Na2S Aqueous Solution Research Articles

Structural and optical properties of ZnS/ZnO core/shell nanowires grown on ITO glass

ZnO@ZnS core/shell nanowires have been synthesized by an easy conversion process from ZnO nanowire precursors. Firstly, vertically aligned ZnO nanowires approximately 3µm long and 200nm in diameter were electrodeposited on an ITO-coated glass substrate. The surface of these wires was then converted into ZnS by immersion in an aqueous Na2S solution. After rigorous water and alcohol washing and air drying, the resulting hybrids were investigated by UV–visible absorption and photoluminescence spectroscopies. These showed an additional band in the visible region which cannot be attributed to the ZnO or ZnS band-gaps, but to a type-II interfacial transition between the valence band of ZnS and the conduction band of ZnO. This proves the relevance of the ZnO@ZnS/ITO nanostructures to potential solar cell applications.

Activated Carbons Impregnated with Na2S and H2SO4: Texture, Surface Chemistry and Application to Mercury Removal from Aqueous Solutions

The effects of treatment of an activated carbon with Sulphur precursors on its textural properties and on the ability of the complex synthesized for mercury removal in aqueous solutions are studied. To this end, a commercial activated carbon has been modified by treatments with aqueous solutions of Na2S and H2SO4 at two temperatures (25 and 140 °C) to introduce sulphur species on its surface. The prepared adsorbents have been characterized by N2 (-196 °C) and CO2 (0 °C) adsorption, thermogravimetric analysis, temperature-programmed decomposition and X-ray photoelectron spectroscopy, and their adsorption capacities to remove Hg(II) ions in aqueous solutions have been determined. It has been shown that the impregnation treatments slightly modified the textural properties of the samples, with a small increase in the textural parameters (BET surface area and mesopore volumes). By contrast, surface oxygen content was increased when impregnation was carried out with Na2S, but it decreased when H2SO4 was used. H...

ZnSe Etching of Zn‐Rich Cu2ZnSnSe4: An Oxidation Route for Improved Solar‐Cell Efficiency

Cu2ZnSnSe4 kesterite compounds are some of the most promising materials for low-cost thin-film photovoltaics. However, the synthesis of absorbers for high-performing devices is still a complex issue. So far, the best devices rely on absorbers grown in a Zn-rich and Cu-poor environment. These off-stoichiometric conditions favor the presence of a ZnSe secondary phase, which has been proved to be highly detrimental for device performance. Therefore, an effective method for the selective removal of this phase is important. Previous attempts to remove this phase by using acidic etching or highly toxic organic compounds have been reported but so far with moderate impact on device performance. Herein, a new oxidizing route to ensure efficient removal of ZnSe is presented based on treatment with a mixture of an oxidizing agent and a mineral acid followed by treatment in an aqueous Na2S solution. Three different oxidizing agents were tested: H2O2, KMnO4, and K2Cr2O7, combined with different concentrations of H2SO4. With all of these agents Se(2-) from the ZnSe surface phase is selectively oxidized to Se(0), forming an elemental Se phase, which is removed with the subsequent etching in Na2S. Using KMnO4 in a H2SO4-based medium, a large improvement on the conversion efficiency of the devices is observed, related to an improvement of all the optoelectronic parameters of the cells. Improvement of short-circuit current density (J(sc)) and series resistance is directly related to the selective etching of the ZnSe surface phase, which has a demonstrated current-blocking effect. In addition, a significant improvement of open-circuit voltage (V(oc)), shunt resistance (R(sh)), and fill factor (FF) are attributed to a passivation effect of the kesterite absorber surface resulting from the chemical processes, an effect that likely leads to a reduction of nonradiative-recombination states density and a subsequent improvement of the p-n junction.

A Facile One-Pot Synthesis of Copper Sulfide-Decorated Reduced Graphene Oxide Composites for Enhanced Detecting of H2O2 in Biological Environments

The high levels of H2O2 are closely associated with cancer and progressive neurodegenerative diseases, such as Parkinson's disease. In this study, we developed a novel CuS nanoparticle-decorated reduced graphene oxide-based electrochemical biosensor for the reliable detection of H2O2. The new electrocatalyst, CuS/RGO composites was successfully prepared by heating the mixture of CuCl2 and Na2S aqueous solutions in the presence of PVP-protected graphene oxide at 180 °C. A potential application of CuS/RGO composite-modified electrode as a biosensor to monitor H2O2 has been investigated. The steady-state current response increases linearly with H2O2 concentration from 5 to 1500 μM with a fast response time of less than 2 s. The detection limit (3σ) for determination of H2O2 has been estimated to be 0.27 μM, which was lower than certain enzymes and noble metal nanomaterial-based biosensors. In addition, the study of storage time on the amperometric response of the sensor indicates super stability. Due to these remarkable analytical advantages, the as-made sensor was applied to determine the H2O2 levels in human serum and urine samples and H2O2 released from human cervical cancer cells with satisfactory results. These results demonstrate that this new nanocomposite with the high surface area and electrocatalytic activity is a promising candidate for use as an enhanced electrochemical sensing platform in the design of nonenzymatic biosensors.

Dye Modification Effects on TaON for Photocatalytic Hydrogen Production from Water

Modification effects of porphyrin dyes on the photocatalytic activity of tantalum (oxy)nitride (TaON) were investigated. The nitrogen content in tantalum (oxy)nitride was increased by increasing the heat treatment period. The optimized nitridation conditions were found to be calcination at 800 °C for 14 h under a NH3 gas flow (25 mL min−1). Among the porphyrin dyes examined, pentamethylene bis[4-(10,15,20-triphenylporphine-5-yl) benzoate]-dizinc (II) (Zn-TPPD) showed the most positive effect on the photocatalytic activity of TaON for H2 production from Na2S aqueous solution. From the results of the photocatalytic reaction using various combinations of catalyst components, it was found that the modification dye and PtOx co-catalysts were necessary to achieving photocatalytic H2 formation. In the PtOx/Zn-TPPD/TaON photocatalyst, the expected charge transfer mechanism was a two-step excitation of both TaON and Zn-TPPD, and the oxidation and reduction sites were TaON and PtOx co-catalyst, respectively. These results indicate that dye modification has the potential to improve the photocatalytic activity of various (oxy)nitride photocatalysts.

Chemical passivation of InSb (100) substrates in aqueous solutions of sodium sulfide

The elemental composition and electronic structure of both native-oxide-covered InSb (100) substrates and substrates treated in aqueous solutions of sodium sulfide are analyzed by X-ray photoelectron spectroscopy. It is found that, as a result of treatment in a 1 M aqueous solution of Na2S and subsequent annealing in vacuum at 150°C, the surface layer consisting of complex antimony and indium oxides of nonstoichiometric composition is removed completely with the formation of a continuous layer of chemisorbed sulfur atoms coherently bound to indium atoms. According to atomic-force microscopy data, no etching of the host substrate material occurs during sulfide passivation. A shift (by 0.37 eV) of the In-Sb bulk photoemission towards higher binding energies is found, which indicates that the surface Fermi level shifts deeper into the conduction band.

Synthesis and tribological properties of CuS/ZnS nanoparticles doped polyelectrolyte multilayers

Polyelectrolyte multilayer thin films [poly(diallyl dimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA)] for the synthesis of CuS and ZnS nanoparticles were prepared. The CuS/ZnS nanoparticles in situ synthesised by immersing the PDDA/PAA polyelectrolyte multilayer thin films into Cu2+(or Zn2+) and Na2S aqueous solutions alternately, which were characterised in detail by UV visible absorption spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) analysis. The CuS and ZnS nanoparticles doped polyelectrolyte multilayer thin films were synthesised by the layer-by-layer molecular deposition technology and in situ synthesis method. The coefficient of friction (COF) decreased with the in situ synthesis CuS and ZnS nanoparticles doped into the polyelectrolyte layers. The in situ nanoparticles exhibited enhanced wear resistance performance of the plain polyelectrolyte multilayers.

Stability and Optical Properties of ZnO Nanoparticles Capped by ZnS

ZnO nanoparticles were grown by decomposing of zinc acetate dehydrate. ZnS shells formed on ZnO nanoparticle surfaces in Na2S aqueous solution with the help of ultrasonic at room temperature. The nanoparticle structures and optical properties were characterized. Stability of the shells and effects of capping on the nanoparticle optical properties were studied. Luminescence of the nanoparticles was sensitive to the shell structures and excitation laser density. Single crystal shells could enhance ZnO nanoparticle emission more obviously under higher excitation, but the suppression of the green emission depended on the shell thickness. Single crystal shell could suppress while nanoparticle shells enhance the interface defect vibration. ZnS nanoparticle shells were unstable under exposure to laser light.

Optical characterization of CdS nanoparticles embedded into the comb-type amphiphilic graft copolymer

This study refers to the synthesis and characterization of a novel organic/inorganic hybrid nanocomposite material containing cadmium sulfide (CdS) nanoparticles. For this purpose, a series of polypropylene (PP)-g-polyethylene glycol (PEG), PP-g-PEG comb-type amphiphilic graft copolymers were synthesized. PEGs with Mn = 400, 2000, 3350, and 8000 Da were used and the graft copolymers obtained were coded as PPEG400, PPEG2000, PPEG3350, and PPEG8000. CdS nanoparticles were formed in tetrahydrofuran solution of PP-g-PEG amphiphilic comb-type copolymer by the reaction between aqueous solutions of Na2S and Cd(CH3COO)2 simultaneously. Micelle formation of PPEG2000 comb-type amphiphilic graft copolymer in both solvent/non-solvent (petroleum ether–THF) by transmission electron microscopy (TEM). The optical characteristics, size morphology, phase analysis, and dispersion of CdS nanoparticles embedded in PPEG400, PPEG2000, PPEG3350, and PPEG8000 comb-type amphiphilic graft copolymer micelles were determined by high resolution TEM (HRTEM), energy dispersive spectroscopy, UV–vis spectroscopy, and fluorescence emission spectroscopy techniques. The aggregate size of PPEG2000-CdS is between 10 and 50 nm; however, in the case of PPEG400-CdS, PPEG3350-CdS, and PPEG8000-CdS samples, it is up to approximately 100 nm. The size of CdS quantum dots in the aggregates for PPEG2000 and PPEG8000 samples was observed as 5 nm by HRTEM analysis, and this result was also supported by UV–vis absorbance spectra and fluorescence emission spectra.

Using a precursor in lamellar structure for the synthesis of uniform ZnS nanocrystals

Uniform ZnS nanocrystals of about 15 nm were prepared through a low temperature hydrothermal approach by treating Zn-PhPO nanosheets with Na2S aqueous solution. Both the precursor and the final product were studied by the means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The photo-luminescent spectrum of the synthesized ZnS nanocrystals showed their good crystalline nature. Based on this study, the precursor structure-controlling effect was discussed, and in addition, the relevant factors possibly affecting the particle formation and the growth possessed were applied in the discussion to interpret the transformation mechanism. Further research showed that both the structure characters of the precursors and the mass transportation which occurred during the synthesis greatly affected the morphology and organization state of the final products. This research may provide some facts on the structure-controlling approaches along with a general method for the preparation of uniform sulfide nanocrystals.

Photoelectrochemical performance of gallium-doped AgInS 2 photoelectrodes prepared by electrodeposition process

Gallium-doped silver–indium–sulfide (Ga-doped AgInS 2) samples were deposited onto fluorine-doped-tin-oxide (FTO) glass substrates using a one-step electrodeposition method. The effect of the [Ga]/[In] molar ratio in the solution bath on the structure, morphology, and photoelectrochemical (PEC) properties of samples is reported. X-ray diffraction (XRD) patterns of samples reveal that the peaks of samples shifted to higher angles with increasing [Ga]/[In] ratio in the solution bath. The thickness, direct band gap, and indirect band gap of the samples were in the ranges of 643–580 nm, 1.84 eV–1.93 eV, and 1.42–1.59 eV, respectively. The flat-band potentials of the films were in the range from –0.76 to –0.99 V vs. a normal hydrogen electrode (NHE), as obtained using Mott–Schottky plots and open-circuit potential (OCP) measurements of samples. The maximum photoenhancement current density (10.37±0.13 mA cm −2) was obtained for Ga-doped AgInS 2 films with a precursor ratio of [Ga]/[In]=0.03 at an applied bias of +1.0 V vs. Ag/AgCl electrode in K 2SO 3 (0.25 M) and Na 2S (0.35 M) aqueous solution. Results show that high-quality Ga-doped AgInS 2 thin films can be deposited on FTO glass using one-step electrodeposition for PEC applications. Stability test of the AgInS 2 thin films in aqueous solution is also reported in this study.

ChemInform Abstract: Synthesis of Trifluoromethylated Heterocycles Using Partially Fluorinated Epoxides.

Abstract Reaction of 2-trifluoromethyl- (1) and 2,2-bis(trifluoromethyl)- (2) oxiranes with a variety of sulfur nucleophiles proceeds rapidly and under mild conditions. For example, epoxide 2 reacts with aqueous solution of Na2S, producing S[CH2C(CF3)2OH]2. Reaction of 2 with Na2S2O3 leads to the formation of the corresponding Bunte salt. Interaction of 2 with NaSCN in water proceeds exothermically and results in high-yield formation of cyclic imine 5. Although this material can be isolated, it has limited stability and undergoes cyclotrimerization at ambient temperature, giving the corresponding 1,3,5-triazine. A number of heterocyclic compounds containing pendant –CH2C(CF3)2OH group were prepared by the reaction of the corresponding thio-derivatives, such as pyridine-2-thiole with epoxide 2. It was found that fluoride anion catalyzes the reaction of epoxides 1 and 2 with isothiocyanates carrying electron withdrawing groups at nitrogen. The reaction results in nucleophilic cyclization and formation of the corresponding exocyclic imines containing a 1,3-oxothiolane moiety. Carbon disulfide was also found to be active in this process, reacting with epoxides 1 and 2 at ambient to give the corresponding trifluoromethylated 1,3-oxathiolane-2-thiones in 58–65% yield.

Pilot study of absorption of NO2 with Na2S aqueous solutions

A pilot-scale study of sodium sulfide (Na2S) aqueous solutions for NO2 absorption was conducted to obtain field data for process design and system operations. Considered parameters include Na2S concentrations in the scrubbing solutions, gas mass flow rate, liquid mass flow rate, liquid/gas ratio (L/G), pH, and gas residence time. The effects of these parameters on NO2 absorption in a packed tower were investigated thoroughly. The height of transfer unit of the system was deducted as a function of the tested parameters that can be used for designing a NOx scrubbing system. The absorption of NO2 is not sensitive to the inlet NO2 concentration. However, as expected, the NO2 absorption increases with the increase of L/G ratio. An L/G greater than 2.5 is essential to a practical NO2 scrubbing application. The pilot test suggested that the scrubbing solution is with Na2S concentration greater than 0.0015 M at pH 9. The solution effectively removed more than 90% of the incoming NO2 in the five-foot height packed bed scrubber. The study also indicates that a gas residence time of 4.5 s is essential to achieve more than 80% NO2 absorption. © 2011 American Institute of Chemical Engineers Environ Prog, 2011.

Synthesis of a stable sol of Mn2+-doped ZnS nanoparticles by low-temperature heating of sulfide precipitate in ethylene glycol

A sol of Mn2+-doped ZnS nanoparticles was prepared by heating a ZnS precipitate with Mn2+ ions in ethylene glycol at 348 K for 24 h. The precipitate was prepared by mixing the aqueous solution of Zn(NO3)2·6H2O and Mn(NO3)2·6H2O with an aqueous solution of Na2S According to the UV–VIS absorption spectra, when the wavelength was more than 400 nm, the optical absorptions of the obtained sols with the molar fraction of Mn2+ ions in the solution (XSolution: the molar fraction of Mn2+/(Mn2+ + Zn2+) in the aqueous solution) less than 0.02 were less than 0.12 and the obtained sols were clear and transparent for the visible light. The sol of Mn2+-doped ZnS nanoparticles showed PL characteristics when irradiated with an excitation light with a wavelength of 345 nm. Accordingly, a simple process to heat the mixture of the sulfide precipitate and ethylene glycol at 348 K enabled us to obtain a homogeneous transparent sol of Mn2+-doped ZnS nanoparticles with PL characteristics. According to the results of the chemical analysis of the molar fraction of Mn2+ in the obtained precipitate (XPrecipitate) and the nanoparticles in the sols (XNano), the XNano was less than that the XPrecipitate as compared with the same XSolution. The Mn2+ ions in the nanoparticles were dissolved in the solvent during the heat treatment since the solubility product of MnS was much larger than that of ZnS. As such, the dissolution-precipitate process played an important role in the formation of the sol.

ZnO–ZnS heterostructures with enhanced optical and photocatalytic properties

ZnO–ZnS heterostructures were fabricated via using ZnO rods as template in different Na2S aqueous solutions. These heterostructures are 5–6 μm in length and formed by coating ZnO rod with a layer of porous ZnS shell comprising primary crystals about 10 nm in diameter. Subsequently, intact ZnS polycrystalline tubes were obtained by removing the ZnO cores with 25% (wt) ammonia. The as-prepared products were characterized by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), Fourier transform infrared (FT-IR), and electrochemical impedance spectroscopy (EIS). It was found that the electron transfer between ZnS shell and ZnO core strongly affect the photoluminescence and photocatalytic performances of these heterostructures. The rapid transfer of photo-induced electrons from the ZnS shell to the ZnO core leads to enhanced ultraviolet emission. However, if this correlation was destroyed, then the corresponding heterostructure exhibits improved photocatalytic efficiency due to the reduced volume recombination of the charge carries and the multiple reflection effect. Finally, a model based on band-gap alignment was proposed to elucidate the underlying mechanism of the enhanced UV emission and photocatalytic activity of these unique heterostructures.

Synthesis of trifluoromethylated heterocycles using partially fluorinated epoxides

Reaction of 2-trifluoromethyl- ( 1) and 2,2-bis(trifluoromethyl)- ( 2) oxiranes with a variety of sulfur nucleophiles proceeds rapidly and under mild conditions. For example, epoxide 2 reacts with aqueous solution of Na 2S, producing S[CH 2C(CF 3) 2OH] 2. Reaction of 2 with Na 2S 2O 3 leads to the formation of the corresponding Bunte salt. Interaction of 2 with NaSCN in water proceeds exothermically and results in high-yield formation of cyclic imine 5. Although this material can be isolated, it has limited stability and undergoes cyclotrimerization at ambient temperature, giving the corresponding 1,3,5-triazine. A number of heterocyclic compounds containing pendant –CH 2C(CF 3) 2OH group were prepared by the reaction of the corresponding thio-derivatives, such as pyridine-2-thiole with epoxide 2. It was found that fluoride anion catalyzes the reaction of epoxides 1 and 2 with isothiocyanates carrying electron withdrawing groups at nitrogen. The reaction results in nucleophilic cyclization and formation of the corresponding exocyclic imines containing a 1,3-oxothiolane moiety. Carbon disulfide was also found to be active in this process, reacting with epoxides 1 and 2 at ambient to give the corresponding trifluoromethylated 1,3-oxathiolane-2-thiones in 58–65% yield.

ChemInform Abstract: Novel Stannite‐Type Complex Sulfide Photocatalysts A2I‐Zn‐AIV‐S4 (AI: Cu and Ag; AIV: Sn and Ge) for Hydrogen Evolution under Visible‐Light Irradiation.

AbstractRu cocatalyst‐loaded Cu2ZnGeS4, Ag2ZnGeS4, and Ag2ZnSnS4 show high activities for photocatalytic H2 evolution from an aqueous solution of Na2S and K2SO3 solution under visible‐light irradiation.

Narrow gap III–V materials for infrared photodiodes and thermophotovoltaic cells

The paper describes liquid phase epitaxial growth and characterization of the GaSb- and InAs-related materials for the photodiodes and thermophotovoltaic applications. It was shown that doping of the melt with holmium results in obtaining the high purity GaInAsSb and InAs layers. The passivation with the 1 M Na 2S aqueous solution makes it possible to prepare flat growth surfaces of GaSb(1 0 0) and InAs(1 0 0) substrates after annealing. A reproducible technique has been developed for fabrication of the high-efficiency GaInAsSb/GaAlAsSb and InAs/InAsSbP photodiodes with the long-wavelength photosensitivity edge of 2.4 and 3.8 μm, respectively. Room temperature detectivity in the spectral peak reaches D∗ = (0.8–1.0) × 10 11 W −1 cm Hz 1/2 for the GaInAsSb/GaAlAsSb photodiodes and D∗ = (3.0–5.0) × 10 9 W −1 cm Hz 1/2 for the InAs/InAsSbP devices. We have adapted the technology for thermophotovoltaic cells operating at an emitter temperature of 1000–1700 °C.

Wet sulfur passivation of GaSb(1 0 0) surface for optoelectronic applications

A comparative analysis of the properties of the non-passivated and S-passivated GaSb(1 0 0) surfaces has been performed through PL, AFM and RHEED characterization. The samples treated with a 1 M Na 2S aqueous solution demonstrate an increase in the 5 K PL intensity. According to AFM data, the annealing of the S-passivated GaSb(1 0 0) leads to the formation of the clean flat (1 0 0) surface. Moreover, after annealing the PL intensity of the S-passivated GaSb(1 0 0) surfaces decreases by 20%, whereas for the non-passivated samples it drops by more than a factor of 4. The method of wet sulfur passivation has shown great effectiveness in pre-epitaxial processing for LPE and MBE growth of the GaSb-related materials for optoelectronics.

Structural Studies of ZnS Nanoparticles by High Resolution Transmission Electron Microscopy

Zinc sulfide (ZnS), a representative of wide band gap semiconductor nanocrystals, has an excitonic Bohr radius (aBZnS ) of 2.5 nm. It makes ZnS nanoparticles (ZnS NP) having such size very interesting as small biomolecular probes for fluorescence and laser scanning microscopy. To date, ZnS NP of diameters larger than aBZnS has been subject of extensive experimental and theoretical studies. However many questions remain open concerning the synthesis of undoped and uncapped ZnS NP of diameters less than 2.5 nm. To further probe into the physical properties of undoped and uncapped ZnS NP, in this work we report on studies of uncapped ZnS nanoparticles synthesized by a wet chemical process at room temperature. Three colloidal suspensions (named A, B and C, respectively) were obtained from 9:1, 1:1 and 1:9 volume mixtures of 1mM ZnSO4 and 0.85mM Na2S aqueous solutions. Qualitative differences in UV-Vis absorption spectra are discussed in the context of Z-contrast scanning transmission electron microscopy (Z-contrast), low and high resolution transmission electron microscopy (TEM) results. Distribution of particle size is dependent on different volumes of source solutions. For the intermediate mixture, it has been found that about 78% of ZnS nanoparticles have a diameter smaller than the excitonic Bohr Radius of 2.5 nm. HRTEM studies have revealed that nanoparticles grow preferentially with hexagonal structure.