Species Distribution Diagrams Research Articles

Optical and Structural Characterization of Cd-Free Buffer Layers Fabricated by Chemical Bath Deposition

Chemical bath deposition (CBD) is a suitable, inexpensive, and versatile synthesis technique to fabricate different semiconductors under soft conditions. In this study, we deposited Zn(O;OH)S thin films by the CBD method to analyze the effect of the number of thin film layers on structural and optical properties of buffer layers. Thin films were characterized by X-ray diffraction (XRD) and UV-Vis transmittance measurements. Furthermore, we simulated a species distribution diagram for Zn(O;OH)S film generation during the deposition process. The optical results showed that the number of layers determined the optical transmittance of buffer layers, and that the transmittance reduced from 90% (with one layer) to 50% (with four layers) at the visible range of the electromagnetic spectrum. The structural characterization indicated that the coatings were polycrystalline (α-ZnS and β-Zn(OH)2 to four layers). Our results suggest that Zn(O;OH)S thin films could be used as buffer layers to replace CdS thin films as an optical window in thin-film solar cells.

Algorithm to obtain the species distribution diagrams and solubility curves for depositing ZnS, ZnO, and Zn(OH)2 films in aqueous solution

This work presents an algorithm to obtain the species distribution diagrams and the solubility curves for a chemical bath system containing ZnCl2, NH4NO3, KOH, and SC(NH2)2 in aqueous solution. This algorithm is useful to obtain the better chemical conditions for synthesizing high quality ZnO, ZnS, or Zn(OH)2 films by the chemical bath deposition technique. The algorithm requires to identify all the formed species from the chemical reagents. The chemical conditions can be obtained in a range of temperature from 25 °C to 90 °C. The better conditions to obtain the mentioned films are explained and justified with the respective optical, morphological and structural characterizations.

Critical Reappraisal of Methods for Measuring Urine Saturation with Calcium Salts.

Background: Metabolic and physicochemical evaluation is recommended to manage the condition of patients with nephrolithiasis. The estimation of the saturation state (β values) is often included in the diagnostic work-up, and it is preferably performed through calculations. The free concentrations of constituent ions are estimated by considering the main ionic soluble complexes. It is contended that this approach is liable to an overestimation of β values because some complexes may be overlooked. A recent report found that β values could be significantly lowered upon the addition of new and so far neglected complexes, [Ca(PO4)Cit]4− and [Ca2H2(PO4)2]. The aim of this work was to assess whether these complexes can be relevant to explaining the chemistry of urine. Methods: The Ca–phosphate–citrate aqueous system was investigated by potentiometric titrations. The stability constants of the parent binary complexes [Cacit]− and [CaPO4]−, and the coordination tendency of PO43− toward [Ca(cit)]− to form the ternary complex, were estimated. βCaOx and βCaHPO4 were then calculated on 5 natural urines by chemical models, including or not including the [CaPO4]− and [Ca(PO4)cit]4− species. Results: Species distribution diagrams show that the [Ca(PO4)cit]4− species was only noticeable at pH > 8.5 and below 10% of the total calcium. β values estimated on natural urine were slightly lowered by the formation of [CaPO4]− species, whereas [Ca(PO4)cit]4− results were irrelevant. Conclusions: While [CaPO4]− species have an impact on saturation levels at higher pHs, the existence of ternary complex and of the dimer is rejected.

Synthesis and characterisation of ZnS thin films obtained without complexing agent by the chemical bath technique

ABSTRACT Zinc sulphide (ZnS) thin films were synthesised by chemical bath deposition technique without using complexing agent. A physicochemical study was realized on the growth solution composed of ZnCl2, KOH, and SC(NH2)2. The bath solution was at 60°C and pH values of 11.5, 12, and 12.5 were selected for growing the material. The species distribution diagrams, and solubility curves show that the growth mechanism requires the presence of zinc-hydroxide ions, and alkaline pH for growing the ZnS. The physicochemical properties of the samples improve as the pH of the solution increases. Samples deposited at pH=12.5 present a cubic structure (sphalerite) and bandgap energy of 3.72 eV, consistent with bulk-ZnS. For comparison, additional chemical baths were prepared by using NH3 as complexing agent; however, the properties of those samples result inferior. This methodology was validated by depositing ZnS films at 40°C without the complexing agent, obtaining similar results.

Flotation behavior and mechanism of styrene phosphonic acid as collector on the flotation separation of fluorite from calcite

SPA was selected as the collector to separate fluorite from calcite. The greatest difference of recovery of fluorite and calcite was achieved with SPA dosage of 20 mg/L and pH 6.0, at which the recovery of fluorite and calcite was 98.79% and 12.55% respectively. The AFM 3D images of fluorite and calcite in the absence and presence of SPA revealed that the amount of SPA adsorbed on fluorite was much more than that on calcite, which accounted for the difference of flotation recovery. The flotation adsorption mechanism of SPA on fluorite was further explored by FT-IR, zeta potential measurements, XPS and first-principles calculation. It was found that SPA was adsorbed on fluorite surface by chemical interaction, and the calcium atom on fluorite was the main active site to react with SPA. The species distribution diagram of SPA in different pH revealed that when pH was 6, the main species of SPA were monovalent ion (C8H7PO3H−) and divalent ion (C8H7PO32−). Thus, there were three possible adsorption models for SPA to be adsorbed on fluorite surface, including coordination between single oxygen and single calcium, coordination between double oxygen and single calcium, and coordination between double oxygen and double calcium. The first-principles calculation demonstrated that among these three possible adsorption models, the adsorption model of coordination between single oxygen and single calcium was the most possible adsorption model.

Role of Ammonia on the Growth Mechanism of ZnO Films Deposited at Ambient Temperature

Zinc oxide (ZnO) was synthesized by chemical bath deposition (CBD) technique at room temperature. The species distribution diagrams, and the solubility curves were used for determining the better chemical conditions required to evaluate the ammonia role for obtaining high quality ZnO films. ZnSO4, NH4NO3, and KOH were the chemical reagents used for the bath. Three different pH zones between 9 and 13 were selected to synthesize the films. X-ray diffraction analysis showed that the pH value of the chemical bath and the ammonia concentration influences on the structure crystalline of the deposited films. Three different surface morphologies were obtained according to the pH of the solution. The bandgap energy values measured in the deposited films range from 3.52 eV to 3.77 eV. The estimated Urbach’s tails energy values confirmed that samples exhibited high crystallinity. By controlling the ammonia concentration and pH, deposition of high quality ZnO films can be obtained at room temperature.

Solvent Extraction of Sc(III) by D2EHPA/TBP from the Leaching Solution of Vanadium Slag

The solvent extraction of scandium by the mixture of di-(2-ethylhexyl) phosphate (D2EHPA) and tri-n-butyl phosphate (TBP) has been investigated in the acidic leaching solution of vanadium slag. Thermodynamic analysis of the species distribution diagrams on the Sc-S-H2O system showed that scandium mainly exists as Sc3+ and Sc(SO4)+, and sulfur mainly exists as HSO4− in the actual leaching solution of vanadium slag (pH = −0.75). The extraction process was studied to optimize various parameters such as the extractant concentration, dosage of TBP, phase ratio, and stirring speed. The results indicated that 83.64% of scandium and less than 2% of co-extracted elements were extracted under optimal conditions. Then, over 95% of the co-extracted elements and less than 1.1% of scandium were scrubbed from the loaded organic phase by 4.0 mol/L of HCl. Finally, 87.20% of scandium was stripped with 2 mol/L of NaOH and 1 mol/L of NaCl at a stripping O/A of 1:1.

Physical properties of chemically deposited ZnS thin films: Role of the solubility curves and species distribution diagrams

A physicochemical analysis was carried out on the chemically deposited ZnS/glass thin films. Solutions were prepared by considering the better chemical conditions obtained from the solubility curves (SCs) and the species distribution diagrams (SDDs) for the ZnCl2–NH4NO3-KOH-SC(NH2)2 system. The range of pH from 11.73 to 12.47 is proposed as a chemical condition obtained from the SCs and SDDs. The effects of these conditions on the structural, optical, morphological and stoichiometric properties of the films deposited at 70 °C were analyzed by x-ray diffraction (XRD), UV–Vis spectroscopy, scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS). XRD results show a main cubic crystalline structure (sphalerite) with (111) orientation, while the bandgap energy of the samples increases value from 3.44 eV to 3.72 eV with the increased pH. XPS technique evidenced a reduction of the Zn(OH)2 compound while the [Zn]/[S] ratio improved when the pH increased. SEM images allowed observing homogeneous surfaces and coalescence of grains on the surface of films.

Protocatechuic acid-metal-nicotine complexation study for chelation of smoking-related poisoning

Nephropathy in tobacco smoker is postulated to be caused by nicotine (Nic) and catalyzed by various heavy metals (M(II) = Ni(II), Pb(II), and Cd(II)) contained in commercial cigarettes. Once absorbed through the lungs, these compounds will eventually be ended in the kidney, and thus, trigger various diseases. Metal chelation therapy is known as one of the efficient treatments to reduce the level of toxic metal in intoxicated patients. Here the interaction tendency of Nic and heavy metals to form complexes was investigated at a physiological condition (310.15 K and 0.15 mol·dm−3 NaCl). The stability constant of the metal-Nic complex obtained in this study shows the possible binding between these two compounds. For the simultaneous removal of heavy metals and Nic, protocatechuic acid (PCA) was used since this antioxidant is also known to be deposited in the kidney. Thus, the interaction between PCA, Nic, and heavy metals is possible. In this work, stability constant of NiPCANic, NiPCA2Nic, PbPCANic, CdPCANic, and CdPCA2Nic were determined. Species distribution diagram of the ternary system showed that MPCANic complexes could be dominantly formed in pH 7.4 system when an excess amount of antioxidant was added. This result suggests the possible usage of antioxidants for the simultaneous removal of Nic and heavy metals via the metal chelation principle.

Thiosulphate leaching of gold in the Cu–NH3–S2O32−–H2O system: An updated thermodynamic analysis using predominance area and species distribution diagrams

Thiosulphate, as an environmentally friendly lixiviant, is currently identified as the most promising alternative to cyanide for the extraction of gold from ores in sensitive locations. The Cu(II) ammine complexes acts as the catalytic oxidant to increase the thiosulphate leaching rate of gold, which also causes an undesirable high consumption of thiosulphate. Due to the complex solution chemistry of Cu–NH3–S2O32−–H2O system, fundamentally supported mechanisms to justify the catalytic effects and the consumption of thiosulphate are yet to be developed. Thermodynamic analysis offers essential information on which chemical species that could form and how these species influence the solution chemistry under various conditions. In this paper, predominance area and species distribution diagrams for gold leaching in the Cu–NH3–S2O32−–H2O system were constructed from a series of calculations using updated thermodynamic data. The diagrams reveal insights into the thermodynamics of gold dissolution, thiosulphate stability and redox behaviour of Cu(II)/Cu(I) couples. Analysis of the results presented in this paper can provide a theoretical basis for the complex thiosulphate leach solution chemistry that allows for a better understanding on the relationships between the redox behaviour of Cu(II)/Cu(I) couples and the behaviours of gold leaching and thiosulphate decomposition.

Binary and ternary nickel (II) complexes with 2-methylquinoline-8-carboxylic acid and some amino acids

ABSTRACT In this work, the ligand 2-methylquinoline-8-carboxylic acid (HL) was prepared using a modification of a previous protocol, and its protonation constants were studied. The stability constants of the binary nickel (II) – ligand L− and the ternary nickel (II) – ligand L− – amino acids (B−) systems were investigated. The amino acids selected for this study were glycine (Gly), α-alanine (αAla), β-alanine (βAla), proline (Pro), serine (Ser), methionine (Met), threonine (Thr), phenylalanine (Phe), aspartic acid (Asp), glutamic acid (Glu), histidine (His) and cysteine (Cys). The stability constants were pH-metrically measured in 1.0 mol dm−3 NaCl at 25°C. The least squares program LETAGROP was used for the analysis of the potentiometric data. Species distribution diagrams as a function of pH are briefly discussed.

The effect of dissolved calcite species on the flotation of bastnaesite using sodium oleate

The flotation behavior of bastnaesite, a major mineral source of rare earth elements, is strongly affected by the dissolved species of gangue minerals that change the solution chemistry and mineral surface properties. In this work, the effect of dissolved calcite species on the flotation of bastnaesite was investigated by conducting micro-flotation experiments, zeta potential measurements, Fourier-transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) analysis. Micro-flotation experiments confirmed that calcium and carbonate ions in calcite supernatant significantly reduced the flotation of bastnaesite in strongly alkaline condition. Zeta potential measurements showed that the IEP of higher bastnaesite was obtained after the addition of calcite supernatant species. Species distribution diagram demonstrated that the adsorption of sodium oleate on the surface species of bastnaesite was inhibited by the generation of calcium-containing hydroxy complexes and precipitates. FT-IR analysis suggested that the decrease the sodium oleate concentration in solution and the generation of calcium oleate precipitate on the mineral surface are possible reasons for the reduced recovery. XPS analysis further revealed that the metal carbonates and hydroxy complexes of calcium adsorbed on the bastnaesite surface in the presence of calcite supernatant, which concealed the surface active sites, caused the decrease in bastnaesite flotation recovery.

Methoxyphenyl N-sulfamoyloxazolidinone Cu(II) and Co(II) complexes: Synthesis, DFT/B3LYP (B2PLYP) study and molecular docking

Abstract Interactions of methoxyphenyl N-sulfamoyloxazolidinone (SOZ) with Cu(II) and Co(II) ions in ethanol at 25 °C were studied experimentally using UV–Vis spectrophotometry. The data processing with a nonlinear least square fitting allowed the determination of stoichiometries, stability constants of the complexes and species distribution diagrams for each complex against ligand concentration. The solid-state complexes were synthesized and characterized by FT-IR,1 HNMR, thermogravimetric analysis techniques (TGA) and differential scanning calorimetry (DSC) to account for the thermal decomposition of Cu(II) complex. DFT study was performed to obtain insights on SOZ: Cu(II) and/or Co(II) interaction. First, the predicted structural properties of the ligand were compared with the experimental ones obtained from crystallographic data. DFT calculations were performed at B3LYP, B3LYP-D3, B2PLYP and B2PLYP-D3 levels with the same 6–311++G(d,p) basis set and consequently the performance of each exchange functional was tested in the structural properties prediction. Also, global and local chemical reactivity parameters were computed. The most stable metal complexes (1:2) were optimized at B3LYP level in ethanol medium with the CPCM model. Computed FT-IR spectra and TD-DFT results agree with the corresponding experimental data. The interactions were also analyzed and characterized by NBO, MEP and NLO. Finally, a molecular docking was performed to investigate the relative biological activities of the ligand alone and of the metal complexes.

Mechanism of MoO2 electrodeposition from ammonium molybdate solution

Abstract A mechanism study on MoO2 electrodeposition from ammonium molybdate solution was presented via linear sweep voltammetry, species distribution diagram, Raman spectra, Fourier transform infrared spectrometry and X-ray diffractometry. The results show that there exist two reducible species in ammonium molybdate aqueous solution, i.e. M o 7 O 24 6 - and molybdenum ammonium complex. In weak acid medium without NH 4 + , an obvious reduction peak denoting the reduction of M o 7 O 24 6 - to molybdenum(IV) oxides emerges at around −0.7 V (vs SCE). While in neutral and basic solutions without NH 4 + , the dominant species changes to MoO 4 2 - , and accordingly, no reduction peak appears except hydrogen evolution. NH 4 + plays an important role in MoO2 electrodeposition. A new current peak appears at −1.25 V (vs SCE) in both acid and basic solutions, which is attributed to the reduction of molybdenum complex. The effects of solution composition and the electrodeposition conditions on the current efficiency were discussed systematically. By optimizing the electrodeposition conditions, the current efficiency can reach up to 51.9%.

3-Hydroxy-2-Pyrrolidinone as a Potential Bidentate Ligand for in Vivo Chelation of Uranyl with Low Cytotoxicity and Moderate Decorporation Efficacy: A Solution Thermodynamics, Structural Chemistry, and in Vivo Uranyl Removal Survey.

Uranium poses a threat for severe renal and bone damage in vivo. With the rapid development of nuclear industry, it is more urgent than ever to search for potential in vivo uranium chelators. In this work, 3-hydroxy-2-pyrrolidinone (HPD) is investigated as a new potential uranium decorporation ligand. The potentiometric titration measurements were carried out, and the stability constants were determined to be log β110 = 10.5(7), log β120 = 20.7(9), and log β130 = 28.2(4). The species distribution diagram shows that nearly all uranyl is complexed by HPD at pH 7.4 under the defined condition. A single crystal of uranyl and HPD complexes, [(UO2)3O(H2O)3(C4H6NO2)3]·NO3·12H2O (uranyl-HPD), was obtained via an evaporation method. The overall structure of uranyl-HPD is a trimer that consists of three uranyl units and three HPD ligands. The uranyl unit is equatorially coordinated by three oxygen atoms from two HPD agents, one coordinated water molecule, and one μ3-O atom that is shared by three uranyl units. The results of the cytotoxicity assay indicate that the ligand is less toxic than the chelators used clinically (i.e., DTPA-ZnNa3 and 3-hydroxy-1,2-dimethyl-4(1 H)-pyridone (DFP)). The results of the uranium removal assay using the NRK-52E cell show that it could reduce as much as 58% of the uranium content at the cellular level. Furthermore, the in vivo uranium decorporation assays demonstrate that HPD can remove 52% of uranium deposited in the kidney but shows poor uranium removal efficacy in the bone.

Speciation Study of L-ascorbic Acid and its Chelated Cu(II) & Ni(II) Complexes: an Experimental and Theoretical Model of Complex Formation

Different species of L-ascorbic acid and their corresponding complex formation ability with Cu(II) and Ni(II) metal ions in aqueous medium has been studied in the pH range from 2.0-12.5. The stability constants of different complexes of Cu(II) and Ni(II) with the bidentate ligand, L-ascorbic acid were determined theoretically using MINIQUARD software. Speciation of ligand and complex of Cu(II)/Ni(II) ascorbate were experimentally investigated by the titration method in solution within this pH range. Different Cu (II) and Ni(II)-L-ascorbic acid species percentages with variation of pH were calculated within the studied pH range with the help of another computer programs SIM and SPECIES. Different species distribution diagrams and the equilibria for the formation of the species were also investigated and at higher pH, ML2 species was found to be the major species in the case of both the metal complexes. All the theoretical possible structures of Cu(II) and Ni(II) complexes with L-ascorbic acid were optimized and square pyramidal and square planer geometry have been evaluated for Cu(II) and Ni(II) respectively by Gaussian09 software. Their corresponding HOMO-LUMO energy and reactivity parameters such as chemical hardness (ç), ionization potential (I), electron affinity (A), electro negativity (χ), chemical potential («), electrophilicity index (ω) have been calculated in order to provide a better understanding of the electronic structure of complexes with the experimental results. Keywords: Cu(II)and Ni(II) complexes, ascorbic acid, molecular speciation, DFT, reactivity parameters.

Deposition of ZnO Thin Films by Chemical Bath Technique: Physicochemical Conditions and Characterization

Zinc oxide (ZnO) was synthesized by chemical bath deposition (CBD) technique at two temperatures (70°C and 90°C). Chemical analysis was carried out on the Zn-NH3-OH zone growth using the species distribution diagrams and the solubility curves in order to determine the parameters to obtain good quality ZnO films. Results show that ZnO films can be obtained when the pH solution is up than 7. Three different pH zones between 7 and 12 were selected for deposition. ZnCl2, NH4NO3, and KOH were the chemical reagents used for the bath. The morphology of the deposited films shows a strong dependence on the pH range of the solution. When the samples are prepared into the Zn(NH3)42+ complexes zone, nano-flowers structures were obtained; whereas, if they are prepared in the zone where the Zn(OH)n2-n ions dominate, nano-flakes were formed. ZnO films deposited at 90°C present highly oriented hexagonal structure (zincite) and a [Zn]/[O]≈1 stoichiometry. While samples deposited at 70°C show degradation in their properties when the pH of the solution increases. By controlling the growth parameters, deposition of the ZnO films and their physical properties can be regulated for determined applications.

Determination of stability constants of ternary copper(II) complexes formed with 2,6-pyridinedicarboxylic acid and several amino acids

ABSTRACTIn this work, the formation of ternary complexes with their respective formation constants in the systems formed by copper (II), 2,6-pyridinedicarboxylic acid (H2Dipi) and the amino acids = histidine (His), aspartic acid (H2Asp), glutamic acid (H2Glu), glycine (HGly), proline (HPro), α-alanine (HαAla), β-alanine (HβAla), serine (HSer), threonine (HThr), phenylalanine (HPhe) and methionine (HMet)). The analysis used potentiometric data analysed with the least-squares program LETAGROP in aqueous solution at 25°C in 1.0 mol.dm−3 KNO3 solution. The relative stability of the ternary complexes is compared with the binary ones using the values of Δlog K and log χ. Subsequently, by using the formation constants, the species distribution diagrams were generated and are briefly discussed here. The Cu (II) -dipicolinic acid-glutamic acid, Cu (II) -dipicolinic acid-glycine and Cu (II) – dipicolinic acid-histidine systems were characterised by UV-Vis molecular absorption spectroscopy and cyclic voltammetry, confirming the formation of ternary complexes with octahedral geometry.

Determination of stability constants of ternary copper(II) complexes formed with picolinic acid and several amino acids

ABSTRACTIn this work, the formation of ternary complexes with their respective formation constants in the systems formed by copper (II), picolinic acid and the amino acids = histidine (His), aspartic acid (HGly), proline (HPro), α-alanine (HαAla), β-alanine (HβAla), serine (HSer), threonine (HThr), phenylalanine (HPhe) and methionine (HMet)) was detected. The analysis involves the use of the potentiometric data with the least-squares program LETAGROP in aqueous solution at 25°C in 1M KNO3 solution. The relative stability of the ternary complexes was compared with the binary ones considering the values of Δlog K and log χ. Subsequently using the formation constants, the species distribution diagrams were generated and are briefly discussed here. The Cu (II)–picolinic acid–glutamic acid, Cu (II)–picolinic acid–serine and Cu (II)–picolinic acid–histidine systems were characterised by UV–Vis molecular absorption spectroscopy and cyclic voltammetry, obtaining results that confirm the formation of ternary complexes with octahedral geometry.

Kinetic of growth of chemically deposited ZnS films near room temperature conditions

The growth mechanism of ZnS films deposited by chemical bath at temperatures ranging between 25 °C and 55 °C was investigated by a kinetic analysis. For the ZnS thin films deposition, zinc chloride, potassium hydroxide, ammonium nitrate, and thiourea were used as chemical reagents. The effects of the bath temperature, thiourea concentration and deposition time on the ZnS formation were investigated. The species distribution diagrams suggested that the growth mechanism involves bisulfide ions (HS−) for the sulfur species as well as zinc hydroxide complexes ( and ). Higher thickness and growth rates were observed for increased bath temperature. The activation energy of the system was estimated as 127 ± 5 kJ/mole and the order of reaction with a value of 1.03 ± 0.05. These results suggest that the growing mechanism of the ZnS films is a chemical process with formation and absorption of Zn(OH)2 in the substrate followed by an exchange reaction between OH− and HS− ions. Chemical, morphological and optical characterizations of the deposited ZnS thin films are reported. The formation of the ZnS and Zn(OH)2 compounds was identified by x-ray photoelectron spectroscopy technique. An increase in the [Zn]/[S] ratio from 0.367 at 25 °C to 0.906 at 55 °C, was obtained. The estimated bandgap energy of the deposited films ranged from 3.5 to 3.8 eV. Optical transmittance higher than 80% above 500 nm on films makes proper as optical window for thin film solar cells.