Energy Dispersive X-ray Powder Diffraction Research Articles

Hydrothermal Synthesis of Polyoxometalate Containing Cobalt Ion, and Its Polyurethane Composites for Dielectric Material Applications

ABSTRACT Polyurethane (PU) composites were prepared with different diisocyanate and diol compounds by adding cobalt ion-based polyoxometalate (Co-POM) as reinforcement. For the determination of using potential in microelectronic applications, the dielectric behavior and dielectric constant of these PU composites were investigated and compared to pure polyurethane structures. For this aim, firstly, Co-POM with Keggin structure was obtained from ammonium heptamolybdate, 1,10-phenanthroline ligand and a cobalt (II) salt by hydrothermal synthesis technique. Then, polyurethane/Co-POM composites (PU/Co-POM) were prepared with ethylene glycol, nonaromatic diisocyanate and different amounts of Co-POM reinforcement (1%, 3%, 5% and 10%, w/w) by in situ polymerization and mix-blend technique. Obtained PU/Co-POM composites were characterized in detail by infrared spectroscopy, Elemental Mapping, Energy-dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (XRD) spectroscopy. The surface structure, morphology and roughness of PU/Co-POM composites were investigated by SEM and AFM analysis. The elemental maps of the PU/Co-POM surface were examined by EDX elemental mapping analysis methods. Thermal stability, Tg values and thermal decomposition temperatures of PU/Co-POM structures were determined by different thermal analysis techniques. Thermal analysis results showed that the PU/Co-POM composites are thermally stable up to approximately 200°C and Tg values of synthesized PU composites are seen between 54.72°C and 75.15°C. The dielectric properties and dielectric constants of the PU/Co-POM composites were determined in the frequency range 1 Hz to 1000 kHz at room temperature using impedance analyzer. Dielectric constants of these composites were ranged from 5.50 to 9.26 according to their polarizability and H-bonding ability of PU matrix structure. According to the dielectric measurements, the dielectric constants of the PU/Co-POM structures were significantly decreased compared to the pure PU structures.

Bismuth and oxygen valencies and superconducting state properties in Ba1-xKxBiO3 superconductor

Relationship between variation of Bi and O valence states in perovskite bismuthates Ba1-xKxBiO3 (BKBO), grown in modified synthesis conditions, and their superconducting state properties is presented. Chemical composition, crystal structure and phase purity of BKBO was determined via micro X-ray fluorescence (μXRF), energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction technique (XRD). X-ray photoemission spectroscopy (XPS) and SQUID magnetometry showed variations of electronic structure and superconducting state properties, i.e., lower and upper critical fields, and transition temperature for the samples synthesized at various conditions. We report that, multiple valencies of bismuth, observed already in BKBO systems and assigned to disproportionation of bismuth valence states, lead in fact to deterioration of superconducting state properties.

Electrohydromodulation for phosphate recovery from wastewater

The mining of phosphate rock to produce fertilizer, and subsequent disposal of the municipal wastewater containing a significant fraction of the phosphate applied agriculturally, has led to environmental impacts of phosphate mining as well as surface water eutrophication. However, recovery of phosphate (H2PO4-, HPO42-, PO43-) from wastewater, either chemically or biologically, has not been sufficiently economical at low phosphate concentrations in raw wastewater (~2.4 mg-P l−1) to motivate widespread adoption. In this work, we demonstrate phosphate recovery directly from raw and mineral-spiked septic tank effluent by electrochemical pH shifting, termed electrohydromodulation (EHM), without expensive chemical addition. EHM using a CMI-7000 multivalent cation exchange membrane (MCEM) at 5 V at 1.347 mA/cm2 resulted in the highest efficiency at lowest energy consumption. 94 and 95% phosphate were recovered from mineral-spiked septic tank effluent (simulating advanced oxidation-based direct potable reuse water), and raw septic tank effluent, at an energy demand of 1.046 kWh/m3 (3.960 kWh/1000 Gal) and 1.863 kWh/m3 (7.054 kWh/1000 Gal), respectively, low despite use of non-toxic, inexpensive graphite electrodes. Results from scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD) indicated that recovered precipitates consisted principally of amorphous calcium phosphate (ACP), with minor amounts of amorphous calcium carbonate (ACC), having an overall Ca:P ratio of 2. CO2 stripping at low pH prior to pH shifting was found to minimize competitive calcite precipitation to improve product purity. Electrodes used intermittently, with polarity reversal, over 1.5 years of experiments were intact from fouling.

Single-Step Hydrometallurgical Method for the Platinum Group Metals Leaching from Commercial Spent Automotive Catalysts

Platinum group metals (PGMs) are considered critical raw materials, thus their recycling and re-use is of outmost importance. Among the PGMs, platinum (Pt), palladium (Pd) and rhodium (Rh) are the basic metals used in catalytic converters. Concerning the stringent EU standards for emission control imposed to car manufacturers (Euro 6d nowadays), the worldwide demand for PGMs is being increased. As for PGM recovery methods, research is focusing on greener, plain recovery techniques, which utilize milder reagents and offer energy efficiency. In this work, a state-of-the-art hydrometallurgical process is proposed resulting in recovery rates for Pt, Pd and Rh, namely 100%, 92% and around 60%, respectively. A batch of more than 20 commercial spent catalyst samples has been mechanically pre-processed (i.e. sorted, decanned, milled, grinded, homogenized and characterized), in order for a 20 kg sample of homogenized fine pent catalytic powder to be derived. The proposed hydrometallurgical method does not involve any kind of thermal pre-treatment or chemical reduction, thus energy consumption is minimized, while the use of chemicals has been restricted to simple and cheap inorganic solvents (namely HCl, NaCl and H2O2). The aforementioned recovery rates have been validated through X-ray fluorescence spectroscopy analysis (XRF). The equipment used has been successfully calibrated to measure low PGM concentrations (less than 50 ppm for each metal). The kinetics of the hydrometallurgical process have also been studied, in short intervals, and spent catalyst material has been characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy analysis (EDS) and X-ray powder diffraction (XRD).

Development of reproducible thiourea sensor with binary SnO2/V2O5 nanomaterials by electrochemical method

In this methodology, the thiourea (TU)sensor was made-up by means of glassy carbon electrode (GCE) layered by the wet-chemically prepared binary SnO2/V2O5 nanomaterials (NMs). The existence of SnO2 and V2O5 in prepared spherical NPs were categorized by X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM), Energy-dispersive X-ray spectroscopy and X-ray Powder Diffraction (XRD). The TU sensor was displayed the linear responses in concentration range (LDR) of 0.1 nM ~ 0.01 mM. The calibration curve of TU sensor was made by plotting current verses concentration of TU, which was measured by electrochemical technique. The sensitivity and lower limit of detection (DL) for TU sensor were calculated from calibration curve, which are found as 17.0918 µAµM-1cm−2 and 95.40 ± 4.77 pM respectively. The analytical parameters of TU sensor such as reproducibility, response time and stability were measured and found efficient results. It also was validated in the detection of TU in presence of real bio-samples. Thus, this unique and prospective method is introduced to develop the selective biosensor by electrochemical approach, which might be a pioneer sensor probe for its simple and reliable approach for the safety of healthcare and biomedical fields in a large scales.

An experimental study of sepiolite dissolution rates and mechanisms at 25 °C

The steady-state dissolution rates of sepiolite were measured as a function of pH from mixed-flow reactor experiments at 25 °C in both citrate bearing and citrate-free aqueous solutions. Dissolution at pH ≤ 5.5 and pH ≥ 9.18 was found to be non-stoichiometric, with relatively more Mg being released at low pH, while Si was preferentially released at high pH. The steady-state dissolution rate of sepiolite at 25 °C, based on Si release rates at far from equilibrium conditions, r+ in mol/cm2/s at pH ≥ 4.44 can be described by.r+=10-15.291aH+2/aMg2+1/8,where ai refers to the activity of the subscripted aqueous species. This rate equation is based on a dissolution mechanism by which interstitial Mg is exchanged for 2H+, followed by the rate limiting release of partially detached Si-tetrahedra. At pH ≤ 4.44 and in citrate-free aqueous solutions, sepiolite dissolution rates based on Si release are similar to those measured for amorphous SiO2 despite the fact that the bulk fluid phase was undersaturated with respect to this solid. In contrast, in citrate bearing aqueous solutions, the Si release rate increases with decreasing pH following a trend consistent with the corresponding higher pH values. This difference is attributed to the increase of amorphous SiO2 dissolution rates in citrate bearing aqueous fluids, preventing the formation of substantial SiO2-rich surface layers. To further examine the extent of non-stoichiometric dissolution and its implications on solid phase transformations, batch experiments were performed in citrate bearing aqueous solutions at pH 2.57, 3.40 and 4.31. During these longer term experiments the fluid phase attained saturation with respect to amorphous SiO2. From mass balance calculations, Energy-Dispersive X-ray spectroscopy (EDS) and X-Ray powder Diffraction (XRD), it can be inferred that after 688 hours, 98% of the Mg was removed from the solid structure during pH 2.57 batch experiments, while SiO2 was retained in an amorphous solid phase, demonstrating the independence of the Mg compared to Si release to the aqueous solution.

Effect of Carbon Support on the Electrocatalytic Performance of the Pt Nanoparticles Toward Oxidation of Formic Acid

Nowadays, fuel cells (FCs) attracted a great deal of attention due to their many applications and advantages: Higher efficiency than diesel or gas engines, less pollution than fossil fuels, no using fuels such as oil and gas and reducing economic dependence on fossil fuel producing countries and easy maintenance are the advantages of FCs. However, the obstacles encountered FCs commercialization’s are mainly expensive electrocatalyst materials such as platinum (Pt), it’s poisoning by intermediates like as CO and sluggish electrooxidation kinetics of fuels. For this reasons, in order to minimize the amount of Pt and accordingly total cost of FCs and also decreasing the poisoning effects, Pt particles are deposited on/in different conductive supports. Herein we investigated the effect of carbon nanoparticles (CNPs) and reduced graphene oxide (RGO) nanosheets on the carbon-ceramic electrode (CCE) as support for Pt nanoparticles (PtNPs) toward formic acid electro-oxidation. PtNPs were successfully deposited on the CNPs and RGO with electrochemical method. The fabricated nanocomposites were characterized by the field emission scanning electron microscopy, energy-dispersive X-ray and X-ray powder diffraction spectroscopy. The electrocatalytic activities of the prepared electrocatalysts for oxidation of formic acid were investigated in 0.1 M H2SO4 solution by electrochemical techniques including cyclic voltammetry (CV) and chronoamperometry (CA). The results of the experiments revealed that the PtNPs on the CNPs, PtNPs/CNPs/CCE, shows more electrocatalytic activity than the RGO nanosheets support. This high electrocatalytic efficiency of the PtNPs/CNPs/CCE can be attributed to large specific surface area and unique structure of CNPs that is being used as support. The influence of some experimental agents on the electrocatalytic activity of the PtNPs/CNPs/CCE was investigated and the optimal conditions were suggested. The present investigation reveals that the PtNPs/CNPs/CCE is a promising electrocatalyst for the formic acid electro-oxidation reaction in FCs. Preparation and electrocatalytic performance of carbon support and alone PtNPs toward oxidation of formic acid.

Preparation of magnetite/multiwalled carbon nanotubes/metal-organic framework composite for dispersive magnetic micro solid phase extraction of parabens and phthalate esters from water samples and various types of cream for their determination with liquid chromatography

In the current study, MMWCNTs@MIL-101(Cr) (Fe3O4/multiwalled carbon nanotubes/MIL-101(Cr)) was synthesized and utilized as a new sorbent for the first time. It was employed successfully for the extraction of parabens and phthalate esters (PEs) from water and cream samples prior to their quantification with HPLC-DAD. The prepared metal-organic-framework (MOF) was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDX), EDX mapping, thermogravimetric analysis (TGA), vibrating-sample magnetometer (VSM) and X-ray powder diffraction (XRD). Three phthalate esters (dimethyl phthalate (DMP), diethyl phthalate (DEP), diallyl phthalate (DAP)) and two parabens (methylparaben (MP) and butylparaben (BP)) were chosen as model analytes. Several experimental factors affecting the extraction efficiency, including pH value, nanosorbent amount, sorption time, salt concentration, sample volume, type and volume of the eluent, and elution time were investigated. The optimization of the extraction method was carried out by response surface methodology (RSM) and desirability function (DF) approach. Under the opted conditions, the method was linear in the range of 0.1–1500 μg L−1 with coefficients of determination > 0.9991. The limits of detection of PEs and parabens were found in the range of 0.03-0.15 μg L−1 (S/N = 3). The relative standard deviations were less than 7.5% and the extraction recoveries ranged from 38.04 to 70.62%. The present method was simple, rapid, inexpensive and environmentally friendly and was successfully utilized for the determination of PEs and parabens in water samples and various types of cream samples with satisfactory results.

Synthesis of MCM-41 Immobilized (Phenoxy)Imine Palladium(II) Complexes as Recyclable Catalysts in the Methoxycarbonylation of 1-Hexene

The immobilization of 2-phenyl-2-((3(tryethoxysicyl)propyl)imino)ethanol (HL1) and 4-methyl-2-(((3(triethoxysilyl)propyl)imino)methyl)phenol (HL2) on MCM-41 afforded the respective ligands HL1-MCM-41 (HL3) and HL2-MCM-41 (HL4). The treatment of complexes Pd(L1)2 and Pd(L2)2 with MCM-41 afforded the immobilized complexes (Pd(L1)2)-MCM-41 (1) and (Pd(L2)2)-MCM-41 (2) respectively. Separately, the reactions of HL3 and HL4 with Pd(NCMe)2Cl2 produced the immobilized complexes Pd(HL3)Cl2 (3) and Pd(HL4)Cl2 (4) respectively. The immobilized compounds were characterized by FT-IR, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), energy-dispersive X-ray (EDX), Thermogravimetric Analysis (TGA) and X-ray Powder Diffraction (XRD). All the complexes (1–4) formed active catalysts in the methoxycarbonylation of 1-hexene to give linear and branched esters. The catalysts were recycled four times without the loss of catalytic activity. Hot filtration experiments established the absence of leaching, and the heterogeneous nature of the active species was derived from mercury drop experiments.

Microstructural, Mineralogical and Petrographical Characteristics of the Medieval Ceramics from the Studenica Monastery (UNESCO World Heritage Site): Implications on the Pottery Technology and Provenance of The Raw Material.

On the basis of optical microscopy, scanning electron microscopy with energy-dispersive spectrometry and X-ray powder diffraction analyses, we present detailed mineralogical and petrographical characteristics of 63 samples of cooking and tablewares, which originate from two Medieval horizons (S1 and S2) in the Studenica Monastery, as well as of three samples of clays regarded as possible pottery raw material. The composition of the ceramic matrix is compatible with the composition of local clay and clasts that reflect the geology of the Studenica's surroundings. This indicates that almost all studied vessels are unequivocally made locally. However, four wares may represent imports because they show similarities with Byzantine sgraffito wares, and ceramics from the Peloponnese (13th century). In terms of technological and morphological characteristics, the studied pottery collection represents a standardized production. Firing temperatures, estimated according to the level of matrix crystallinity, mineral reactions, and the mode of the appearance of fracture surfaces, indicate that most of cooking wares were fired at 600-700°C. All glazed wares, including tablewares and cooking pots from both S1 and S2, were fired at minimum 800-900°C. Along with technological and morphological standardization the characteristics of the studied collection show knowledge of traditional skills as well as trends within the Byzantine artistic craft circle.

Rapid room-temperature synthesis of cadmium zeolitic imidazolate framework nanoparticles based on 1,1′-carbonyldiimidazole as ultra-high-efficiency adsorbent for ultrasound-assisted removal of malachite green dye

In this paper, zeolitic imidazolate framework nanoparticles based on cadmium and 1,1′-carbonyldiimidazole (Cd-ZIF) were prepared. The Cd-ZIF was utilized for ultrasound-assisted removal of malachite green (MG) dye. The Cd-ZIF was characterized through scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectrometry, Brunauer–Emmett–Teller (BET), energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD). Experimental results revealed that Cd-ZIF could bind the cationic dye using ultra-high adsorption capacity more easily compared with other absorbents. The pseudo second-order and Sips models presented better fit for the uptake of MG as compared with other kinetic and isotherm models. The experimental maximum adsorption capacity of MG onto Cd-ZIF was 3324.17 mg/g at 25 °C. The extremely high performance of Cd-ZIF for adsorption of the MG dye with high adsorption capacity indicated that the Cd-ZIF could be developed to a large scale. The thermodynamic parameters and Ea values confirmed that the adsorption was a spontaneous, chemical and endothermic reaction. The investigation exhibited that the adsorption mechanism may be mainly controlled by both the π-π stacking and electrostatic interaction. Finally, regeneration results illustrated that the adsorbent can be recycled seven times such that its high stability and applicability will continue to be maintained.

Characterization of Brittle Phase in Magnesium Based Materials Prepared by Powder Metallurgy

Magnesium-zinc based materials are characteristic with the creation of intermetallic phases, strongly influencing material mechanical properties. Mg-Zn powder mixture (10 % wt. Zn) was processed by the hot pressing method under 500 MPa at 300 °C. Microstructure of the prepared material was analyzed in terms of light optical microscopy and scanning electron microscopy. Chemical and phase composition of the processed material were analyzed by energy-dispersive X-ray spectroscopy and X-ray powder diffraction, respectively. Microhardness testing was adopted to characterize created structure mechanical properties on the microscopic level. Depending on the Mg-Zn powder mixture local chemical composition, the structural and chemical analysis of the processed material revealed that it consisted of magnesium and zinc rich areas, and MgZn2 intermetallic phase. The MgZn2 intermetallic phase belongs to the so-called Laves phases group with the general formula AB2. Laves phases are characteristic with high hardness and the related high brittleness. Their presence in the material usually results in deterioration of mechanical properties such as strength and toughness. The microhardness of magnesium and zinc rich areas in the processed material was 58±1 HV 0.025 and 47 ±1 HV 0.025, respectively, while the value of the microhardness for MgZn2 intermetallic phase was 323±12 HV 0.025. Different behavior and mechanical properties of the present phases was observed on the fracture surfaces of specimens broken during the 3-point bend test. While brittle fracture was a characteristic feature for MgZn2 intermetallic phase, the rest of the material exhibited more ductile fracture behavior with characteristic transgranular failure.

High pressure high temperature devitrification of Fe78B13Si9 metallic glass with simultaneous x-ray structural characterization

Changes in bulk crystallization behavior following devitrification at high pressure are investigated for a Fe78B13Si9 composition metallic glass using in-situ energy dispersive x-ray powder diffraction. Crystallization with time was evaluated for a series of measurements to a maximum pressure of 5.63 ± 0.15 GPa for the Fe78B13Si9 glass. Pressure was found to strongly affect onset bulk crystallization temperature Tx. Crystallization at each pressure was found to progress in two stages. In the first stage, α-Fe precipitates and in the second Fe2B forms while α-Fe continues to crystallize. Complementary high pressure room temperature studies were conducted.

Isothermal Section of Er-Ag-Sn System at 873 K

The isothermal section of the Er-Ag-Sn system at 873 K was constructed with the use of scanning electron microscopy, energy-dispersive x-ray microanalysis and x-ray powder diffraction. Two ternary compounds were confirmed at this temperature: ErAgSn (LiGaGe structure type, P63mc, Z = 2, a = 4.6595(2) A, c = 7.2872(3) A) and non-stoichiometric phase ErAg1−xSn2+x (Cu3Au structure type, Pm-3m, Z = 1). For the last one homogeneity range was established (0.08 < x < 0.24) and lattice parameters were determined (a = 4.5007(4), 4.5040(2), 4.5107(1), 4.5412(1) A for the compositions Er25.4Ag23.4Sn51.2, Er25.7Ag23.0Sn51.3, Er25.7Ag21.7Sn52.6, Er25.2Ag18.6Sn56.2 (at.%) respectively). Melting point of the phase Er25.7Ag21.7Sn52.6 (at.%) was determined to be 1199 K by differential thermal analysis.

Simultaneous voltammetric determination of hydroquinone and catechol by using a glassy carbon electrode modified with carboxy-functionalized carbon nanotubes in a chitosan matrix and decorated with gold nanoparticles

The authors describe a method to anchor gold nanoparticles (AuNPs) on carboxy-functionalized multi-walled carbon nanotubes (c-MWCNTs) utilizing chitosan as dispersing and protective agent. A sensor for the simultaneous determination of hydroquinone and catechol was then fabricated by placing this nanocomposite on a glassy carbon electrode (GCE). The morphology and composition of the nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray powder diffraction. The electrochemical behavior of the modified GCE was studied by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The modified GCE exhibits good electrooxidative activity towards hydroquinone and catechol and therefore was used for simultaneous determination of both, with typical voltages of 30 and 130 mV (vs. SCE). A linear reponse is found for the 0.5 μM to 1.5 mM hydroquinone concentration range, and for the 5.0 μM to 0.9 mM catechol concentration range. The respective lower detection limits are 0.17 and 0.89 μM (at an S/N ratio of 3). The sensitivity is 644.44 μA mM−1 cm−2 for hydroquinone and 770.98 μA mM−1 cm−2 for catechol.

Determination of 200 °C Isothermal Section of Al-Ag-Ga Phase Diagram by Microanalysis, X-ray Diffraction, Hardness and Electrical Conductivity Measurements

Ternary Al-Ag-Ga system at 200 °C was experimentally and thermodynamically assessed. Isothermal section was extrapolated using optimized thermodynamic parameters for constitutive binary systems. Microstructure and phase composition of the selected alloy samples were analyzed using light microscopy, scanning electron microscopy combined with energy-dispersive spectrometry and x-ray powder diffraction technique. The obtained experimental results were found to be in a close agreement with the predicted phase equilibria. Hardness and electrical conductivity of the alloy samples from four vertical sections Al-Ag80Ga20, Al-Ag60Ga40, Ag-Al80Ga20 and Ag-Al60Ga40 of the ternary Al-Ag-Ga system at 200 °C were experimentally determined using Brinell method and eddy current measurements. Additionally, hardness of the individual phases present in the microstructure of the studied alloy samples was determined using Vickers microhardness test. Based on experimentally obtained results, isolines of Brinell hardness and electrical conductivity were calculated for the alloys from isothermal section of the ternary Al-Ag-Ga system at 200 °C.

Synergic analytical strategy to follow the technological evolution of Campanian medieval glazed pottery

Three classes of medieval lead-tin-glazed ceramics (protomajolica, transition enamel pottery and white enamel pottery), from the archaeological site of Castello del Monte in Montella (Avellino, southern Italy), were investigated. Inductively coupled plasma–mass spectrometry (ICP-MS), optical and scanning electron microscopy with energy-dispersive X-ray spectroscopy (OM and SEM-EDS) and X-ray powder diffraction (XRPD) were carried out on ceramic bodies, coatings and decorations in order to outline the technological features and define the nature of glazes and pigments. The aim of this work, in addition to delineating the features of production, is to confirm the archaeological hypothesis that transition enamel pottery produced between the fourteenth and fifteenth centuries, although having much in common with the protomajolica, is in fact a version of white enamel pottery, characterised by morphological and ornamental diversity. Our results show that both ceramic bodies and coatings feature different structural and compositional characteristics, linking the three ceramic classes and making it possible to confirm the archaeological hypothesis that transition enamel pottery can be defined as a ceramic class with transitional features between protomajolica and white enamel pottery.

Hydrothermal synthesis of α-Zn2SiO4:V phosphor, determination of oxidation states and structural localization of vanadium ions

The monophase morphologically homogeneous phosphor α-Zn2SiO4:V has been produced by the hydrothermal method. With the use of energy-dispersive analysis and X-ray powder diffraction analysis, it was established that the ratio of cations Zn:Si:V corresponded to the formula Zn2Si0.9V0.1O4. The charge state of vanadium ions was determined by the spectroscopic methods. Maxima of the bands in the luminescence spectra correspond to V5+ (523nm) and V3+ (720nm) centers. The small width of the EPR signal hyperfine structure components indicates the presence of single V4+ centers, their contribution is not greater than 0.1% of the total vanadium content. The presence of a broad structureless component in the EPR spectrum was explained by the fact that the main amount of the dopant ion was united in the areas containing V5+, V4+ and V3+ ions. V4+ ions and V5+ ions with high probability occupy silicon positions in the lattice.

Reduced graphene oxide–multiwalled carbon nanotubes composites as sensing membrane electrodes for DNA detection

Thin films of reduced graphene oxide–multiwalled carbon nanotube (rGO–MWCNT) composites were demonstrated as sensing membrane electrodes for single-stranded DNA (ssDNA) detection. The morphology of the rGO–MWCNT composite thin films was observed via field emission scanning electron microscopy. The GO sheet and MWCNTs were clearly obtained, and the MWCNTs were uniformly distributed on the surface of the GO. The chemical bonding of the rGO–MWCNTs was examined using Fourier transform infrared spectroscopy. The element compositions of carbon, silicon, and oxygen were confirmed via energy-dispersive X-ray spectroscopy and X-ray powder diffraction analysis. The biosensor demonstrated high sensitivity to the ssDNA target with a linear range from 500 to 100 pM. Furthermore, the biosensor demonstrated good selectivity, reproducibility, and long-term stability for DNA detection. Since, the biosensor responded very-well and demonstrated excellent detection capabilities, it is highly recommended to be used in detecting specific biomarkers and other targeted proteins.

Bacterial bioleaching of low grade nickel limonite and saprolite ores by mixotrophic bacteria

Utilization of indigenous bacteria should be considered to establish a successful biohydrometallurgical process. In this study, mixrotrophic iron-oxidizing bacterial consortia consisting of Comamonas testosteroni, Alicyclobacillus ferrooxydans and Pantoea septic which were isolated from Indonesian mineral ores were examined to determine their abilities to recover nickel from limonite and saprolite ores in the bioleaching experiments using stirred tank reactors. The nickel bioleaching experiments inoculated with the bacterial consortia were carried out using coarse limonite ores and weathered saprolite ores with pulp density of 10% w/v. Abiotic controls were also carried out replacing the inocula by the sterile medium. The bioleaching processes were monitored by measuring Ni and Fe contents and pH of the leaching solution as well as the total bacterial enzymatic activity measured as FDA hydrolytic activity. The effect of leaching on the mineralogy of laterite ores was investigated by the scanning electron microscope equipped with energy-dispersive spectroscopy (SEM-EDS) and X-ray powder diffraction (XRD). After 28 days of incubation, the FDA hydrolytic activity was observed in both bioleaching experiments containing limonite (17.2 μg fluorescein/mL) and saprolite ores (16.9 μg fluorescein/mL). The leached Ni and Fe in the bioleaching experiments containing limonite ores (30% Ni and 5.6% Fe) was greater than that in abiotic controls (1% Ni and 0.1% Fe) with the pH range of 2.5 to 3.5. However, the bacterial consortia were less capable of bioleaching of Ni (2.5%) with the similar leached Fe (6%) from the saprolite ores. In abiotic controls, the medium pH remained relatively constant (pH 6). It was concluded that these bacterial isolated as the consortium were capable of nickel bioleaching (precious metal) more effectively than iron (gangue metal), thus being applicable to the commercial processing of the difficult-to-process low-grade nickel laterite ores in Indonesia.