1,721,207 research outputs found
Surface behaviour of modified-polystirene triblock copolymers with different macromolecular architectures
No full textWe synthesized novel amphiphilic triblock copolymers of the ABC, ACB, ACD and ADC
types composed of polystyrene (A), hydrophilic polyethylene glycol-modified polystyrene
(B), hydrophobic/lipophilic polysiloxane-modified polystyrene (C) and hydrophobic/
lipophobic perfluoroalkyl-modified polystyrene (D) blocks. Surface domain morphology,
chemical composition and wettability of the polymer films were investigated by atomic
force microscopy (AFM), angle-resolved X-ray photoelectron spectroscopy (XPS) and contact
angle analyses, respectively. Each analysis proved that the surface (nano)structure of
the polymer films was strongly affected by the chemistry of the triblock copolymer and
weakly depended on the sequential position of the blocks in the copolymer. The low
surface energy component (C or D) populated the surface in any case. Contact angle and
XPS measurements carried out on the films after six–seven days of immersion in water
showed that triblock copolymers containing the lowest surface energy fluoroalkyl block
(D) underwent surface reconstruction to a greater extent than those possessing the polysiloxane
block (C)
Interaction of formic acid with Fe2O3 powders under different atmospheres: an XPS and FTIR study
No full textThe interaction between haematite powder and formic acid has been studied at atmospheric pressure by FTIR and under high-vacuum conditions by X-ray photoelectron spectroscopy (XPS) and mass spectroscopy (MS). At room temperature formic acid is adsorbed mainly molecularly whereas dissociative chemisorption is prevalent at higher temperatures. Heating to >500 K causes decomposition of the formate with the formation of carbon monoxide, carbon dioxide, hydrogen and water. Suggestions are made concerning the surface acid sites in connection with the chemisorption and the reaction pathway. The results obtained are compared with those previously achieved by the chemisorption of methanol on iron oxid
The reactivity of a Fe-Ti-O mixed oxide under different atmosphere: study of the interaction with simple alcohol molecules
No full textIn this paper, the interaction between simple alcohols(methanol to 1-butanol ) and a Fe–Ti mixed oxide was investigated.
The reactivity of the mixed system was studied both at atmospheric pressure and in vacuum conditions and compared with
that of the pure oxides (TiO2and Fe2O3). To understand the influence of the oxygen presence in the reaction mixture, the
reactivity was investigated both in inert gas as well as in oxygen atmosphere. X-ray photoelectron spectroscopy(XPS.and
quadrupole mass spectrometry have been used for the experiment in high vacuum, while Fourier transform
infrared spectroscopy and QMS have been used for the experiment in rough vacuum and under atmospheric pressure
conditions). The characterisation of the sample by means of XPS, X-ray diffraction and IR spectroscopy preceded the
reactivity study. When compared with Fe2O3, the Fe–Ti–O mixed oxide seems to be less reactive with respect to the
alcohols; the interaction between alcohol and surface is mainly molecular, as in the case of TiO2. Moreover, the oxidising
power of the mixed oxide is lower than that of Fe2O3 (only traces of carbonic compounds are evident)
Surface acidity and basicity of a rutile powder
No full textIn this work, the interaction of a rutile powder sample with pyridine, 2,6-lutidine, CO,
and CO2 was studied, at atmospheric pressure and under high-vacuum conditions, to
investigate the acid/base character of the surface. The rutile powder has been characterized
with DRIFT and XP spectroscopies, XRD, and thermal analysis. The adsorption experiments
carried out at atmospheric pressure have been studied by means of DRIFT spectroscopy,
whereas QMS and XPS have been used to follow the reactions under HV conditions. The
comparison between the obtained results revealed the presence of Lewis acid sites on the
TiO2 rutile surface. At least two nonequivalent Lewis acidic sites have been observed by
means of CO chemisorption; basic sites were studied by adsorption of CO
XPS study of MgO nanopowders obtained by different preparation procedures
No full textNanosized magnesium oxide powders have been prepared by different preparation procedures (surfactant method with different surfactants, precipitation, ...) and their surfaces have been compared by means of XPS
Synthesis, characterization and reactivitystudy of nanoscale magnesium oxide
No full textIn this study, different samples of nanoscale magnesium oxide (MgO) were synthesized using “aqueous wet chemical method (MgO-OX)”
and “surfactant method (MgO-BR: surfactant used Brij 56, MgO-TR: surfactant used Triton 100-X)”. The samples were then characterized by:
X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy and
Thermogravimetric analysis (TGA). From the analyses performed, it was noticed that the amount of hydroxyl and carbonate groups differs as a
function of the synthesis procedure. The estimated dimensions of the particles are smaller in the MgO-OX sample (around 13 nm) compared to
the 16 nm of the MgO-BR samples and 18 nm of the MgO-TR samples. Studies on the reactivity of MgO nanoparticles were performed using the
DRIFT spectroscopy. Methanol and carbon monoxide were used to study the catalytic activity of MgO. At relatively low temperatures, methanol
dissociates to methoxide species. At higher temperatures, different oxidation products (formates and formic acid, CO and CO2) were observed to
form. MgO-OX showed more oxidative properties than the MgO-TR/BR samples. Moreover, the basic and acidic sites were investigated using
carbon dioxide and pyridine, respectively; the obtained results indicate a different distribution of acidic/basic sites in the different samples
Study of the interaction between simple molecules and W-Sn based oxide catalysts. Part I: the case of WO3 powders
No full textIn this work, the interaction betweenWO3 powder and methanol, 1-butanol, and benzyl alcohol has been
studied, at atmospheric pressure as well as under high-vacuum (HV) conditions, both in the presence and
in absence of oxygen. The chemisorptions carried out at atmospheric pressure have been studied by means
of diffuse reflectance IR spectroscopy while quadrupolar mass spectrometry and X-ray photoelectron
spectroscopy have been used to follow the reactions underHVconditions. At atmospheric pressure, methanol
oxidizes to formic acid and CO2 when chemisorbed in mixture with oxygen at temperature higher than
423 K. Formic acid chemisorption was investigated for comparison. Methanol chemisorption under HV
conditions results in the alcohol oxidation to formaldehyde (when oxygen is present) with desorption
maxima around 520 and 720 K. These results are compared with those obtained after the chemisorption
of formaldehyde. At atmospheric pressure, 1-butanol chemisorption leads mainly to the formation of CO2
while the benzyl alcohol oxidizes to benzaldehydewhenchemisorbed in mixture with Ar and to benzaldehyde
and benzoate when chemisorbed in mixture with O2. Under HV conditions, butanol decomposes to carbon
oxides and to hydrocarbons both with and without oxygen. Benzyl alcohol is very resistant to decomposition
or oxidation. The catalyst has been characterized with DRIFT spectroscopy, XPS, and XRD, and particular
attention has been paid to the behavior of the active site, such as OH groups with Bro ̈nsted acid character
Reactivity of Simple Alcohols on iron Oxide and Mixed Titanium Iron Oxide Powders: An XPS and FTIR Study
No full textStudy of the surface acidity of an hematite powder
No full textIn this work, the interaction between alpha-Fe2O3 (hematite) powder samples and pyridine, 2,6-dimethyl pyridine, carbon
monoxide and carbon dioxide was studied, at atmospheric pressure as well as under high vacuum (HV) conditions. The
powder was characterised by means of diffuse reflectance infrared Fourier transform (DRIFT) and X-ray photoelectron
spectroscopies (XPS), X-ray diffraction (XRD) and thermal analysis (TGA-DSC).
Chemisorption experiments at atmospheric pressure were studied by means of DRIFT spectroscopy while those carried out
under HV conditions were followed by means of quadrupolar mass spectrometry (QMS) and XPS.
The study of the interaction of pyridine with -Fe2O3 allowed us to appreciate the presence of both Brönsted and Lewis
acid sites on the powder surfaces. Moreover, the use of CO as probe molecule indicated the existence of non equivalent Lewis
acid sites. Finally, CO2 may interact with the powder sample either reacting with surface OH groups giving rise to bicarbonate
species, or with surface cations and neighbouring oxide ions to originate bidentate carbonate species
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