Nanometric powder particles of white zirconia were synthesized through precursor route by the pyrolysis of zirconium (IV) butoxide at varied temperatures in air ranging from 900–1400 °C and were predominantly monoclinic in nature. To control the defect chemistry, the precursor was also pyrolyzed in a reduced atmosphere at 900 °C, eventually resulting in black zirconia. The stabilization of tetragonal phase and observed color change from white to black in samples pyrolyzed under reduced atmosphere was attributed to the creation of oxygen vacancies and disorder. The black and white zirconia produced delineated the influence of crystal structure and oxygen vacancies on the photocatalytic performance. Furthermore, zirconia synthesized at lower temperatures (600 and 800 °C) in air confirmed the detrimental role of tetragonal phase on the degradation behavior of methylene blue dye. High photocatalytic degradation rate for white zirconia was attributed to the presence of increased density of nano-sized pores and low recombination rate of electron-hole pairs as confirmed by PL measurements. Interestingly, black zirconia exemplified relatively limited activity albeit presence of oxygen vacancies. This negative effect was attributed to the presence of tetragonal phase and possibly, the insufficient creation of new energy states near valence and conduction band towards Fermi energy level.

The pyrolysis (1000 °C) of a liquid poly(vinylmethyl-co-methyl)silazane modified by tetrakis(dimethylamido)titanium in flowing ammonia, nitrogen and argon followed by the annealing (1000–1800 °C) of as-pyrolyzed ceramic powders have been investigated in detail. We first provide a comprehensive mechanistic study of the polymer-to-ceramic conversion based on TG experiments coupled with in-situ mass spectrometry and ex-situ solid-state NMR and FTIR spectroscopies of both the chemically modified polymer and the pyrolysis intermediates. The pyrolysis leads to X-ray amorphous materials with chemical bonding and ceramic yields controlled by the nature of the atmosphere. Then, the structural evolution of the amorphous network of ammonia-, nitrogen- and argon-treated ceramics has been studied above 1000 °C under nitrogen and argon by X-ray diffraction and electron microscopy. HRTEM images coupled with XRD confirm the formation of nanocomposites after annealing at 1400 °C. Their unique nanostructural feature appears to be the result of both the molecular origin of the materials and the nature of the atmosphere used during pyrolysis. Samples are composed of an amorphous Si-based ceramic matrix in which TiNxCy nanocrystals (x + y = 1) are homogeneously formed “in situ” in the matrix during the process and evolve toward fully crystallized compounds as TiN/Si3N4, TiNxCy (x + y = 1)/SiC and TiC/SiC nanocomposites after annealing to 1800 °C as a function of the atmosphere.

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The mesoporous N-doped TiO 2 /Si-O-C-N ceramic nanocomposites has been revealed to be a potential candidate Mesoporous towards visible light photocatalytic degradation of organic dyes. The polymer-derived ceramic route was im-Nanocomposite plemented to prepare uniformly distributed in-situ crystallized N-doped TiO 2 nanocrystals in a mesoporous Photocatalysis amorphous siliconoxycarbonitride matrix. This chemical approach assisted by the hard template pathway re-Adsorption sulted in a high surface area (186 m 2 /g) nanocomposite exhibiting predominantly mesoporous structure with an Heterojunction 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.

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.

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in 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. Large scale industrialization and urbanization has led to extensive pollution and contamination of rivers and water bodies, posing a threat to future generations and sustainable development 1. Chemical industries, leather factories, paint manufactures, dyeing and plating units release harmful untreated waste directly into our water bodies 2-4. These are non-biodegradable and toxic to humans as well as flora and fauna. Filtration with activated carbon, coagulation using chemical agents, ozonization, flocculation and reverse osmosis are some of the techniques that are frequently used to remove these harmful substances 5-8. However, these techniques are not effective in complete removal and merely result in the transfer of chemicals from one source to another. The photocatalytic phenomenon is capable of converting these toxic substances (EDTA, Cr(VI), nitrite) to harmless counterparts such as hydrogen, Cr(III) and nitrates 9-11. This is achieved via a catalyst that upon subsequent excitation produces electrons and holes. These electrons and holes produce superoxide and hydroxyl radicals that are responsible for the oxidation and reduction processes 12-15. But the efficiency of photocatalyst is largely dependent on the recombination rate of these electrons and holes. This drives the need for developing suitable catalysts which could be eventually scaled up for a large-scale clean-up drive 16-19. The wide band gap (3.25-5.1 eV) combined with a negative conduction band potential (−1.0 V vs. NHE at pH 0) 11 has recently spurred a lot of research on zirconia as a photocatalyst 20-23. It is important to note that the band gap value depends on the crystal structure (3.84 eV for cubic, 4.11 eV for tetragonal and 4.51 eV for monoclinic) 24 , defects and processing route of the ceramics 25. From the available limited literature, it is known that the presence of both monoclinic and tetragonal phases of zirconia 26-28 is beneficial for photocatalysis. The high temperature tetragonal phase of zirconia namely t-ZrO 2 can be stabilized at room temperature by using suitable

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