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Application of a new system of solid ionic conductors based on multi-doped ceria as electrolytes for it-sofc technology- test in a single cell
No full textNanopowders of CeO2 as a major component and different rare earth oxides added as dopants were synthesized using the modified glycine-nitrate procedure (MGNP) for the purpose of fabrication of electrolytes for IT-SOFC. Synthesized nanopowder was characterized by XRPD and Raman spectroscopy. According to results, single phase solid solution of fluorite structure were evidenced. Produced powder was then subjected to sintering at 1550 ºC for 2 h in air. By SEM analysis, highly ordered microstructure of sintered sample was verified, while EDS method revealed that the sintered sample have chemical composition very similar to a nominal one. Afterwards, the ionic conductivity of the sintered sample was measured by EIS method. The highest value was obtained at 700 ºC, amounting to 1.92×10-1 Ω-1 cm-1
Ultra-low Pt loading catalyst on (Nb–Ti)2AlC support as advanced material for low-temperature fuel cell application
No full textThe oxygen reduction reaction was investigated at 10 monolayers (MLs) of Pt electrodeposited on (Nb–Ti)2AlC substrate. Following the discussion of detailed kinetics and electrodeposition optimisation in the authors’ previous paper, the focus of this research was on stability testing. Previously performed optimisation results showed the best activity shown by 10 monolayers of Pt. Catalyst characterisation was performed by scanning electron microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. SEM, EDS and XPS analysis showed that the surface was covered with a homogeneous layer of Pt. TEM analysis of a cross-section confirmed the presence of Pt layer of thickness ∼3.5 nm, corresponding to the 10 MLs of Pt. Although the mass activity for the ORR at 0.8 V vs. RHE of 37.4 A g−1 was comparable with the best one for the Pt/C benchmark, US Department of Energy Protocols revealed excellent catalyst stability – the loss of electrochemically active surface area (EASA) was found to be only 9.3%
A three-step process of manganese acquisition and storage in the microalga Chlorella sorokiniana
Get PDFMetabolism of metals in microalgae and adaptation to metal excess are of significant environmental importance. We report a three-step mechanism that the green microalga Chlorella sorokiniana activates during the acquisition of and adaptation to manganese (Mn), which is both an essential trace metal and a pollutant of waters. In the early stage, Mn2+ was mainly bound to membrane phospholipids and phosphates in released mucilage. The outer cell wall
was reorganized and lipids were accumulated, with a relative increase in lipid saturation. Intracellular redox settings were rapidly altered in the presence of Mn excess, with increased production of reactive oxygen species that resulted in lipid peroxidation and a decrease in the concentration of thiols. In the later stage, Mn2+ was chelated by polyphosphates and accumulated in the cells. The structure of the inner cell wall was modified and the redox milieu established a new balance. Polyphosphates serve as a transient Mn2+ storage ligand, as proposed previously. In the final stage, Mn was stored in multivalent Mn clusters that resemble the structure of the tetramanganese–calcium core of the oxygen-evolving complex. The present findings elucidate the bioinorganic chemistry and metabolism of Mn in microalgae, and may shed new light on water-splitting Mn clusters
TUNING OF FERROELECTRIC PROPERTIES OF BiFeO3 CERAMICS BY CATION SUBSTITUTIONS AT Bi-SITE AND Fe-SITE
Get PDFIn this study, we tried various cation substitutions at Bi-site (La3+, Eu3+) and Fesite (Nb5+
, Zr4+
) to explore their possible synergism and improvement of the
ferroelectric properties of bismuth ferrite. The cations with higher valence ought to
suppress the formation of structural defects during syntheses, such as oxygen and
bismuth vacancies. These defects are responsible for high leakage currents and low
breakdown voltages characteristic of pure BiFeO3. On the other hand, rare earth
cations at the Bi-site usually enable densification of the ceramics at a broader range
of temperatures, preventing bismuth loss and formation of defects and secondary
phases during sintering. However, dopant concentrations above 10–15 mol% may
give rise to a transition from polar, rhombohedral (R3c) to non-polar, orthorhombic
(Pnma) symmetry.
Thus, we synthesized pure and selected compositions doped BiFeO3 by a hydroevaporation method and determined the optimal calcination temperature by thermal
analyses of the precursor powders. Then we characterized ceramics samples using
X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and
polarization techniques. Although only 1 mol% Nb5+ decreased the leakage current,
it surprisingly deteriorated the ferroelectric properties of BiFeO3. Similar effect
exhibited the samples containing Zr4+ that showed no improvement compared with
undoped bismuth ferrite. On the contrary, La3+ and Eu3+ (incorporated at the Bi-site)
improved the ferroelectric properties as their concentrations increased, whereby the
samples doped with 15 mol% La exhibited higher remnant electric polarizations at
observed electric fields. The highest remnant electric polarization of 31.9 µC/cm2
at 150 kV/cm, was measured for Bi0.85La0.15Fe0.998Zr0.002O3, indicating the synergetic
effect of La3+ and Zr4+, which is limited to low Zr4+ concentrations
Application of microalga Chlorella sorokiniana in wastewater bioremediation – case of lake Robule
Get PDFHeavy metals remain a major pollutant in waters near mining sites. Water pollution is a current, longterm problem that affects plants and organisms that live in these water systems, and the effect is very harmful not only for individual species and populations, but also for the entire biological community. This study analyzed the potential of the microalga Chlorella sorokiniana in the adsorption of four selected metals: Fe, Cu, Zn and Ni, all present in high amounts in Lake Robule. This pilot study was conducted to evaluate the potential of these microalgae for possible use in future bioremediation treatment of these water. A laboratory study of metal accumulation in lake water samples lasted for 7 days, after which a total decrease in metal concentration was observed, namely Fe ~25%, Cu ~17%, and Zn ~4% on the seventh day. This study confirms the strong potential of microalgae C. sorokiniana to reduce the presence of heavy metals in conditions known for the low pH value of water with a high percentage of Fe and other heavy metals
ASSESSMENT OF PLASTIC POLLUTION OF THE SOIL ENVIRONMENT
Get PDFPlastic pollution is fast becoming a serious global environmental problem with the increase in plastic waste over recent decades. One of the first investigations of plastic and microplastic (MP) in the soil on the territory of Serbia is currently underway and is being carried out within the project "Evaluation of the microplastic in the Soils of Serbia – EMIPLAST – SoS" funded by the Science Fund of the Republic of Serbia. The aim of the research is to reveal the impact of the presence of plastic materials on soil’s main chemical, physical and biological properties. The examination of the impact of MP on the soil is being carried out through a comparative analysis of samples from localities that are and are not exposed to MP pollution. Sampling was done in three seasonal repetitions in the 2022 and will be done in the same way in 2023 in all selected plots. Microbial respiration is measured from all samples using the alkaline trap method as an indicator of microbial activity. The parameters related to the soil structure are not variable in such a short time frame, which is why they were determined at the beginning and will be determined at the end of the experimental period: mechanical composition, volumetric mass, specific mass, porosity, aggregate stability and organic matter content. Soil parameters that may affect aggregate stability such as pH, electrical conductivity and total carbon content, as well as soil nutritional status (N, P2O5, K2O, Cu, Zn, Mn and CaCO3) were determined.
These parameters are used to characterize the soil at the research sites. Preliminary results showed that some soil properties are significantly affected by the presence of plastic materials. In order to establish the level of the negative impact of microplastics on soil properties and microbial activity in the longer term, the study is ongoing
Influence of acid-base equilibria on the rate of the chemical reaction in the advanced oxidation processes: Coumarin derivatives and hydroxyl radical
No full textThe decomposition and chemical manipulation of stable aromatic pollutants into less toxic products is an
important topic for wastewater management and natural water remediation. The mechanism of the Advanced
Oxidation Process (AOPs) of 4,7-dihydroxycoumarin (4,7-DHC) and 7-hydroxycoumarin (7-HC), as examples of
stable naturally-occurring industrially-important compounds, in the presence of hydroxyl radical (HO•
) in the
aqueous solution has been analyzed using Electron Paramagnetic Resonance spectroscopy (EPR) and Quantum
Mechanics-based test for Overall Free Radical Scavenging Activity (QM-ORSA). The effect of pH values of the me-
dium on the investigated reaction mechanisms has been fully investigated. The rate constants were estimated by
the conventional transition state theory (TST) and Eckart’s method (ZCT_0). Estimated values of the overall rate
constant (koverall) higher than >4.06 × 109 M 1 s 1 at all pH values showed that both compounds undergo a
chemical transformation when exposed to HO•
. When pH increased in the range of 0–14, the koverall increased
from 4.06 × 109 to 1.11 × 1010 (4.7-DHC) and 2.09 × 109 to 1.76 × 1010 M 1s 1 (7-HC). At physiological pH =
7.4 value, 7-HC was ~1.5 times more prone to radical action, as shown by EPR and QM-ORSA, due to the
dominant anionic form. Both compounds were more reactive towards HO•
than Trolox at this pH value. The
ecotoxicity assessment of the starting compounds, intermediates and oxidation products indicated that the
formed products show lower acute and chronic toxicity effects on aquatic organisms than starting compounds,
which is a prerequisite for the development of novel AOPs procedures
Quantitative traits of white cabbage cultivars in association with two biofertilisers
Get PDFCabbage is one of the most important vegetables from the Brassicaceae family to
which biofertilisers are increasingly applied following the current trend in cabbage
organic farming. The main goal of our study was to examine whether solely
applicated biofertilisers enhance head weight and other morphological parameters
in cabbage. Experiment with three Bejo Zaden cultivars ('Farao' F 1 , 'Tiara' F 1 , and
'Excalibur' F 1 ) were conducted under the open field conditions from April to June
2019. Two different microbiological fertilisers, Organic balance and FitoHelp,
were applied foliar, six times during the vegetation period, with a battery sprayer.
After harvest, several parameters were estimated: head weight, width and height,
number of leaves, internal core height and width. The results showed the highest
value of head weight (1264.89 g), head width (15.06 cm), head height (15.57 cm),
number of leaves (22.56), internal core height (8.01 cm) and internal core width
(3.51 cm) in cultivar 'Excalibur' F1 compared to other two cultivars for fresh
market. Application of both fertilisers led to increased levels of all tested
parameters compared to the control. Furthermore, fertiliser Organic balance
showed the highest impact on all tested parameters, resulting in an increasing value
of head weight by 78.6%. This study revealed that mixed culture fertiliser showed
a greater impact in terms of head weight, number of leaves, and internal core width
compared to fertiliser containing a single strain of bacteria. Accordingly, with
an exception in head and internal core height, all examined factors showed a
statistically significant impact on tested parameters, including their interaction
Monitoring of groundwater level fluctuations at flooded area of lowland forests of the Sava River (Serbia)
Get PDFLowland pedunculate oak forests in the alluvium of the river Sava are of a great economic and ecological importance. Their growth and development features, and their survival, as well, mostly depend on soil moisture and available water. The paper deals with the influence of groundwater level on pedunculate oak forests condition in flooded area of Donji Srem. During four-year long research, the average (reference) groundwater level was determined, and extremes, the wettest and the driest year, were determined based on climate factors such as temperature and rainfalls. Deviation of the average from the reference groundwater level in the vegetation period during some years indicates possibility of risk zones presence. These zones are defined according to geostatistical analysis – ArcGIS, Kriging model and they are very significant for forestry practice, because they can predict some drought events and warn forestry experts to react in time in order to prevent big damages. Bearing in mind that investigated area is flooded, and that groundwater level is close to the soil surface, these anaerobic site conditions are obviously more suitable for another hygrophilous species than for pedunculate oak
Structural adaptibility of Haematococcus pluvialis green phase cells exposed to manganese excess
Get PDFHaematococcus pluvialis is a unicellular green alga with a complex life cycle and a
remarkable metabolic and structural adaptability that allows it to thrive in metal-infested
environments. H. pluvialis could be potentially used in the remediation of waters polluted
with metals, such as manganese (Mn). Mn is also an essential element involved in different
metabolic processes, such as photosynthesis and antioxidantive defence. Herein, we
examined morphological response of metabolically active green cell type of H. pluvialis
(microzooids) to high Mn concentrations exceeding their physiological quota. When exposed
to 1 mM Mn2+, cell viability remained stable over a 3-day period. Inductively coupled plasma
atomic emission spectroscopy showed the prompt uptake of Mn by the microzooid cells after
1 h of the treatment, with a modest increase of the concentration of Mn in the biomass at 24
h. Scanning electron microscopy revealed granular deposits on microzooid surfaces after 1
hour, likely Mn deposits, while transmission electron microscopy (TEM) micrographs
showed that some cells had wall rupture and degraded intracellular content and damaged
organelles. After 24 and 72 h, a different type of cell morphology emerged, characterized by
thickened cell wall, preserved intracellular compartments, and reduced total area of lipid
droplets. Both cell types exhibited vacuoles containing dark granules, possibly indicative of
Mn accumulations. Quantitative TEM analysis demonstrated that an excess of Mn reduced
cell cross-section and lipid droplet area while increasing vacuole cross-section and cell wall
thickness. The intricate adaptive responses of H. pluvialis to elevated Mn concentrations
exemplified by cell wall thickening, reduction in lipid droplets total area due to increased
energy demand, and the accumulation of Mn in vacuoles, exhibits the impressive structural
adaptability. Further investigation using analytical methods will provide a more profound
understanding of the metabolic dimensions of adaptive respons