Chemical transformations on the surface of commercially available 3C-SiC nanoparticles were studied by means of FTIR, XPS, and temperature-programmed desorption mass spectrometry methods. Thermal oxidation of SiC NPs resulted in the formation of a hydroxylated SiO surface layer with CSi-H and CH groups over the SiO/SiC interface. Controllable oxidation followed by oxide dissolution in HF or KOH solution allowed the SiC NPs size tuning from 17 to 9 nm. Oxide-free SiC surfaces, terminated by hydroxyls and CSi-H groups, can be efficiently functionalized by alkenes under thermal or photochemical initiation. Treatment of SiC NPs by HF/HNO mixture produces a carbon-enriched surface layer with carboxylic acid groups susceptible to amide chemistry functionalization. The hydroxylated, carboxylated, and aminated SiC NPs form stable aqueous sols.

Electrochemical dissolution of highly doped (ρ ∼ 1 mΩ•cm, n-type) polycrystalline 3C-SiC in HF/H 2 O and HF/H 2 O/ethanol solutions allowed production of porous silicon carbide (por-SiC) and soluble carbon fluorooxide nanoparticles as a byproduct. The por-SiC is a crystalline material with large pore volume, surface area close to 100 m 2 g −1 , and open mesoporous structure. The surface of por-SiC is covered with a thin carbon-enriched layer, bearing carboxylic acid groups. Depending on the SiC resistivity, etchant composition, and current density, three different types of por-SiC morphology, namely, a macroporous tubular, mesoporous hierarchical, and mesoporous filamentary were revealed. A qualitative physical model of SiC electrochemical dissolution, based on the phenomena of quantum confinement, charge carriers trapping onto the surface defects, and the surface passivation, was proposed, and the model successfully interpreted the dependencies of por-SiC morphology and material balance on the etching conditions. The por-SiC is anticipated to be a prospective material for catalytic, nanofiltration, and sensing applications.

a b s t r a c tElectrochemically-derived well-crystalline mesoporous silicon carbide (pSiC) was used as a host for cobalt nanoparticles to demonstrate superior catalytic performance during the CO hydrogenation according to Fischer-Tropsch. Colloidal Co nanoparticles (9 ± 0.4 nm) were prepared independently using colloidal recipes before incorporating them into pSiC and, for comparison purposes, into commercially available silica (Davisil) as well as foam-like MCF-17 supports. The Co/pSiC catalyst demonstrated the highest (per unit mass) catalytic activity of 117 lmol CO g Co À1 s À1 at 220°C which was larger by about one order of magnitude as compared to both silica supported cobalt catalysts. Furthermore, a significantly higher C 5+ hydrocarbons selectivity was observed for Co/pSiC. The stable performance of the catalyst is attributed to the high dispersion of the active phase and the use of pSiC acting as a thermally conductive and chemically inert mesoporous support.

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A colloidal solution of uniformly sized butoxylated SiO2 nanoparticles in o-xylene was prepared from Ludox HS-30 sol. Using these nanoparticles as a template for nanocasting and polycarbosilane (PCS) as a replica precursor, mesoporous SiC was produced by thermal decomposition of the PCS. More precisely, our synthesis allowed porous SiC to be obtained with uniformly sized (11 nm) spherical pores, high surface area (up to 800 m2/g), and large pore volume (up to 1.25 cm3/g). It is anticipated that such SiC with well-defined texture will find major applications as a mesoporous support for nanosized metal particles in exothermic catalytic reactions.