Aqueous Solutions Of Metal Salts Research Articles

Metallic Nanostructures via Static Plowing Lithography

A facile route to metallic nano- and microstructures of varying size and geometry is reported. Both nanoparticle formations as well as continuous structures are formed spontaneously on Ge(111) substrates via galvanic displacement from aqueous metal salt solutions. Utilizing an atomic force microscope, patterning is achieved via static plowing lithography through a thin polymeric photoresist. Metal deposition proceeds on exposed portions of the substrate, and the resist is subsequently removed to yield the desired metallic features.

Preparation of Acrylate-Stabilized Gold and Silver Hydrosols and Gold−Polymer Composite Films

Gold and silver nanoparticles were prepared by reducing aqueous solutions of the respective metal salts with sodium acrylate (SA), which also acts as capping agent. Gold nanoparticles were also prepared using poly(sodium acrylate) (PSA) with various molecular weights (2100, 5100, 15 000, and 30 000 g/mol). These polymers act as both reducing and stabilizing agents for the gold nanoparticles. Gold nanoparticles formed using SA are nearly spherical and have a narrow size distribution (11−17 nm). These particles are similar in size and stability to those formed by the conventional citrate reduction method. PSA-stabilized gold nanoparticles are somewhat less uniform in size but also highly stable. The polymer-stabilized gold particles can be used to form composite polymer films with optical properties that depend on the volume fraction of gold.

Substitution of the chloro ligands in cis-[CoCl 2(2-C 5H 4NCO 2Pr i) 2]: structural characterization of four mononuclear products showing both cis and trans configurations at Co(II)

Cobalt(II) complexes obtained by the reaction of cis-[CoCl 2(2-C 5H 4NCO 2Pr i) 2] ( 1) with aqueous solutions of simple alkali metal salts have been prepared and characterized. While the reaction of 1 with KPF 6 affords both trans-[Co(2-C 5H 4NCO 2Pr i) 2(H 2O) 2](PF 6) 2·2(2-C 5H 4NCO 2Pr i) ( 2) and trans-[Co(2-C 5H 4NCO 2Pr i) 2(H 2O) 2](PF 6) 2 ( 3), that with NaBPh 4 leads to trans-[Co(2-C 5H 4NCO 2Pr i) 2(H 2O) 2](BPh 4) 2·2H 2O ( 5) exclusively. X-ray diffraction data show that the mononuclear cationic units in 2, 3 and 5 share common structural features. The reaction of 1 with KSCN leads to cis-[Co(NCS) 2(2-C 5H 4NCO 2Pr i) 2] ( 4), whose crystal structure shows that it consists of mononuclear discrete molecules. The analogous reaction with NaN 3 yields the very slightly soluble complexes [Co(N 3) 2(2-C 5H 4NCO 2Pr i)] ( 7) and [Co 2(N 3)(2-C 5H 4NCO 2Pr i) 4(H 2O)]·3H 2O ( 8) and that with NaOAc results in the formation of the already known complex trans-[Co(2-C 5H 4NCO 2) 2(H 2O) 2] ( 6) as the only product. Electronic UV–Vis and NIR spectral data for 2– 5, 7 and 8 and the calculated magnetic moments from NMR measurements on 2– 4 and 7 are indicative of high-spin octahedral Co(II) complexes, as already reported for 1 of known structure.

Surface Characterization of Silica Aerogels with Different Proportions of Hydrophobic Groups, Dried by the CO2Supercritical Method

Silica aerogels, dried by the CO2 supercritical method, were made from tetramethoxysilane (TMOS) and methyltrimethoxylsilane (MTMS) in different proportions to change the proportions of hydrophilic and hydrophobic surface groups. The aerogel hydrophobic or hydrophilic properties were related to their textural and surface structural characteristics. In particular, water adsorption isotherms were recorded by successive equilibrium with saturated aqueous metal salt solutions. They were compared to nitrogen adsorption isotherms. The relative proportion of Si−OH, Si−OCH3, or Si−CH3 end groups present on the gel surface was determined by nuclear magnetic resonance (NMR) of 1H. The results obtained were correlated with measurements of the contact angle with water, after equilibration of the gels at various water activity. From these data, a possible description of the mixed hydrophilic−hydrophobic nature of the surface of these materials is finally proposed.

Electroless Nanoparticle Film Deposition Compatible with Photolithography, Microcontact Printing, and Dip-Pen Nanolithography Patterning Technologies

Nanoparticles of Au, Pd, and Pt form spontaneously as thin, morphologically complex metallic films upon various semiconducting or metal substrates such as Ge(100), Cu, Zn, and Sn, via galvanic displacement from aqueous metal salt solutions. Patterning of these high surface area metal films into ordered structures utilizing photolithography, microcontact printing (μ-CP), and dip-pen nanolithography (DPN) is demonstrated on flat Ge(100), and (for μ-CP) on rough Zn foil.

Hydrothermal Dechlorination and Denitrogenation of Municipal-Waste-Plastics-Derived Fuel Oil under Sub- and Supercritical Conditions

The hydrothermal processing of municipal-waste-plastics-derived fuel oil (kerosene fraction; Cl content = 62 ppm, N content = 1150 ppm) under sub- and supercritical conditions has been investigated so as to demonstrate the possible use of water and aqueous solutions of metal salts and hydroxides for the dechlorination and denitrogenation of the fuel oil. The hydrothermal processing was carried out in a small SUS316 stainless steel batch reactor under nitrogen atmosphere. Although the two reactions took place in water, they proceeded much more readily under basic conditions, especially in aqueous solutions of alkaline metal hydroxides. That is, the nitrogen content in the product oil decreased to 297 ppm upon processing with water for 15 min at 425 °C, whereas it decreased to 49 ppm when 0.10 mol/L NaOH was used instead of water at 375 °C. Under these hydrothermal conditions, the chlorine content in the product oil was always nearly 0 ppm. Organic acids such as benzoic acid and phthalic acid in the fuel oil could also be removed.

Synthesis of BiSrCaCu(Ni)O Ceramics from the Gel Precursors and the Effect of Ni Substitution

Superconducting BiSrCaCu(Ni)O ceramicss have been prepared by the gel method using an aqueous solution containing a tartaric acid. The aqueous solution of metal salts was concentrated without precipitation. The precursor so prepared was homogeneous and calcined at 825 °C for 24 h to produce superconducting phase. The thermal decomposition of gels, the formation of superconducting phase, and their ceramic microstructure were studied using IR, TGA, XRD, resistance measurements, and SEM. This method is highly reproducible and leads to powders with excellent homogeneity and small particle size for easy sinterability. The nickel dopant substituting for Cu gives rise to the gradual decrease of the T c . Phase pure 2212 ceramics were obtained at 825 °C for 24 h. SEM pictures showed that liquid phase was formed when the samples were sintered temperatures higher than 825 C.

A new approach to the synthesis of intermetallic compounds: mild synthesis of submicrometric CoxMy (M = Mo, W; x∶y = 3∶1 and 7∶6) particles by direct reduction of freeze-dried precursors

A simple processing route to cobalt–molybdenum and cobalt–tungsten intermetallics (CoxMy, where M = Mo and W, and x∶y = 3∶1 and 7∶6) has been developed, on the basis of the use of precursors resulting from freeze-drying of aqueous solutions of the appropriate common metal salts. The influence of the preparative variables on the outcomes of this procedure is examined. These compounds are prepared as single phases by thermal reduction of amorphous freeze-dried powders under a hydrogen–argon atmosphere (8% H2), followed by slow cooling of the samples. The materials have been characterised by X-ray powder diffraction, metal analysis, scanning electron microscopy and thermogravimetry under an oxygen flow. CoxMoy and CoxWy grains are aggregates of submicrometric spherical particles.

Self-assembled poly(metal tetrathiooxalate) films

Abstract Ultrathin poly(metal tetrathiooxalate) films are described which were prepared by a reactive self-assembly process. The polymer films were prepared upon alternate dipping of a negatively charged substrate into aqueous solutions of transition metal salts (e.g. salts with Cu2+, Ni2+, Co2+ and Pd2+) and tetraethylammonium tetrathiooxalate, which led to sequential adsorption of the metal and tetrathiooxalate ions under simultaneous complexation and formation of poly(metal tetrathiooxalate). The polymer films exhibit a brownish coloration with strong metallic reflection. Optical measurements indicate a very broad absorption extended from the ultraviolet to the near-infrared up to 2000 nm. Scanning force microscopy indicates a rather smooth surface with isolated peaks of a height up to 2 μm. Preliminary studies of the specific surface conductivity of poly(nickel tetrathiooxalate) films indicate a value of 2.5×10−3 S cm−1.

Aqueous Solution-Based Ceramic Thin Film Deposition Using Organic Polymers with Amide Groups

Abstract An aqueous solution-based dip-coating technique was presented for ceramic thin film deposition. Organic polymers with amide groups such as polyvinylpyrrolidone, polyvinylacetamide and polyacrylamide, incorporated in aqueous solutions of metal salts, were demonstrated to offer much better wetting of the substrates and gel film formability. Transparent, crack-free TiO2 and ZrO2 thin films of 0.07–0.1 µm in thickness could be obtained from aqueous solutions of Ti(SO4)2 and ZrCl2O, respectively, containing these organic polymers.

The production of a novel stain-etched porous silicon, metallization of the porous surface and application in hydrocarbon sensors

Novel stain (chemical)-etch solutions based on the strong fluorine-contained acids (fluoroboric (HBF 4), hexafluorantimonic (HSbF 6) acids, etc.) for the reproducible production of porous silicon (PSi) are described for the first time. The PSi-films, thus produced, exhibit very intense luminescence and are characterized by high thickness homogeneity and of the luminescence characteristics. The etchants do not attack standard photoresist so they have been successfully employed for production of micron-size patterned PSi areas by stain etching through photoresist mask. The PSi, thus produced, has been used as a bearer of catalytic coatings. Platinum and palladium have been successfully deposited onto the PSi, also without current, by the reduction of metal salts in aqueous solutions. The material, thus prepared, has been applied in the manufacture of gas sensors for hydrocarbons, instead of a smooth platinum layer. The sensor testing showed a much quicker response to a changing hydrocarbon concentration in comparison with a smooth platinum sensor and also, less energy consumption. Moreover, such sensors would be relatively cheap to produce commercially in comparison with analogous sensors based on platinum or palladium sponge.

The preparation of high-surface area, thermally-stable, metal-oxide catalysts and supports by a cellulose templating approach

A simple and convenient templating approach for the preparation of metal-oxide catalysts and supports has been studied. The method, based on the absorption of an aqueous solution of metal salts by cellulose material, followed by drying and combustion of the organic matrix, leads to the formation of high-surface area mesoporous materials with unusually high thermal stability. Examples include Ce–Zr mixed oxides (BET surface areas of 90–130 m 2/g after calcination at 800°C for 2 h; 21–30 m 2/g after 12 h at 1050°C) and La-stabilized alumina (BET surface areas of 275–320 m 2/g after calcination at 800°C for 2 h, 88–141 m 2/g after 12 h at 1050°C). The pore-size distribution, morphology, and the effect of preparation parameters on surface area are discussed.

Molecular Engineered Porous Nanocomposites of Metal Oxide and Clay Using Surfactants

ABSTRACTA novel synthesis route of metal oxide nanoparticles dispersed in a silicate framework is reported here. This composite nanostructure is highly thermally stable and porous, rendering large surface area and rich surface chemistry promising for catalytic applications. Aqueous solutions of metal salts were used as the precursors of the nanoparticles, and added in an aqueous dispersion of synthetic clay, laponite, in which the clay exists in exfoliated silicate sheets. Acid leaching of the clay sheets occurs in the reaction due to the strong acidity of the metal salt solution. Meanwhile, the metal hydrate ions polymerise because of the high pH of the clay dispersion and condense on the leached silicates. This mechanism is distinctly different from conventional pillaring process. The nanocomposites of various oxides and binary oxides were synthesised. By introducing polyethylene oxide surfactants, we obtained mesoporous nanocomposites with very large surface areas (400-900 m2/g) and porosity. These nanocomposites are superior catalysts or catalyst supports over of microporous pillared clays [1-3] due to their structure and surface properties.

Pd2Mo3N: a new molybdenum bimetallic interstitial nitride

The molybdenum bimetallic nitride Pd2Mo3N has been synthesized by ammonolysis of the stoichiometric mixture of low sized pure oxide crystallites (2PdO/3MoO3) as resulting from low temperature thermal decomposition of precursor powders obtained by freeze-drying of aqueous solutions of the appropriate metal salts. This compound has been characterized by elemental analysis, energy dispersive analysis of X-rays, X-ray diffraction, scanning electron microscopy (field emision) and thermogravimetry under oxygen atmosphere. Pd2Mo3N crystallizes in the cubic space group P4132 (no. 213) (Pd2Mo3N, a = 6.81770(3) A, Z = 4), and presents the unusual filled β-manganese structure. It is stable under oxygen atmosphere up to 550 K, the oxidation of the bulk reverting to the oxide mixture being complete at 850 K.

Controlled Aqueous Chemical Growth of Oriented Three-Dimensional Crystalline Nanorod Arrays: Application to Iron(III) Oxides

The ability to create thin films of highly oriented anisotropic nanoparticles of transition metal oxides onto polycrystalline and single-crystalline substrates is demonstrated by the fabrication of large three-dimensional arrays of perpendicularly oriented nanorods of crystalline iron(III) oxides onto tin oxide and sapphire substrates. An enchanced control of the thermodynamics and kinetics of nucleation and growth processes allows one to grow such novel materials directly onto substrates from a simple aqueous solution of metal salts.

A low-energy CAD study of the ions MOH(H 2O) + (M = Mn, Co, Ni, Cu, Zn) and [M(H 2,O 2)] + (M = Cr, Fe, La, Pr)

The ions [MOH(H 2O)] + (M = divalent Mn, Co, Ni, Cu, Zn)and [M,O 2,H 2] + (M = trivalent Cr, Fe, La, Pr) have been formed using an electrospray technique from aqueous solutions of metal salts. Their low-energy, collisionally activated dissociations have been studied in a triple sector instrument. At the lowest collision energies, [MOH(H 2O)] + (M = Co, Mn, Ni,) dissociates by loss of water, but with increasing energy loss of OH and formation of [M(H 2O)] + becomes the major reaction. This behavior correlates more with M +OH than with M +—OH 2 bond energies. [ZnOH(H 2O)] + dissociates only to [ZnOH] + at all available collision energies, which is inconsistent with published relative bond energies. [CuOH(H 2O)] + dissociates to [Cu(H 2O)] + and OH at low collision energy, but [CuOH] + becomes slightly greater in yield at high energy, implying that, in [CuOH(H 2O)] +, D(Cu +—OH) is less than D(Cu +—OH 2). The dissociation spectra of [M,O 2,H 2] + (M = Cr, Fe), which may be [M(OH) 2] +, show only loss of water at low collision energy, yielding MO +, but with increasing collision energy simple bond scission yields [MOH] + as the major product. [M,O 2,H 2] + (M = La, Pr) shows the same behavior, but the threshold energy for the appearance of MOH + is much higher, consistent with the considerably higher M +—O bond energy.

Formation of Gold and Silver Nanoparticles in Aqueous Solution of Sugar-Persubstituted Poly(amidoamine) Dendrimers

Stable nanosize gold and silver particles are spontaneously formed by reduction of aqueous metal salt solutions in the presence of sugar-persubstituted poly(amidoamine) dendrimers (sugar ball). Two sugar balls consisting of generations 3 and 5 are used. The nanoparticles are characterized by absorption spectroscopy, electron microscopy, and FT-IR spectroscopy. In the formation of silver particles, alkaline solution is required. In the process of reduction, characteristic absorption bands appear for the respective metal particles and the intensities increase with reaction time. The sigmoidal curve of intensity vs the reaction time suggests an autocatalytic reaction. The apparent rate constants for the formation of gold particles increase with the concentration of sugar ball, where the rate constants are greater for generation 3 than for generation 5 at the same weight percent of sugar ball. On the other hand, an opposite trend is observed for the formation of silver particles. The average diameters of gold and silver range between 2 and 6 nm and their size distributions are relatively wide.

Controlled Doping of Transition Metal Cations in Alumina Pillared Clays

A two-step method of loading controlled amounts of transition metal cations into alumina pillared clays (Al-PILCs) is proposed. First, calcined Al-PILC was dispersed into an aqueous solution of sodium or ammonium ions. Increasing the pH of the dispersion resulted in an increase in the amount of cations loaded into the clay. The ion-doped Al-PILC was then exchanged with an aqueous solution of transition metal salt at a pH of ∼4.5 to replace Na+ or NH4+ ions by transition metal cations. Analytical techniques such as atomic absorption spectroscopy, X-ray diffraction, diffuse reflectance−ultraviolet−visible spectroscopy, as well as N2 adsorption were used to characterize the PILC products with and without the loading of metal ions. The introduced transition metal species exist in the forms of hydrated ions in the PILC hosts. The content of transition metal ions in the final product increased with the amount of Na+ or NH4+ loaded in the first step so that by controlling the pH of the dispersion in the first step, one can control the doping amounts of transition metal cations into Al-PILCs. A sample containing 0.125 mmol/g of nickel was thus obtained, which is ∼3 times of that obtained by directly exchanging Al-PILC with Ni(NO3)2 solution, while the pillared layered structures of the Al-PILC remained. The porosity analysis using N2 adsorption data indicated that most of the doped transition metal ions dispersed homogeneously in the micropores of the Al-PILC, significantly affecting the micropore structure.

Osmotic swelling of polyacrylate hydrogels in physiological salt solutions.

The swelling behavior of fully neutralized sodium polyacrylate gels was investigated in aqueous solutions of alkali metal (LiCl, NaCl, KCl, CsCl) and alkaline earth metal salts (CaCl2, SrCl2, BaCl2). The total salt concentration and the ratio of monovalent to divalent cations were varied in the biologically significant range. It is found that the concentrations of both monovalent and divalent cations vary continuously and smoothly in the gel despite the abrupt change in the gel volume. The individual elastic, mixing, and ionic contributions to the free energy of the gel were separately determined as a function of the degree of network swelling to elucidate the thermodynamics of swelling. Shear modulus measurements performed at different Ca2+ concentrations suggest that Ca2+ does not form stable cross-links between the polymer chains. At low and moderate swelling ratios the concentration dependence of the shear modulus follows a power law behavior, G variation of phi n, with n = 0.34 +/- 0.03. At high swelling degrees, however, the shear modulus increases with increasing swelling. The value of the Flory-Huggins interaction parameter, chi, determined from osmotic swelling pressure and shear modulus measurements, strongly depends on the ionic composition of the equilibrium solution and increases with increasing Ca2+ concentration.

Powder prepared by spray pyrolysis as an electrode material for solid oxide fuel cells

A variety of spray pyrolysis (SP) techniques have been developed to directly produce ceramic powders from solutions. Examples that are discussed include the following powders: (La0.8Sr0.2)0.9MnO3-YSZ (La(Sr)MnO3-YSZ), La0.6Sr0.4CoO3 (La(Sr)CoO3), (CeO2)0.8(SmO1.5)0.2-NiO (SDC-NiO) and La0.9Sr0.1Ga0.8Mg0.2O3-NiO (LSGM-NiO). For all these powders, spherical, non-agglomerated, submicrometer particles were obtained from aqueous solution of metal salts into a furnace using an ultrasonic atomizer at 1.7 MHz. After SP some of the particles exhibit a hollow-shell morphology. Subsequent calcination at 1000°C yielded crystalline particles. The electrical performance of Ni-SDC/LSGM/La(Sr)CoO3 fuel cells operating at 800°C, prepared from the powders obtained by SP, is reported.