Liquid pyrolysis is presented as a new production method of SnO 2 nanocrystalline powders suitabl... more Liquid pyrolysis is presented as a new production method of SnO 2 nanocrystalline powders suitable for gas sensor devices. The method is based on a pyrolytic reaction of high tensioned stressed drops of an organic solution of SnCl 4 ·5(H 2 O). The main advantages of the method are its capability to produce SnO 2 nanopowders with high stability, its accurate control over the grain size and other structural characteristics, its high level of repeatability and its low industrialization implementation cost. The characterization of samples of SnO 2 nanoparticles obtained by liquid pyrolysis in the range between 200ºC and 900ºC processing temperature is carried out by X-ray diffraction, transmission electron microscopy, Raman and X-ray photoelectron spectroscopy. Results are analyzed and discussed so as to validate the advantages of the liquid pyrolysis method.
The modification of the surface reception properties of nanocrystalline structures is of great in... more The modification of the surface reception properties of nanocrystalline structures is of great interest in environmental, catalysis and energy related applications. For instance, an oxide surface covered with a layer of another oxide opens the possibility of creating the nanosized counterparts of bulk catalytic systems. A relevant example is the TiO2-WO3, which is an active catalysts in a broad range of reactions. The chemical synthesis of the colloidal, nanocrystalline version of such system will first be exposed, by coupling suitable sol-gel chemistry with solvothermal processing. Then, the range of obtained structures will be discussed, ranging from WOx-surface modified TiO2 to TiO2-WO3 heterojunctions. The complex structural evolution of the materials will be discussed, depending on the W concentration. A summary of the acetone sensing properties of these systems will be shown. In particular, the surface activation of the otherwise almost inactive pure TiO2 by surface deposition of WO3-like layers will be highlighted. Addition of the smallest W concentration boosted the sensor response to values comparable to those of pure WO3, ranging over 2-3 orders of magnitude of conductance variation in presence of ethanol or acetone gases. Simple analysis of the sensing data will evidence that the combination of such nanocrystalline oxides results in catalytic activation effects, with exactly opposite trend, with respect to pure TiO2, of the activation energies and best responses.
ABSTRACTThin films in the SnO2-In2O3 system, with relative concentrations of the two oxides rangi... more ABSTRACTThin films in the SnO2-In2O3 system, with relative concentrations of the two oxides ranging from 2% to 98% (molar percentage of the oxide), were deposited by sol-gel and solution processes. The films for the physical characterizations were deposited onto oxidized silicon substrates, while the films for the gas-sensing tests were deposited onto alumina. The starting solutions were characterized by FTIR spectroscopy, while the films on silicon, heated at various temperatures, were characterized by X-ray diffraction and SEM observations. The interaction between the two systems is particularly evident in the case of the system described by a 50% In2O3-50% SnO2 nominal composition. The crystallization on In2O3 during the film heat-treatment hinders the crystallization of SnO2, thus Sn is dispersed as an n-dopant in the In2O3 lattice, indeed showing a current signal, in the gas-sensing test, two orders of magnitude higher than the pure film. The response of the mixed-oxide based d...
ABSTRACT TiO2 anatase nanocrystals were surface modified by deposition of V(V) species. The start... more ABSTRACT TiO2 anatase nanocrystals were surface modified by deposition of V(V) species. The starting amorphous TiO2 nanoparticles were prepared by hydrolytic processing of TiCl4-derived solutions. A V-containing solution, prepared from methanolysis of VCl4, was added to the TiO2 suspension before a solvothermal crystallization step in oleic acid. The resulting materials were characterized by X-ray diffraction, transmission electron microscopy (TEM), Fourier transform infrared, Raman, and magic angle spinning solid-state 51V nuclear magnetic resonance spectroscopy (MAS NMR). It was shown that in the as-prepared nanocrystals V was deposited onto the surface, forming Ti–O–V bonds. After heat treatment at 400 °C, TEM/electron energy loss spectroscopy and MAS NMR showed that V was partially inserted in the anatase lattice, while the surface was covered with a denser V–O–V network. After heating at 500 °C, V2O5 phase separation occurred, further evidenced by thermal analyses. The 400 °C nanocrystals had a mean size of about 5 nm, proving the successful synthesis of the colloidal counterpart of the well-known TiO2–V2O5 catalytic system. Hence, and also due to the complete elimination of organic residuals, this sample was used for processing chemoresistive devices. Ethanol was used as a test gas, and the results showed the beneficial effect of the V surface modification of anatase, with a response improvement up to almost 2 orders of magnitude with respect to pure TiO2. Moreover, simple comparison of the temperature dependence of the response clearly evidenced the catalytic effect of V addition.
Perovskite-type barium stannate obtained from a simple wet chemical route has been structural and... more Perovskite-type barium stannate obtained from a simple wet chemical route has been structural and electrical characterised. The resulting powders calcined at different temperatures have been studied by XRD, Raman and TEM. Thick films of BaSnO3 screen printed on an alumina substrate have been electrically studied as a function of the temperature and as a function of the ambient composition.
ABSTRACT In the present study, we report the microstructural characterization and the electrochem... more ABSTRACT In the present study, we report the microstructural characterization and the electrochemical performance of six activated carbons with varied textural properties. Activated carbons were investigated in terms of specific surface area, pore size distribution, surface chemistry and electrochemical behaviour in acidic, neutral and organic electrolytes. For this purpose, N2 adsorption isotherms, thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR) and cyclic voltammetry (CV) techniques were used. Electrochemical properties of symmetric supercapacitors using these carbons were investigated by galvanostatic charge–discharge experiments and electrochemical impedance spectroscopy (EIS).Differences in textural properties of the activated carbons were analysed and correlated with their electrochemical behaviour indicating that mesoporous carbons of high surface area are promising materials for high power applications, whereas microporous carbons with higher specific capacitances would be preferred for high energy and medium power applications.
Atomic Force Microscopy Study of the Silicon Doping Influence on the First Stages of Platinum Ele... more Atomic Force Microscopy Study of the Silicon Doping Influence on the First Stages of Platinum Electroless Deposition. [Journal of The Electrochemical Society 144, 909 (1997)]. Pau Gorostiza, Raül Díaz, Jordi Servat, Fausto Sanz, Joan Ramon Morante. Abstract. ...
ABSTRACT A tungsten chloromethoxide was prepared by the methanolysis of WCl(6) The resulting solu... more ABSTRACT A tungsten chloromethoxide was prepared by the methanolysis of WCl(6) The resulting solutions were modified by addition of acetylacetone to improve their stability. The resulting deep blue solutions were studied by infrared and Raman spectroscopy. The Structure of the solutions was characterized by polynuclear tungsten species containing W-O-W bonds. The solutions were used for preparing thin films, by spin-coating onto oxidized silicon substrates, and powders, by evaporation at reduced pressure. The as-dried thin films and powders were heat-treated at various temperatures up to 700 degrees C and characterized by infrared and Raman spectroscopy and X-ray diffraction. The investigations showed that the precursor structure follows it continuous evolution to the final WO(3) structure, by further condensation and thermally activated reorganization of the initial species. The filial crystalline structure was a mixture of the most stable delta-triclinic and gamma-monoclinic phases. The absence of W=O groups both in the solutions and the final materials and the weakness of the W-Cl bond explained the lower stability of the solutions. if compared to oxychloride precursors like WOCl(4). The structure and morphology of the Mills, characterized by scanning and transmission electron microscopy, was constituted by discrete spheroidal grains, elongated along the substrate surface. Chemoresistive gas sensing devices were prepared with the WO(3) Powders heat-treated at 500 degrees C and tested for the detection of ammonia and nitrogen dioxide. The results indicated the capability of the sensors to detect the target gases over a broad range of concentrations, with a stable signal
The electrochemical behavior of chemically polished polycrystalline tin is investigated in borate... more The electrochemical behavior of chemically polished polycrystalline tin is investigated in borate buffer solutions at pH=7.5 using in-situ Raman measurements. Experiments reveal the appearance of “luminescence” under continuum red laser light only for a narrow range of sample potentials within the anodic plateau. The phenomenon is discussed in view of the tin oxides formed on the surface, and correlated with the assignation of the oxido-reduction processes observed in the voltammograms.
TiO2 anatase nanocrystals were prepared by solvothermal processing of Ti chloroalkoxide in oleic ... more TiO2 anatase nanocrystals were prepared by solvothermal processing of Ti chloroalkoxide in oleic acid, in presence of W chloroalkoxide, with W:Ti nominal atomic concentration (RW) ranging from 0.16 to 0.64. The as-prepared materials were heat-treated up to 500 °C for thermal stabilization and sensing device processing. For R0.16, the as-prepared materials were constituted by an anatase core surface-modified by WOx monolayers. This structure persisted up to 500 °C, without any WO3 phase segregation. For Rw up to R0.64, the anatase core was initially wrapped by an amorphous WOx gel. Upon the heat-treatment, the WOx phase underwent structural re-organization, remaining amorphous up to 400 °C and forming tiny WO3 nanocrystals dispersed into the TiO2 host after heating at 500 °C, when part of tungsten also migrated into the TiO2 structure, resulting in structural and electrical modification of the anatase host. The ethanol sensing properties of the various materials were tested and compa...
Liquid pyrolysis is presented as a new production method of SnO 2 nanocrystalline powders suitabl... more Liquid pyrolysis is presented as a new production method of SnO 2 nanocrystalline powders suitable for gas sensor devices. The method is based on a pyrolytic reaction of high tensioned stressed drops of an organic solution of SnCl 4 ·5(H 2 O). The main advantages of the method are its capability to produce SnO 2 nanopowders with high stability, its accurate control over the grain size and other structural characteristics, its high level of repeatability and its low industrialization implementation cost. The characterization of samples of SnO 2 nanoparticles obtained by liquid pyrolysis in the range between 200ºC and 900ºC processing temperature is carried out by X-ray diffraction, transmission electron microscopy, Raman and X-ray photoelectron spectroscopy. Results are analyzed and discussed so as to validate the advantages of the liquid pyrolysis method.
The modification of the surface reception properties of nanocrystalline structures is of great in... more The modification of the surface reception properties of nanocrystalline structures is of great interest in environmental, catalysis and energy related applications. For instance, an oxide surface covered with a layer of another oxide opens the possibility of creating the nanosized counterparts of bulk catalytic systems. A relevant example is the TiO2-WO3, which is an active catalysts in a broad range of reactions. The chemical synthesis of the colloidal, nanocrystalline version of such system will first be exposed, by coupling suitable sol-gel chemistry with solvothermal processing. Then, the range of obtained structures will be discussed, ranging from WOx-surface modified TiO2 to TiO2-WO3 heterojunctions. The complex structural evolution of the materials will be discussed, depending on the W concentration. A summary of the acetone sensing properties of these systems will be shown. In particular, the surface activation of the otherwise almost inactive pure TiO2 by surface deposition of WO3-like layers will be highlighted. Addition of the smallest W concentration boosted the sensor response to values comparable to those of pure WO3, ranging over 2-3 orders of magnitude of conductance variation in presence of ethanol or acetone gases. Simple analysis of the sensing data will evidence that the combination of such nanocrystalline oxides results in catalytic activation effects, with exactly opposite trend, with respect to pure TiO2, of the activation energies and best responses.
ABSTRACTThin films in the SnO2-In2O3 system, with relative concentrations of the two oxides rangi... more ABSTRACTThin films in the SnO2-In2O3 system, with relative concentrations of the two oxides ranging from 2% to 98% (molar percentage of the oxide), were deposited by sol-gel and solution processes. The films for the physical characterizations were deposited onto oxidized silicon substrates, while the films for the gas-sensing tests were deposited onto alumina. The starting solutions were characterized by FTIR spectroscopy, while the films on silicon, heated at various temperatures, were characterized by X-ray diffraction and SEM observations. The interaction between the two systems is particularly evident in the case of the system described by a 50% In2O3-50% SnO2 nominal composition. The crystallization on In2O3 during the film heat-treatment hinders the crystallization of SnO2, thus Sn is dispersed as an n-dopant in the In2O3 lattice, indeed showing a current signal, in the gas-sensing test, two orders of magnitude higher than the pure film. The response of the mixed-oxide based d...
ABSTRACT TiO2 anatase nanocrystals were surface modified by deposition of V(V) species. The start... more ABSTRACT TiO2 anatase nanocrystals were surface modified by deposition of V(V) species. The starting amorphous TiO2 nanoparticles were prepared by hydrolytic processing of TiCl4-derived solutions. A V-containing solution, prepared from methanolysis of VCl4, was added to the TiO2 suspension before a solvothermal crystallization step in oleic acid. The resulting materials were characterized by X-ray diffraction, transmission electron microscopy (TEM), Fourier transform infrared, Raman, and magic angle spinning solid-state 51V nuclear magnetic resonance spectroscopy (MAS NMR). It was shown that in the as-prepared nanocrystals V was deposited onto the surface, forming Ti–O–V bonds. After heat treatment at 400 °C, TEM/electron energy loss spectroscopy and MAS NMR showed that V was partially inserted in the anatase lattice, while the surface was covered with a denser V–O–V network. After heating at 500 °C, V2O5 phase separation occurred, further evidenced by thermal analyses. The 400 °C nanocrystals had a mean size of about 5 nm, proving the successful synthesis of the colloidal counterpart of the well-known TiO2–V2O5 catalytic system. Hence, and also due to the complete elimination of organic residuals, this sample was used for processing chemoresistive devices. Ethanol was used as a test gas, and the results showed the beneficial effect of the V surface modification of anatase, with a response improvement up to almost 2 orders of magnitude with respect to pure TiO2. Moreover, simple comparison of the temperature dependence of the response clearly evidenced the catalytic effect of V addition.
Perovskite-type barium stannate obtained from a simple wet chemical route has been structural and... more Perovskite-type barium stannate obtained from a simple wet chemical route has been structural and electrical characterised. The resulting powders calcined at different temperatures have been studied by XRD, Raman and TEM. Thick films of BaSnO3 screen printed on an alumina substrate have been electrically studied as a function of the temperature and as a function of the ambient composition.
ABSTRACT In the present study, we report the microstructural characterization and the electrochem... more ABSTRACT In the present study, we report the microstructural characterization and the electrochemical performance of six activated carbons with varied textural properties. Activated carbons were investigated in terms of specific surface area, pore size distribution, surface chemistry and electrochemical behaviour in acidic, neutral and organic electrolytes. For this purpose, N2 adsorption isotherms, thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR) and cyclic voltammetry (CV) techniques were used. Electrochemical properties of symmetric supercapacitors using these carbons were investigated by galvanostatic charge–discharge experiments and electrochemical impedance spectroscopy (EIS).Differences in textural properties of the activated carbons were analysed and correlated with their electrochemical behaviour indicating that mesoporous carbons of high surface area are promising materials for high power applications, whereas microporous carbons with higher specific capacitances would be preferred for high energy and medium power applications.
Atomic Force Microscopy Study of the Silicon Doping Influence on the First Stages of Platinum Ele... more Atomic Force Microscopy Study of the Silicon Doping Influence on the First Stages of Platinum Electroless Deposition. [Journal of The Electrochemical Society 144, 909 (1997)]. Pau Gorostiza, Raül Díaz, Jordi Servat, Fausto Sanz, Joan Ramon Morante. Abstract. ...
ABSTRACT A tungsten chloromethoxide was prepared by the methanolysis of WCl(6) The resulting solu... more ABSTRACT A tungsten chloromethoxide was prepared by the methanolysis of WCl(6) The resulting solutions were modified by addition of acetylacetone to improve their stability. The resulting deep blue solutions were studied by infrared and Raman spectroscopy. The Structure of the solutions was characterized by polynuclear tungsten species containing W-O-W bonds. The solutions were used for preparing thin films, by spin-coating onto oxidized silicon substrates, and powders, by evaporation at reduced pressure. The as-dried thin films and powders were heat-treated at various temperatures up to 700 degrees C and characterized by infrared and Raman spectroscopy and X-ray diffraction. The investigations showed that the precursor structure follows it continuous evolution to the final WO(3) structure, by further condensation and thermally activated reorganization of the initial species. The filial crystalline structure was a mixture of the most stable delta-triclinic and gamma-monoclinic phases. The absence of W=O groups both in the solutions and the final materials and the weakness of the W-Cl bond explained the lower stability of the solutions. if compared to oxychloride precursors like WOCl(4). The structure and morphology of the Mills, characterized by scanning and transmission electron microscopy, was constituted by discrete spheroidal grains, elongated along the substrate surface. Chemoresistive gas sensing devices were prepared with the WO(3) Powders heat-treated at 500 degrees C and tested for the detection of ammonia and nitrogen dioxide. The results indicated the capability of the sensors to detect the target gases over a broad range of concentrations, with a stable signal
The electrochemical behavior of chemically polished polycrystalline tin is investigated in borate... more The electrochemical behavior of chemically polished polycrystalline tin is investigated in borate buffer solutions at pH=7.5 using in-situ Raman measurements. Experiments reveal the appearance of “luminescence” under continuum red laser light only for a narrow range of sample potentials within the anodic plateau. The phenomenon is discussed in view of the tin oxides formed on the surface, and correlated with the assignation of the oxido-reduction processes observed in the voltammograms.
TiO2 anatase nanocrystals were prepared by solvothermal processing of Ti chloroalkoxide in oleic ... more TiO2 anatase nanocrystals were prepared by solvothermal processing of Ti chloroalkoxide in oleic acid, in presence of W chloroalkoxide, with W:Ti nominal atomic concentration (RW) ranging from 0.16 to 0.64. The as-prepared materials were heat-treated up to 500 °C for thermal stabilization and sensing device processing. For R0.16, the as-prepared materials were constituted by an anatase core surface-modified by WOx monolayers. This structure persisted up to 500 °C, without any WO3 phase segregation. For Rw up to R0.64, the anatase core was initially wrapped by an amorphous WOx gel. Upon the heat-treatment, the WOx phase underwent structural re-organization, remaining amorphous up to 400 °C and forming tiny WO3 nanocrystals dispersed into the TiO2 host after heating at 500 °C, when part of tungsten also migrated into the TiO2 structure, resulting in structural and electrical modification of the anatase host. The ethanol sensing properties of the various materials were tested and compa...
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