Dissertation•
Porous silicon / noble metal nanocomposites for catalytic applications
01 Sep 2010-
TL;DR: In this paper, specific functionalities of porous silicon prepared, utilising both solid (via electrochemical or stain etching processes) and gas phase (from silane) syntheses, were investigated.
Abstract: Today, bulk silicon is one of the best studied semiconductors. However, in its different nano-modifications, e.g. as porous silicon, totally new properties are exhibited. Despite the fact, that porous silicon is widely known and has been extensively studied since the 1990s, many unique features of this material are still unexplored. In this work, specific functionalities of porous silicon prepared, utilising both solid (via electrochemical or stain etching processes) and gas phase (from silane) syntheses, were investigated. Since this study was in-part industry oriented, the emphasis has been placed upon the investigation of porous silicon nanostructures, made from low cost metallurgical grade polycrystalline silicon powder. It has been previously demonstrated that porous silicon exhibits a very large, hydrogenated internal surface area (up to 500 m2 g−1). It is verified in this work, that · morphological properties of this material result in a high reductive potential of its internal surface due to hydrogen passivation. Therefore, in this thesis, we would like to show that porous silicon-based reactive templates are promising for their applications in nanometal-supported catalysis. We used salts of platinum, gold, palladium, silver and their mixtures, which were reduced on the silicon nanocrystalline internal surface, resulting in formation of metal nanoparticles embedded into porous silicon matrix. Various experimental techniques were used to evaluate the morphology, size and composition of metal nanoparticles, as well as their growth rates. Hydrogen effusion experiments proved the crucial difference between porous silicon and other chemically inert supporting templates for the process of metal nanoparticles formation. The catalytic activity of the synthesised materials was evaluated in gas phase conversion of CO to CO2. Furthermore, the new porous silicon-based catalysts were tested in gas/liquid phase reactions as well, using hydrogenation, oxidation, dehalogenation and C-C coupling class reactions. Following the trends of “state of the art” current Si technology, we present the design of the developed flow microreactor, based on patterned Si wafer, which can be implemented in future work to catalyse selected reactions. Results obtained in this work suggest that porous silicon matrices are promising supports for metal nanoparticle based catalysis.
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1,003 citations
TL;DR: Advances in Catalysis and related subjects as mentioned in this paper, edited by W. G. Frankenburg, V. I. Komarewsky and E. K. Rideal.
Abstract: Advances in Catalysis and related Subjects Edited by W. G. Frankenburg, V. I. Komarewsky and E. K. Rideal. Vol. 3. Pp. xi + 360. 7.80 dollars. Vol. 4. Pp. xi + 457. 9.50 dollars. (New York: Academic Press, Inc., 1951 and 1952.)
381 citations
01 Jan 2001
TL;DR: In this paper, the classification, synthesis, characterization, and characterization of catalysts, and reactors are discussed, including general solid acid catalysts and miscellaneous solid base catalysis, including catalytic hydrogenation and dehydrogenation oxidation.
Abstract: Basic principles: including classification, synthesis, characterization of catalysts, reactors. Solid acid catalysts - general solid acid catalysts - aromatic substitution solid acid catalysis - rearrangement & isomerizations solid acid catalysis - miscellaneous solid base catalysis - catalytic hydrogenation and dehydrogenation oxidation C-C bond formation.
77 citations
TL;DR: The Cu-PS powders show excellent catalytic reduction on the p-nitrophenol regardless of the Cu loadings, and H2-temperature programmed reduction profiles reveal that re-oxidation of theCu particles occurs after deposition.
Abstract: Porous structured silicon or porous silicon (PS) powder was prepared by chemical etching of silicon powder in an etchant solution of HF: HNO3: H2O (1:3:5 v/v). An immersion time of 4 min was sufficient for depositing Cu metal from an aqueous solution of CuSO4 in the presence of HF. Scanning electron microscopy (SEM) analysis revealed that the Cu particles aggregated upon an increase in metal content from 3.3 wt% to 9.8 wt%. H2-temperature programmed reduction (H2-TPR) profiles reveal that re-oxidation of the Cu particles occurs after deposition. Furthermore, the profiles denote the existence of various sizes of Cu metal on the PS. The Cu-PS powders show excellent catalytic reduction on the p-nitrophenol regardless of the Cu loadings.
26 citations
29 Aug 2008
TL;DR: In this article, hydrogen-terminated porous silicon (PSi) layers and powders can serve as highly efficient reductive templates for noble metal salts, which results in metal nanoparticle (NP) formation in the pores of PSi.
Abstract: In this Letter we demonstrate that hydrogen-terminated porous silicon (PSi) layers and powders can serve as highly efficient reductive templates for noble metal salts. The reduction results in metal nanoparticle (NP) formation in the pores of PSi. Gold NP formation has been monitored in-situ by measuring the plasmon resonance response. Pt NPs, formed in the PSi matrix, were investigated by transmission electron microscopy and energy-dispersive X-ray analysis. Furthermore, hybrid Pt/PSi nanocomposites exhibit a high catalytic activity for CO oxidation.
15 citations
References
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TL;DR: In this paper, the optical constants for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV.
Abstract: The optical constants $n$ and $k$ were obtained for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV. The film-thickness range was 185-500 \AA{}. Three optical measurements were inverted to obtain the film thickness $d$ as well as $n$ and $k$. The estimated error in $d$ was \ifmmode\pm\else\textpm\fi{} 2 \AA{}, and that in $n$, $k$ was less than 0.02 over most of the spectral range. The results in the film-thickness range 250-500 \AA{} were independent of thickness, and were unchanged after vacuum annealing or aging in air. The free-electron optical effective masses and relaxation times derived from the results in the near infrared agree satisfactorily with previous values. The interband contribution to the imaginary part of the dielectric constant was obtained by subtracting the free-electron contribution. Some recent theoretical calculations are compared with the results for copper and gold. In addition, some other recent experiments are critically compared with our results.
17,509 citations
11,414 citations
Book•
01 Jan 1967
10,303 citations
"Porous silicon / noble metal nanoco..." refers background or methods in this paper
...From these data, the BET surface area of PSi could be derived using procedures described in [133, 156]....
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...The explanation for that phenomenon is most likely the capillary condensation, indicating different pressures in the pores involved during adsorption and desorption, respectively [156, 157]....
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...The isotherm in Figure 40 represents a characteristic shape typical for 2 to 50 nm pore sized porous material, as so-called type IV isotherm [156]....
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...This, so-called BET model, which is still widely used today, served afterwards as the theoretical background for a method of characterisation of solid surface areas [156]....
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TL;DR: In this paper, free standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography using electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers.
Abstract: Indirect evidence is presented that free‐standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two‐dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.
7,393 citations
TL;DR: In this article, the first observation of single molecule Raman scattering was made using a single crystal violet molecule in aqueous colloidal silver solution using one second collection time and about $2.
Abstract: By exploiting the extremely large effective cross sections ( ${10}^{\ensuremath{-}17}--{10}^{\ensuremath{-}16}{\mathrm{cm}}^{2}/\mathrm{molecule}$) available from surface-enhanced Raman scattering (SERS), we achieved the first observation of single molecule Raman scattering. Measured spectra of a single crystal violet molecule in aqueous colloidal silver solution using one second collection time and about $2\ifmmode\times\else\texttimes\fi{}{10}^{5}\mathrm{W}/{\mathrm{cm}}^{2}$ nonresonant near-infrared excitation show a clear ``fingerprint'' of its Raman features between 700 and $1700{\mathrm{cm}}^{\ensuremath{-}1}$. Spectra observed in a time sequence for an average of 0.6 dye molecule in the probed volume exhibited the expected Poisson distribution for actually measuring 0, 1, 2, or 3 molecules.
6,454 citations