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We present here the single-source-precursor synthesis of Fe3Si and Fe5Si3-containing SiOC ceramic nanocomposites and investigation of their magnetic properties. The materials were prepared upon chemical modification of a hydroxy- and ethoxy-substituted polymethylsilsesquioxane with iron (III) acetylacetonate (Fe(acac)3) in different amounts (5, 15, 30 and 50wt%), followed by cross-linking at 180°C and pyrolysis in argon at temperatures ranging from 1000°C to 1500°C. The polymer-to-ceramic transformation of the iron-modified polysilsesquioxane and the evolution at high temperatures of the synthesized SiFeOC-based nanocomposite were studied by means of thermogravimetric analysis (TGA) coupled with evolved gas analysis (EGA) as well as X-ray diffraction (XRD). Upon pyrolysis at 1100°C, the non-modified polysilsesquioxane converts into an amorphous SiOC ceramic; whereas the iron-modified precursors lead to Fe3Si/SiOC nanocomposites. Annealing of Fe3Si/SiOC at temperatures exceeding 1300°C induced the crystallization of Fe5Si3 and β-SiC. The crystallization of the different iron-containing phases at different temperatures is considered to be a consequence of the in situ generation of a Fe–C–Si alloy within the materials during pyrolysis. Depending on the Fe and Si content in the alloy, either Fe3Si and graphitic carbon (at 1000–1200°C) or Fe5Si3 and β-SiC (at T >1300°C) crystallize. All SiFeOC-based ceramic samples were found to exhibit soft magnetic properties. Magnetization versus applied field measurements of the samples show a saturation magnetization up to 26.0emu/g, depending on the Fe content within the SiFeOC-based samples as well as on the crystalline iron silicide phases formed during pyrolysis. [ABSTRACT FROM AUTHOR]

Abstract: Mesoporous SiOC/TiO2 and SiOC/N-doped TiO2 (nitrogen-doped TiO2) ceramic composites were prepared by the incorporation of TiO2 (containing 65wt.% anatase and 35wt.% rutile) and N-doped TiO2 powders into vinyl-functionalized polysiloxane polymer followed by pyrolysis at 700–900°C for 2h in argon atmosphere. The N-doped TiO2 powders were obtained by ammonolysis of commercial TiO2 nanopowders. The resulting samples were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and nitrogen physisorption. The specific surface area (S BET) values of the as-prepared SiOC ceramic and SiOC/TiO2 and SiOC/N-doped TiO2 ceramic composites decreased with increasing the pyrolysis temperature due to a gradual collapse of small pores. A transformation from microporous SiOC ceramic (pore-size <2nm) to mesoporous SiOC/TiO2 and SiOC/N-doped TiO2 ceramic composites (pore-size ∼4nm) was analyzed. Adsorption and photocatalytic activity of the resulting samples were evaluated by measuring the decrease in concentration of methylene blue (MB) after adsorption in the dark and photodegradation reaction under UV–vis light irradiation, respectively. Pure microporous SiOC ceramic showed no significant adsorption as well as photocatalytic activity for MB because of its high microporosity and low solid acidity, respectively, whereas mesoporous SiOC/TiO2 and SiOC/N-doped TiO2 ceramic composites exhibited higher adsorption and photocatalytic activities. The photodegradation rate constant k(×10−3 min−1) of the samples increased in the following order: 1.3 for SiOC ceramic <2.2 for SiOC/TiO2 <3.4 for SiOC/N-doped TiO2. The highest k for the SiOC/N-doped TiO2 ceramic composite is discussed in terms of the change of the electronic structures and crystallinity of N-doped TiO2 if compared with pure TiO2. These polymer-derived ceramic composites can be applied for the purification of water contaminated with organic dyes without the need for hydrogen peroxide. [Copyright &y& Elsevier]

Abstract: Polymer-derived mesoporous SiOC/ZnO nanocomposite for water decontamination was prepared by a simple mechanical incorporation of ZnO nanopowders into the commercial vinyl-functionalized polysiloxane followed by pyrolysis at 700°C for 2h. The as-prepared nanocomposite was characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen physisorption measurement and UV–vis spectroscopy. The effects of pyrolysis temperature (700–900°C) and ZnO content (0–20wt.%) on the formation of SiOC/ZnO nanocomposite were investigated. The polymer-to-ceramic transformation of pure polymer resulted in the formation of an amorphous microporous SiOC ceramic (pore size <2nm). With the incorporation of ZnO nanopowders into the polymer, the microporosity-to-mesoporosity transformation was observed for all the nanocomposites regardless of pyrolysis temperature and ZnO content. The SiOC ceramic obtained at 700°C indicated the highest specific surface area (S BET =398m2/g) value with the pore size of <2nm while the SiOC/20wt.% ZnO nanocomposite prepared at 700°C showed the S BET value of 220m2/g with the pore size of ∼4nm. The adsorption and photocatalytic properties of the as-prepared samples were evaluated by measuring the decrease in concentration of methylene blue (MB) after adsorption in the dark and photochemical reaction under UV irradiation, respectively. The lowest MB adsorption was noted for SiOC ceramic, and MB adsorption by SiOC/ZnO nanocomposite monotonically decreased with the increase in the ZnO content. The photocatalytic activity of porous SiOC ceramic for the degradation of MB is enhanced significantly by the incorporation of ZnO nanopowders into the SiOC matrix. [Copyright &y& Elsevier]

Abstract: Herein we report on the thermal decomposition of SiCN polymer-derived ceramics leading to materials with high specific surface area and defined pore sizes. The ceramics were obtained by means of pyrolysis of a carbon-rich poly(diphenylsilylcarbodiimide) precursor and by varying the thermolysis parameters, namely temperature, annealing time and using additional annealing steps. The thermal decomposition of SiCN ceramics is correlated with the carbothermal reaction of amorphous silicon nitride phase with excess carbon and this detrimental event leads to high specific surface area up to 568m2 g−1 and micro- and mesopores formation in these materials. High-resolution TEM investigations have confirmed that the pores are embedded only in the carbon phase. Moreover, the relationship between the pore sizes and the organization of free carbon phase is discussed. [Copyright &y& Elsevier]

A dual-phase nitrogen-doped TiO 2 –SrTiO 3 macroporous monolithic photocatalyst was fabricated through the impregnation of the preformed TiO 2 gel in a Sr 2+ -containing alcohol–water solution followed by nitridation under a modest flow of ammonia gas at 800 °C for 2 h. The fabricated monolithic photocatalyst was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury porosimetry, N 2 gas adsorption ( S BET ), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible (UV–vis) spectroscopy. The XRD results showed that the fabricated monolithic photocatalyst is comprised of two crystalline phases (anatase TiO 2 and SrTiO 3 ) and possesses a highly interconnected (co-continuous) macroporous framework. The photocatalytic activity of the fabricated monolithic photocatalyst was evaluated by the photodegradation of organic dye (Rhodamine B) over the samples under visible light. As expected, the N-doped TiO 2 –SrTiO 3 macroporous monolithic photocatalyst showed a higher photodegradation rate constant (0.0019 min −1 ) compared to the undoped TiO 2 –SrTiO 3 (0.0010 min −1 ) under the identical experimental conditions due mainly to the band gap reduction. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nitrogen-doped porous TiO2 monolith was fabricated by sol–gel and ammonolysis. [•] Nitrogen-doped porous TiO2 monolith has macrochannels with the diameter of 1.5–3.0μm. [•] The O Ti N bonds were formed after nitrogen doping into the lattice of TiO2. [•] The photocatalytic activity of the samples was investigated under visible light. [•] About 50% of Rhodamine B was degraded by N-doped TiO2 porous monolith within 120min. [ABSTRACT FROM AUTHOR]

Abstract: Macroporous TiO2 monolith was first prepared by the sol–gel method and then macroporous TiO2–SrTiO3 heterostructured monolith was obtained by the impregnation of the as-prepared macroporous TiO2 monolith in the strontium-containing aqueous solution followed by calcination at different temperatures. The formation of SrTiO3 crystals in the TiO2 network was confirmed by X-ray diffraction and electron microscopy analyses. Macroporous structure of the heterostructured monolith was analyzed by mercury porosimetry. The photocatalytic activity of macroporous TiO2–SrTiO3 heterostructured monolithic photocatalyst was evaluated for the photodegradation of Rhodamine B over the samples under visible light irradiation. The obtained results reveal that the samples show an enhanced photocatalytic activity for the degradation of organic dye molecules. [Copyright &y& Elsevier]