Micropore to macropore structure-designed silicas with regulated condensation of silicic acid nanoparticles

A new preparation method for porous silica particles was developed using activated silica sols which are called nano-silica solutions in this paper. Several kinds of organic and inorganic acids are employed to neutralize diluted sodium silicate solutions to form the nano-silica solutions: formic acid, acetic acid, propionic acid, oxalic acid, succinic acid, dl-malic acid, citric acid, and tricarballylic acid as carboxylic acids, and sulfuric acid and hydrochloric acid as inorganic acids. The effect of salts in the nano-silica solution is also studied. The products were investigated using a field emission scanning electron microscope, an X-ray diffractometer, the nitrogen adsorption technique, and a mercury porosimeter. Microporous silicas were produced when carboxylic acids were applied; the formation of micropores was influenced by the pH of the nano-silica solutions and molecular sizes of the carboxylic acids. Addition of a salt in a citric acid solution increased the mesopore volume. Macropores were formed when inorganic acids including salts were applied; the salt nanoparticles which were crystallized in silica spheres acted as templates. The anion types and salt concentrations in the nano-silica solutions affected the aggregation condition of silica nanoparticles, following the Schulze-Hardy rule.     

Nanofibrillar cellulose aerogels

Highly porous aerogels consisting of cellulose nanofibrils were prepared by dissolution/regeneration of cellulose in aq. calcium thiocyanate followed by regeneration and carefully controlled drying. The influence of drying method (regular freeze drying, rapid freeze drying, and solvent exchange drying) on resulting porosity was studied by electron microscopy and nitrogen adsorption. While regular freeze drying caused significant coalescence of microfibrillar units, solvent exchange drying gave highly porous aerogel composed of approx. 50 nm-wide cellulose microfibrils. Correspondingly, specific surface area of the solvent-exchange-dried aerogels ranged 160–190 m²/g, in contrast to 70–120 m²/g of regular freeze-dried materials. Rapid freeze technique using liquid nitrogen-cooled metal plate gave aerogel sheets with asymmetrical porosity, with the face contacted by copper having porous structure similar to those of solvent-exchange dried material.     

Opening mechanism of internal nanoporosity of single-wall carbon nanohorn

Single-wall carbon nanohorn (SWNH), which is a tubular particle with a cone cap, was oxidized in an oxygen flow at various temperatures. N(2) adsorption at 77 K, thermogravimetry (TG), differential thermal analysis (DTA), transmission electron microscopy, and Raman spectroscopy measurements were carried out on the oxidized SWNHs. The specific surface area of the oxidized SWNHs can be controlled by oxidation temperature, giving the maximum value of 1420 m(2)/g. The pore size distribution by the BJH method and the comparison plot of the N(2) adsorption isotherms of SWNH oxidized at different temperatures against that of as-grown SWNH revealed the minimum oxidation temperature for opening internal nanopores. TG-DTA analyses determined the components of as-grown SWNH: amorphous carbon 2.5 wt %, defective carbon at the cone part 15 wt %, tubular carbon 70 wt %, and graphitic carbon 12 wt %. These systematic analyses provided the exact internal nanopore volume of 0.49 mL/g for pure SWNH particles.     

Flow-injection simultaneous determination of selenium(IV) and selenium(IV + VI) using photooxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine

A flow-injection spectrophotometric method has been developed for the simultaneous determination of selenium(IV) and (IV + VI) at nanogram per milliliter levels. It is based on the catalytic effect of selenium(IV) on the photooxidative coupling of p-hydrazinobenzenesulfonic acid (HBS) with N-(1-naphthyl)ethylenediamine (NED) to form an azo dye (λ_max = 538 nm). In this reaction, bromide acted as an activator for the catalysis of selenium(IV) and an reducer for selenium(VI) to selenium(IV) in an acidic medium which allowed the determination of selenium(IV + VI). A sample solution, being split by Y-piece into two portions, passed through the low-temperature coil (4 m, 25 °C) and the high-temperature coil (20 m, 100 °C). By monitoring the absorbance of the dye produced in the two portions, selenium(IV) and (IV + VI) in the range of 0.2–6 ng ml⁻¹ were determined simultaneously. The relative standard deviations for 3 ng ml⁻¹ selenium(IV) and (VI) (n = 10) were 1.2 and 1.3%, respectively. There were few interfering ions in the selenium determination. The proposed method was applied to the determination of selenium(IV) and (VI) in natural water samples.     

Fine-tuning of copper(I)-dioxygen reactivity by 2-(2-pyridyl)ethylamine bidentate ligands

Copper(I)-dioxygen reactivity has been examined using a series of 2-(2-pyridyl)ethylamine bidentate ligands (R1)Py1(R2,R3). The bidentate ligand with the methyl substituent on the pyridine nucleus (Me)Py1(Et,Bz) (N-benzyl-N-ethyl-2-(6-methylpyridin-2-yl)ethylamine) predominantly provided a (mu-eta(2):eta(2)-peroxo)dicopper(II) complex, while the bidentate ligand without the 6-methyl group (H)Py1(Et,Bz) (N-benzyl-N-ethyl-2-(2-pyridyl)ethylamine) afforded a bis(mu-oxo)dicopper(III) complex under the same experimental conditions. Both Cu(2)O(2) complexes gradually decompose, leading to oxidative N-dealkylation reaction of the benzyl group. Detailed kinetic analysis has revealed that the bis(mu-oxo)dicopper(III) complex is the common reactive intermediate in both cases and that O[bond]O bond homolysis of the peroxo complex is the rate-determining step in the former case with (Me)Py1(Et,Bz). On the other hand, the copper(I) complex supported by the bidentate ligand with the smallest N-alkyl group ((H)Py1(Me,Me), N,N-dimethyl-2-(2-pyridyl)ethylamine) reacts with molecular oxygen in a 3:1 ratio in acetone at a low temperature to give a mixed-valence trinuclear copper(II, II, III) complex with two mu(3)-oxo bridges, the UV-vis spectrum of which is very close to that of an active oxygen intermediate of lacase. Detailed spectroscopic analysis on the oxygenation reaction at different concentrations has indicated that a bis(mu-oxo)dicopper(III) complex is the precursor for the formation of trinuclear copper complex. In the reaction with 2,4-di-tert-butylphenol (DBP), the trinuclear copper(II, II, III) complex acts as a two-electron oxidant to produce an equimolar amount of the C[bond]C coupling dimer of DBP (3,5,3',5'-tetra-tert-butyl-biphenyl-2,2'-diol) and a bis(mu-hydroxo)dicopper(II) complex. Kinetic analysis has shown that the reaction consists of two distinct steps, where the first step involves a binding of DBP to the trinuclear complex to give a certain intermediate that further reacts with the second molecule of DBP to give another intermediate, from which the final products are released. Steric and/or electronic effects of the 6-methyl group and the N-alkyl substituents of the bidentate ligands on the copper(I)-dioxygen reactivity have been discussed.     

Catalytic determination of ultratrace amounts of Cu(II) by the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline

Summary Copper (II) catalyzes the coupling reaction of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with N,N-dimethylaniline (DMA) to form an intensely colored dye (_max=590 nm) in the presence of hydrogen peroxide and ammonia as an activator. On the basis of this reaction, a highly sensitive and selective catalytic method for Cu(II) has been developed. As little as 10^–9 M Cu(II) can be determined by measuring the absorbance of the reaction product at a fixed time (20 min at 40°C). Sandell's sensitivity calculated from the working curve is 1.3×10^–3 ng cm^–2. The method was applied to water analysis and some comments on the analysis of copper in river water were added.Presented at the 1st International Symposium on Kinetics in Analytical Chemistry, Córdoba, Spain, September 28th, 1983.     

Extraction of Quasi-Straightforward-Propagating Photons Through a Scattering Medium by Up-Conversion Method as a Coherent Light Detection Technique

Aiming at the realization of optical CT (computed tomography), the extraction of quasi-straightforward-propagating photons from optical pulses transmitting through a standard scattering medium of Intralipid-10% aqueous solution has been demonstrated by an up-conversion method (second harmonic generation). We have found that this operates as a coherent light detection method rather than a time-gate one and extends the dynamic range where the Lambert-Beer’s law holds to − 86 dB. We have also proposed improvements to obtain the largest possible dynamic range by such an up-conversion technique.     

WDM filter modules consisting of minimum elements

We propose a novel wavelength-division-multiplexing WDM filter module which consists of minimum elements of an input fiber, two output fibers, and two lenses. A wavelength-selective multilayer is coated on a convex surface of one of the lenses. The direct splicing method is used to attach the lens to the fiber edge without adhesion, polishing or antireflection coating. Considering the theoretical beam-angle dependences of the fiber cutting angle and the lens length theoretically and fabrication constraints on the module design, we present an optimal fabrication condition. The fabricated modules showed less than 0.7-dB insertion losses, over 65-dB return losses, and over 20-dB isolations.