Synthesis and characterization of precursor derived TiN@Si–Al–C–N ceramic nanocomposites for oxygen reduction reaction

The development of efficient and durable catalysts is critical for the commercialization of fuel cells, as the catalysts’ durability and reactivity dictate their ultimate lifetime and activity. In this work, amorphous silicon-based ceramics (Si–C–N and Si–Al–C–N) and TiN@Si–Al–C–N nanocomposites were developed using a precursor derived ceramics approach. In TiN@Si–Al–C–N nanocomposites, TiN nanocrystals (with sizes in the range of 5–12 nm) were effectively anchored on an amorphous Si–Al–C–N support. The nanocomposites were found to be mesoporous in nature and exhibited a surface area as high as 132 m2/g. The average pore size of the nanocomposites was found to increase with an increase in the pyrolysis temperature, and a subsequent graphitization of free carbon was observed as revealed from the Raman spectra. The ceramics were investigated for electrocatalytic activity toward the oxygen reduction reaction using the rotating disk electrode method. The TiN@Si–Al–C–N nanocomposites showed an onset potential of 0.7 V versus reversible hydrogen electrode for oxygen reduction, which seems to indicate a 4-electron pathway at the pyrolysis temperature of 1000°C in contrast to a 2-electron pathway exhibited by the nanocomposites pyrolyzed at 750°C via the Koutecky–Levich plot

Mechanical properties of ultra-high pressure sintered sphene (CaTiSiO5)

The investigation of nano-mechanical properties of sphene sintered under ultra-high pressures in the order of 4 GPa is done using indentation techniques. An indentation hardness of 6.6 GPa and reduced elastic modulus of 112.3 GPa is reported at maximum load of 7 mN. The material exhibits a high elastic recovery (similar to 59.1%) and the nature of deformation mechanism has been comprehended from the plastic work ratio. In addition, the fracture toughness of the material is also evaluated using indentation crack length method

Metal-Like Thermal Conductivity Possessed By Atmosphere Assisted Synthesis Of Spark Plasma Sintered Mayenite (Ca12Al14O33): Supporting Information

Supporting information of the article Metal-Like Thermal Conductivity Possessed By Atmosphere Assisted Synthesis Of Spark Plasma Sintered Mayenite (Ca12Al14O33).Supplementary material for: [https://vinar.vin.bg.ac.rs/handle/123456789/9936

Metal-Like Thermal Conductivity Possessed By Atmosphere Assisted Synthesis Of Spark Plasma Sintered Mayenite (Ca12Al14O33)

Mayenite (Ca12Al14O33) samples have been synthesized in ambient air, argon, and nitrogen atmospheres to vary the defect chemistry and to investigate its role in thermal conductivity. Highly dense sintered pellets (SEM) were obtained through spark plasma sintering and the X-ray diffractograms revealed predominantly mayenite phase with the presence of a minor amount of secondary phases. Thermal conductivity was measured for the sintered samples and it was observed that mayenite synthesized in nitrogen atmosphere exhibited a colossal value of 579 Wm-1K-1 at room temperature close to that of cubic-BN, comparable with that of metals.Supplementary material: [https://vinar.vin.bg.ac.rs/handle/123456789/9937

Design of nanoscaled heterojunctions in precursor-derived t-ZrO2/SiOC(N) nanocomposites: Transgressing the boundaries of catalytic activity from UV to visible light

International audiencein this work, nanocomposites made of nanosized zirconia crystallized in situ in an amorphous silicon oxycarbo(nitride) (Sioc(n)) matrix have been designed through a precursor route for visible light photocatalytic applications. the relative volume fraction of the starting precursors and the pyrolysis temperatures not only influences the phase fraction of zirconia crystallites but also stabilizes the tetragonal crystal structure of zirconia (t-Zro 2) at room temperature. the presence of carbon in interstitial sites of zirconia and oxygen vacancy defects led to drastic reduction in the band gap (2.2 eV) of the nanocomposite. Apart from being a perfect host avoiding sintering of the active phase and providing mechanical stability, the amorphous matrix also reduces the recombination rate by forming heterojunctions with t-Zro 2. the reduction in band gap as well as the formation of heterojunctions aids in harnessing the visible light for photocatalytic activity

Disordered mesoporous polymer derived N-doped TiO2/Si-O-C-N nanocomposites with nanoscaled heterojunctions towards enhanced adsorption and harnessing of visible light

International audienceThe mesoporous N-doped TiO 2 /Si-O-C-N ceramic nanocomposites has been revealed to be a potential candidate towards visible light photocatalytic degradation of organic dyes. The polymer-derived ceramic route was implemented to prepare uniformly distributed in-situ crystallized N-doped TiO 2 nanocrystals in a mesoporous amorphous siliconoxycarbonitride matrix. This chemical approach assisted by the hard template pathway resulted in a high surface area (186 m 2 /g) nanocomposite exhibiting predominantly mesoporous structure with an average pore size of 11 nm. The two-step process involved pyrolysis of the polyhydridomethyilsiloxane impregnated in CMK3 (hard template) under argon generating SiOC-C composites and functionalizing it with titanium n-tetrabutoxide to be pyrolyzed under ammonia to form the titled nanocomposite. Interestingly, pyrolysis in a reactive ammonia atmosphere resulted in the incorporation of nitrogen in the titania lattice while decomposing the template. The Si-O-C-N support on which N-doped TiO 2 exhibited superior adsorption of organic dye molecules and photocatalytically active in the visible wavelength. The nanoscaled heterojunctions reduced the recombination rate and the presence of superoxide anions/hydroxyl radicals was found to be responsible for the dye degradation

Plasmon enhanced visible light photocatalytic activity in polymer-derived TiN/Si-O-C-N nanocomposites

International audienceHerein, we provide a detailed insight into the precursor chemistry, precursor-to-material transformation and characterization of nanocomposites made of a TiN nanophase and a Si-O-C-N ceramic. The polymer-derived ceramics (PDCs) route applied to synthesize these nanocomposites resulted in the formation of nanocrystals less than 4 nm in size and the calculated lattice parameter value for the nanocrystals (a = 0.4239 nm) matched the theoretical value of TiN (a = 0.4241 nm). The Si-O-C-N ceramic served as a platform for anchoring TiN nanocrystals. As a proof of concept, we have attempted to exploit the plasmonic properties of nanocomposites to achieve photocatalytic degradation of organic dyes. The absorption spectra clearly showed plasmonic resonance in the visible region with peak positioned around 670 nm according to the presence of TiN nanocrystals which resulted in the enhancement of dye degradation. (C) 2018 Elsevier Ltd. All rights reserved

Combustion synthesis of luminescent Eu-doped single phase Mayenite

Rare earth luminescent materials based on alkali metal oxides such as calcium aluminates have grabbed the attention due to their high luminescent efficiency, non-toxic and eco-friendly nature. Calcium aluminates as host materials for luminescent applications are extremely stable, suppressing the release of non-radiative energy resulting in the characteristic emission of rare earth luminescent centre. Moreover, calcium aluminates are inexpensive for their use as host material for luminescent applications. With texture and color giving the aesthetic contribution, Europium (Eu) doped single phase Mayenite may find potential applications in the design of energy efficient buildings when used as a coating material. Eu doped single phase Mayenite powders in varying concentrations (0%, 0.5%, 1%, and 1.5%) were prepared using self-propagating combustion synthesis method using metal nitrates and glycine as the fuel. The X-ray diffractograms confirmed the formation of single phase Mayenite with some of the Ca2+ ions getting replaced by Eu3+ ions. The photoluminescence emission spectra revealed 5D0 → 7F2 transition due to the crystal field effect and was characterized by the bright red luminescence. The doping of Eu resulted in a decrease of band gap from 4.8 ​eV for undoped Mayenite to 3.5 ​eV for 1.5% Eu doped Mayenite. The samples were found to exhibit excellent fluorescent properties under UV irradiation

Novel Precursor-Derived Meso-/Macroporous TiO2/SiOC Nanocomposites with Highly Stable Anatase Nanophase Providing Visible Light Photocatalytic Activity and Superior Adsorption of Organic Dyes

Titania (TiO2) is considered to have immense potential as a photocatalyst, the anatase phase in particular. There have been numerous attempts to push the limits of its catalytic activity to higher wavelengths to harness the visible electromagnetic radiation. Most of the investigations till date have been restricted to fine-tuning the bandgap by doping, control of defect chemistry at the surface and several to first principle simulations either with limited success or success at the cost of complexities in processing. Here, we report a simple and elegant way of preparing ceramics through precursor chemistry which involves synthesis of macroporous and mesoporous nanocomposites with in situ formation of TiO2 nanocrystals into a robust and protecting SiOC matrix. The in situ nanoscaled TiO2 is anatase of size 9–10 nm, which is uniformly distributed in an amorphous SiOC matrix forming a new generation of nanocomposites that combine the robustness, structural stability and durability of the SiOC matrix while achieving nanoscaled TiO2 functionalities. The stabilization of the anatase phase even at temperature as high as 1200 °C was evident. With an average pore size of 6.8 nm, surface area of 129 m2/g (BET) and pore volume of 0.22 cm3/g (BET), mesoporosity was achieved in the nanocomposites. The composites exhibited visible light photocatalytic activity, which is attributed to the Ti–O–C/TiC bonds resulting in the reduction of band gap by 0.2 to 0.9 eV. Furthermore, the heterojunction formed between the amorphous SiOC and crystalline TiO2 is also expected to minimize the recombination rate of electron-hole pair, making these novel nanocomposites based on TiO2 extremely active in visible wavelength regime