799 research outputs found
“Canton: uno sguardo alla Cina marittima nel nuovo assetto internazionale del Settecento”
No full textIl saggio prende in esame Canton, quale porto internazionale della Cina tra la fine del secolo XVII ed il XVIII, mettendo a fuoco la politica marittima dell'impero Qing
Controlled Synthesis of Gold Nanoparticles Incarcerated in Syndiotactic Polystyrene Matrix
No full textCONTROLLED SYNTHESIS OF GOLD NANOPARTICLES INCARCERATED IN SYNDIOTACTIC POLYSTYRENE MATRIX
Antonio Buonerba,a Cinzia Cuomo,a Sheila Ortega Sánchez,a Patrizia Canton,b Alfonso Grassi.a
a Dipartimento di Chimica, Università degli Studi di Salerno.
b Dipartimento di Chimica Fisica, Università Ca’ Foscari di Venezia.
[email protected]
1. Introduction
Gold Nanoparticles (AuNPs) of controlled dimension (<10 nm) and with narrow dimensional distribution have found application in alcohols oxidation using oxygen as oxidizing agent under very mild conditions.1 To prevent the coalescence, the AuNPs need to be protected e.g. by dispersion in polymer matrices. Here we report on the controlled synthesis of AuNPs using the multiblock copolymer syndiotactic polystyrene-co-cis-1,4-polybutadiene (sPSB) and the use of this catalyst in 1-phenylethanol oxidation.
2. Results and Discussion
sPSB samples having different styrene molar fractions (xS = 0.61 - 0.93) were synthesized by copolymerization of styrene and 1,3-butadiene catalyzed by CpTi(MBMP)Cl [MBMP = 2,2’-methylenebis(6-tert-butyl-4-methylphenoxo)].2 The treatment of THF solutions of the sPSBs and of gold compounds [HAuCl4 or AuCl(PPh3)] with NaBHEt3 (B/Au molar ratio = 4) yielded AuNPs incarcerated in the sPSB matrix which were isolated by precipitation with appropriate solvents. The X-ray Debye-Scherrer method and TEM analysis suggest for the AuNPs a size of 1-7 nm at variance of the synthetic route employed. The aromatic polymer matrix strongly stabilize the AuNPs: actually no leaching as well as no dimensional variation were observed even after treatment with neat chloroform or in mixture of this solvent with water (1:1v/v) for 4 days at room temperature. Oxidation of 1-phenyl ethanol to acetophenone readily proceeds in good yields (75% in 24h) at room temperature using air or oxygen at atmospheric pressure. The catalyst was repeatedly used several times without loss of catalytic activity.
3. References
[1] Hutchings, G. J. Chem. Commun. 2008, 1148-1164.
[2] Cuomo, C. Serra, M. C. Gonzalez Maupoey, M. Grassi, A. Macromolecules. 2007, 40, 7089-7097
Il laboratorio di scienze dell’educazione (secondo biennio): il ruolo del tutor e della discussione
No full text
Seeded growth of gold nanorods: the effect of sulfur-containing quenching agents
No full textHerein we present a study on the efficacy of\ud
selected sulfur-containing species as growth quenchers\ud
andmetal ion scavengers in the framework of gold nanorod\ud
(GNR) synthesis. The here utilized seeded growth method\ud
is the referenceGNRsynthesis approach.However,GNRs\ud
synthesized according to it are prone to morphological\ud
changesuponaging,promotedbythepresenceofunreacted\ud
metal ions in the stock suspension. This, in turn, leads to\ud
optical property changes. Sodium sulfide is an efficient\ud
GNR growth quencher and metal ion scavenger, because\ud
sulfide ion has a strong affinity towards noble metals used\ud
for the GNRs’ synthesis. Moving from these considerations,\ud
different sulfur-containing moleculeswere selected\ud
and their interaction with GNR surface was investigated:\ud
sulfate, sulfite, thiourea, and dodecyl sulfate were chosen\ud
for their difference in terms of net charge, size, and hydrophobicity.\ud
We initially assessed the best synthesis\ud
conditions in terms of reaction time, seed amount, silver\ud
concentration, and quencher amount. Consequently, the\ud
quencher/scavenger was varied. Thiourea, sulfite, and sulfate\ud
ions all showeda feeble, yet non-negligible, interaction\ud
with metals. Although sodium sulfide turned out to be the\ud
most efficient quencher/scavenger, also dodecyl sulfate\ud
showed evidences of adsorption on theGNRsurface, probablypromptedbyhydrophobic\ud
interactions.These findings\ud
are expected to contribute as a background for further\ud
advancements in the perfection of GNR synthetic approaches\ud
specifically in terms of post-synthesis treatments
Determining the degree of crystallinity in semicrystalline materials by means of the Rietveld analysis
No full textRietveld analysis has enabled a determination, by an internal approach, of the degree of crystallinity of a sample of polyethylene terephthalate (PET) and three samples of zirconium oxide obtained by precipitation from ZrOCl2 followed by crystallization at a different temperature. After subtraction of the air scattering, a global diffuse scattering produced by the amorphous phase, by the thermal and lattice disorder and, lastly, by the incoherent or Compton scattering, was built up in the frame of the DBWS-9006PC computer program written by Sakthivel and Young [(1990), Georgia Institute of Technology, Atlanta, GA, USA], modified as described by Riello, Fagherazzi, Clemente and Canton [J. Appl. Cryst. (1995), 28, 115-120]. All these contributions (and the corresponding spending scale factors) were simultaneously optimized, together with the crystalline peak profiles. On the basis of the modified Rietveld analysis, an equation has been suggested that calculates the degree of crystallinity. The value found in the examined PET sample is very close to that already calculated [Polizzi, Fagherazzi, Benedetti, Battagliarin and Asano (1990). J. Appl. Cryst. 23, 359-365] with nonstructural fitting procedur
Polymer-Hematite Nanocomposites: Templating Effect of Commercial Ion-Exchangers in the Growth of Size-Controlled Iron Oxide Nanoparticles
No full textGeneration of size-controlled Pd0 nanoclusters inside of the nanoporous domains of gel-type resins: diverse and convergent support to a strategy of "Template Controlled Synthesis"
No full textIn the realm of supported metal catalysis, the metal component
is usually present as nanoparticles dispersed on the
surface of suitable metal oxides or on active carbon.
Synthetic procedures are normally directed to the generation
of size-controlled metal nanoclusters, whose circumstances
become mandatory when reactions to be catalyzed are
“structure sensitive”.In general, size control has been achieved by: directly
manufacturing metal-oxide-supported catalysts;by the
generation of kinetically stabilized metal nanoclusters in the
liquid phase and subsequent transfer of the protected
nanoclusters on to suitable supports; by generating metal
nanoclusters inside isoporous inorganic materials such as
mesoporous silicas. Herein, we report on three independent, convergent
pieces of structural evidence of this template-controlled
synthesis strategy to obtain size-controlled metal nanoclusters
suitable for synthesizing resin-supported metal catalysts
Template Controlled Synthesis of MonometallicZerovalent Metal Nanoclusters inside Cross-linked Polymer Frameworks: the Effect ofa Single Matrix on the Size of different Metal Nanoparticles
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