Low-temperature Scanning Electron Microscopy Research Articles

Effect of microwave irradiation on the synthesis of zeolite with ferrierite structure: Study of acid and catalytic properties

Ferrierite zeolite (FER) was synthesized under microwave conditions while varying the microwave exposure time from 6 to 12 h. For comparison, commercial FER and a FER zeolite synthesized by the conventional hydrothermal synthesis (72 h) were studied. The structure, texture, and acidic properties of the samples were investigated by XRD, low-temperature N2 adsorption, ICP-AES, SEM, and DRIFT spectroscopy using adsorption of CO, CD3CN and pyridine as probe molecules. The catalytic characteristics of the obtained zeolites were studied in the cyclocondensation reaction of 1,2-phenylenediamine and acetone to produce 1,5-benzodiazepine. The activity of the zeolites in this reaction was found to increase with increasing microwave exposure time. The FER-MW sample synthesized in 12 h showed the best results.

Regulating pore structure of diatomite with alkali dissolution and its influence on humidity control performance

Alkali dissolution is an effective method to regulate the pore structure of porous mineral material. The main chemical composition of diatomite is amorphous SiO2, which can be dissolved in alkali dissolution. The diatomite samples with alkali dissolution treatment were systematacially characterized by the particle size analysis, low temperature nitrogen adsorption, MIP, fractal theory, SEM, TEM, XRD, FTIR and surface hydroxyl density to analyze the pore structure and surface properties. And the humidity control performance of diatomite was tested under different temperatures and relative humidities. The relationship among pore structure, surface properties and humidity control performance were analyzed. The results show that alkali dissolution can regulate the mesoporous and macroporous of diatomite, and some new microporous can generate at high alkali dosage. The specific surface area, mesoporous pore volume, proportion of macroporous volume, surface roughness, heterogeneity of pore structure and number of hydroxyl groups on the surface of diatomite are important factors which determining the humidity control performance. The humidity control performance of diatomite is positively correlated with the specific surface area, mesoporous volume, surface roughness, heterogeneity of pore structure and number of hydroxyl groups on the surface, while is negatively correlated with the proportion of macroporous volume.

The sound of lichens: ultrasonic acoustic emissions during desiccation question cavitation events in the hyphae.

Lichens are a mutualistic symbiosis between a fungus and one or more photosynthetic partners. They are photosynthetically active during desiccation until relative water contents (RWC) as low as 30% (on dry mass). Experimental evidence suggests that during desiccation, the photobionts have a higher hydration level than the surrounding fungal pseudo-tissues. Explosive cavitation events in the hyphae might cause water movements towards the photobionts. This hypothesis was tested in two foliose lichens by measurements of ultrasonic acoustic emissions (UAE), a method commonly used in vascular plants but never in lichens, and by measurements of photosystem II efficiency, water potential and RWC. Thallus structural changes were characterised by low-temperature scanning electron microscopy. The thalli were silent between 380% and 30% RWCs, i.e. when explosive cavitation events should cause movements of liquid water. Nevertheless, the thalli emitted UAE at approximately 5% RWC. Accordingly, the medullary hyphae were partially shrunk at about 15% RWC, whereas they were completely shrunk below 5% RWC. These results do not support the hypothesis of hyphal cavitation and suggest that the UAE originate from structural changes at hyphal level. The shrinking of hyphae is proposed as an adaptation to avoid cell damage at very low RWCs.

Effect of Thermal Activation on the Structure and Electrochemical Properties of Carbon Material Obtained from Walnut Shells.

A simple activation method has been used to obtain porous carbon material from walnut shells. The effect of the activation duration at 400 °C in an atmosphere with limited air access on the structural, morphological, and electrochemical properties of the porous carbon material obtained from walnut shells has been studied. Moreover, the structure and morphology of the original and activated carbon samples have been characterized by SAXS, low-temperature adsorption porosimetry, SEM, and Raman spectroscopy. Therefore, the results indicate that increasing the duration of activation at a constant temperature results in a reduction in the thickness values of interplanar spacing (d002) in a range of 0.38-0.36 nm and lateral dimensions of the graphite crystallite from 3.79 to 2.52 nm. It has been demonstrated that thermal activation allows for an approximate doubling of the specific SBET surface area of the original carbon material and contributes to the development of its mesoporous structure, with a relative mesopore content of approximately 75-78% and an average pore diameter of about 5 nm. The fractal dimension of the obtained carbon materials was calculated using the Frenkel-Halsey-Hill method; it shows that its values for thermally activated samples (2.52, 2.69) are significantly higher than for the original sample (2.17). Thus, the porous carbon materials obtained were used to fabricate electrodes for electrochemical capacitors. Electrochemical investigations of these cells in a 6 M KOH aqueous electrolyte were conducted by cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy. Consequently, it was established that the carbon material activated at 400 °C for 2 h exhibits a specific capacity of approximately 110-130 F/g at a discharge current density ranging from 4 to 100 mA/g.

Evolution of shale wetting properties under long-term CO2/brine/shale interaction: Implications for CO2 storage in shale reservoirs

In the case of Carbon Geological Storage (CGS), the wettability is one of the main parameters controlling the CO2 injection capacity and CO2 plume movement, which affects the safety of long-term CO2 storage. A full evaluation of this parameter is essential for risk evaluation and storage capacity estimation. The objective of this study was to investigate the wettability changes of shales from the Chang 7 Formation in the Ordos Basin by exposing the samples to ScCO2/brine for 10/20/30/and 60 days. The mineral composition, pore structure, chemical functional groups, and surface morphology changes of the shale were analyzed using x-ray diffractometer (XRD), low-temperature nitrogen adsorption (LN-N2), infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). In addition, the solid-drop method was used to measure the contact angle of shale samples at different times of ScCO2 soaking. The results show that after 60 days of continuous ScCO2 soaking, the shale water contact angle and chemical group peak spectrum generally show an increasing trend, which is caused by the reduction of carbonate and clay mineral content. The prolonged time of ScCO2 soaking weakens the shale's water wettability and reduces the water-locking effect (water has a sealing effect in the pore channel of the reservoir), capillary force, and the height of CO2 sequestration columns, which is favorable for shale gas extraction (a method of extracting natural gas from shale rock by CO2 fracturing), but it may increase the CO2 geological leakage risk. The results have important implications for regulating the change of shale water wettability, and this study can also better provide theoretical references for Carbon Geological Storage programs.

Coupling control of organic and inorganic rock components on porosity and pore structure of lacustrine shale with medium maturity: A case study of the Qingshankou Formation in the southern Songliao Basin

Shale components affect organic–inorganic diagenesis, control the formation and evolution of pore structure, and lead to heterogeneity of shale reservoirs. Therefore, revealing the coupling control of shale components on the porosity and pore structure is crucial for selecting the dominant lithofacies. In this study, the lacustrine shale with medium maturity in the first member of the Qingshankou Formation (Qing1 Member) in the Changling Sag, southern Songliao Basin, China, was analyzed. Using pressurized sealed original shale samples and 2-D nuclear magnetic resonance (2D-NMR) analysis, the effective porosity of shale was accurately determined. The pore structure was characterized via experiments such as low-temperature nitrogen adsorption, NMR, and scanning electron microscope (SEM) analyses. In addition, the joint influences of the shale rock components, sedimentary structure, and maturity on the porosity and pore structure were investigated. Finally, the favorable reservoirs in the lacustrine shale with medium maturity and their formation conditions were identified. Studies have shown that for lacustrine shale with medium maturity: (1) a moderate total organic carbon (TOC) content (between 1% and 2.5%) is a key factor for improving the effective porosity and the proportions of mesopores (100–1000 nm) and small-pores (30–100 nm). This is related to the generation of organic acids and the cracking of organic matter into pores. An excessive TOC content can lead to increased plasticity of the rock and filling of the pores by bitumen. (2) The porosity and pore structure are controlled by the organic matter and inorganic minerals as well as sedimentary structure. Organic matter has dual impacts on the porosity improvement related to clay minerals, promotion of clay conversion and filling of clay-related pores, and the ratio of the clay content to the TOC (Vsh/TOC) can reflect the degree of influence of organic matter, the greater the Vsh/TOC ratio is, the greater the effective porosity and proportion of micropores are. (3) Organic matter and felsic minerals jointly effect the improvement of the effective porosity and larger pores (>30 nm), which is related to their good compression resistance, organic pore retention, and dissolution-enhanced porosity effect. The product of the TOC and felsic mineral content (Vsi*TOC) can reflect the degree of their coupled effect. For moderate TOC contents, a higher felsic mineral content, and moderate shell laminae (Vca>10%) are conducive to the development of the effective porosity and larger pores. (4) The organic medium-rich argillaceous laminated felsic shale and organic-medium argillaceous laminated clayey shale have a higher effective porosity and higher proportion of larger pores, making them the dominant lithofacies for shale oil sweet spots.

Revised description of the blueberry bud mite, Acalitus vaccinii (Acari: Trombidiformes: Eriophyidae), and a key to all Eriophyoidea on Vaccinium

In 2014 the blueberry bud mite, Acalitus vaccinii (Acari: Trombidformes: Eriophyidae), was detected in the Mpumalanga province of South Africa for the first time causing significant damage to cultivated blueberries. This was the first detection of this pest outside of North America, to which it is native. However, its taxonomic description at that time lacked critical detail and omitted characters and life stages important for easy and accurate identification. Using an integrative taxonomic approach, we combined phase contrast light microscopy with low-temperature SEM and DNA barcoding data to revise the description of A. vaccinii using South African specimens. Additional characters not included in previous descriptions but reported here are the h1 (accessory) setae, leg I & II u’ (mesal) setae, and leg II bv (femoral) setae. Detailed descriptions and measurements of all life stages are included, along with a discussion of morphological variation and biology. Two DNA sequences of common barcode regions (nuclear and mitochondrial) are provided to further aid in identification. In addition, a key to all known species of eriophyoid mites present on Vaccinium is provided.

Influence of temperature on the population size of Aceria litchii (Acari: Eriophyidae) and the development of its galls.

The lychee erinose mite, Aceria litchii (Keifer), is a tiny eriophyid mite known to induce the formation of open galls (erinea) on lychee plants, Litchi chinensis Sonn. In lychee infested by A. litchii, four stages of erineum are observed, based on erineum color: hyaline, white, amber and dark brown. The cause of the color change in erinea is unknown, but it might be linked to the extent of A. litchii infestation. Artificially infested lychee seedlings were used to determine the developmental time, trichome density, and mite population size in each of the four erineum stages. The effect of temperature (15, 25, and 35°C) on A. litchii population size and erineum developmental time was also investigated. Overall, each erineum stage lasted approximately 50 days and the population size of A. litchii increased gradually through the hyaline, white and amber stages, and a strong decline was observed in dark brown erinea. Visual comparisons of the low-temperature scanning electron microscope (LT-SEM) images revealed that the trichome density was lower in the hyaline stage than in the other stages. Temperature influenced mite population size and amber erinea developmental time. Mite population was lower at 35°C than at 15 and 25°C, suggesting that high temperatures promote detrimental effects on A. litchii. Amber erinea developed slower at 15°C than at 25 and 35°C. Possible effects of the temperature on A. litchii population in lychee plants are discussed.

A new flat mite of the genus Brevipalpus Donnadieu (Trombidiformes: Tenuipalpidae) from Brazil, with complete ontogenetic pattern of setal additions

A new species of flat mite (Acari: Tenuipalpidae), Brevipalpus canastra Castro, Beard & Ochoa sp. nov., is described from the adult female, deutonymph, protonymph and larval stages collected on Sabicea brasiliensis (Rubiaceae), in the Cerrado region of Brazil. The new species belongs to the Brevipalpus phoenicis species group. The ontogenetic changes in the idiosoma and leg chaetotaxy of all stages are presented and micrographs using low-temperature scanning electron microscopy (LT-SEM) are provided.

Synthesis and Characterization of Proton-Conducting Composites Prepared by Introducing Imidazole or 1,2,4-Triazole into AlPO-5 and SAPO-5 Molecular Sieves.

The present work concerns proton-conducting composites obtained by replacing the water molecules present in aluminophosphate and silicoaluminophosphate AFI-type molecular sieves (AlPO-5 and SAPO-5) with azole molecules (imidazole or 1,2,4-triazole). Both the introduction of azoles and the generation of Brønsted acid centers by isomorphous substitution in aluminophosphate materials were aimed at improving the proton conductivity of the materials and its stability. In the presented study, AlPO-5 and several SAPO-5 materials differing in silicon content were synthesized. The obtained porous matrices were studied using PXRD, low-temperature nitrogen sorption, TPD-NH3, FTIR, and SEM. The proton conductivity of composites was measured using impedance spectroscopy. The results show that the increase in silicon content of the porous matrices is accompanied by an increase in their acidity. However, this does not translate into an increase in the conductivity of the azole composites. Triazole composites show lower conductivity and significantly higher activation energies than imidazole composites; however, most triazole composites show much higher stability. The different conductivity values for imidazole and triazole composites may be due to differences in chemical properties of the azoles.

Effect of TiO2 on Pd/La2O3-CeO2-Al2O3 Systems during Catalytic Oxidation of Methane in the Presence of H2O and SO2.

New results on the effect of TiO2 on Pd/La2O3-CeO2-Al2O3 systems for catalytic oxidation of methane in the presence of H2O and SO2 have been received. Low-temperature N2-adsorption, XRD, SEM, HRTEM, XPS, EPR and FTIR techniques were used to characterize the catalyst. The presence of Ce3+ on the catalytic surface and in the volume near the lantana was revealed by EPR and XPS. After aging, the following changes are observed: (i) agglomeration of the Pd-clusters (from 8 nm to 12 nm); (ii) transformation of part of the TiO2 from anatase to larger particles of rutile; and (iii)-the increase in PdO/Pd-ratio above its optimum. The modification by Ti of the La2O3-CeO2-Al2O3 system leads to higher resistance towards the presence of SO2 most likely due to the prevailing formation of unstable surface sulfites instead of thermally stable sulfates. Based on kinetic model calculations, the reaction pathway over the Pd/La2O3-CeO2-TiO2-Al2O3 catalyst follows the Mars-van Krevelen mechanism. For evaluation of the possible practical application of the obtained material, a sample of Pd/La2O3-CeO2-TiO2-Al2O3, supported on rolled aluminum-containing stainless steel (Aluchrom VDM®), was prepared and tested. Methane oxidation in an industrial-scale monolithic reactor was simulated using a two-dimensional heterogeneous reactor model.

Effect of the Pore Structure of Nanosilicas Decorated with Cobalt and Cerium Oxides on Catalytic Activity in the Selective Oxidation of Carbon Monoxide

Two types of nanosilicas with different pore structures are synthesized and decorated via impregnation with cobalt and cerium oxides. Meso–microporous spherical silica particles with thin walls of SiO2 nanochannels having specific surface area and pore volume of up to 1400 m2/g and 0.8 cm3/g, respectively, are used. Macroporous three-dimensionally ordered structures based on SiO2 (so-called synthetic opals) consisting of close-packed submicron spherical silica particles with respective porosity characteristics of 11 m2/g and 0.2 cm3/g are also used. The synthesized materials are characterized via low-temperature nitrogen adsorption, X-ray diffraction, SEM, XPS, and Fourier transform IR spectroscopy, and tested as catalysts for the selective oxidation of CO in excess H2 (CO-PROX). The effect of silica, the ratio of introduced oxides, and the order of their introduction on the structure and catalytic properties of Co–Ce/SiO2 are revealed. The catalytic behavior of the synthesized materials is determined from the specificity of interactions among the metal oxides and with the silica surface.

Experimental Study and Thermodynamic Analysis of Carbon Dioxide Adsorption onto Activated Carbons Prepared from Biowaste Raw Materials

Nutshells are regarded as cost-effective and abundant raw materials for producing activated carbons (ACs) for CO2 capture, storage, and utilization. The effects of carbonization temperature and thermochemical KOH activation conditions on the porous structure as a BET surface, micropore volume, micropore width, and pore size distribution of ACs prepared from walnut (WNS) and hazelnut (HNS) shells were investigated. As a result, one-step carbonization at 900/800 °C and thermochemical KOH activation with a char/KOH mass ratio of 1:2/1:3 were found to be optimal for preparing ACs from WNS/HNS: WNS-AC-3 and HNS-AC-2, respectively. The textural properties of the WNS/HNS chars and ACs were characterized by low-temperature nitrogen vapor adsorption, XRD, and SEM methods. Dubinin’s theory of volume filling of micropores was used to evaluate the microporosity parameters and to calculate the CO2 adsorption equilibrium over the sub- and supercritical temperatures from 216.4 to 393 K at a pressure up to 10 MPa. The CO2 capture capacities of WNS- and HNS-derived adsorbents reached 5.9/4.1 and 5.4/3.9 mmol/g at 273/293 K under 0.1 MPa pressure, respectively. A discrepancy between the total and delivery volumetric adsorption capacities of the adsorbents was attributed to the strong binding of CO2 molecules with the adsorption sites, which were mainly narrow micropores with a high adsorption potential. The high initial differential heats of CO2 adsorption onto ACs of ~32 kJ/mol confirmed this proposal. The behaviors of thermodynamic functions (enthalpy and entropy) of the adsorption systems were attributed to changes in the state of adsorbed CO2 molecules determined by a balance between attractive and repulsive CO2–CO2 and CO2–AC interactions during the adsorption process. Thus, the chosen route for preparing ACs from the nutshells made it possible to prepare efficient carbon adsorbents with a relatively high CO2 adsorption performance due to a substantial volume of micropores with a size in the range of 0.6–0.7 nm.

Experimental study on the effects of ultrasonic excitation on pore structure of water-bearing coal

Coal seam water injection is one of the main coal mine dust control measures. To study the effects of ultrasonic excitation on the pore structure of water-bearing coal in depth, ultrasonic excitation experiments were conducted with varied variables including ultrasonic excitation time, ultrasonic power, and fluid pressure on coal. The effects of sodium dodecyl sulfate (SDS) treatment and ultrasonic excitation were also compared. The coal samples treated under different conditions are characterized by low-temperature nitrogen adsorption and scanning electron microscopy (SEM) respectively for the quantitative analysis of pore volume and specific surface area and qualitative analysis of surface pore and fracture structure. The results show that ultrasonic excitation can significantly increase the pore volume and specific surface area of coal and damages the inner wall surfaces of the pore to different extents, making the pore inner surfaces rougher. However, the effect of ultrasonic excitation becomes weaker after the pore volume increases to a certain extent, resulting in more uniform pore size and volume distributions. Ultrasonic excitation time affects the pores with smaller size more significantly, and there is a time threshold effect. The volume and specific surface area of large pores and fractures show limited responses (or increases) to as the excitation time increased. The energy is mainly used for the fracturing and expanding the pores with smaller size. The effect of ultrasonic excitation on pore expansion is more obvious under the fluid pressures lower than 4 MPa. High fluid pressures weaken the fracturing and expanding effect of ultrasonic excitation on the pore structure of water-bearing coal. The ultrasonic power threshold effect is also observed. Once exceeding a certain value, further increasing the ultrasonic power does not dramatically affect the pore structure of water-containing coal. Ultrasonic excitation can enlarge the primary pores and fracture and generate secondary pores and fracture in coal. In contrast, the 0.85% SDS treatment is only able to clean the primary small pores, and no new pore structures are formed.

Evolution of the pore structure and fractal characteristics of coal under microwave-assisted acidification

Coal reservoir usually requires stimulation to enhance coalbed methane (CBM) production. As a novel stimulation method, microwave heating contributes to methane desorption and coalbed fracturing. However, the microwave-induced fractures are easily closed under in-situ stresses. Acidic stimulation is a process of demineralisation in the coal reservoir using hydrochloric, acetic, or formic acids, resulting in opening and interconnecting pores and fractures to flow gas. However, it is difficult for acids to enter microfissures under normal pressures. Microwave-asisted acidification may offer an alternative. In this work, the evolution of the pore structure and fractal characteristics of coal under microwave-assisted acidification was evaluated using low-temperature nitrogen adsorption and Scanning electron microscope. Compared to microwave heating or acidification, microwave-assisted acidification greatly increases the pore volume of coal and extends the length and width and connectivity of fractures. In addition, the isolated pores were interconnected and the methane migration was facilitated. This work demonstrates the potential of microwave-assisted acidification for CBM recovery.

Low Temperature Scanning Electron Microscopy (LTSEM) Findings on the Ultrastructure of Trebouxia lynnae (Trebouxiophyceae, Lichenized Microalgae)

The lichenized green microalga Trebouxia lynnae Barreno has been recently described and is considered a model organism for studying lichen chlorobionts. Its cellular ultrastructure has already been studied in detail by light, electron, and confocal microscopy, and its nuclear, chloroplast and mitochondrial genomes have been sequenced and annotated. Here, we investigated in detail the ultrastructure of in vitro grown cultures of T. lynnae observed by Low Temperature Scanning Electron Microscopy (LTSEM) applying a protocol with minimum intervention over the biological samples. This methodology allowed for the discovery of ultrastructural features previously unseen in Trebouxiophyceae microalgae. In addition, original Transmission Electron Microscopy (TEM) images of T. lynnae were reinterpreted based on the new information provided by LTSEM. The nucleolar vacuole, dictyosomes, and endoplasmic reticulum were investigated and reported for the first time in T. lynnae and most likely in other Trebouxia lineages.

SYNTHESIS OF TIO2 BY SOLVOTHERMAL METHOD AND ITS PHOTOCATALYTIC ACTIVITY TOWARDS BISEPTOL AND CONGO RED

The creation of ceramic membranes with additional functional properties, such as antibacterial and photocatalytic, is a popular and promising area of research in the field of water treatment. The article is devoted to the synthesis of titanium (IV) oxide powders by the solvothermal method for their further usage as a photocatalytic selective layer in ceramic membranes. The study of the peculiarities of the photocatalytic materials synthesis for the creation of photocatalytic and at the same time antimicrobial ceramic membranes on their basis is extremely relevant, because it will allow to develop a method of synthesis of photocatalysts active to various pollutants. Therefore, the aim of the work was the synthesis of TiO2 powders by solvothermal method at different ratios of the starting reagents, the study of their physicochemical properties and the study of their photocatalytic properties in relation to different pollutant – antibiotics and dyes. The obtained powders were characterized by diffraction analysis, infrared spectroscopy, low-temperature nitrogen adsorption-desorption and scanning electron microscopy. It is established that the ratio of the initial components significantly affects the final properties and characteristics of TiO2 powders. It was shown that the synthesis with a significant excess of the starting reagent (titanium isopropoxide) does not lead to the crystalline TiO2 sample, which was confirmed by diffraction analysis and infrared spectroscopy. The revealed porous structure of all TiO2 samples indicates a high specific surface area in them, which is also consistent with scanning electron microscopy studies. The highest photocatalytic activity is possessed by TiO2 samples, which are nanocomposites of anatase and rutile modifications. Such nanocomposites showed quite high activity towards antibiotics (Biseptol) and anionic dyes (Congo red).

Evaluation of pollen morphology of Passiflora species and hybrids (Passifloraceae)

Passiflora L. is a diverse genus of mostly New World species, many of which are still evolving to overcome the challenges of competition, predation, and habitat expansion. Pollen collected from 195 Passiflora L. taxa across six subgenera; Astrophea (DC.) Mast., Decaloba (DC.) Rchb., Deidamioides (Harms) Killip, Passiflora, Tetrapathaea (DC.) P.S. Green) and Tryphostemmatoides (Harms) Killip and 40 F1 hybrids (cultivars) were examined using Scanning Electron Microscopy (SEM) and low temperature SEM. Passiflora pollen grains are divided into two major morphological groups: species with three pairs (6 apertures) of colpi found in species in subgenera Astrophea, Deidamioides, Passiflora and Tryphostemmatoides, and those with six pairs (12 apertures) of colpi found in most species from subgenus Decaloba (Tetrapathea unknown). This study shows polymorphism and surface anomalies in the morphology of pollen grains of some species. Pollen from many Passiflora F1 hybrids were examined: many have a high percentage of sterile pollen grains, others in section Dysosmia DC. and Tacsonia Juss. in subgenus Passiflora recorded a minimal percentage of sterile grains. This may be a key evolutionary advantage as several species in these groups are now recorded as invasive weeds with worldwide distribution. The term, “sticky pollen” is revealed to be the pre-germination of pollen grains without stigmatic contact. The success of some invasive species to outcompete native flora and thrive in extreme environments is in part due to the evolution of their pollen, with the absence of pollen deformation following hybridization events promoting hybrid fitness. Pollen grain morphological evidence supports keeping three endemic Australian Passiflora species in subgenus Decaloba as a unique group.

Electrochemical and Catalytic Properties of Carbon Dioxide-Activated Graphite Felt.

The commercial graphite felt GFA 10 was subjected to an activation process with the use of CO2 at 900 °C for 35 and 70 min. Pristine and heat-treated materials were characterized using various methods: low-temperature N2 adsorption, SEM, and EDS. Voltammetric measurements of GFA samples (before and after activation) as the working electrode were carried out. Voltammograms were recorded in aqueous solutions of 4-chlorophenol and sodium sulfate as supporting electrolyte. The catalytic activity of GFA samples in the process of 4-chlorophenol oxidation with the use of H2O2 was also investigated. The influence of graphite felt thermal activation in the CO2 atmosphere on its electrochemical and catalytic behavior was analyzed and discussed. Results of the investigation indicate that GFA activated in CO2 can be applied as an electrode material or catalytic material in the removal of organic compounds from industrial wastewater. However, the corrosion resistance of GFA, which is decreasing during the activation, needs to be refined.

Sodium Accumulation in Infected Cells and Ion Transporters Mistargeting in Nodules of Medicago truncatula: Two Ugly Items That Hinder Coping with Salt Stress Effects.

The maintenance of intracellular nitrogen-fixing bacteria causes changes in proteins’ location and in gene expression that may be detrimental to the host cell fitness. We hypothesized that the nodule’s high vulnerability toward salt stress might be due to alterations in mechanisms involved in the exclusion of Na+ from the host cytoplasm. Confocal and electron microscopy immunolocalization analyses of Na+/K+ exchangers in the root nodule showed the plasma membrane (MtNHX7) and endosome/tonoplast (MtNHX6) signal in non-infected cells; however, in mature infected cells the proteins were depleted from their target membranes and expelled to vacuoles. This mistargeting suggests partial loss of the exchanger’s functionality in these cells. In the mature part of the nodule 7 of the 20 genes encoding ion transporters, channels, and Na+/K+ exchangers were either not expressed or substantially downregulated. In nodules from plants subjected to salt treatments, low temperature-scanning electron microscopy and X-ray microanalysis revealed the accumulation of 5–6 times more Na+ per infected cell versus non-infected one. Hence, the infected cells’ inability to withstand the salt may be the integral result of preexisting defects in the localization of proteins involved in Na+ exclusion and the reduced expression of key genes of ion homeostasis, resulting in premature senescence and termination of symbiosis.