Low-temperature Scanning Electron Microscopy Research Articles

New method for the synthesis of Al2O3\u2013CaO and Al2O3\u2013CaO\u2013CaCO3 systems from a metallic precursor by the sol\u2013gel route

A series of binary Al2O3–CaO and Al2O3–CaO–CaCO3 systems with Ca/Al molar ratios of 0.05, 0.1, 0.25, 0.5 and 1.0 have been synthesised by the sol–gel technique from aluminium isopropoxide and metallic calcium powder. The rate of the metal reaction is used as a limiting factor to control the binary gel formation. The proposed modification of the traditional sol–gel method was used to examine the influence the effect of the metallic form of the second component as an oxide precursor on the form of the final product. By applying acetic acid instead of mineral acid, calcium acetate is formed and then decomposed to calcium carbonate upon thermal processing. During the synthesis of the binary systems, metallic calcium acts both as a precursor of calcium acetate and as a secondary pH modifier of the gel system. Calcination in air at 600 °C did not produce systems containing only oxides and the calcium carbonate phase was still present. Due to particle size reduction, the CaCO3 to CaO decomposition temperature was lowered. The systems were characterised by X-ray powder diffraction, low-temperature nitrogen adsorption, transmission and scanning electron microscopy (TEM, SEM and SEM/EDS), thermogravimetric analysis (TGA) and FTIR spectra.

Meervein-Ponndorf-Vereley reduction of carbonyl compounds in monolithic siliceous microreactors doped with Lewis acid centres

Meerwein-Ponndorf-Vereley chemoselective reduction of cyclohexanone and benzaldehyde was studied in monolithic continuous-flow microreactors, with various Lewis acid centres derived from different metal precursors, i.e. metal alkoxides, chelated metal alkoxides and salts. The productivities achieved in the microreactors, doped with metal centres terminated by propoxy ligands, were significantly higher, ca. 30%, than those obtained for oxides modified monoliths. The highest efficiency of Zr-doped microreactors was proved and their superiority over aluminium and titanium functionalized ones was demonstrated. Higher efficiency of microreactors compared to batch reactors with powdered catalysts has been shown. Stability of proposed materials has been demonstrated. The catalytic outcomes were correlated with structural and physicochemical properties of materials, obtained using low-temperature nitrogen adsorption, mercury porosimetry, SEM microscopy, ICP-MS, FTIR study and pyridine adsorption.

A new species of cave dwelling Neocarus (Acari: Opilioacaridae) from Bahia state, Brazil, with remarks on taxonomic characters.

Neocarus coronatus n. sp., is described from caves and the surrounding epigean habitats from a karst area of São Desidério county, Bahia state, Brazil. A dissection procedure is presented for the better use of scarce Opilioacaridae material, especially to analyze gut contents. Sexual dimorphism is presented, mainly differences in the density of setae on the dorsal shield in the prominent triangular anterior region. Females have an ovipositor with 3 pairs of smooth digitiform projections and 6-8 eugenital setae. Adults have a palpal tibiotarsus with 4 d setae. Using Low-Temperature Scanning Electron Microscopy (LT-SEM), evaluation of the chaetotaxy (especially setal shape) and morphology are greatly improved over standard light microscopy techniques enhancing the interpretation of characters for species differentiation. Also, we discuss the fragility of microinvertebrates in cave habitats.

Synthesis and Characterization of Platinum-Cerium Oxide Nanocatalysts for Methanol Oxidation

CeO2-C(Vulcan) catalyst materials activated with Pt nanoclusters have been synthesized using different methods comprising microwave synthesis, reduction with hydrogen and reduction with NaBH4. The materials have been analyzed using low temperature nitrogen adsorption, X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy methods. Methanol oxidation has been studied using cyclic voltammetry, chronoamperometry and impedance methods. Very noticeable influence of catalyst surface structure and porosity, depending on the complex catalyst preparation conditions, has been demonstrated. High electrochemically active surface area values have been calculated. High current densities of MeOH oxidation have been established for several catalysts. Fitting of the impedance data has been performed, and the results have been discussed.

Study on reduction behavior of two-component Fe[sbnd]Mg[sbnd]O oxide system prepared via a sol-gel technique

Two-component FeMgO oxide system was prepared via sol-gel technique. An aqueous solution of iron nitrate was used to hydrolyze the magnesium methoxide instead of distilled water. The iron loading in a final sample was 15 wt% with respect to Fe2O3. The method was shown to provide a uniform distribution of iron oxide within MgO matrix. The sample was characterized by means of a low-temperature nitrogen adsorption and scanning electron microscopy. Reduction behavior of the sample was studied in a temperature-programmed regime using hydrogen as a reducing agent. In order to follow the possible phase transformations, the sample was examined by an in situ X-ray diffraction analysis in both reductive and oxidative atmospheres within the temperature range of 25–700 °C. It was found that after the first cycle of reduction/re-oxidation, the sample stabilizes in a novel state, and hydrogen uptake profiles of further cycles of reductive/oxidative treatment become completely reproducible. According to X-ray diffraction data, the sample consists of small particles (9 nm) of Fe3O4 phase well-dispersed within the structure of nanocrystalline MgO.

Removal of phosphate from water by lanthanum-modified zeolites obtained from fly ash

The possibility and effectiveness of removal of phosphate from aqueous solutions with the use of new low-cost synthetic zeolites obtained from fly ash and modified with lanthanum, was studied. Physicochemical properties of the zeolites were characterized by different techniques such as X-ray diffraction, low-temperature nitrogen sorption and scanning electron microscopy. It has been established that lanthanum is preferentially located in the zeolites channels and cages, which is related to the ion-exchange method of modification. Introduction of lanthanum cations leads to a reduction in BET surface area, mainly due to a decrease in the area of micropores and reduction in the pore volume. The key element of the study was a series of tests of phosphate adsorption from aqueous solutions. The efficiency of adsorption process was found to depend on the concentration of adsorbate, pH of its solution and temperature. The sorption capacity of zeolites obtained from fly ashes (La-P1, La-A) towards phosphate was compared with that of a natural zeolite – clinoptilolite, modified with lanthanum (La-CLP). The sorption capacities of the particular samples were as follows: La-P1 – 58.2 mg/g, La-A – 44.0 mg/g and La-CLP – 24.6 mg/g. The experimental data were well fitted by the Langmuir isotherm model. The sorption capacities of all samples towards phosphate increased with temperature increasing from 25 to 60 °C. The values of the thermodynamic parameters ΔH0 and ΔG0 revealed that the adsorption was spontaneous and endothermic.

One-pot synthesis of Al2O3-La2O2CO3 systems obtained from the metallic precursor by the sol-gel method

A series of mixed oxide‑carbonate Al2O3-La2O2CO3 systems with the La/Al molar ratios of 0.05, 0.1, 0.25, 0.5 and 1.0 have been synthesized by the sol–gel technique from aluminum isopropoxide and metallic lanthanum powder. During the synthesis of Al2O3- La2O2CO3 system, metallic lanthanum acts both as a precursor of lanthanum oxide and as secondary pH modifier of the gel solution. The traditional sol-gel method was modified to provide a better control over the final product surface parameters and structure. The obtained systems were amorphous and highly homogenic. The rate of the metal reaction was used as a limiting factor to control the gel formation. The obtained oxide systems are intended as a support for metallic phase catalysts. Calcination in air at 600°C did not produce systems containing only oxides and the lanthanum (dioxy)carbonate phase was still present. This observation can be explained by the multi stage decomposition process of lanthanum acetate forming during the gel synthesis.The systems were characterized by X-ray powder diffraction, low temperature nitrogen adsorption, transmission and scanning electron microscopy (TEM, SEM and SEM/EDS), thermogravimetric analysis (TGA), and FTIR spectra.

Studies of anionic dendrimer adsorption mechanism on the zirconium(IV) oxide surface – Electrokinetic and thermal properties of nanosized composites

The adsorbed amount of the third generation dendrimer containing carboxyl groups on the surface of zirconium(IV) nanooxide was determined using spectrophotometry. The effects of solution pH (in the range 3–9) and polymer concentration were examined. At the same beginning the metal nanooxide (textural parameters) and dendrimer (dissociation, hydrodynamic radius in the solution) were characterized using the following experimental techniques: low-temperature nitrogen adsorption-desorption, SEM, DLS, SLS and viscosimetry. Additionally, the impact of dendrimer adsorption on the electrokinetic properties of the ZrO2-polymer solution interface was studied. For this purpose the potentiometric titration and Doppler laser electrophoresis methods were applied. The thermal behaviour of ZrO2 unmodified and modified with the dendrimer layer was also examined. Based on the obtained results the most probable mechanism of dendrimer adsorption on the nanooxide surface was proposed. This can be of great importance in nanomedicine in the process of tissue reconstruction and implant coatings formation.

Surface Properties of Al-Functionalized Mesoporous MCM-41 and the Melting Behavior of Water in Al-MCM-41 Nanopores.

We report an experimental investigation of structural and adhesive properties for Al-containing mesoporous MCM-41 and MCM-41 surfaces. In this work, highly ordered hexagonal mesoporous structures of aluminosilica with two different Si/Al molar ratios equal to 50 and 80 and silica samples were studied; Al was incorporated into the MCM-41 structures using the direct synthesis method, with CTAB as a surfactant. The incorporation of aluminum was evidenced simultaneously without any change in the hexagonal arrangement of cylindrical mesopores. The porous materials were examined by techniques such as low-temperature nitrogen sorption, energy-dispersive spectroscopy, and scanning and transmission electron microscopy. Surface properties were determined through X-ray photoelectron spectroscopy, potentiometric titration, and static contact angle measurements. It was shown that an increase in surface acidity leads to an increase in the wetting energy of the surface. To investigate the influence of acidity on the confinement effects, the melting behavior of water in Al-MCM-41 and MCM-41 with the same pore size was determined by using dielectric relaxation spectroscopy and differential scanning calorimetry methods. We found that the melting-point depression of water in pores is larger in the functionalized pores than in pure silica pores of the same pore diameter.

New and little known feather mites (Acariformes: Astigmata) analysed with low-temperature scanning electron microscopy

ABSTRACTFeather mites (Acari: Astigmata) were analysed with low-temperature scanning electron microscopy, including the description of three new species: Plicatalloptes atrichogynus sp. nov. (Analgoidea: Alloptidae) from the Neotropical cormorant Phalacrocorax brasilianus (Gmelin) (Pelecaniformes: Phalacrocoracidae), Metapterodectes saturninus sp. nov. (Analgoidea; Proctophyllodidae) from the chalk-browed mockingbird Mimus saturninus (Lichtenstein) (Passeriformes: Mimidae), and Neumannella crypturella sp. nov. (Analgoidea: Dermoglyphidae) from the small-billed tinamou Crypturellus parvirostris (Wagler) (Tinamiformes: Tinamidae). In addition, two previously known species are analysed, Oustaletia pegasus Trouessart, 1855 (Pterolichoidea: Vexillariidae) from the bushy-crested hornbill Anorrhinus galeritus (Temminck) (Bucerotiformes: Bucerotidae), and Opisthocomacarus umbellifer (Trouessart, 1899) (Pterolichoidea: Pterolichidae) from the hoatzin Opisthocomus hoazin (Müller) (Opisthocomiformes: Opisthocomidae). The latter two mite species display a rich variety of setal structures. Alloptes umbrettae Gaud, 1960 (Analgoidea: Alloptidae), known from Scopus umbretta Gmelin (Pelecaniformes: Scopidae), is transferred from the genus Alloptes Canestrini to Plicatalloptes Dubinin and given a new valid name, Plicatalloptes umbrettae (Gaud, 1960) comb. nov.http://zoobank.org/urn:lsid:zoobank.org:pub:5866FF00-1206-4551-9544-8A002ADF7626

Growth of indoor fungi on gypsum.

To have a better understanding of fungal growth on gypsum building materials to prevent indoor fungal growth. Gypsum is acquired by mining or as a by-product of flue-gas desulphurization or treatment of phosphate ore for the production of fertilizer. Natural gypsum, flue-gas gypsum and phosphogypsum therefore have different mineral compositions. Here, growth of fungi on these types of gypsum was assessed. Conidia of the indoor fungi Aspergillus niger, Cladosporium halotolerans and Penicillium rubens were inoculated and observed using microscopic techniques including low-temperature scanning electron microscopy. Elemental analysis of gypsum was done using inductively coupled plasma atomic emission spectroscopy and segmented flow analysis. Moisture content of the gypsum was determined using a dynamic vapour sorption apparatus. Aspergillus niger, C. halotolerans and P. rubens hardly germinated on natural gypsum and flue-gas gypsum. The latter two fungi did show germination, outgrowth, and conidiation on phosphogypsum, while A. niger hardly germinated on this substrate. Other experiments show that C.halotolerans and P. rubens can develop in pure water, but A. niger does not. The observations show that the lack of germination of three indoor fungi is explained by the low amount of phosphor in natural, flue-gas and laboratory-grade gypsum. Additionally, C. halotolerans and P. rubens can develop in pure water, while conidia of A. niger do not show any germination, which is explained by the need for organic molecules of this species to induce germination. Indoor fungal growth is a potential threat to human health and causes damage to building materials. This study possibly helps in the application of the right type of gypsum in buildings.

Promotion effect of zirconia on Mg(Ni,Al)O mixed oxides derived from hydrotalcites in CO2 methane reforming

Hydrotalcite-derived catalysts promoted with Zr species were prepared via co-precipitation method, resulting in materials with various Zr loading. Physicochemical properties of catalysts precursors and final catalysts were investigated via XRF, XRD, low temperature N2 sorption, H2-TPR, CO2-TPD, TG, SEM and TEM techniques. So characterized catalysts were subsequently tested in the dry methane reforming reaction at 550°C. Zr-loading introduced into brucite-like layers influenced the process of thermal decomposition of HTs and, as a result, their properties and performance in DRM. Although Zr promotion decreased activity, it strongly increased the stability and selectivity of the catalysts. The catalyst with Zr species present in the framework of periclase-like mixed oxide exhibited high resistance to coking due to the rearrangement of Ni particles upon DRM reaction.

BENTONITE/IRON OXIDE MAGNETIC COMPOSITES: CHARACTERIZATION AND APPLICATION AS Pb(II) ADSORBENTS

<p>The natural clay bentonite (B) as adsorbent of lead cations was studied. To enhance its adsorption capacity, the coating by iron oxide particles, in two selected weight ratios: 2:1 (BM1) and 4:1(BM2), was used. The changes of the textural and surface parameters after the modification were studied by the low temperature nitrogen adsorption, XRD and SEM method, Mössbauer spectroscopy. The Pb(II) adsorption experiments were studied under the different conditions, such as pH of the model solutions, contact time and initial metal ion concentration. Higher adsorption rates of BM1 and BM2 samples were observed for lower initial metal ion concentrations.</p>

δ-Alumina supported cobalt catalysts promoted by ruthenium for Fischer-Tropsch synthesis

The paper presents the low-temperature nitrogen adsorption, TG, XRD, IR spectroscopy, XPS, TEM and SEM data for ruthenium promoted (0.2–1wt.%) Сo-δAl2O3 catalysts and characteristics of the catalysts in Fischer-Tropsch synthesis after their activation under the conditions ensuring the reduction of comparable fractions of metallic cobalt. It was shown that cobalt in oxide precursors is a component of the spinel-like Со3-xAlxO4 phase containing the impurity anions СО32−, NO3−, ОН−, and NO in promoted samples, which belong to the thermolysis product of the Ru precursor. Average sizes of Со3-xAlxO4 crystallites are in a range of 5–10nm. As ruthenium content in the catalyst increases upon reduction, the temperature of metallic phase formation decreases substantially (by more than 150°C). After the reduction, selectivity of promoted catalysts for α-olefins and high-molecular hydrocarbons was higher in comparison with unpromoted catalysts, without a noticeable decrease in catalytic activity. Therewith, in 0.5–1.0wt.% catalysts, a part of ruthenium forms individual ultradispersed metallic particles ca. 1nm in size that are located on the surface of oxide support and are not active in Fischer-Tropsch synthesis. The oxide layer decorating the surface of metallic cobalt particles is also strongly enriched with ruthenium. In the 0.2wt.% catalyst, the major part of ruthenium resides in metallic cobalt particles. Although the ruthenium-cobalt alloy segregates with enrichment of the surface with cobalt, the presence of ruthenium in the metallic particles and probably in the decorating oxide layer exerts a considerable effect on selectivity of the catalysts.

Lyotropic Lamellar Structures of a Long-Chain Imidazolium and Their Application as Nanoreactors for X-ray-Initiated Polymerization.

The lyotropic behavior of the ternary system formed by 1-tetradecyl-3-methylimidazolium chloride, 1-decanol, and water is investigated. A lamellar mesophase is formed for a wide range of compositions and is characterized by polarized optical microscopy, low-temperature scanning electron microscopy, small- and wide-angle X-ray scattering with synchrotron radiation, and differential scanning calorimetry. This phase presents onionlike structures. Two lamellar structures are formed: an Lα mesophase between 25 and 50 °C, with an isobaric thermal expansivity of the bilayer thickness of -3.2 × 10-3 K-1, and a lamellar gel phase, when the temperature decreases below 25 °C. This new medium is employed to perform in situ X-ray-initiated polymerization of N-isopropylacrylamide. When the monomer is incorporated in the lamellar structure, it is distributed between the water layer and bilayer interface and its polymerization can be followed by variations in the diffractograms with time.

Valorization of Toxic Weed Lantana camara L. Biomass for Adsorptive Removal of Lead

Valorization of Lantana camara L., which is a recognized invasive plant, as a potential source of activated carbon is proposed in this study. Its stem and leaf have been utilized for the preparation of activated carbon (ACL and ACS) by following acid-impregnation technique, followed by thermal treatment. The developed activated carbon samples were characterized for their structural and surface related properties by low-temperature nitrogen adsorption isotherm, SEM techniques, and pHPZC method. The samples show reasonable high surface area and pore volume; nonetheless, these properties are higher in case of ACL as compraed to ACS. Both of these samples developed negative charge on their surface due to acid treatment that resulted in an increase in adsorption at pH > 5. The batch adsorption studies on these samples shows the Pb(II) ion adsorption capacities of ACL and ACS were 36.01 and 32.24 mg·g−1, respectively, at 25°C. The kinetics of adsorption with both the sample systems follow the pseudo-second-order model, whereas the experimental equilibrium isotherm data of ACL and ACS were explained by Freundlich and Langmuir models, respectively. For these samples, the HCl shows maximum desorption with which the recycling test on these samples shows that ACS has better recycling potential over ACL samples.

Understanding the role of mobility of ITO films for silicon heterojunction solar cell applications

Transparent conducting oxides (TCO) are crucial in amorphous/crystalline silicon heterojunction solar cells performance as they have to be highly conductive to ensure the transport of photogenerated charges while remaining highly transparent to the sun spectrum. The key parameter to improve the transparency/conductivity compromise of TCO is mobility, since it allows increasing conductivity without losing transparency in the infrared region. A deep understanding of the factors influencing the mobility is then fundamental, and this is the objective of this paper. For this study, thin films of tin-doped indium oxide (ITO) were prepared by magnetron sputtering with different oxygen content. They were deeply characterized by standard and Low Temperature Hall Effect measurement, scanning and transmission electron microscopy and X-ray diffraction. The impact of oxygen on the microstructure was studied and the electrical properties were deeply investigated. In particular, the different mechanisms impacting the mobility were quantified as a function of oxygen content during ITO deposition.

Local Electrical Imaging of Tetragonal Domains and Field-Induced Ferroelectric Twin Walls in Conducting SrTiO_{3}.

We demonstrate electrical mapping of tetragonal domains and electric field-induced twin walls in SrTiO_{3} as a function of temperature and gate bias utilizing the conducting LaAlO_{3}/SrTiO_{3} interface and low-temperature scanning electron microscopy. Conducting twin walls appear below 105K, and new twin patterns are observed after thermal cycling through the transition or on electric field gating. The nature of the twin walls is confirmed by calculating their intersection angles for different substrate orientations. Numerous walls formed when a large side- or back-gate voltage is applied are identified as field-induced ferroelectric twin walls in the paraelectric tetragonal matrix. The walls persist after switching off the electric field and on thermal cycling below 105K. These observations point to a new type of ferroelectric functionality in SrTiO_{3}, which could be exploited together with magnetism and superconductivity in a multifunctional context.

Selectivity and detrimental effects of epiphytic Pseudanabaena on Microcystis colonies

The cyanobacterium Microcystis aggregates into colonies with a mucilaginous sheath that constitutes a special microhabitat for many microorganisms that associate to it. Here, we examine the notorious, yet scarcely studied case of epiphytic association by the cyanobacterium Pseudanabaena sp. to colonial Microcystis. Co-cultivation of Pseudanabaena with different Microcystis strains evidenced strong specificity in the interaction, with dramatically different outcomes in each case, including (1) inability of Pseudanabaena to access the slime of Microcystis, (2) neutral co-existence of epiphytic Pseudanabaena and Microcystis, and (3) rapid epiphytic proliferation of Pseudanabaena, followed by lysis and rapid decay of Microcystis cells. Whereas strain-specific oligopeptide production could not explain the observed specificity, differences in slime microstructures among Microcystis strains revealed by low-temperature scanning electron microscopy suggest that slime structural features might initially determine the ability of Pseudanabaena to colonize Microcystis, subsequently driving the outcome of the interaction. Furthermore, even under “neutral” co-existence, Pseudanabaena proliferation results in an increase in density that leads to colony settling, implying potential selective losses under natural conditions. Both the selective and antagonistic characters of the interaction indicate that epiphytic Pseudanabaena have the potential to contribute to the dynamics of strains in natural Microcystis communities.

Facile, low-cost, and sustainable preparation of hierarchical porous carbons from ion exchange resin: An improved potassium activation strategy

Active carbons were prepared from low cost ion exchange resin, the samples were characterized by means of low temperature (−196°C) N2 adsorption, XPS, SEM, TEM, etc., and performance in CO2 and phenol adsorption were evaluated. It was found that samples with hierarchical structures and highly developed micro–mesoporous system could be obtained owing to the pre-induced highly dispersed potassium species by ion exchange, which served as an efficient activation agent, this represents an important improvement as compared with the normally reported KOH activation protocol in terms of lowering the usage of the corrosive KOH, and thus the sustainability of the obtained material. The optimized sample, R-K-700, showed the highest CO2 and phenol uptake of 13.6wt.% and 167.3mg/g, respectively, and more importantly, samples with an ordered spherical form and similar adsorption performance to the powdered sample can be easily fabricated, making the current carbons and preparation methodology a great promise for practical applications.