Showing papers by "Chantal Guillard published in 2018"

Precursor-mediated synthesis of Cu2−xSe nanoparticles and their composites with TiO2 for improved photocatalysis

Abstract: The direct synthesis of copper selenide nanoparticles from the reaction of ditertiarybutyl selenide tBu2Se with copper(ii) trifluoroacetate Cu(TFA)2 under mild conditions is reported. The isolation of a molecular species during the course of this reaction, established as [Cu2(TFA)2(tBu2Se)3], by spectroscopic studies and single crystal X-ray structure analysis, confirmed that metal selenide NPs are formed via this intermediate species containing a reduced copper center. Extending this reaction in the presence of commercial TiO2 (P25) offered an easy synthesis of copper selenide-titania nanocomposites with different Cu/Ti ratios. These nanocomposites, well-characterized by powder XRD, STEM, TEM, BET, XPS, EDX and UV-Vis studies, were examined as photocatalysts for the degradation of formic acid (FA). The nCu2-xSe-TiO2 nanocomposites with low mol% of copper selenide, i.e. n = 0.1 and 0.3 mol%, displayed a superior catalytic activity over P25, which is an established benchmark for photocatalysis under UV light.

Understanding the photocatalytic degradation by P25 TiO2 of acetic acid and propionic acid in the pursuit of alkane production

Abstract: Towards the application of harvesting valuable hydrocarbon products from wastewater and associated fermentation processes, the traditional P25 Degussa TiO2-assisted decarboxylation of simple carboxylic acid substrates - in this case acetic and propionic acids – was re-examined for its alkane production capacity. Avoiding doping or the introduction of other elements into the commercially available TiO2 lattice, we modified other parameters of the reaction not yet explored. Under nitrogen, highly concentrated (50%) and pure (100%) solutions of both acetic acid and propionic acid demonstrated good selectivity for the decarboxylation over any other side reaction or complete mineralization, nearing or exacting a 1:1 hydrocarbon/CO2 ratio in each case. This behaviour proves that the direct reaction of h+ with the acid in either case is the key parameter to favour this selectivity. In the case of acetic acid, methane’s yield was increased significantly by the periodic aeration of the catalyst when exhausted under nitrogen. The modification of solution pH to more physiological and fermentation-compatible levels (pH of 6.0) lead to improve the selectivity and the ethane’ yield in 50% propionic acid degradation and also resulted in virtually no unidentified carbon products. The Photo-Kolbe coupling and dehydration products, meanwhile, were favoured in the less concentrated solutions, suggesting that more dilute solutions may be more promising for deriving longer length hydrocarbons from substrates of smaller size. Mechanistically, these results also implicate that OH° radicals are at the origin of product generation by way of Photo-Kolbe coupling and dehydration. Finally, acetic acid and propionic acid were degraded simultaneously, in which the latter was degraded preferentially or at least initially before the former, along with the appearance of propane as a result of cross-coupling.

Photocatalytic activity of titania deposited on luminous textiles for water treatment

Abstract: The originality of the present photocatalytic system consists in using luminous textiles for a double purpose: (i) supporting TiO2 photocatalysts and (ii) conveying UV-light all along the optical fibers and distributing it to the TiO2 particles deposited. Photocatalytic luminous textiles were tested in terms of stability and their photocatalytic activities were determined in the purification of water containing either formic acid or phenol. Luminous textiles were coated with TiO2 sols and or suspensions. The location of TiO2 was analysed by ESEM and EDX analysis and was shown to be uniform over the surface of optical fiber textiles, except for TiO2 powder coating, exhibiting titania present as clusters. A good adhesion and stability of the photocatalyst layer were found. The photocatalytic performances of the different TiO2 coatings, tested in the degradation of two model pollutants (formic acid and phenol), in a batch reactor indicated an optimum mass of TiO2 of about 2 mg/cm2. Degradation tests highlighted the higher activity of TiO2 powder coating in comparison with others coating tested, whatever the catalyst mass or pollutant tested. Photonic yields depend on the absorption properties of the coating. They range from 23 to 60% for formic acid degradation and from 6 to 8% for that of phenol, proving the efficiency of such luminous textile coating by TiO2. The performances observed indicate that luminous textiles are good candidates for supporting titania photocatalysts, thus avoiding tedious final filtrations when using suspensions

Heterogeneous Photocatalysis: Use in Water Treatment and Involvement in Atmospheric Chemistry

Abstract: Heterogeneous photocatalysis (HP) involves redox reactions initiated by the optical excitation of a semiconductor. This chapter considers the role of HP in the environment with two viewpoints. First, HP is at the basis of a new technology for water treatment, and a study of the destruction of some organic micropollutants is presented. Second, the importance of HP in tropospheric chemistry needs to be assessed, and laboratory studies in this direction are included. Isolated Titanium dioxide (TiO2) is a less abundant component; however, since titanium is the seventh element in the Earth's crust, this dioxide can be encountered as an impurity in other oxides or can form titanates, especially ilmenite (FeTiO3), which is a semiconductor. Consequently, HP phenomena susceptible to occur on these semiconducting particles cannot be a priori neglected in atmospheric chemistry. The disappearance of naphthalene (NPH), previously adsorbed onto TiO2 in the dark, was also determined in a dry-air-filled static reactor as a function of the irradiation time.