Na2S Aqueous Solution Research Articles

Ternary Ag–In–S polycrystalline films deposited using chemical bath deposition for photoelectrochemical applications

This paper describes the preparation and characterization of ternary Ag–In–S thin films deposited on indium tin oxide (ITO)-coated glass substrates using chemical bath deposition (CBD). The composition of the thin films was varied by changing the concentration ratio of [Ag]/[In] in the precursor solutions. The crystal structure, optical properties, and surface morphology of the thin films were analyzed by grazing incidence X-ray diffraction (GIXRD), UV–vis spectroscopy, and field-emission scanning electron microscopy (FE-SEM). GIXRD results indicate that the samples consisted of AgInS 2 and/or AgIn 5S 8 crystal phases, depending on the composition of the precursor solutions. The film thicknesses, electrical resistivity, flat band potentials, and band gaps of the samples were between 1.12 and 1.37 μm, 3.73 × 10 −3 and 4.98 × 10 4 Ω cm, −0.67 and −0.90 V vs. NHE, and 1.83 and 1.92 eV, respectively. The highest photocurrent density was observed in the sample with [Ag]/[In] = 4. A photocurrent density of 9.7 mA cm −2 was obtained with an applied potential of 0.25 V vs. SCE in the three-electrode system. The photoresponse experiments were conducted in 0.25 M K 2SO 3 and 0.35 M Na 2S aqueous electrolyte solutions under irradiation by a 300 W Xe light (100 mW cm −2). The results show that ternary Ag–In–S thin film electrodes have potential in water splitting applications.

Synthesis of lead chalcogenide nanoparticles in block copolymer micelles: investigation of optical properties and fabrication of 2-D arrays of nanoparticles

Narrow band gap PbS and PbSe semiconductor nanocrystals were prepared in the poly(4-vinyl pyridine) core of self assembled polystyrene-block-poly(4-vinyl pyridine) copolymer micelles in toluene at room temperature, and characterized by high resolution-transmission electron microscopy and X-ray diffractograms. Optical absorption and photoluminescence (PL) studies of the nanocrystals showed the quantized phenomena. The PL intensity of the PbSe nanocrystals was strongly enhanced, with a slight red shift in the peak position, by treating with aqueous Na2S solution. Interestingly, the inclusion of ZnS amorphous nanoparticles into the P4VP/PbSe core leads to a large red shift in the peak position, which covers the technologically important range (1.3 to 1.55 µm), with strong enhancement of the emission intensity. We fabricated a monolayer thin film of PbSe nanocrystals by spin coating on a silicon wafer, and it showed similar PL behavior to that in solution.

Characterisation of mackinawite by Raman spectroscopy: Effects of crystallisation, drying and oxidation

Iron(II) sulphides were precipitated by mixing FeCl 2 · 4H 2O (or FeSO 4 · 7H 2O) and Na 2S aqueous solutions with various [Fe(II)]/[S(-II)] concentration ratios at [Fe(II)] = 0.1 mol L −1. They were analysed by micro-Raman spectroscopy and X-ray diffraction immediately after precipitation and after various times of ageing in suspension at room temperature. In any case, the initial precipitate was nanocrystalline mackinawite. Its Raman spectrum is made of two sharp peaks at 208 ± 1 and 282 ± 1 cm −1. For [Fe(II)]/[S(-II)] ⩾ 1, ageing of the precipitate led to crystalline mackinawite, as testified by X-ray diffraction. The Raman spectrum of crystalline Fe(II) mackinawite shows three main peaks at 208, 256 and 298 cm −1. Drying of nanocrystalline mackinawite under an argon flow favoured crystallisation. The removal of interparticle and surface adsorbed water molecules led to coalescence of the nanoparticles and increase of the size of the domains of coherent scattering. For [Fe(II)]/[S(-II)] = 1/2, the precipitate still consisted of nanocrystalline mackinawite after 70 days of ageing. Finally, the early oxidation stages of mackinawite led to the formation of Fe(III) cations inside the tetrahedral sites of the crystal structure. The most oxidised form of Fe(III)-containing mackinawite is characterised by a Raman spectrum with sharp peaks at 125, 175, 256, 312 and 322 cm −1, and a large vibration band at 350–355 cm −1 that may be attributed to stretching modes of Fe(III)-S tetrahedrons. Analyses of the rust layers of a roman ingot that remained 20 centuries in the Mediterranean Sea revealed the presence of iron sulphides, more likely generated by sulphate-reducing bacteria. Micro-Raman analyses demonstrated the presence of nanocrystalline mackinawite and Fe(III)-containing mackinawite.

Spontaneously Formed Sulfur Adlayers on Gold in Electrolyte Solutions: Adsorbed Sulfur or Gold Sulfide?

High coverage S phases (surface coverage ≥0.33), spontaneously formed by immersion of Au(111) in Na 2S aqueous solutions at room temperature, have been studied by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), surface enhanced Raman spectroscopy (SERS), electrochemistry, and density functional theory (DFT) calculations. XPS data show no evidence of a AuS phase, as no oxidized gold is detected. Voltammetric data are also inconsistent with the formation of a AuS phase with 0.5 stoichiometry. In situ and ex situ SERS measurements of S-covered nanostructured gold substrates demonstrate that the surface species present at the gold surface consist of a mixture of chemisorbed S and polysulfide species, as already proposed based on in situ STM images. A DFT surface model that is energetically feasible and reproduces well the experimental STM images is presented. The proposed model involves only a small rearrangement of the upper Au layer and coexistence of monomeric and polymeric S. ...

Synthesis, characterization and photoelectrochemical properties of poly(3,4-dioctyloxythiophene)–CdS hybrid electrodes

CdS–poly(3,4-dioctyloxythiophene) (CdS–PDOT) hybrid electrode has been prepared by electrosynthesis of PDOT on Au substrate followed by electrodeposition of Cd and its chemical transformation into CdS. The polymer and semiconductor obtained by this method form hemispherical structures dispersed on the substrate. The synthesized composites were characterized by UV–vis absorption spectra and energy dispersive X-ray spectra (EDS). The AFM images of the electrodes covered with different amounts of each component were correlated with photoactivity of the hybrid electrodes. Photoresponses of Au/PDOT–CdS electrodes under illumination in aqueous solution of Na 2S were also compared with those of CdS without polymer. Enhancement of the photocurrent achieved for some polymer-to-semiconductor ratio is discussed in terms of the hybrid electrode morphology and hole-mediating properties of PDOT. The power conversion efficiency of the device based on CdS–PDOT hybrid electrode was determined from photocurrent–potential behavior of two electrode system, Au/CdS–PDOT/0.1 M Na 2S/Pt with a variable resistance in series in the external circuit.

Ultra-thin crystalline films of ZnS and PbS formed at the organic–aqueous interface

Ultra-thin films of ZnS have been prepared by the reaction of zinc cupferronate or zinc stearate in a toluene solution with an aqueous solution of Na 2S. The films have been examined by electron microscopy and other techniques. The reaction at the interface yields excellent films which are generally single-crystalline. The effects of reaction parameters such as temperature and reactant concentration have been examined. Ultra-thin crystalline films of PbS have been obtained by the reaction of a toluene solution of lead cupferronate with the aqueous solution of Na 2S. The organic–aqueous interface provides a simple and elegant method of producing good crystalline films of important semiconducting materials.

Ambient‐temperature synthesis of nanocrystalline ZnO and its application in the generation of hydrogen

The conditions leading to the direct formation of nanocrystalline ZnO particles from aqueous solutions at 25 °C are presented. The synthesis of ZnO was made possible by the suitable selection of the solution chemistry and the control of the alkaline conditions established during the formation and conversion of the precursor solid. XRD and FT-IR analyses revealed that the progressive removal of molecular and coordinated water from the precursor basic zinc sulphate and the diminution of sulphate contents took place at a temperature as low as 25 °C, making unnecessary any further thermal treatment of the as-synthesized powders. SEM observations evidenced the formation of sub-micron aggregates of ZnO (sizes below 100 nm). Depending on synthesis and precipitation conditions, it was possible to decrease the crystallite size from 25 down to 11 nm. The ambient-temperature ZnO nanocrystals were used in the photo-catalytic generation of hydrogen from alkaline Na2S aqueous solutions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of polypropylene/ZnS composite using the template prepared by supercritical CO 2

A new template membrane, acrylic acid grafted microporous polypropylene (PP) membrane, was prepared using the supercritical (SC) CO 2 as a solvent. Then zinc ions were anchored in the membrane by forming a monodentate complex with the carboxyl groups in the template membrane. Subsequent treatment with Na 2S aqueous solution led to the formation of ZnS nanoparticles within the PP matrix, resulting in ZnS/PP nanocomposite. UV–Vis and Fourier Transform Infrared (FTIR) spectra, and energy-dispersive X-ray analysis (EDS) confirmed the existence of ZnS in the grafted membrane. Field emission scanning electronic microscopy (FE-SEM) and transmission electron microscopy (TEM) images showed that the ZnS nanoparticles distributed uniformly in the composite.

PbS nanocrystals embedded in microstructures produced by micromoulding in capillaries

The study presents a new method to prepare PbS nanocrystals embedded in poly(acrylic acid) (PAA) microstructures by micromoulding in capillaries (MIMIC). The micropatterns were fabricated first from aqueous solution of acrylic acid lead monomer, and subsequently solidified by γ-ray polymerization. The resulting samples were treated with aqueous Na 2S solution to convert Pb precursor to PbS in the matrix. The final micropatterns of PAA embedded with PbS nanocrystals were of high resolution. The products were characterized by IR, XRD, TEM and SPM, respectively, and the results demonstrated that PbS embedded in PAA was nanocrystals.

Photo-production of hydrogen over the CdS–TiO 2 nano-composite particulate films treated with TiCl 4

Nanosize CdS and TiO 2 sol were prepared by precipitation reaction of Cd(NO 3) 2 and Na 2S aqueous solutions and by sol–gel reaction of Ti alkoxide, respectively. They were mixed together mechanically with variation of the mole ratio ( r) of TiO 2/(CdS+TiO 2). Then, the CdS−TiO 2 mixed sols were further treated with the hydrothermal processing at the temperatures of 120–240°C. CdS–TiO 2 composite particulate films were thus prepared by casting the resulting sol onto F:SnO 2 conducting glass and a subsequent heat-treatment at 400°C under air. Again, the physical properties of these films were controlled by the surface treatment with TiCl 4 aqueous solution. With the hydrothermal treatment, the crystallinity of both CdS and TiO 2 particles increased, and CdS particles were seen to be surrounded homogeneously by TiO 2 particles. Hydrogen photo-production rates measured under the present experimental conditions varied according to the mole ratio ( r) and showed the maximum value at r=0.8, which were in consistent with the photocurrent trend of the composite films, suggesting the importance of effective distribution and contacts among the particles. Also, the film surface treatment with TiCl 4 aqueous solution caused a considerable improvement in photocatalytic activity and photocurrent of the films, probably as a result of closer contacts between the primary particles by the etching effect of TiCl 4.

Formation of semiconductor clusters in zeolites

CdS and ZnS particles were synthesised inside some synthetic and natural zeolite frameworks by treating the calcined Cd 2+ or Zn 2+ ion exchanged forms with 1 molar aqueous solution of Na 2S. The absorption and photoluminescence emission spectra suggest that clusters interconnect to form well-defined aggregates with a behaviour intermediate between that of discrete clusters and the bulk semiconductor. The dynamics and the optical absorption are strongly influenced by the interface and host.

Convenient arc-electrodeposition technique to synthesize CdS nanotubes at room temperature

Over the past few years, shape control of nanomaterials has raised significant concerns in the fabrication of onedimensional (1D) nanomaterials such as nanowires, nanotubes and interesting nanobelts [1]. These 1D nanostructures are ideal systems for investigation of the relationship between the properties (e.g. electrical transport, optical and magnetic behaviors) and dimensionality [2]. For example, considerable progress has been made in the synthesis of 1D semiconductor nanostructured materials due to their unique properties [3]. Especially, much more efforts have been focused on the fabrication of nanotubes. A particularly significant breakthrough in the preparation of MX2 (M: Mo or W; X: S or Se) nanotubes was made by Tenne and co-workers [4]. Later, various approaches to other nanotubes such as BN [5], vanadium oxide [6], InS [7] and metal Bi [8] have also been reported. Recently we explored a novel convenient arcelectrodeposition technique to prepare shapecontrolled metal nanorods [9], nanorods or nanotubes of metal oxides and hydroxides [10]. The so-called arcelectrodeposition technique is based on the momentary contact of two metallic electrodes on an electrolyte aqueous solution, forming instantaneous circulation between two electrodes and the arc discharge sparks at the point ends of the electrodes. The arc discharge of the electrodes releases great exothermic heat, leading to dissolution of the metallic electrodes in a form of metallic clusters into the aqueous solution. The produced metallic clusters either aggregate into metal nanowires or are oxidized into the corresponding oxides and further grow into nanorods or nanotubes. Herein we extend the arc-electrodepostion technique to prepare CdS nanotubes at room temperature. The basic experimental setup and procedure for the preparation of the CdS nanotube by the arcelectrodepostion technique at room temperature are similar to those in our previous reports [9, 10]. In the present work, the mixture of Na2S and KCl aqueous solution was used as electrolyte solution. Two highpurity metallic Cd filaments of 1 mm in diameter were employed as electrodes with the applied alternating current (AC) voltage of 100 V. In the arc-electrodeposition process, the colorless transparent electrolyte aqueous solution turned into yellow gradually, indicating the formation of CdS nanoparticles. The produced solution was allowed to stand for 24 h. The final product was collected by centrifugation, followed by washing using distilled water and ethanol several times. The phase identification of as-prepared product was conducted at room temperature using an X-ray diffractometer (Cu Kα, Philips X’pert system). A transmission electron microscope (Jeol 2010) was employed to observe particle morphology. Fig. 1 shows the XRD trace of as-prepared CdS nanoparticles using this technique, in which two Cd metallic wires of 1 mm in diameter were employed as electrodes and an aqueous solution containing 0.1 M Na2S and 0.1 M KCl as electrolyte medium. In this XRD pattern, all the detectable peaks are indexed as those from CdS according to the standard card (JCPDSICDD 10-0454). The morphology of the as-prepared CdS was examined by TEM observation. The typical image is shown in Fig. 2a. It can be seen that the CdS nanoparticle obtained using this arc-electrodeposition technique under the conditions mentioned above exhibits a tubular structure in nanoscale. The length of the nanotubes ranges from 50 nm to 80 nm, and the outer diameter is around 10–15 nm with the inner that of 3–8 nm. A magnified TEM image, as shown in Fig. 2b, further reveals this structure. The formation mechanism of the CdS nanotubes produced by the present arc-electrodeposition technique was proposed as follows:

Synthesis and photocatalytic properties of iron oxide pillared hydrogen tetratitanate via soft solution chemical routes

Iron oxide pillared H 2Ti 4O 9 was prepared by two different methods, i.e., hydrothermal reaction of H 2Ti 4O 9 in FeSO 4 aqueous solution followed by calcining in air and stepwise ion exchange reaction of H 2Ti 4O 9 with n-propylamine aqueous solution and trinuclear ferric iron acetate aqueous solution, followed by UV light irradiation. The samples showed absorption in the visible region and were capable of hydrogen evolution under visible light irradiation ( λ>400 nm) in the presence of 0.1 M Na 2S aqueous solution as a hole acceptor, although no noticeable hydrogen evolution was observed when H 2Ti 4O 9 and Fe 2O 3 were used independently. Hydrogen evolution activity of iron oxide pillared tetratitanate fabricated by the hydrothermal crystallization method increased by calcining in air at 300 °C after hydrothermal reaction, and was ca. five times greater than that produced by ion exchange reaction method.

Synthesis of various size CdS nanocrystals in pore of polyacrylamide gels at room temperature

In this letter, polyacrylamide gels were prepared by using free-radical aqueous polymerization method and varying the concentration of the N, N′-methylene-bis-acrylamide from 0.1% to 0.3%, which act as crosslinker. CdS nanocrystals were formed in pore of the polyacrylamide by immersing the gels in 0.1 mol l −1 CdCl 2 and 0.1 mol l −1 Na 2S aqueous solution at room temperature. The effect of pore size of polyacrylamide gels on the size of CdS nanocrystals in the samples was investigated by X-ray powder diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The CdS crystallite structure was investigated from the XRD spectra of the samples and the CdS crystallite average sizes in the pore of polyacrylamide gels were 4.1, 3.4 and 2.2 nm in diameter, respectively. From HRTEM, we can see the size distribution is narrow. The chemical mechanism for the formation of CdS nanocrystals is discussed.

CoS thin films prepared with modified chemical bath deposition

Cobalt sulfide (CoS) thin films were deposited on glass substrates using a modified chemical bath deposition with cobalt dichloride (CoCl 2) and sodium sulfide (Na 2S) aqueous solutions. Structure properties of the films were measured using X-ray diffraction and scanning electron microscopy in the as-deposited and annealed states. Band gaps were determined using optical absorption measurements and carrier transport properties using conductivity measurements. The result shows that thermal annealing promotes the growth of grains, decreases band gap, and enhances electrical conductivity. The conductivity activation energy measurements show that the Fermi level always stays at the middle of the band gap for both as-deposited and annealed states, indicating an intrinsic semiconductor that may be suitable for photovoltaic or photothermal applications.

Sulfide passivating coatings on GaAs(100) surface under conditions of MBE growth of 〈II–VI〉/GaAs

Atomic-force microscopy was applied to compare the topographies of naturally oxidized surfaces of GaAs(100) substrates and those substrates treated with aqueous solutions of sodium sulfide in various stages of their preparation for growth of ZnSe-based heterostructures by molecular beam epitaxy (MBE). It was found that annealing of oxidized substrates strongly disrupts the surface planarity and leads to the appearance of pits with density of 1010 cm−2. The pit density can be reduced by two orders of magnitude by treating the substrate surface with an aqueous solution of Na2S. Transmission electron microscopy demonstrated that sulfidation of GaAs substrates makes it possible to reduce the number of stacking faults at the ZnSe/GaAs interface to ∼3×105 cm−2 and, correspondingly, to improve the structural perfection of MBE-grown II–VI layers and heterostructures.

Chemical synthesis and characterization of Cu doped ZnS nano-powder

In the past few years, II–VI compounds semiconductor nanocrystal have received much interest because their optical properties are different from the corresponding bulk crystals [1, 2]. Among II–VI compounds, ZnS is one of the most promising host materials for the production of commercial thin film phosphors for electroluminescent (EL) device application [3–7]. Since its absorption and emission lie in the ultraviolet regime, the studies of its small size particles did not evoke much interest until the 1980s. In 1994, Bhargava and Gallagher first synthesized ZnS semiconductor microcrystallites doped with Mn2+ ions; they found that the photoluminescence of Mn2+doped in ZnS nanoparticles had much higher quantum efficiency than bulk crystals [8]. Hereafter, the metal doped ZnS nanoparticles have received increasing interest. Recently, many methods have been developed in preparation of Cu doped ZnS nanopowder [9, 10]. In this paper, we report a new chemical synthesis method for preparation of Cu doped ZnS nanopowder as shown in Fig. 1. This process concluded two steps: First, selection to synthesize different lengths of the zinc methacrylate polymer by adjusting the molar ratio of mercaptoacetic acid to monomer of the methacrylic acid; second, the polymer reaction with sodium sulfide and cupric sulfate, giving the Cu doped ZnS nanopowder. During formation of the nanoparticles, the nanoparticles were capped by the methacrylic polymer, which passivated the surface atoms, eliminated the energy levels inside of gap, and increased the luminescence intensity. The size of nanoparticles can be well controlled from 1.8 nm to 3 nm by adjusting the molar ratio of mercaptoacetic acid to monomer of methacrylic acid. The production of Cu doped ZnS nanopowder was also characterized by TEM, XRD and PL. Methacrylic acid (99%) monomers were purified by distillation under reduced pressure prior to use. The cupric sulfate (99%), zinc acetate dihydrate (99%), sodium sulfide (99%), potassium persulfate (99.5%) and mercaptoacetic acid (HSCH2COOH) (85%) were used without further purification. All of the chemicals were purchased from Beijing chemical reagent corporation. To synthesize Cu doped ZnS nanopowder, 40 × 10−6 m3 of water, 0.03 mol of zinc acetate, and 5.5 × 10−6 m3 (6.49 × 10−4 molar) of methacrylic acid were added to a three-neck flask equipped with condenser, then heated and stirred. When the temperature increased about 60 ◦C, 40 × 10−6 m3 of 0.005 M potassium persulfate aqueous solution and 10−5 m3 of 0.032 M (3.2 × 10−6 molar) mercaptoacetic acid aqueous solution were added, respectively. The temperature was kept at 80 ◦C for 1 h. 20 × 10−6 m3 of 0.008 M CuSO4 aqueous solution was added into reactor vessel and stirred for 5 min. 40 × 10−6 m3 of 0.8 M sodium sulfide aqueous solution was dropped into the reactor at a constant rate. When the Na2S aqueous solution was complete, the reaction was continued for an additional 30 min at 80 ◦C. The powder was well separated from the solution by centrifuging, rinsed with methanol and dried in vacuum. The Cu doped ZnS nano-powder was obtained. The PL spectra of Cu doped ZnS nanopowder were recorded with a Hitachi F-4500 fluorescence spectrophotometer. The spectra were obtained by exciting the sample with 368 nm wavelength at room temperature. X-ray powder diffraction was performed on the Cu doped ZnS powder on a Rigaku RU-200B rotaflex diffractometer using Cu Kα λ = 0.15406 nm. TEM

Synthesis and photocatalytic properties of iron oxide pillared hydrogen tetratitanate by the hydrothermal crystallization method

Iron oxide pillars, less than 1 nm in height, were constructed in the interlayer of tetratitanate by the hydrothermal reaction of H2Ti4O9 and FeSO4 aqueous solution, followed by calcining in air. The samples showed absorption in the visible region and were capable of hydrogen evolution under visible light irradiation (λ>400 nm) in the presence of 0.1 M Na2S aqueous solution as a hole acceptor, although no noticeable hydrogen evolution was observed when H2Ti4O9 and Fe2O3 were used independently. Hydrogen evolution activity of iron oxide pillared tetratitanate increased by calcining in air at 300°C after hydrothermal reaction.

Effects of the removal of matrix substances as a pretreatment in the production of high strength resin impregnated wood based materials

The unique microstructure of wood has many anatomical features, which provide both high toughness and strength of wood. Considering its outstanding microstructure and the fact that the Young’s modulus of microfibril, a cellulose crystal and the framework of the cell wall, reaches 140 to 150 GPa, it is believed that wood has the possibility to be the basis for high strength materials. For this reason, we are studying the production of high strength wood based materials using a low molecular weight phenolic resin impregnation followed by heat curing under compression [1–5]. The wood cell wall is composed of 50% of matrix substances, such as lignin and hemicellulose, whose mechanical properties are not as high as microfibril. Thus, in a previous report [5], we studied the effects of the removal of matrix substances as a pretreatment using alkaline cooking which is the most widely used procedure in pulping to remove the matrix substances of wood. Veneers of Hoop pine (Araucaria cunninghamiii) were treated with a NaOH + Na2S aqueous solution (25% active alkali, 25% sulphidity) at 120 ◦C or 135 ◦C for 4 h, which resulted in 20% weight loss. These veneers were subjected to a low molecular weight phenolic resin (PF resin) impregnation and compression after parallel lamination, 20% higher Young’s modulus and bending strength than without pretreatment of wood were obtained. However, when veneers were treated at higher temperatures such as 150 ◦C or 170 ◦C a further increment in the mechanical properties could not be observed despite an increase of weight loss of up to 30%. The results of the wood analysis for Klason lignin showed that the weight loss due to the alkaline cooking in this study is mainly attributable to the removal of hemicellulose. Thus, it was considered that the removal of lignin due to the alkaline cooking requires a higher temperature than that for hemicellulose. However, further increment of cooking temperature also causes damage to the microfibril, a kind of carbohydrate the same as hemicellulose, and this may result in the reduction of mechanical properties. Hence, in this study, to obtain a further weight loss with less damage to microfibril, the removal of lignin by NaClO2 treatment and the removal of lignin and hemicellulose by a combination of NaClO2 treatment and NaOH treatment under mild conditions were attempted with Hoop pine veneer as used in the previous work [5]. Hoop pine veneers (70 g), with dimensions of 80 mm in the longitudinal direction (fiber direction), 60 mm in the cross longitudinal direction and 1 mm thickness were treated at 45 ◦C for 12 h with 2000 ml of 1 or 2% NaClO2 aqueous solution at pH 4.5. This treatment was repeated up to 3 times after rinsing in running water for 2 h. The weight loss due to this treatment reached 14% and 24% for a NaClO2 concentration of 1 or 2%, respectively as shown in Table I. After drying, these samples were then soaked in a 10% aqueous solution of a low molecular PF resin (Aika Ko-gyo Co. Ltd; average molecular weight, 200, pH 8) under a reduced pressure for three days. The materials were then dried successively at room temperature for 7 days and at 70 ◦C for 1 h. The weight gain for the untreated wood and treated wood were 25% and 21 to 23%, respectively. The resin impregnated veneers were parallel laminated (nine-ply) and compressed at 80 MPa and 160 ◦C for 1 h. The specimens were then cut to dimensions of 60 mm (longitudinal direction) by 10 mm (cross-longitudinal direction). The final thickness of the compressed specimens was about 2 mm. The specimens were conditioned at 90 ◦C for 1 h to regulate the moisture content before a three point bending testing at a cross-head speed of 5 mm/min and a test span of 50 mm in an Instron 1185 universal testing machine. As shown in Table I, the mechanical properties of the resin impregnated compressed wood were improved due to the NaClO2 treatment, and the 2% NaClO2 treated samples showed a 40% higher Young’s modulus and bending strength than the untreated wood (control) at the same density. The effect of alkaline cooking on the increment in Young’s modulus and bending strength was about 20% at a weight loss between 20 and 30%

UV photoinduced reduction of water to hydrogen in Na2S, Na2SO3, and Na2S2O4 aqueous solutions

Hydrogen was produced by ultraviolet (UV) light irradiation (>200nm) in an Na2S aqueous solution without photocatalysts. Water (protons) appeared to be directly reduced to hydrogen by excited electrons produced in photon absorption with sulfide ions (S2−). The maximum quantum efficiency for hydrogen formation, 8.9%, was obtained in a 25mmoldm−3 Na2S solution. Marked amounts of hydrogen were produced under UV light irradiation in the aqueous solutions of SO32− and S2O42− ions. S2− ion absorption began at 290nm, SO32− at 275nm, and S2O42− at 400nm. Hydrogen hardly formed at all, however, in SO42−, I−, and SCN− solutions.