21,119 research outputs found
Hydrogenations without Hydrogen: Titania Photocatalyzed Reductions of Maleimides and Aldehydes
No full textA mild procedure for the reduction of electron-deficient alkenes and carbonyl compounds is described. UVA irradiations of substituted maleimides with dispersions of titania (Aeroxide P25) in methanol/acetonitrile (1:9) solvent under dry anoxic conditions led to hydrogenation and production of the corresponding succinimides. Aromatic and heteroaromatic aldehydes were reduced to primary alcohols in similar titania photocatalyzed reactions. A mechanism is proposed which involves two proton-coupled electron transfers to the substrates at the titania surface
Titania-silica composite
No full textThis product was prepared by synthesizing a suspension of titania powder using tetraethyl orthosilicate (TEOS) at two concentrations (w/v): 1% and 4%, in the presence of the n-octylamine surfactant. After the application of titania-silica composite, the rocks were submitted to contact angle test, spectrophotometry, sorptivity, thermal shock resistance and UV radiation resistance tests
Sintering of Titania Ceramics and Bioactivity Assessment
No full textThe wide range of application of titania (TiO2) ceramics in many technological fields is related to its characteristics, such as high refractive index, good stability in aggressive environments, high hardness and biocompatibility. Bioactive materials form a bone-like apatite layer on their surfaces in the living body and bond to living bone trough apatite layer. Bioactivity of such a material can be enhanced tailoring surface morphology. The apatite forming ability on bioactive materials can be evaluated in simulated body fluid (SBF).
This work aims at presenting the effects of particle size of raw material on the sintering process and formation of bone-like apatite on sintered ceramic in SBF.
Reducing powder particle size to nanometer level (15 nm) green compact sintering begins at 450 °C. At the same conditions of thermal treatment smaller particle size of anatase powder leads to formation of smaller grain size of obtained TiO2 ceramic. Bioactivity of ceramic is enhanced using nanopowder as raw material
Laponite-supported titania photocatalysts
No full textThis thesis describes the synthesis and characterisation of titania photocatalysts for incorporation into a polyethylene film. Monodisperse, anatase-phase titania nanoparticles are prepared and the synthesis conditions necessary for attraction to a laponite clay support are determined. Methods of preventing agglomeration of the laponite system such as the use of a polyethylene oxide surfactant or chemical modification of the laponite plate edges with a dimethyloctyl methoxysilane are also explored. Finally, photocatalytic studies on the laponite-supported titania nanoparticles are performed, and the compatibility and photoactivity of these materials in the polyethylene film are examined
Surface Modification, Characterization and Photocatalytic Performance of Nano-Sized Titania modified with Silver and Bentonite Clay
No full textIn many textile industries dyes are used as coloring agents. Advanced oxidation processes are used for degrading or removing color from dye baths. Catalysts play a key role in these industries for the treatment of water. Solid catalysts are usually composed of metals that form supports onto the surface and create metal particles with high surface areas. TiO2 composites containing transition metal ions (silver) and/or bentonite clay were prepared. Photocatalytic efficiencies have been investigated for the degradation of Orange G an azo dye. Various analytical techniques were used to characterize the surface properties of nano-sized titania modified using silver and/or bentonite clay. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analyses showed that TiO2 (10 ± 2 nm) and Ag (2 to 3 nm) particles were supported on the surface of the bentonite clay and the size was in the range of 100 ± 2 nm. The modified catalysts P-25 TiO2/Bentonite/Ag and P-25 TiO2/Ag were found to be very active for the photocatalytic decomposition of Orange G. The percent decolorization in 60 min was 98% with both P-25 TiO2/Ag and P-25 TiO2/Bentonite/Ag modified catalysts. Whereas mineralization achieved in 9 hr were 68% and 71% with P-25 TiO2/Bentonite/Ag and P-25 TiO2/Ag catalyst respectively
Morphological investigations of supported titania photocatalysts
No full textDue in no small part to an increasing need to augment existing water purification strategies, the synthesis of titania photocatalysts has been under considerable examination. However, in order to make the use of titania photocatalysts commercially viable there needs to be an increase in the efficiency of the catalysts while decreasing the potential toxicity. Due to its high porosity and novel optical properties, inverse opal titania derived from colloidal crystal templating offers one of the most efficient solutions. While a number of synthesis methods for inverse opal titania have been presented in the literature, the co�]deposition method offers the most effective method of generating the relative large areas of inverse opal material. The factors which affect the codeposition method and the mechanism by which titania inverse opals form in general remain relatively unstudied. This manuscript presents an examination of the morphology of inverse opals generated by the co�]deposition method while proposing a mechanism by which the inverse structures form
Surface Modification, Characterization and Photocatlytic Performance of Nano-Sized Titania modified with Silver and Bentonite clay
No full textIn many textile industries dyes are used as coloring agents. Advanced oxidation processes are used for degrading
or removing color from dye baths. Catalysts play a key role in these industries for the treatment of
water. Solid catalysts are usually composed of metals that form supports onto the surface and create metal
particles with high surface areas. TiO2 composites containing transition metal ions (silver) and/or bentonite
clay were prepared. Photocatalytic efficiencies have been investigated for the degradation of Orange G an
azo dye. Various analytical techniques were used to characterize the surface properties of nano-sized titania
modified using silver and/or bentonite clay. Scanning electron microscopy (SEM), Transmission electron
microscopy (TEM), X-ray diffraction (XRD) and FTIR analyses showed that TiO2 (10 ± 2 nm) and Ag (2 to 3
nm) particles were supported on the surface of the bentonite clay and the size was in the range of 100 ± 2
nm. The modified catalysts P-25 TiO2/Bentonite/Ag and P-25 TiO2/Ag were found to be very active for the
photocatalytic decomposition of Orange G. The percent decolorization in 60 min was 98% with both P-25
TiO2/Ag and P-25 TiO2/Bentonite/Ag modified catalysts. Whereas mineralization achieved in 9 hr were 68%
and 71% with P-25 TiO2/Bentonite/Ag and P-25 TiO2/Ag catalyst respectively
Photocatalytic activity of titania layer prepared by oxidizing titanium compounds on titanium plate surface
No full textAnatase-type nanocrystalline titania layers were prepared by oxidizing the crystalline titanium nitride and carbon-doped titanium nitride phases prepared on a titanium plate surface. Identification of the crystalline phase was confirmed by the XRD patterns and Raman spectra of these plates. The photocatalytic activity of the plates was evaluated by observing the photocalytic degradation process of acetaldehyde gas during UV irradiation by gas chromatography. A relatively larger amount of the anatase phase was formed on the very thin surface layer by heating the carbon-doped titanium nitride phase at 500 degrees C, and it exhibited a higher photocatalytic activity for the acetaldehyde degradation. The activity was determined not only by the amount of the anatase phase, but also by the crystallite size depending on the surface area and charge transfer efficiency. The photocatalytic activity is suggested to be due to the anatase phase existing on the thin surface layer accessible to the reactants.ArticleAPPLIED CATALYSIS B-ENVIRONMENTAL. 127:227-233 (2012)journal articl
Laponite-supported titania photocatalysts
No full textThis study builds on previous results published on the synthesis and characterisation of laponite-supported titania photocatalysts. Titania nanocrystals are prepared prior to addition to the clay dispersion, by a sol-gel synthesis incorporating a microwave hydrothermal step. In addition to previously examinations with XRD, TEM and FT-IR, the samples are further characterised with SEM, 29Si NMR and BET N2 sorption to gain an insight into the effect of Ti concentration and surface area on the photoactivity of the samples
Titania-Carbon Nitride Interfaces in Gold-Catalyzed CO Oxidation
No full textGold-catalyzed CO oxidation is a
reaction of both practical and
fundamental interest. In particular, rate-determining oxygen activation
pathways have attracted a lot of attention. They have been found to
depend on the surface chemistry of the catalyst support, titania providing
the most active catalysts and carbon nitride leading to inactive catalysts.
Here, we show that C3N4-TiO2 composites
with rather similar surface chemistries can be engineered by using
titania nanotubes as hard templates and by performing the polycondensation
of melamine and dicyandiamide in air and in ammonia. By varying the
C3N4 content from 2 to 75 wt %, the mesoporosity
can be tuned from 8 to 40 nm. A systematic study of CO oxidation turnover
numbers in the absence and in the presence of hydrogen over the composites
loaded with well-calibrated 2–4 nm gold nanoparticles clearly
shows that (1) the chemical composition of the support surface has
much less impact on PROX (preferential oxidation of CO in excess hydrogen)
than on dry CO oxidation, (2) NH2-terminated supports are
as active as OH-terminated supports in PROX, (3) hydrogen/water-mediated
CO oxidation pathways are active on C3N4-based
Au catalysts, and (4) PROX activity requires a rather large porosity
(40 nm), which suggests the involvement of much larger intermediates
than the usually postulated peroxo-type species
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