Effect of fuels on combustion synthesis of TiO2 - Towards efficient photocatalysts for methylene blue oxidation and Cr (VI) reduction under natural sunlight

A facile synthesis of carbon and nitrogen co-doped nano-TiO2 with pure anatase phase and high surface area was achieved by using combustion synthesis without the need of surfactants in a single step approach. Organic fuels such as hexamine, triethyl amine and glycine were tested as different fuels with titanylnitrate as the common oxidant. Effect of mixture of fuels has also been studied by taking the combinations of the above mentioned fuels. X-ray diffraction confirms the anatase phase titania and nano-crystalline size of the prepared catalysts was confirmed by transmission electron microscopy (TEM). N-2 adsorption confirmed the high surface area of nanocrystalline titania. Red shifts in UV-Vis absorption spectra was assigned due to the C and N-doping into the TiO2 matrix, whereas the presence of C and N in the TiO2 matrix was confirmed by X-ray photoelectron spectroscopy. Photocatalytic activity of the catalysts has been estimated from the oxidation of methylene blue (MB) and reduction of Cr (VI) under natural sunlight in open atmosphere. Among the TiO2 catalysts prepared, the one obtained with glycine as the fuel showed the best photocatalytic activity, which was correlated to the number of moles of gases evolved during the synthesis. (C) 2013 Elsevier B.V. All rights reserved.

Facile synthesis of efficient visible active C-doped TiO2 nanomaterials with high surface area for the simultaneous removal of phenol and Cr(VI)

Nicolas Xanthopoulos

A single step synthesis of carbon doped TiO2 (anatase) nanomaterials have been reported by using combustion synthesis using ascorbic acid and citric acid fuels. X-ray diffraction studies indicated the formation of nanosized anatase titania, whereas, transmission electron microscopy confirmed the formation of nanosized TiO2 anatase. The carbon doping into TiO2 matrix was identified by X-ray photoelectron spectroscopy, whereas, thermogravirnetric study quantified the carbon doping. Diffuse reflettance UV-vis spectra indicated the band gap of less than 3 eV, a prerequisite for the photocatalytic activity under visible light irradiation. The N-2 adsorption studies revealed the high surface area (upto 290 m(2)/g) of the synthesized photocatalysts. Typical photocatalytic activity data indicated that the simultaneous removal of Cr(VI) and phenol is advantageous than degradation of the individual pollutants. (C) 2014 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2015

Abatement of an Azo Dye on Structured C-Nafion/Fe-Ion Surfaces by Photo-Fenton Reactions Leading to Carboxylate Intermediates with a Remarkable Biodegradability Increase of the Treated Solution

Juan Kiwi, Lioubov Kiwi, Sandra Parra Cardona

A novel C-Nafton/Fe-ion structured fabric capable of mediating Orange II decomposition in Fenton-immobilized photoassisted reactions is presented. The catalyst preparation requires the right balance between the amount of the Nafion necessary to protect the C-surface and the minimum encapsulation of the Fe-cluster catalytic sites inside the Nafion to allow the photocatalysis to proceed. The C-Nafion/Fe fabric can be used up to pH 10 under light to photocatalyze the disappearance of Orange II in the presence of H2O2. The photocatalysis mediated by the C-Nafion/Fe-ion fabric increased with the applied light intensity and reaction temperature in the reaction needing an activation energy of 9.8 kcal/mol. This indicates that ion- and radical-molecule reactions take place during Orange II disappearance. The build up and decomposition of intermediate iron complexes under light involves the recycling of Fe2+ and was detected by infrared spectroscopy (FTIR). This observation, along with other experimental results, allows us to suggest a surface mechanism for the dye degradation on the C-Nafion/Fe-ion fabrics. The C-Nafion/Fe-ion fabric in the presence of H2O2 under solar simulated light transforms the totally nonbiodegradable Orange II into a biocompatible material with a very high BOD5/COD value. X-ray photoelectron spectroscopy (XPS) and sputtering by Ar+-ions of the upper surface layer of the C-Nafion/Fe-ion fabric allow us to describe the intervention of the photocatalyst down to the molecular level. Most of the Fe clusters examined by transmission electron microscopy (TEM) showed particle sizes close to 4 nm due to their encapsulation into the Gierke cages of the Nafion thin film observed by scanning electron microscopy (SEM) and optical microscopy (OM).

2003

Thermal stability of size-selected copper nanoparticles: Effect of size, support and CO2 hydrogenation atmosphere

Alexandre Borsay, Mostapha Dakhchoune, Mo Li, Wen Luo, Kun Zhao, Andreas Züttel

Metal nanoparticles with a precisely controlled particle size distribution are ideal model catalysts for fundamental studies in catalysis. In this work, the thermal stability of size-selected Cu nanoparticles (Cu NPs) were deposited by magnetron sputtering, and their thermal stability was investigated using transmission electron microscopy and X-ray photoelectron spectroscopy. The influence of particle size, support, temperature, as well as CO2 hydrogenation atmosphere was systematically studied. We found that at 220 °C in ultra-high vacuum (UHV), carbon-supported 4 nm Cu NPs sintered through particle migration while the 8 nm Cu NPs were relatively stable. As the temperature increased to 320 and 460 °C, both samples sintered severely, and Ostwald ripening was suggested to be the dominant mechanism. In addition, we observed that SiO2 support can better stabilize Cu NPs upon heat treatment under both UHV and CO2 hydrogenation atmosphere (1 mbar of 1:1 CO2/H2 mixture), due to the stronger interaction between SiO2 and Cu compared to that between carbon and Cu. Furthermore, under a CO2 hydrogenation atmosphere, the stability of Cu NPs is suggested to be influenced by the interplay of redispersion, agglomeration, and volatilization. These findings from model systems can offer new insights for understanding the deactivation of Cu-based catalysts.

2020

Abatement of an Azo Dye on Structured C-Nafion/Fe-Ion Surfaces by Photo-Fenton Reactions Leading to Carboxylate Intermediates with a Remarkable Biodegradability Increase of the Treated Solution

Juan Kiwi, Lioubov Kiwi, Sandra Parra Cardona

2003