Na2S Aqueous Solution Research Articles

Effects of the Surfactant and pH on Linear Potential Scan of Aqueous Na 2S Solution

Effects of the Surfactant and pH on Linear Potential Scan of Aqueous Na 2S Solution

Oxidation and Carbon Contamination in GaAs (100) Wet Treatments

ABSTRACTOxidation and carbon contamination of n-type GaAs (100) surfaces have been investigated by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) for a variety of cleaning and etching pretreatment procedures prior to immersion in either (NH4)2S, Na2S aqueous solutions or S2Cl2 solution in dichloromethane. The study has shown that sulfur passivation removes surface oxide and minimize carbon contamination for surfaces treated in (NH4)2S and S2Cl2 solutions. A significant oxygen and carbon contamination in the anodic passivation of GaAs (100) in (NH4)2Sx aqueous solution have been quantitatively measured. In addition, pretreatment in basic solutions have shown minimal oxygen and carbon level in comparison with the acidic solutions. Surface pretreatment carried out ex-situ has shown a higher risk of surface contamination prior to sulfur passivation.

Coverage evolution of sulfur on Pt(111) electrodes: From compressed overlayers to well-defined islands

The paper examines formation of a monolayer and submonolayers of S chem on Pt(111) electrodes accomplished through its immersion in aqueous Na 2S solution. The S chem monolayer, having the (1×1) structure at θ S chem =1, can be gradually removed by oxidative desorption at E≥0.95 V, RHE, and the S chem coverage can be precisely controlled. The S chem layer suppresses the H UPD and anion adsorption as well as it affects the oxide growth behavior on Pt(111). LEED data reveal that S chem forms well-defined structures on Pt(111) for 0.50≥ θ S chem ≥0.25: c(2×2) at θ S chem =1/2, ( 3 × 3 )R30° at θ S chem =1/3, and p(2×2) at θ S chem =1/4; when θ S chem ≤0.20, structured islands of S chem are observed. AES and CEELS data indicate that the adsorbed S is not present in an oxidized state; it is almost of atomic character with an incomplete negative charge due to partial charge transfer between S chem and the Pt(111) substrate. Presence of S chem influences thermodynamics of the H UPD on Pt(111) resulting in less-negative values of Δ G ads(S)(H UPD). In the absence of S chem, the H UPD is enthalpy-driven whereas in the presence of S chem it becomes entropy-driven. The Pt(111)–H UPD bond energy is weaker in the presence of S chem than in its absence, and this bond energy diminution may be assigned to local electronic effects arising from presence of S chem.

Surface Properties of Precipitated CdS Nanoparticles Studied by NMR

CdS and CdS:Mn nanoparticles were studied by 113Cd and proton NMR. Nanoparticle samples were synthesized by precipitation of CdS from an aqueous solution of Na2S and CdSO4. The nanoparticles were n...

CdS Nanocrystals in Chelate Polymer Microparticles: Polymer Size Dependence of The Optical Properties

Abstract CdS nanocrystals were prepared in micrometer-sized chelate polymer particles by nucleation of Cd2+ ions with an aqueous Na2S solution. Simulation of the absorption spectral band shapes of CdS under an effective mass approximation was conducted on the basis of the size distributions of the crystals in the polymer, which were estimated by the relevant transmission electron micrograph images. The optical properties and the size distributions of CdS were dependent on the diameter of the polymer particle, when the concentration of an added S2− solution was sufficiently high for rapid nucleation. In the case of the reaction of Cd2+ with a diluted S2− solution, contrarily, the formation of CdS was confined in the surface layer of the host polymer particle with layer-by-layer size distributions. Effects of the host polymer particle size and the concentration of the Na2S solution on the size distributions and the optical properties of CdS are discussed in terms of the apparent rate of nucleation of Cd2+ to CdS.

Simultaneous Sulfur Dioxide Absorption and Hydrogen Sulfide Generation in an Aqueous Solution of Sodium Sulfide

In flue gas desulfurization (FGD) processes, elemental sulfur is the desirable end product for SO2 producers located in remote areas, since it is easier to handle and transport. To convert sulfur dioxide to elemental sulfur via the Claus reaction, hydrogen sulfide is needed as a reductant. In the present work, an attempt was made to generate H2S from aqueous sodium sulfide using SO2. The behavior of the Na2S(aq)−SO2(g)−H2S(g) system was studied experimentally and by modeling. A three-stage pattern was observed in a semi flow batch reactor (SFBR) in regard to chemical properties of this system. It was concluded that aqueous Na2S solution can be used to absorb SO2 in flue gas and to generate H2S under conditions of the second stage. The simultaneous SO2 absorption and H2S generation in an aqueous Na2S solution were confirmed using a continuous flow tank reactor (CFTR). To simulate both the SFBR and the CFTR, two mathematical models were developed based on chemical equilibria of acid−base reactions and mass ...

Visible Light Induced Hydrogen Evolution on CdS/K4Nb6O17 Photocatalyst

Abstract The photocatalytic ability of CdS/K4Nb6O17 photocatalyst for H2 evolution by visible light irradiation was studied in connection with its structure. CdS/K4Nb6O17 was prepared by cation exchange reaction of K+ to Cd2+ ions in aqueous Cd(NO3)2 solution, followed by sulfurization in aqueous Na2S solution. The catalyst obtained by this procedure showed much higher H2 evolution activity in aqueous K2SO3 solution under visible light irradiation (λ > 420 nm) than a physical mixture of CdS and K4Nb6O17 powders. This result was interpreted as due to more intimate contact of CdS and K4Nb6O17 in CdS/K4Nb6O17 photocatalyst, which enabled the efficient transfer of excited electrons. The activity of the catalyst was greatly dependent on the sulfurization condition, with this optimum condition: at room temperature for one week. XRD, EXAFS, TEM, and UV-DRS showed that most CdS particles, ca. 10 nm in diameter, existed on the external surface of K4Nb6O17, while a small amount of CdS was inferred to be located at the interlayer space of K4Nb6O17 as ultra fine particles.

Sulfide passivation of III–V semiconductors: The starting electronic structure of a semiconductor as a factor in the interaction between its valence electrons and the sulfur ion

In the experiments on GaAs, InP, and GaP treated in aqueous solutions of Na2S:9H2O, it has been shown that in the process of sulfide passivation of III–V semiconductors a significant role is played by both the starting electronic structure of the semiconductor surface (prior to sulfidizing) and the energy state of the sulfur ion in solution. A model of the interaction of the sulfur ion in a solution with the valence electrons of a III–V semiconductor in the course of the sulfidizing process has been suggested and verified. During the interaction process, a change takes place in the electrochemical potential (Fermi level) of the semiconductor, which affects the electron work function at the surface. Between various semiconductors the amount of this change in the work-function value varies in proportion to the negative of the starting electron work-function value in the untreated semiconductor and depends on the treatment temperature. In a semiconductor such that its starting work-function value is equal to the effective electronegativity of the sulfur ion in solution, the work function will not be changed by sulfidization. The effective electronegativity of the sulfur ion in solution depends on the ionicity of the chemical bonds of the semiconductor being treated.

Size Control of Ultrasmall CdS Particles in Aqueous Solution by Using Various Thiols

Size of ultrasmall CdS particles was controlled by adding four kinds of thiols (mercaptoethylamine, mercaptopropionic acid, mercaptoethanol, and cysteine) to a Cd 2+ aqueous solution before mixing with an Na 2S aqueous solution. The adsorption of thiols on the CdS surface was verified as the effect of surface charges by measuring the yield of photoinduced electron transfer from CdS to positively charged molecules in solution. Observations of growth process by means of stroboscopic stopped-flow spectroscopy indicate that of the four thiols the thiolate group is mainly responsible for obstructing the growth of ultrasmall CdS particles. The effect of the other ionic groups of thiols on the growth feature is of secondary importance. For mercaptoethanol and cysteine, a transient absorption band attributable to a relatively stable small CdS cluster appeared at an early stage of the growth.

Influence of cobalt phthalocyanine: Deposited onto the particles of mixed Cd/CuxS suspensions on photocatalytic evolution of hydrogen from aqueous solutions of Na2S

Deposition of water-insoluble cobalt phthalocyanine CoPc onto the particles of mixed suspensions of CdS and CuxS can increase the rate of photoinduced evolution of H2 from Na2S and Na2SO3 solutions. At [Na2S]=5×10−2 M, the rate of photocatalytic reaction is almost doubled upon deposition of 6.4×10−10 mol CoPc onto 4×10−5 mol of CdS and of 2.9×10−8 mol of CoPc onto 10−5 mol of CuxS. At [Na2S]=10−1 M, which is close to the optimal concentration of Na2S, the deposition of CoPc can provide only a 30% increase of the reaction rate.

Chalkogenderivative des cyclopentadienyl-tricarbonyl-mangans und -rheniums, [(CO) 3MC 5H 4] 2E n (M = Mn, Re; E = S, Se, Te; n = 2, 1)

The lithio derivatives of the half-sandwich complexes C 5H 5M(CO) 3 (M = Mn, Re) take up chalcogens E to give chalcogenolate intermediates of the type {(CO) 3MC 5H 4ELi} which, upon air oxidation, are transformed into the dichalcogenides [(CO) 3MC 5H 4] 2E 2 (E = S, Se, Te). Direct reaction of the lithio derivatives with SCl 2 gives the sulfides [(CO) 3MC 5H 4] 2S, whereas the corresponding reaction with SeCl 4 and TeCl 4, followed by reductive dehalogenation using aqueous Na 2S solution, gives the analogous selenides and tellurides, [(CO) 3MC 5H 4] 2E (M = Mn, Re; E = S, Se, Te). The phenylphosphino-substituted complexes [(CO) 3MC 5H 4] 2P(C 6H 5) (M = Mn, Re) are also described. All new compounds are characterized by their IR and mass spectra, and, in particular, by their 1H, 13C and 31P NMR spectra.

Study of novel chemical surface passivation techniques on GaAs p n junction solar cells

Novel methods of GaAs surface passivation are investigated. Passivation is acheived by simple chemical treatments using aqueous solutions of Na2S, KOH, RuCl3, and K2Se. GaAs pn homojunction solar cells are used to evaluate the effectiveness of these passivation techniques. A significant reduction in minority-carrier surface recombination velocity is demonstrated. In the best case, the surface recombination velocity decreased from 5×106 cm/s (untreated surface) to 103 cm/s. In addition, we observe improvements in solar cell photogenerated current, short wavelength spectral response, open-circuit voltage, and junction ‘‘dark’’ current.

New materials which respond to visible light: functional polymers containing zirconium

Photoresponsive polymers which change their magnetic properties when illuminated by visible light have been found. n-Butyl zirconate was polymerized in tetrahydrofuran and other solvents. The polymer, when illuminated, changes its conformation and a new spin-nuclear interaction in the electron spin resonance spectrum is observed. These polymers, when 1 wt% Pt was added, exhibited photocatalytic activities and photolysed a 1:1 methanol-H2O mixture and a 0.24 M Na2S aqueous solution, using visible light of wavelength 480 to 730 nm.

Determination of sulphur oxoacids in sodium sulphide by isotachophoresis

In order to determine directly ▪ contained as impurities in sodium sulphide (Na 2S) by isotachophoresis, an investigation was made of the electrolyte system, the stability of the standard ▪ solution and the denaturation of the Na 2S solution under different conditions of pH, temperature, concentration and dissolved oxygen content. The electrolyte system was a water-acetone (1:1) solution of 5 · 10 −3 M hydrochloric acid-1 · 10 −2 M l-histidine as the leading electrolyte and a 0.01 M solution of sodium acetate as the terminating electrolyte, which were found to give the best results. For the solvent for the standard solution of sulphur oxoacids and the Na 2S solution, a 5% aqueous solution of glycerine prepared with water that had been degassed by boiling was found to be satisfactory. The detection limit for ▪ in the direct analysis of an aqueous solution of Na 2S was 0.015%. The analysis time was about 15 min.

Removal of hair from the operation field in experimental animals

To remove hair from the operation field in animals the skin area may be treated with a 10% aqueous Na2S solution. 2–3 minutes later the hair is easily washed off together with the solution; the operation field is completely devoid of hair. This method does not require any morphine administration and is much quicker and more convenient than cutting or shaving the hair.