Silica-based hybrid materials having covalently immobilized vinyl (SiO 2 -C 2 H 3 ), chloropropyl (SiO 2 -R-Cl), trimethylsilyl (SiO 2 -SiMe 3 ), ethyl sulfonic acid (SiO 2 -R-SO 3 H), and aminopropyl (SiO 2 -R-NH 2 ) groups, as well as the salt of the latter with HNO 3 (SiO 2 -R-NH 2 ‚HNO 3 ) were studied by different thermoanalytical methods: thermogravimetry (TGA), differential thermal analysis (DTA), and temperatureprogrammed desorption mass spectrometry (TDP-MS). It was demonstrated that TPD MS can be successfully used for the investigation of the interfacial layer in such materials. Particularly, it was shown that a side reaction between the grafted group and aromatic solvents is possible during the preparation of SiO 2 -C 2 H 3 and SiO 2 -R-Cl. For SiO 2 -SO 3 H the formation of 2-Si-ethanesulfonic, 1-Si-ethanesulfonic, and 2,4-Si-butanesulfonic acid grafted groups with the predominance of the 2-Si isomer was found. The process of SiO 2 -NH 2 ‚HNO 3 decomposition at 500 K may be applied for the preparation of silica modified by aldehyde groups. Mechanisms of thermal transformations of bonded layer were established and the key role of the reactions of grafted groups with silanols in such processes was demonstrated. As was found for SiO 2 -R-Cl and SiO 2 -R-NH 2 , the decomposition process with participation of silanols is realized in two stages. The first one occurs in the 400-700 K range and includes the interaction between organic groups and the neighboring silanol. The second decomposition stage occurs above 700 K and includes migration of the bonded groups on the silica surface.

Porous SiC (PSC) freestanding layers were prepared via UV light-assisted electrochemical etching of an n-type 6H-SiC wafer. Fourier transform infrared (FTIR) spectroscopy and temperature-programmed desorption mass spectrometry (TPD-MS) were applied to characterize functional groups on the PSC surface and their chemical reactivity. It was shown that as-prepared PSC contains silanol groups, carboxylic acid groups, minor amounts of SiH and CH x groups, and also a carbon-rich surface phase. Annealing of PSC in air at 673 K resulted in the oxidation of the carbon-containing surface species and the formation of a hydrated silicon oxide surface layer. Using −Si(CH3)3 groups as a model, it was demonstrated that organic functional groups can easily be grafted on oxidized PSC via common silanization chemistry. Treatment of oxidized PSC with HF resulted in the formation of a surface terminated with methyl groups. It confirms that the walls of the PSC pores are constituted of the (0001) “silicon” crystal face of SiC and faces with similar atomic structure.

The amount of hydrogen present in porous silicon (PS) nanostructures is analyzed in detail. Concentration of atomic hydrogen chemically bound to the specific surface of PS is quantitatively evaluated by means of attenuated total reflection infrared (ATR-IR) spectroscopy and temperature-programmed desorption (TPD) spectroscopy. The concentration values are correlated to the PS nanoscale morphology. In particular, the influence of porosity, silicon nanocrystallite dimension, and shape on hydrogen concentration values is described. Hydrogen concentrations in fresh, aged, as well as in chemically and thermally treated PS layers are measured. Maximal hydrogen concentration of 66 mmol/g is detected in nanoporous layers with high (>95%) porosity consisting of nanocrystallites with dimensions of about 2 nm. Mass energy density that can be potentially obtained from this amount of hydrogen through a low-temperature fuel cell is estimated to be about 2176 W-h/kg and is found to be comparable with other substances containing hydrogen, such as hydride materials and methanol, which are usually used as hydrogen reservoirs.

No abstract

Steady‐state and time‐resolved photoluminescence of silicon nanoparticles dispersed in low‐polar liquids at above room temperature is studied. The roles of low‐polar liquids as well as mechanisms responsible for their temperature‐dependent photoluminescence are discussed. The thermal sensitivity of the photoluminescence is estimated and application of the nanoparticles as nanothermometers is proposed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Chemical nature of products, formed during electrochemical dissolution of polycrystalline 3C-SiC substrate in HF:ethanol mixture, was studied by means of FTIR spectroscopy, temperature-programmed desorption mass-spectrometry (TPD-MS), nanoparticles (NPs) with sizes of 1 -10 nm is described. CFO NPs easily dissolves in polar organic solvents (ethanol, CH 2 Cl 2 , etc); their solutions demonstrate intense yellowish-green photoluminescence under UV excitation. A model of the CFO chemical structure based on relatively small graphene domains interconnected with partially fluorinated hydrocarbon groups and terminated by carboxylic acid (-CO 2 H), ethyl ester (-CO 2 C 2 H 5 ), perfluorinated functional groups and polycarboxylated alkyl chains is proposed. Presence of carboxylates allows easy functionalization of the CFO NPs via amide chemistry. In particular, grafting of octadecyl groups makes CFO NPs soluble in hydrocarbons.

Surface chemistry of as-prepared 3CSiC nanoparticles obtained by electrochemical etching of bulk 3CSiC substrates was studied. Chemical environment was found to influence strongly the photoinduced electronic transitions in the 3CSiC nanoparticles. The influence of different interfacial chemical environments of the 3CSiC nanoparticles, such as surface chemistry, solvent nature, and surface charges on the photoinduced absorption and luminescence of the nanoparticles at room temperature, is described and discussed in detail. For example, oxidation induced passivation of the radiative band gap states allows visualization of the transitions between energy levels in the nanoparticles in which photogenerated charge carriers are quantumly confined. Electrostatic screening of the radiative band gap states by highly polar solvent media leads to a blueshift and a decrease in the width at half maximum of the photoluminescence spectra of the nanoparticles. As for the surface charges, they govern band bending slope and thus influence strongly the radiative transitions via energy states in the band gap.

Covalent grafting of amino groups onto the carboxylic acid functionalities, naturally covering the surface of fluorescent nanoparticles produced from silicon carbide (SiC NPs), allowed tuning of their surface charge from negative to highly positive. Incubating 3T3-L1 fibroblast cells with differently charged SiC NPs demonstrates the crucial role of the charge in cell fluorescent targeting. Negatively charged SiC NPs concentrate inside the cell nuclei. Close to neutrally charged SiC NPs are present in both cytoplasm and nuclei while positively charged SiC NPs are present only in the cytoplasm and are not able to move inside the nuclei. This effect opens the door for the use of SiC NPs for easy and fast visualization of long-lasting biological processes taking place in the cell cytosol or nucleus as well as providing a new long-term cell imaging tool. Moreover, here we have shown that the interaction between charged NPs and nuclear pore complex plays an essential role in their penetration into the nuclei.