эффективность излучения светодиода с длиной волны 272 нм (272 нм светодиод) в отношении госпитальных штаммов бактерий Klebsiella pneumoniae, характеризующихся множественной лекарственной устойчивостью.Материал и методы. Исследования выполнены с использованием экспериментального образца светодиодного аппарата УФ облучения с максимумом излучения при длине волны 272 нм и суммарной электрической мощностью 10 Вт. Доза УФ излучения (энергетическая экспозиция), достигаемая за один сеанс облучения (12 секунд) на расстоянии 10 см от облучателя, составляла 8 мДж/см2 . В экспериментах использовали госпитальный штамм бактерии Klebsiella pneumoniae, выделенный из крови больного. Штамм характеризовался множественной лекарственной устойчивостью. Суспензию суточной культуры K. pneumoniae с концентрацией 108 КОЕ/мл в объеме 100 мкл переносили в чашку Петри диаметром 9 см с мясопептонным агаром и равномерно распределяли по поверхности диаметром 8 см. Чашки Петри облучали с расстояния 10 см от облучателя. Изменение дозы УФ облучения от 4 до 80 мДж/см2 осуществляли варьированием продолжительности облучения. После облучения экспериментальные и контрольные (без облучения) чашки Петри помещали в термостат при 37°С на 24 часа, а затем проводили подсчет выросших колоний. Всего проведено 60 экспериментов.Результаты. В результате исследований показано, что светодиодный аппарат на основе пяти 272 нм светодиодов обеспечивает глубокое и оперативное обеззараживание поверхности от госпитальных штаммов бактерий K. pneumoniae, характеризующихся множественной лекарственной устойчивостью. Доза УФ излучения, равная 8 мДж/см2 , снижает контаминацию поверхности бактериями K. pneumoniae более чем в миллион раз (эффективность обеззараживания более 99,9999%). При дозах менее 10 мДж/см2 эффективность 272 нм светодиодного аппарата в отношении инактивации бактерий K. pneumoniae на 3–4 порядка выше бактерицидной эффективности ртутных ламп.Вывод. Показана перспективность применения ультрафиолетовых аппаратов на основе светодиодов с максимумом излучения на длине волны 272 нм в системах оперативного обеззараживания массивно контаминированных поверхностей, потенциально включая и раневые поверхности

Морфологические изменения сетчатки при воздействии лазерным излучением пороговых интенсивностей с длиной волны 450 нм и их коррекция синтетическим дипептидом

The analysis of alterations retina of during exposure of threshold laser intensity and opportunities to correct it by synthethic dipeptid. The material and method: 23 rabbits were included in the experiment. Recived matherial was investigated with help of light and electron microscopy. All layers of retina were damaged during laser exposure. The usage of synthethic dipeptide reduced laser damage. Synthethic dipeptid have retinoprotection abilities.Изучены изменения сетчатой оболочки глаза при воздействии лазерным излучением пороговых интенсивностей и возможности их коррекции синтетическим дипептидом. Эксперимент проводился на 23 кроликах. Полученный материал исследовался с помощью методик световой и электронной микроскопии. При лазерном воздействии отмечалось повреждение всех слоев сетчатки. На фоне применения препарата наблюдалось снижение повреждающего влияния, что свидетельствует о наличии у дипептида ретинопротекторных свойств