Beata Zielińska

Photocatalytic hydrogen generation over alkali niobates in the presence of organic compounds

Photocatalytic hydrogen generation over alkali niobates in the presence of organic compounds The photocatalytic efficiency of alkali niobate-based compounds (Li, Na, K) for hydrogen generation has been investigated. The systematic study showed that the highest photocatalytic activity was observed in the case of Na/Nb2O5 catalyst which contained sodium niobate (NaNbO3) phase and that the most efficient electron donor for hydrogen generation was formic acid. In addition, the effect of organic donor (HCOOH) concentration on the amount of the evolved hydrogen was studied.

Photocatalytic performance of titania nanospheres deposited on graphene in coumarin oxidation reaction

In this paper, we present a study on enhanced photocatalytic performance of TiO2 nanospheres deposited on graphene (n-TiO2-G) in a process of coumarin oxidation. The enhancement of the photoactivity has been observed in respect to commercial TiO2 P25. The presented material was prepared in two steps: (i) hydrolysis of titanium (IV) butoxide (TBT) in ethanol solution with simultaneous deposition on graphene oxide (GO) and (ii) calcination of TiO2-GO to form anatase-TiO2 and reduce GO to graphene. The nanomaterial was characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), Fourier-Transformed Infrared spectroscopy and Raman spectroscopy. In the presented photocatalytic process the fluorescence was used to detect •OH formed on a photo-illuminated n-TiO2-G surface using coumarin which readily reacted with •OH to produce highly fluorescent 7-hydroxycoumarin.

Synthesis and Characterization of K-Ta Mixed Oxides for Hydrogen Generation in Photocatalysis

K-Ta mixed oxides photocatalysts have been prepared by impregnation followed by calcination. The influence of the reaction temperature (450°C–900°C) on the phase formation, crystal morphology, and photocatalytic activity in hydrogen generation of the produced materials was investigated. The detailed analysis has revealed that all products exhibit high crystallinity and irregular structure. Moreover, two different crystal structures of potassium tantalates such as KTaO3 and K2Ta4O11 were obtained. It was also found that the sample composed of KTaO3 and traces of unreacted Ta2O5 (annealed at 600°C) exhibits the highest activity in the reaction of photocatalytic hydrogen generation. The crystallographic phases, optical and vibronic properties were examined by X-ray diffraction (XRD) and diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic methods, respectively. Morphology and chemical composition of the produced samples were studied using a high-resolution transmission electron microscope (HR-TEM) and an energy dispersive X-ray spectrometer (EDX) as its mode.

Reduced graphene oxide nanocomposites with different diameters and crystallinity of TiO2 nanoparticles – synthesis, characterization and photocatalytic activity

Abstract TiO2-reduced graphene oxide nanocomposites with different diameters and crystallinity of titania nanoparticles were synthesized via the sol-gel method followed by calcination in air or treatment under vacuum. The materials were characterized with transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, photoluminescence spectroscopy and diffuse-reflectance UV–vis spectroscopy. The photocatalytic activity of the resulting materials was examined in the process of phenol decomposition under UV–vis light irradiation. The influences of TiO2 loading and calcination treatment on photocatalytic activity of the composites were investigated. It was found that higher TiO2 concentrations resulted in higher photocatalytic activity. This is in agreement with the band gap energy values, as lower visible light absorption and higher Eg values were obtained for the samples prepared with higher TiO2 loading. Furthermore, photoactivity was affected by the calcination treatment. Higher activity under UV–vis was shown by the samples calcinated under vacuum, which was attributed to the better crystallinity compared to the samples treated with air.

Photocatalytic hydrogen generation with Ag-loaded LiNbO3

In this contribiution LiNbO3 and Ag-loaded LiNbO3 photocatalysts were tested in the reaction of hydrogen evolution. The silver modified samples contained different loading of co-catalyst in the range of 0.5–4 wt%. It was essential to optimize the sample composition to achieve an efficient hydrogen evolution. The optimal sample contained 2 wt% of silver. The detailed analysis indicated that silver was deposited on the surface of LiNbO3 in the form of Ag2O. Therefore, it is supposed that Ag2O was responsible for the enhanced photocatalytic activity in the studied reaction. The crystallographic phases and optical and vibronic properties were examined by X-ray diffraction (XRD) and diffuse reflectance (DR) UV-Vis and resonance Raman spectroscopic methods, respectively. Morphology of the produced samples were studied using a high-resolution transmission electron microscope (HRTEM).

Time Dependent Influence of Rotating Magnetic Field on Bacterial Cellulose

The aim of the study was to assess the influence of rotating magnetic field (RMF) on the morphology, physicochemical properties, and the water holding capacity of bacterial cellulose (BC) synthetized by Gluconacetobacter xylinus. The cultures of G. xylinus were exposed to RMF of frequency that equals 50 Hz and magnetic induction 34 mT for 3, 5, and 7 days during cultivation at 28°C in the customized RMF exposure system. It was revealed that BC exposed for 3 days to RMF exhibited the highest water retention capacity as compared to the samples exposed for 5 and 7 days. The observation was confirmed for both the control and RMF exposed BC. It was proved that the BC exposed samples showed up to 26% higher water retention capacity as compared to the control samples. These samples also required the highest temperature to release the water molecules. Such findings agreed with the observation via SEM examination which revealed that the structure of BC synthesized for 7 days was more compacted than the sample exposed to RMF for 3 days. Furthermore, the analysis of 2D correlation of Fourier transform infrared spectra demonstrated the impact of RMF exposure on the dynamics of BC microfibers crystallinity formation.

Preparation, characterization and photocatalytic activity of Co3O4/LiNbO3 composite

AbstractThe Co3O4/LiNbO3 composites were synthesized by impregnation of LiNbO3 in an aqueous solution of cobalt nitrate and next by calcination at 400°C. The activity of produced samples has been investigated in the reaction of photocatalytic hydrogen generation. The crystallographic phases, optical and vibronic properties were studied using X-ray diffraction (XRD), diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic techniques, respectively. The influence of cobalt content (range from 0.5 wt.% to 4 wt.%) on the photocatalytic activity of Co3O4/LiNbO3 composites for photocatalytic hydrogen generation has been investigated. Co3O4/LiNbO3 composites exhibited higher than LiNbO3 photocatalytic activity for hydrogen generation. The highest H2 evolution efficiency was observed for Co3O4/LiNbO3 composite with 3 wt.% cobalt content. The amount of H2 obtained in the presence of LiNbO3 and Co3O4/LiNbO3 (3 wt.% of cobalt content) was 1.38 µmol/min and 2.59 µmol min−1, respectively.

A Comparison of Hydrogen Storage in Pt, Pd and Pt/Pd Alloys Loaded Disordered Mesoporous Hollow Carbon Spheres

Comprehensive study to evaluate the ability of hydrogen uptake by disordered mesoporous hollow carbon spheres doped witch metal such as Pt, Pd or Pt/Pd was conducted. They were synthesized facilely using sonication and then calcination process under vacuum at the temperature of 550 °C. The effect on hydrogen sorption at neat-ambient conditions (40 °C, up to 45 bar) was thoroughly analyzed. The results clearly revealed that metal functionalization has a significant impact on the hydrogen storage capacity as the mechanism of gas uptake depends on two factors: metal type and certain size of particles. Thus, functionalized spheres adsorb hydrogen by physisorption forming metal hydrides or metal hydrides combined with hydrogen spillover effect. As a result, a sample with narrower distribution of nanoparticles and smaller specific size exhibited enhanced hydrogen uptake.

Graphitic Carbon Nitride and Titanium Dioxide Modified with 1 D and 2 D Carbon Structures for Photocatalysis

Enhancing the photocatalytic performance of graphitic carbon nitride (g-C3 N4 , GCN) and titanium dioxide (TiO2 ) has played a key role in the energy and environmental protection research community. Therefore, it is necessary to explore the synergy of both materials with carbon nanostructures for photocatalysis. Among the variety of carbon materials, graphene flakes and nanotubes, as nanoadditives to improve electron charge transfer and the optical absorption behavior in the visible-light region, have been widely explored. Thus, flake-like (2 D) and tubular (1 D) carbon structures in composition with GCN and/or TiO2 are reviewed, as are their photocatalytic response. Current trends clearly indicate that this type of molecular hybrids can be efficiently exploited in this field. This Minireview covers state-of-the-art research over the period of 2015 to 2018.

Preliminary study on the influence of UV-C irradiation on microorganism viability and polyphenol compounds content during winemaking of ‘Regent’ red grape cultivar

Abstract In this study, UV-C light was tested as an alternative method to inactivate microorganisms in the must of ‘Regent’ red grape cultivar. The control sample containing the microorganism diluted in a physiological NaCl solution was prepared to take into consideration different conditions of liquids, such as turbidity and colour. Additionally, the changes in the composition of polyphenol compounds in the ‘Regent’ must after UV-C exposure were evaluated. The viability of yeasts (Saccharomyces cerevisiae) and bacteria (Oenococcus oeni) significantly decreased with time; however, the highest decline was noted after the first hour of exposure. The polyphenol compound content was significantly lower after UV-C treatment and this was mainly the result of anthocyanin decomposition. The total content of flavan-3-ols and hydroxycinnamic acids and derivatives increased after irradiation.