Spectroscopic Determination of Fluoride Using Eriochrome Black T (EBT) as a Spectrophotometric Reagent from Groundwater

Fluoride health problem is a great concern worldwide, most often as a result of groundwater intake. Thus, determination of fluoride is vital to take appropriate measures upon fluoride contamination of water. Potentiometric method of analysis is reliable for the determination of fluoride in various samples. In addition, spectroscopic methods are found important to quantify fluoride levels from water; however, several factors hinder its easier determination. Among the bottlenecks, the use of toxic chemicals and tedious steps in preparing chemicals (e.g., SPADNS method) are to mention a few. In this study, a spectrophotometric method was developed for the determination of fluoride from groundwater using Eriochrome Black T (EBT) as a spectroscopic reagent. Experimental parameters that influence the determination of fluoride including ligand type, kinetics, pH, and ligand-to-metal ratio were assayed. Evaluation of fluoride levels showed that Beer–Lambert’s law is obeyed in the range of 0.3–5.0 mg/L at 544 nm. The calibration curve, resulting in good linearity (R2 = 0.9997), was considered during quantitative analysis of the samples and in the spiking analysis. The limits of detection (LOD) and quantification (LOQ) of the method were found to be 0.19 and 0.64 mg/L, respectively. The precision studied in terms of intraday and interday at three concentration levels showed less than 5.4% RSD. Applicability of the method was investigated by analyzing groundwater samples spiked with fluoride standards, and satisfactory recoveries in the range of 98.18–111.4 were demonstrated. The developed spectrophotometric method has been successfully applied for fluoride determinations in groundwater samples. Thus, it could be used as an attractive alternative for the determination of fluoride from groundwater.

Magnetic Phase Diagram of the MnxFe2−xP1−ySiy System

The phase diagram of the magnetocaloric MnxFe2−xP1−ySiy quaternary compounds was established by characterising the structure, thermal and magnetic properties in a wide range of compositions (for a Mn fraction of 0.3 ≤ x < 2.0 and a Si fraction of 0.33 ≤ y ≤ 0.60). The highest ferromagnetic transition temperature (Mn0.3Fe1.7P0.6Si0.4, TC = 470 K) is found for low Mn and high Si contents, while the lowest is found for low Fe and Si contents (Mn1.7Fe0.3P0.6Si0.4, TC = 65 K) in the MnxFe2−xP1−ySiy phase diagram. The largest hysteresis (91 K) was observed for a metal ratio close to Fe:Mn = 1:1 (corresponding to x = 0.9, y = 0.33). Both Mn-rich with high Si and Fe-rich samples with low Si concentration were found to show low hysteresis (≤2 K). These compositions with a low hysteresis form promising candidate materials for thermomagnetic applications.

On the Arrangement of Pentagonal Columns in Tetragonal Tungsten Bronze-Type Nb18W16O93

The evaluation of HAADF-STEM images of a sample with the composition Nb18W16O93 provided new insights into its real structure. The basic structure comprises an intact octahedral framework of the tetragonal tungsten bronze (TTB) type. The partial occupation of the pentagonal tunnels (PT) by metal–oxygen strings determines the oxygen-to-metal ratio (O/ΣM with M = Nb,W). For a large area, the O/ΣM was determined to be 2.755, which is bigger than the value of Nb18W16O93, which is O/ΣM = 2.735. To a large extent, the three-fold TTB superstructure of Nb8W9O47 with a high oxygen content is present (O/ΣM = 2.765). In addition, a new four-fold TTB superstructure was found in small domains. Nb12W11O63 with an O/ΣM = 2.739 obviously accommodates part of the sample’s metal excess compared to the stable phase Nb8W9O47.

On the Arrangement of Pentagonal Columns in Tetragonal Tungsten Bronze-Type Nb18W16O93

The evaluation of HAADF-STEM images of a sample with the composition Nb18W16O93 provided new insights in its real structure. The basic structure comprises an intact octahedral framework of the tetragonal tungsten bronze (TTB) type. The partial occupation of the pentagonal tunnels (PT) by metal-oxygen strings determines the oxygen to metal ratio (O/SM with M = Nb,W). For a large area, the O/SM was determined to be 2.755 which is smaller than the value of Nb18W16O93 which is O/SM = 2. 735. To a large extent, the threefold TTB superstructure structure of Nb8W9O47 with a high oxygen content is present (O/SM = 2.765). In addition, a new fourfold TTB superstructure was found in small domains: Nb12W11O63 with an O/SM = 2.739 obviously accommodates a part of the sample’s metal excess compared to the stable phase Nb8W9O47.

Influence of Carbon: Metal Ratio on Tribological Behavior of Mo-W-C Coating

Mo-W-C coatings with three different C/(Mo+W) ratios (5:1, 2.8:1 and 2.2:1) were deposited by using combined unbalanced magnetron sputtering (UBMS) and high-power impulse magnetron sputtering (HIPIMS) technology. The influence of the C/(Mo+W) ratio on coating microstructure and related tribological properties at ambient temperature and at 200 °C were studied in lubricated condition (up to 7500 m and 1800 m of sliding distances, respectively). Results showed that a decrease in the C/(Mo+W) ratio could be correlated with an increase in coating thickness, adhesion strength, hardness and elastic modulus values, and a decrease in the degree of graphitization. At ambient temperature, outstanding tribological properties (very low friction and negligible wear) were observed irrespective of the C/(Mo+W) ratio. At 200 °C, low C/(Mo+W) ratios (2.8:1 and 2.2:1) were found particularly beneficial to achieve excellent tribological properties. The keys to significant friction reduction at 200 °C were (i) in situ formation of MoS2 and WS2 due to tribo-chemical reactions and (ii) presence of amorphous carbon debris particles in the protective tribolayer. With an increase in sliding distance, the tribolayer gradually lowered the friction coefficient by protecting both the coating and counterpart from severe wear. On the other hand, a high C/(Mo+W) ratio (5:1) led to low friction but noticeable abrasive wear at 200 °C.

Reclamation of Cobalt and Copper from Single- and Co-contaminated Wastewater via Carbonate and Hydroxide Precipitation

Wastewater containing cobalt and copper comprised of plating wash water, plant wash water, and equipment cooling and wash water is generated in the electroplating industry. These metals can be detrimental to humans, animals, plants, and the environment. Thus, it is necessary to treat electroplating wastewater to remove these toxic metals. Carbonate and hydroxide precipitation were utilized for the removal of Co(II) and Cu(II) from synthetic electroplating wastewater by jar tests in this work. The effects of solution pH, precipitant-to-metal ratio, and type of precipitant on the precipitation efficiency of cobalt and copper from the single- and co-contaminated systems were investigated. Carbonate precipitation achieved higher removal efficiency for both target metals in the single- and co-contaminated wastewater streams. Furthermore, it can operate at relatively low pH range of about 7.0-8.0. Cobalt in both pollutant systems was almost completely removed at pH 10.0 using both precipitant systems. Copper was found to be easily removed which was possibly brought about by precipitation-adsorption mechanism. The extent of the co-removal of cobalt with copper is significantly pH dependent. The effect of precipitant-to-metal ratio for cobalt and copper treatment varied in single- and co-contaminated streams. Carbonate precipitation led to lower sludge density than that of hydroxide precipitation.

Influence of Pd and Pt Promotion in Gold Based Bimetallic Catalysts on Selectivity Modulation in Furfural Base-Free Oxidation

Furfural (FF) has a high potential to become a major renewable platform molecule to produce biofuels and bio-based chemicals. The catalytic performances of AuxPty and AuxPdy bimetallic nanoparticulate systems supported on TiO2 were studied in a base-free aerobic oxidation of furfural to furoic acid (FA) and maleic acid (MA) in water. The characterization of the catalysts was performed using standard techniques. The optimum reaction conditions were also investigated, including the reaction time, the reaction temperature, the metal ratio, and the metal loading. The present work shows a synergistic effect existing between Au, Pd, and Pt in the alloy, where the performances of the catalysts were strongly dependent on the metal ratio. The highest selectivity (100%) to FA was obtained using Au3-Pd1 catalysts, with 88% using 0.5% Au3Pt1 with about 30% of FF conversion at 80 °C. Using Au-Pd-based catalysts, the maximum yield of MA (14%) and 5% of 2(5H)-furanone (FAO) were obtained by using a 2%Au1-Pd1/TiO2 catalyst at 110 °C.

Elucidating Synergistic Effects of Different Metal Ratios in Bimetallic Fe/Co-N-C Catalysts for Oxygen Reduction Reaction

Lowering or eliminating the noble-metal content in oxygen reduction fuel cell catalysts could propel the large-scale introduction of commercial fuel cell systems. Several noble-metal free catalysts are already under investigation with the metal-nitrogen-carbon (Me-N-C) system being one of the most promising. In this study, a systematic approach to investigate the influence of metal ratios in bimetallic Me-N-C fuel cells oxygen reduction reaction (ORR) catalysts has been taken. Different catalysts with varying ratios of Fe and Co have been synthesized and characterized both physically and electrochemically in terms of activity, selectivity and stability with the addition of an accelerated stress test (AST). The catalysts show different electrochemical properties depending on the metal ratio such as a high electrochemical mass activity with increasing Fe ratio. Properties do not change linearly with the metal ratio, with a Fe/Co ratio of 5:3 showing a higher mass activity with simultaneous higher stability. Selectivity indicators plateau for catalysts with a Co content of 50% metal ratio and less, showing the same values as a monometallic Co catalyst. These findings indicate a deeper relationship between the ratio of different metals and physical and electrochemical properties in bimetallic Me-N-C catalysts.

The Unusual Role of Pro in Cu(II) Binding by His2-Cyclopentapeptide

In this paper, we present findings from studying the interaction of copper(II) ions with the His2-cyclopentapeptide and the role of proline used for the purpose of potentiometric titration and UV-Vis, CD and EPR spectroscopic measurements. Experiments of two homodetic peptides differing by one amino acid residue were conducted for a ligand to metal ratio of 1:1 in the pH range 2.5–11.0. The presented studies reveal that peptides form only mononuclear complexes, and the CuH2L complex appears in the system first (for both L1 and L2). Study results show that the presence of Pro influences the structure of formed complexes and their stabilities and has a strong impact on the efficiency of copper(II) coordination.

Thermodynamic Study on the Dissociation and Complexation of Coumarinic Acid with Neodymium(III) and Dioxouranium(VI) in Aqueous Media

In the frame of a systematic study on the sequestering ability of natural antioxidants towards metal cations, the complexation of coumarin-3-carboxilic acid (HCCA) with neodymium(III) and dioxouranium(VI) (uranyl, UO22+), and overall stability constants of the resulting complexes, were evaluated from the pH-potentiometric titration data at 37 °C and in an aqueous solution (i.e., 0.16 mol/L NaClO4). The graphic representation of the complex’s concentration curves is given by the distribution diagrams, which provide a depiction of all the species present in the solution in the selected pH ranges. The protonation constant of HCCA was also determined to evaluate the competition of the ligand for the metal cations and H+. The ligand-to-metal concentration ratio was varied between 1 and 10, and the hydrogen ion concentration was decreased stepwise until the incipient precipitation of a basic salt of the metal, which occurred at different values depending on the specific metal cation and the ligand to metal ratio. Speciation profiles obtained by potentiometric titrations and supported by UV-Vis data show that a complexation occurs at a ligand-to-Nd(III) and to –UO22+ ratio of 1:1 and 2:1, with different degrees of deprotonation: Nd(OH)(CCA)+, UO2(OH)(CCA), UO2(OH)2(CCA)−, and Nd(OH)(CCA)2, UO2(CCA)2 and (UO2)2(OH)2(CCA)2.