Redox reactions between metal nitrates and polyols with the formation of nanopowders (original) (raw)
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ACS Omega
Here, in the present study, silver nanoparticles (SNPs) in the size range 6−10 nm have been synthesized by a chemical reduction method using nicotinamide (NTA), an antiinflammatory agent, and cetyltrimethylammonium bromide (CTAB), a good stabilizing agent, to preparing the nanoparticles in the 6−10 nm size range. Kinetic studies on the formation of SNPs have been performed spectrophotometrically at 410 nm (strong plasmon band) in aqueous medium as a function of [AgNO 3 ], [NTA], [NaOH], and [CTAB]. The plot of ln(A ∞ − A t) versus time exhibited a straight line and the pseudo-first-order rate constants of different variables were calculated from its slope. On the basis of experimental findings, a plausible mechanism was proposed for the formation of SNPs colloid. From the mechanism, it is proved that the reduction of silver ions proceeded through the formation of silver oxide in colloidal form by their reaction with hydroxide ions and NTA after performing their function and readily undergo hydrolysis to form nicotinic acid as a hydrolysis product with the release of ammonia gas. The preliminary characterization of the SNPs was carried out by using a UV−visible spectrophotometer. The detailed characterization of SNPs was also carried out using other experimental techniques such as Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and powder X-ray diffraction (PXRD). SNPs show a remarkable catalytic activity of up to 90% for the reduction of the cationic dye methylene blue.
Potential of metal nanoparticles in organic reactions
Journal of Physics: …, 2008
Palladium(0) nanoparticle has been used as efficient catalyst for (a) the stereoselective synthesis of (E)-and (Z)-2-alkene-4-ynoates and -nitriles by a simple reaction of vic-diiodo-(E)-alkenes with acrylic esters and nitriles and (b) for the allylation of active methylene compounds by allylacetate and its derivatives. Copper(0) nanoparticle catalyzes aryl-sulfur bond formation very efficiently. All these reactions are ligand-free.
Silver nanoparticles stabilized by means of poly-(6-N,N-dimethyl-propylenediamino)-(6-deoxy)-cyclodextrin were synthesized, characterized by different techniques (UV–vis spectroscopy, Dynamic Light Scattering, High Resolution Transmission Electron Microscopy, Fourier-transform IR Spectroscopy) and used as catalysts for the reduction of various nitrobenzene derivatives with sodium borohydride. The nanocomposites obtained appear to have an organized structure, with a metal core surrounded by a layer-structured coating shell. Kinetic data, rationalized in terms of a modified Langmuir–Hinshelwood model, evidenced a non-linear dependence of the reaction rate on the concentration of the catalyst. This was explained on the grounds of the catalytic activity of differently covered catalyst areas. Careful analysis of kinetic data, in particular the effect of the para substituent on the nitroarene structure and the trends of the induction period observed at the beginning of the reaction, provided with interesting insights on the reaction course, and brought us to critically reconsider several mechanistic ideas reported in previous literature.
Langmuir, 2013
We report the facile one-pot single-phase syntheses of silver nanoparticles stabilized by norbornene type cationic polymers. Silver nanoparticles (AgNPs) stabilized by polyguanidino oxanorbornenes (PG) at 5 and 25 kDa and polyamino oxanorbornenes (PA) at 3 and 15 kDa have been synthesized by the reduction of silver ions with NaBH 4 in aqueous solutions at ambient temperature. The four different silver nanoparticles have been characterized by UV−vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and transmission electron microscopy (TEM) for their particle size distributions. Interestingly, PG stabilizes the silver nanoparticles better than PA as evident from our spectroscopic data. Furthermore, the AgNP-PG-5K (5K = 5 kDa) was found to serve as an effective catalyst for the reduction of 4-nitrophenol to 4aminophenol in the presence of NaBH 4. The reduction has a pseudo-first-order rate constant of 5.50 × 10 −3 s −1 and an activity parameter of 1375 s −1 g −1 , which is significantly higher than other systems reported in the literature.
Angewandte Chemie International Edition, 2007
Metal (oxide) nanoparticles smaller than about 20 nm have received widespread interest recently because of their envisioned applications in electronics, optics, and magnetic storage devices. [1] They are currently used as catalysts for the production of fuels and chemicals and the reduction of environmental pollution. [2] High surface-to-volume ratios are important for these particles since catalytic processes take place at the metal (oxide) surface; therefore supports such as SiO 2 and Al 2 O 3 are generally used to obtain small and thermally stable particles. Furthermore, the use of inert matrices allows the design of materials for specific applications, such as drug-delivery systems. Small particles on a support material can be obtained by deposition from the vapor or liquid phase, [4] and the most widely used method is based on impregnation of a porous support with a precursor-containing solution, followed by drying. Subsequent thermal treatment in air converts the precursor into the desired metal oxide or metal if followed by high-temperature reduction. Particles with diameters of 1-3 nm can be deposited from organic precursor complexes, but their limited solubility allows only moderate loadings ( 10 wt %) by single-step impregnations; therefore inorganic salts are typically used to achieve higher metal oxide loadings. Nitrates, in contrast to chlorides and sulfates, are the most commonly used salts, because they can be fully converted into the corresponding oxides. However, supported metal oxides prepared from nitrates generally display relatively large particle sizes. [6] Herein we present a new method that allows the preparation of uniform and small metal oxide particles based on impregnation with aqueous metal nitrate solutions. We describe nickel on silica as an example, but also show the relevance of this method for other systems. Moreover, the significance of these nanoparticles for catalysis is illustrated by the activity of Co/SiO 2 in the Fischer-Tropsch synthesis of hydrocarbons. [8] The formation of NiO from aqueous nickel nitrate solution involves two steps: deposition of Ni 3 (NO 3 ) 2 (OH) 4 during drying [Eq. (1)] and subsequent decomposition of this compound into NiO [Eq. (2)]. 3 ½NiðOH 2 Þ 6 ðNO 3 Þ 2 ðaqÞ T¼120 C ! Ni 3 ðNO 3 Þ 2 ðOHÞ 4 ðsÞ þ 4 HNO 3 ðgÞ þ 14 H 2 O ðgÞ ð1Þ Ni 3 ðNO 3 Þ 2 ðOHÞ 4 ðsÞ T¼450 C ! 3 NiO ðsÞ þ 2 NO 2 ðgÞ þ 2 H 2 O ðgÞ þ 1 = 2 O 2 ðgÞ
Complex formation and degradation in poly(acrylonitrile-co-vinyl acetate) containing metal nitrates
Polymer, 2004
Polymers containing metal-nitrates have been proposed as advantageous precursors for high temperature superconductors such as yttriumbarium-copper-oxide (YBCO). The advantage lies in using conventional polymer processing such as fiber spinning or microlithography before pyrolysis. This research investigated complex formation and degradation in poly(acrylonitrile-co-vinyl acetate) (P(AN-VA)) containing either yttrium nitrate (YN) or barium nitrate (BaN) and follows a similar investigation for copper nitrate. Complex formation was observed in P(AN-VA)/YN but not in P(AN-VA)/BaN. The exothermic nitrate degradation below the P(AN-VA)) cyclization temperature involved the release of NO 3 , a reaction with the nitrile group that disrupted cyclization, and, for BaN, P(AN-VA) degradation. For a P(AN-VA)/nitrate ratio of 2/1 there was no cyclization and the degradation temperature was reduced by about 200 8C. The pyrolysis of P(AN-VA)/BaN yielded largely BaCO 3 , which is likely to impede the formation of YBCO.
The oxidation of aniline with silver nitrate to polyaniline-silver composites
Polymer, 2009
Silver nitrate oxidizes aniline in the solutions of nitric acid to conducting nanofibrillar polyaniline. Nanofibres of 10-20 nm thickness are assembled to brushes. Nanotubes, having cavities of various diameters, and nanorods have also been present in the oxidation products, as well as other morphologies. Metallic silver is obtained as nanoparticles of w50 nm size accompanying macroscopic silver flakes. The reaction in 0.4 M nitric acid is slow and takes several weeks to reach 10-15% yield. It is faster in 1 M nitric acid; a high yield, 89% of theory, has been found after two weeks oxidation of 0.8 M aniline. The emeraldine structure of polyaniline has been confirmed by FTIR and UV-vis spectra. The resulting polyaniline-silver composites contain 50-80 wt.% of silver, close to the theoretical expectation of 68.9 wt.% of silver. The highest conductivity was 2250 S cm À1 . The yield of a composite is lower when the reaction is carried out in dark, the effect of daylight being less pronounced at higher concentrations of reactants.
Addition polymerization of nitrile compounds by organotin catalysts
European Polymer Journal, 1973
Absa'aet--A study was made of the polymerization of NC(CH2)nCN (n = 1-4), fumaronitrile and tetracyanoethylene (TCNE) by organotin compounds such as, oxides and alkoxides, as catalysts. It was found that polymerization occurred with malononitrile, succinonitrile, fumaronitrile and TCNE, but not with glutaronitrile and adiponitrile. Initiation of the polymerization is by addition of the tin compounds to the C~N bond leading to the formation of a Sn--N bond, and propagation is probably by insertion of this bond to C~N bonds. Addition of the tin compounds occurred only to nitrile groups that were sufficiently activated by proximity to electron withdrawing groups. The mutual electron withdrawing effect of one nitrile on the other is sufficient to permit this addition if the nitriles are geminal or vicinal, otherwise no reasonable polymerization occurred. The polymerization of the nitrile bond leads to the formation of highly conjugated systems, which give a black colour to the polymers.