Precipitated K-promoted Co-Mn-Al mixed oxides for direct NO decomposition: Preparation and properties

Direct decomposition of nitric oxide (NO) proceeds over Co-Mn-Al mixed oxides promoted by potassium. In this study, answers to the following questions have been searched: Do the properties of the K-promoted Co-Mn-Al catalysts prepared by different methods differ from each other? The K-precipitated Co-Mn-Al oxide catalysts were prepared by the precipitation of metal nitrates with a solution of K2CO3/KOH, followed by the washing of the precipitate to different degrees of residual K amounts, and by cthe alcination of the precursors at 500 degrees C. The properties of the prepared catalysts were compared with those of the best catalyst prepared by the K-impregnation of a wet cake of Co-Mn-Al oxide precursors. The solids were characterized by chemical analysis, DTG, XRD, N-2 physisorption, FTIR, temperature programmed reduction (H-2-TPR), temperature programmed CO2 desorption (CO2-TPD), X-ray photoelectron spectrometry (XPS), and the species-resolved thermal alkali desorption method (SR-TAD). The washing of the K-precipitated cake resulted in decreasing the K amount in the solid, which affected the basicity, reducibility, and non-linearly catalytic activity in NO decomposition. The highest activity was found at ca 8 wt.% of K, while that of the best K-impregnated wet cake catalyst was at about 2 wt.% of K. The optimization of the cake washing conditions led to a higher catalytic activity.Web of Science97art. no. 59

Graphitic carbon nitride as a platform for the synthesis of silver nanoclusters

Graphitic carbon nitride (CN) synthetized by the thermal polycondensation of melamine at 550 degrees C for 4 h was further exfoliated by heating at 500 degrees C for 3 h. Silver cations were adsorbed on the exfoliated graphitic carbon nitride (CNE) and then reduced by sodium borohydride forming silver nanoclusters (NCs) with a size of less than 1 nm.The NCs were located on the CNE surface and did not change the CNE properties except for its pore size distribution and thereby specific surface area (SSA).The Ag NCs were able to collect the photoinduced electrons of CNE and thus reduce their recombination with the holes. It was also documented by the increase in the CNE photocatalytic activity in terms of the degradation of antibiotic Ofloxacin.This study demonstrates the ability of CNE to serve as a platform for a simple and fast synthesis of Ag NCs without any stabilizing compounds.Web of Science161art. no. 16

Co-Mn-Al mixed oxides promoted by K for direct NO decomposition: Effect of preparation parameters

Fundamental research on direct NO decomposition is still needed for the design of a sufficiently active, stable and selective catalyst. Co-based mixed oxides promoted by alkali metals are promising catalysts for direct NO decomposition, but which parameters play the key role in NO decomposition over mixed oxide catalysts? How do applied preparation conditions affect the obtained catalyst's properties? Co4MnAlOx mixed oxides promoted by potassium calcined at various conditions were tested for direct NO decomposition with the aim to determine their activity, stability and selectivity. The catalysts were prepared by co-precipitation of the corresponding nitrates and subsequently promoted by KNO3. The catalysts were characterized by atomic absorption spectrometry (AAS)/inductive coupled plasma (ICP), X-ray photoelectron spectrometry (XPS), XRD, N-2 physisorption, temperature programmed desorption of CO2 (TPD-CO2), temperature programmed reduction by hydrogen (TPR-H-2), species-resolved thermal alkali desorption (SR-TAD), work function measurement and STEM. The preparation procedure affects physico-chemical properties of the catalysts, especially those that are associated with the potassium promoter presence. The addition of K is essential for catalytic activity, as it substantially affects the catalyst reducibility and basicity-key properties of a deNO catalyst. However, SR-TAD revealed that potassium migration, redistribution and volatilization are strongly dependent on the catalyst calcination temperature-higher calcination temperature leads to potassium stabilization. It also caused the formation of new phases and thus affected the main properties-S-BET, crystallinity and residual potassium amount.Web of Science97art. no. 59

K-modified Co-Mn-Al mixed oxide-effect of calcination temperature on N2O conversion in the presence of H2O and NOx

The effect of calcination temperature (500-700 degrees C) on physico-chemical properties and catalytic activity of 2 wt. % K/Co-Mn-Al mixed oxide for N2O decomposition was investigated. Catalysts were characterized by inductively coupled plasma spectroscopy (ICP), X-ray powder diffraction (XRD), temperature-programmed reduction by hydrogen (TPR-H-2), temperature-programmed desorption of CO2 (TPD-CO2), temperature-programmed desorption of NO (TPD-NO), X-ray photoelectron spectrometry (XPS) and N-2 physisorption. It was found that the increase in calcination temperature caused gradual crystallization of Co-Mn-Al mixed oxide, which manifested itself in the decrease in Co2+/Co3+ and Mn3+/Mn4+ surface molar ratio, the increase in mean crystallite size leading to lowering of specific surface area and poorer reducibility. Higher surface K content normalized per unit surface led to the increase in surface basicity and adsorbed NO per unit surface. The effect of calcination temperature on catalytic activity was significant mainly in the presence of NOx, as the optimal calcination temperature of 500 degrees C is necessary to ensure sufficient low surface basicity, leading to the highest catalytic activity. Observed NO inhibition was caused by the formation of surface mononitrosyl species bonded to tetrahedral metal sites or nitrite species, which are stable at reaction temperatures up to 450 degrees C and block active sites for N2O decomposition.Web of Science1010art. no. 113

Synthesis of vacant graphitic carbon nitride in argon atmosphere and its utilization for photocatalytic hydrogen generation

Graphitic carbon nitride (C3N4) was synthesised from melamine at 550 degrees C for 4 h in the argon atmosphere and then was reheated for 1-3 h at 500 degrees C in argon. Two band gaps of 2.04 eV and 2.47 eV were observed in all the synthetized materials. Based on the results of elemental and photoluminescence analyses, the lower band gap was found to be caused by the formation of vacancies. Specific surface areas of the synthetized materials were 15-18 m(2)g(-1) indicating that no thermal exfoliation occurred. The photocatalytic activity of these materials was tested for hydrogen generation. The best photocatalyst showed 3 times higher performance (1547 mu mol/g) than bulk C3N4 synthetized in the air (547 mu mol/g). This higher activity was explained by the presence of carbon (V-C) and nitrogen (V-N) vacancies grouped in their big complexes 2V(C) + 2V(N) (observed by positron annihilation spectroscopy). The effect of an inert gas on the synthesis of C3N4 was demonstrated using Graham ' s law of ammonia diffusion. This study showed that the synthesis of C3N4 from nitrogen-rich precursors in the argon atmosphere led to the formation of vacancy complexes beneficial for hydrogen generation, which was not referred so far.Web of Science121art. no. 1362

DNA methylation profiles in a group of workers occupationally exposed to nanoparticles

The risk of exposure to nanoparticles (NPs) has rapidly increased during the last decade due to the vast use of nanomaterials (NMs) in many areas of human life. Despite this fact, human biomonitoring studies focused on the effect of NP exposure on DNA alterations are still rare. Furthermore, there are virtually no epigenetic data available. In this study, we investigated global and gene-specific DNA methylation profiles in a group of 20 long-term (mean 14.5 years) exposed, nanocomposite, research workers and in 20 controls. Both groups were sampled twice/day (pre-shift and post-shift) in September 2018. We applied Infinium Methylation Assay, using the Infinium MethylationEPIC BeadChips with more than 850,000 CpG loci, for identification of the DNA methylation pattern in the studied groups. Aerosol exposure monitoring, including two nanosized fractions, was also performed as proof of acute NP exposure. The obtained array data showed significant differences in methylation between the exposed and control groups related to long-term exposure, specifically 341 CpG loci were hypomethylated and 364 hypermethylated. The most significant CpG differences were mainly detected in genes involved in lipid metabolism, the immune system, lung functions, signaling pathways, cancer development and xenobiotic detoxification. In contrast, short-term acute NP exposure was not accompanied by DNA methylation changes. In summary, long-term (years) exposure to NP is associated with DNA epigenetic alterations

Preparation of Thin Layers of Ferromagnetic Semiconductors

The paper reports on the experiments of preparation Mn diluted in Silicon. Si:Mn can be a material with the potential of room temperature ferromagnetism. Si:Mn have been prepared by pulsed laser deposition of Mn target under 20 Pa of silane by ArF laser. We estimate initial temperature 1 mm above surface as 1.9 eV. The prepared supersaturated layers contain 11% of manganese atoms, and they are formed by small particles. Diffraction images show no crystallization of Mn or Si, but there are signs of formation of silicides. The prepared material is amorphous or it contains only nanosized crystals below our limit of detection. Electron paramagnetic spectra show unbounded electrons which are needed for ferromagnetic properties. By annealing to 1100 ̊C changes in the crystallization and start of silicon and manganese separation were observed

Electrical and optical characterization of layers of metal nanoparticles deposited on semiconductor substrates

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Pulsed Laser Deposition under Low Background Gas Pressure.

The nucleation of nanoparticles was applied during gold deposition onto TiO2 layers. For nucleation, up to 10 Pa of inert gas (argon) was used. Argon molecules efficiently helped to cool temperature of evolving plume and initiated the nucleation which resulted in deposition of gold nanoislands. Gold nanoparticles incorporated in TiO2 layers provided plasmonic properties. Au/TiO2 layers were used for water splitting as proved by photoelectrochemical measurements