Presence Of Hydrofluoric Acid Research Articles

SELF-ASSEMBLED POLYANILINE MICRO/NANOTUBES DOPED WITH HYDROFLUORIC ACID

Self-assembled micro/nanotubes of polyaniline(PANI) with a high conductivity(10~(-2)～10~(-1)S/cm) were synthesized by a template-free method in the presence of hydrofluoric acid(HF) as the dopant.The formation probability of PANI-HF micro/nanotubes was nearly 100% when the molar ratio of / was equal to 0.5.The SEM and TEM images revealed that the average diameter of the micro/nanotubes was about 85～420 nm.Besides,it was found that the diameter and conductivity of micro/nanotubes at room-temperature increase with the increase of / ratios.The micro/nanotubes characterized by FTIR and UV-Visible absorption spectrums are identical to the emeraldine salt state of PANI.

A versatile approach to develop porous hydrogels with a regular pore distribution and investigation of their physicomechanical properties

AbstractPorous polyacrylamide (PAAm) hydrogels with enhanced mechanical properties and regular pore distribution have been synthesized by a unique and facile methodology, which involves formation of the hydrogel pores by leaching out chemically modified silica particles. To improve the pore distribution and mechanical properties of the hydrogel network, porogen particles have been modified with PAAm chains chemically attached to the silica surface. Grafting polymerization initiated by peroxide groups immobilized on the particle surface has been used for this modification. The grafted PAAm layer on the silica surface improves the dispersibility of the porogen material in the hydrogel composition, and simultaneously forms pore “walls” reinforcing the hydrogel network, after leaching out the silica particles. The proposed synthetic way for the development of porous hydrogels includes three steps: (i) tethering of PAAm chains to silica particles due to the grafting polymerization initiated by an adsorbed polyperoxide macroinitiator (PPM), (ii) simultaneous crosslinking of grafted PAAm chains and PAAm forming hydrogel network, and (iii) pore formation by leaching out silica particles in the presence of hydrofluoric acid. The PPM has been synthesized by a free radical copolymerization of the peroxide monomer (PM) N‐(tert‐butylperoxymethyl)acrylamide with acrylamide. Both PM and PPM have been developed in our lab, and applied for the synthesis of porous polymeric hydrogels. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Synthesis, characterization and intercalation property of layered zirconium benzylamino- N, N-dimethylphosphonate phosphate materials

Layered zirconium benzylamino- N, N-dimethylphosphonate phosphate (ZBMPA) was prepared by the reaction of zirconyl chloride with benzylamino- N, N-dimethylphosphonic acid (H 2BMPA) and phosphoric acid in the presence of hydrofluoric acid. The intercalation of n-alkylamines ( n-butylamine, n-heptylamine and n-decylamine) into ZBMPA was primarily investigated at room temperature. These materials were characterized by elemental analysis, ICP, XRD, SEM, FT-IR, Raman spectra, TG and DSC. The composition of ZBMPA is Zr(HPO 4)(C 6H 5CH 2N(CH 2PO 3) 2) 0.5 · 2.0H 2O. The interlayer distance of ZBMPA, n-butylamine, n-heptylamine and n-decylamine intercalation compounds is 2.03, 2.58, 2.52 and 3.17 nm, respectively. ZBMPA and the n-alkylamine intercalation compounds are different in the morphology and vibration spectra. Thermogravimetries of all materials obtained reveal three step mass losses at temperatures of up to 1000 °C. These results indicate that n-alkylamines are intercalated into the galleries of host ZBMPA.

Surface Chemistry of <I>n</I>-Octane Modified Silicon Nanoparticles Analyzed by IR, <SUP>13</SUP>C CPMAS NMR, EELS, and TGA

The functionalization of silicon nanoparticles by thermally induced hydrosilylation in a one-pot process is reported. In contrast to the commonly applied thermally induced hydrosilylation, the process described here is carried out in the presence of hydrofluoric acid as a second phase and therefore proceeds at a lower conversion temperature. The surface functionalization of silicon nanoparticles was analyzed by IR, 13C CPMAS NMR, EELS, and TGA techniques. The applied procedure resulted in functionalized silicon nanoparticles with good chemical and thermal stability.

Synthesis and Characterization of Water-Soluble Silsesquioxane-Based Nanoparticles by Hydrolytic Condensation of Triethoxysilane Derived from 2-Hydroxyethyl Acrylate

A new family of silsesquioxane-based nanoparticles was synthesized by hydrolytic condensation of a triethoxysilane precursor, R-Si(OCH2CH3)3, R = -CH2CH2CH2N(CH2CH2COOCH2CH2OH)2, derived from 2-hydroxyethyl acrylate. Condensation of the triethoxysilane precursor proceeded as a homogeneous system in methanol in the presence of hydrofluoric acid (HF) to afford water-soluble silsesquioxane-based nanoparticles, as confirmed by NMR, FT-IR, and elemental analyses. Scanning force microscopy (SFM) measurements indicated the formation of nanoparticles having a relatively narrow size distribution with an average particle diameter of less than 2.0 nm without aggregation. The size of the nanoparticles (1.7 nm) was determined by X-ray diffraction (XRD). The narrow polydispersity (Mw/Mn = 1.08) and a reasonable molecular weight (Mn = 3300), corresponding to species having 6-12 silicon atoms, were also confirmed by size-exclusion chromatography. Co-condensation of tetraethoxysilane (TEOS) with the triethoxysilane precursor was carried out under different feed ratios, and water-soluble products were obtained in the cases of TEOS molar ratios up to 70%. Thermal stability and the char yield were found to increase with increasing TEOS content in the feed, as determined by thermogravimetric analysis. The isolated nanoparticles distributed homogeneously without any aggregation were visualized by SFM, when the product was prepared at TEOS/triethoxysilane precursor = 50/50 mol %.

Photochemical etching of silicon by two photon absorption

AbstractPhotochemical etching of silicon assisted by two‐photon absorption (TPA) in the presence of hydrofluoric acid (HF) is demonstrated using a below‐bandgap femtosecond laser source. We investigate the morphology of the etched silicon as a function of the laser power, exposure time, as well as the substrate doping level. Self‐organized periodic silicon trenches with ∼150 nm spacing were observed at the etch front as the initial stage of the TPA photochemical etching process. Since the etching front can be precisely controlled by the focal point, this technique can be used for writing silicon microfluidic systems and for 3D micromachining. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Correlation between Vickers microhardness, porous layer thickness and porosity in p-type nanostructured silicon

Mechanical characteristics via Vickers microindentation technique of nanostructured silicon films have been studied. The samples were grown by the usual electrochemical etching process in presence of hydrofluoric acid in two distinct proportions and for several exposure times. The current density was kept constant for all runs. Porosity and porous layer thickness were measured by gravimetric and optical means, respectively. A linear relation between layer thickness and exposure time shows up, in accordance with previous studies. Correspondingly, a slight decrement in the Vickers hardness is observed. On the contrary, the porosity remains independent of exposure time. A possible explanation is therefore proposed and discussed.

Layered microporous tin(iv) bisphosphonates

This article reports the hydrothermal synthesis and characterization of two new series of porous tin(IV) phosphonophenoxyphenylphosphonates with controlled pore size distributions, using as precursor the 4-(4'-phosphonophenoxy)phenyl phosphonic acid, [H2O3P-C6H4]2-O. Supermicroporous solids (S(BET), 300-400 m2 g(-1)) were obtained employing n-alcohol (C1-C6)-water mixtures (solvents ratio 1 : 1), in the presence of hydrofluoric acid. X-Ray powder diffraction shows that these compounds are semi-crystalline and the local environments around the phosphorus and tin elements have been studied by 31P and 119Sn MAS-NMR spectroscopy, respectively. The microstructure (particle sizes and shapes) of these phosphonates has been analyzed by scanning and transmission electron microscopy. This study shows that the microstructures of single-ligand (for instance tin(IV) phenylphosphonate) and cross-linked tin(IV) bisphosphonates are different. Tin(IV) phenylphosphonate crystallizes as micron-sized spheres, theta approximately 1-2 microm, formed by the aggregation of nanospheres, whereas tin(IV) bisphosphonates crystallize as microparticles larger than 20 microm. The textural properties of these porous solids were characterized by N2 and CO2 sorption isotherms. The key result of this work is that maxima of pore size distributions smoothly shift from 12 to 16 angstroms upon increasing the chain length of the alcohol. The microporosity of tin(IV) bisphosphonates is compatible with a double role played by the phosphonate groups acting as a pillar between adjacent layers and as a component of the hybrid organic-inorganic layers.

Electroreduction of Molybdate Ions in the Presence of Hydrofluoric Acid

The electroreduction of molybdate ions in the presence of hydrofluoric acid was studied. The effective activation energy of the electroreduction of molybdate ions was determined using the Arrhenius equation.

Sb(III) fluoride complexes with DL-valine. Crystal structure of molecular complex SbF3{(CH3)2CHCH(+NH3)COO?}

Preparative method in combination with X-ray diffraction and IR spectroscopy is used to study reaction of Sb(III) fluoride with α-aminoisovaleric acid (DL-valine) in an aqueous solution in the range of the molar ratios of components (0.25–2) : 1 in the presence of hydrofluoric acid. The molecular complex of Sb(III) fluoride with valine (1 : 1) of the composition SbF3{(CH3)2CHCH(+NH3)COO−}(I) and valinium tetrafluoro-antimonate(III) monohydrate {(CH3)2CHCH(+NH3)COOH}SbF4· H2O (II) are synthesized for the first time. Crystal structure was determined for the molecular complex I consisting of SbF3 groups and valine molecules united into polymer chains through bidentate bridging carboxylate groups of amino acid molecules.

Morpholine, an in Situ 13C NMR pH Meter for Hydrothermal Crystallogenesis of SAPO-34

The pH has been measured in situ by 13C NMR during hydrothermal formation of SAPO-34 (SAPO: silicoaluminophosphate) in the presence of hydrofluoric acid and with morpholine as the structure-directing agent. Morpholine, with a pKa of about 8.8 at room temperature, can be used as a pH probe within the region 7.3 < pH < 10.3. The pH was determined to be 5.5 immediately after mixing of the gel and increased by 3 pH units during the synthesis. During the first stage of the heating (25−85 °C), no change in pH was observed by using a conventional pH meter. During formation of the layered intermediate prephase (85−120 °C), the pH increased by ∼2 units. A second sharp pH increase was observed by in situ 13C NMR when the synthesis temperature approached 160−165 °C, which corresponded to the minimum temperature needed to prepare triclinic SAPO-34 within a reasonable time frame (a few days).

DETERMINATION OF NANOMETER-SCALE SIZES IN n+-TYPE POROUS SILICON BY THE USE OF X-RAY AND RAMAN SPECTROSCOPIES

Porous silicon layers were obtained by electrochemical etching on (111) plane surfaces of crystalline phosphorus-doped silicon in the presence of hydrofluoric acid. The photoluminescence of this kind of layers when illuminated with UV light is possibly explained by the quantum confinement model (QCM), which states the presence of nanometer-scale crystallites that enlarge the semiconductor band gap up to optical photon energies when the band-to-band recombination processes take place. In this study, the size determination of those proposed structures was performed by X-ray diffractiometry and by Raman spectroscopy. The obtained results suggest a consistency between the experimental work and the QCM.

Identification of a Key Precursor Phase for Synthesis of SAPO-34 and Kinetics of Formation Investigated by in Situ X-ray Diffraction

The kinetics of formation of SAPO-34 in the presence of HF and with morpholine as a structure-directing agent has been monitored by in situ X-ray powder diffraction. Examination of the gel as a function of various heating profiles and final synthesis temperatures demonstrates the importance of the heating history. At lower temperatures, a layered “prephase” has been obtained with general empirical formula resembling [AlPO4F] × 0.87 C4H9ON−H. On indexing powder X-ray diffraction data, a monoclinic unit cell with dimensions a = 14.473 Å, b = 6.930 Å, c = 9.239 Å, and β = 101.54° was found with high figures of merit. An additional disordered phase, most probably a layered structure, appears as a transient phase during transformation of the prephase to SAPO-34. It has been shown that these two precursors are of major importance for obtaining SAPO-34 under the conditions studied. In addition, use of the prephase as starting material with the addition of water produces triclinic AlPO4-34 (Si free) after hydrothermal treatment at 180 °C for 24 h. The kinetics of formation have been examined in the presence of hydrofluoric acid as a function of the final synthesis temperature using a two-step heating profile. The crystallization curves were fitted to the Avrami−Erofeyev equation, and activation energy of 158 kJ/mol for the formation of triclinic SAPO-34 was determined from an Arrhenius plot.

Extraction of Uranium and Thorium with TBP from Fluoride — Nitric Acid Solutions

The extraction of HNO3, thorium and uranium were studied in the presence of hydrofluoric acid. The extraction constants of both the acids are shown to be close to one another which results in their mutual displacement from the organic phase. Contrary to uranium, the extraction of thorium is much reduced as the concentration of hydrofluoric acid increases which may be explained by a stronger complexation of Th by fluoride ion in the aqueous phase.

Diammonium titanium pentafluoride, (NH4)2TiF5, containing Ti3+

Single crystals of the title compound have been synthesized by low-temperature hydrothermal treatment of titanium isopropoxide in the presence of hydrofluoric acid and ethylenediamine. The compound consists of parallel infinite chains of trans-corner-connected TiF 6 octahedra along the b axis, separated from each other by NH 4 + ions. The Ti atoms lie on inversion centres and the ammonium ions on mirror planes.

Synthesis and properties of some monolithic silica carbogels produced from polyethoxydisiloxanes dissolved in ethylacetoacetate (etac) and acid catalysis

The aim of the present work described in this paper was to synthesize transparent and superinsulating monolithic carbogels in order to use them as transparent double window insulation spacers at the laboratory scale. The monolithic silica carbogels were made by sol–gel technique using mixtures of a new family of precursors noted PEDS-Px (or polyethoxydisiloxanes which are prepolymers of silica differing by their substoichiometric hydrolysis degrees) [G.M. Pajonk et al., J. Non-Cryst. Solids 186 (1995) 1] with organic solvents in the presence of hydrofluoric acid with no excess of water added, and subsequent drying in the supercritical conditions with respect to CO 2 [P.H. Tewari et al., in: L.L. Hench, D.R. Ulrich (Ed.), Science of Ceramic Chemical Processing, Wiley, New York, 1986, p. 123]. Our research was focused at finding the best conditions of preparation of the monolithic silica carbogels in terms of optical and thermal insulation properties. A new solvent ethylacetoacetate (etac) was found to be much more soluble in liquid CO 2 than common alcohols and acetone, and the so obtained carbogels, with etac, present very interesting optical visible transmission and thermal properties respectively. The best samples were prepared from mixtures composed of 60% of a prepolymer prepared with 1.8 moles of water per TEOS mole (noted P 900) and 40% of etac (on a volumetric basis), and presented very good transparency close to the one shown by a flat glass pane together with a very small thermal conductivity (unequalled, to the best of our knowledge, by any other solid material at the present time).

Laser-induced etching of silicon in hydrofluoric acid

Laser-assisted wet etching (LAWE) of n-silicon using a 514.5-nm line from a cw argon-ion laser in the presence of hydrofluoric acid is reported. The effects of laser fluence, doping level, and acid concentration on the etch rate are investigated. By LAWE, vias and lines can be rapidly etched with smooth profiles under conditions described.

Directing Effect Of Fluoride In The Synthesis Of Molecular Sieves With New Characteristics And Of The First Twenty-Membered Ring Microporous Solid

ABSTRACTThe directing effect of fluoride anions in the synthesis of molecular sieves seems to be related to the strength of its interaction with the framework. For example, whereas F is bridging 2 Al atoms of a four-membered ring in AlPO4-5 containing tetrapropylammonium fluoride and in an new triclinic morpholine-containing chabazite-like AlPO4, it is found in double four-rings in three other phases which were synthesized recently. Firstly in the tetragonal all-silica AST-type octadecasil (space group I4/m, a = 9.194(2)Å c = 13.396(4)Å) which was obtained in the presence of quinuclidine and HF. Secondly in two novel cubic microporous gallophosphates which are formed selectively in the presence of hydrofluoric acid. One has the structure type LTA (space group Fm3c, a = 24.0354(1)Å) and crystallizes with di-n-propylamine as a template, and the other shows a novel structure type (space group Fm3c, a = 51.84Å) with a 3-dimensional 20-membered ring channel system. This is the largest membered ring ever reported for a synthetic material.

Radiotracer investigation of the interference of hydrofluoric acid in the determination of arsenic and antimony by hydride generation atomic absorption spectrometry

The influence of hydrofluorica acid on the behavior of arsenic and antimony in hydride generation with NaBH/sub 4/ was investigated by means of the radiotracers /sup 76/As and /sup 124/Sb. Simultaneously, the corresponding extinctions were measured. Up to a concentration of 1% hydrofluoric acid present in hydrochloric acid sample solutions does not affect the hydrogenation of As(III) and Sb(III). In solutions with higher HF concentration, As(V) forms (AsF/sub 5/OH)/sup -/ ions which do not react with NaBH/sub 4/. After the (AsF/sub 4/OH)/sup -/ ions are hydrolyzed, the interference of hydrofluoric acid can be sufficiently reduced by complex formation with boric acid. Antimony(V) is not hydrogenated in the presence of hydrofluoric acid, which, in addition, seriously hinders the reduction of Sb(V) to Sb(III). Improved procedures are proposed which allow the elimination of the interference of hydrofluoric acid in both the hydrogenation and the absorption measurement stages and also in the reduction of Sb(V) to Sb(III) in this medium.

Derivatives of α-zirconium phosphate with two different functional groups

The syntheses of derivatives of α-zirconium phosphate having the general formula Zr(RPO 3) x (R′PO 3) 2− x (where R and R′ are generally organic radicals, but may also indicate −H or −OH groups) have been achieved by precipitating a mixture of two phosphonic acids with a zirconium salt in the presence of hydrofluoric acid. Different mixed compounds, classified in the following three classes 1. (a) Zr (HPO 4) x (R′PO 3) 2− x (R′ = −H; −C 6H 5; −CH 2CH 2COOH) 2. (b) Zr (RPO 3) x (R′PO 3) 2− x (R′ = −CH 2COOH;R′ = −CH 2OH) 3. (c) Zr (HPO 3) x (R′PO 3) 2− x (R′ = −CH 6H 5; −CH 2OH; −CH 2COOH; −CH 2CH 2COOH) were prepared and characterized with regard to their compositions, X-ray powder patterns and densities. It was found that the system is discontinuous, not all x values from 0 to 2 being possible. No single crystals for X-ray structure determination were obtained; however, some chemical evidence shows that the mixed compounds possess a layered structure similar to that of α-zirconium phosphate. Some considerations on the reciprocal disposition of the R and R′ pendent groups in the layered structure are reported. Many other derivatives are expected to be obtained easily by using other mixtures of phosphonic acids than those employed in this work. Owing to the large variety of possible combinations of R and R′ groups, the mixed compounds should exhibit a large spectrum of properties and show promise for application in the field of ion exchange, adsorption, intercalation and heterogeneous catalysis.