TiO2 Catalyzed Dihydroxyacetone (DHA) Conversion in Water: Evidence That This Model Reaction Probes Basicity in Addition to Acidity

In this paper, evidence is provided that the model reaction of aqueous dihydroxyacetone (DHA) conversion is as sensitive to the TiO2 catalysts’ basicity as to their acidity. Two parallel pathways transformed DHA: while the pathway catalyzed by Lewis acid sites gave pyruvaldehyde (PA) and lactic acid (LA), the base-catalyzed route afforded fructose. This is demonstrated on a series of six commercial TiO2 samples and further confirmed by using two reference catalysts: niobic acid (NbOH), an acid catalyst, and a hydrotalcite (MgAlO), a basic catalyst. The original acid-base properties of the six commercial TiO2 with variable structure and texture were investigated first by conventional methods in gas phase (FTIR or microcalorimetry of pyridine, NH3 and CO2 adsorption). A linear relationship between the initial rates of DHA condensation into hexoses and the total basic sites densities is highlighted accounting for the water tolerance of the TiO2 basic sites whatever their strength. Rutile TiO2 samples were the most basic ones. Besides, only the strongest TiO2 Lewis acid sites were shown to be water tolerant and efficient for PA and LA formation

Impact of H2O2 on the Lactic and Formic Acid Degradation in Presence of TiO2 Rutile and Anatase Phases under UV and Visible Light

International audienc

Comparison of hydrothermal and photocatalytic conversion of glucose with commercial TiO 2 : Superficial properties-activities relationships

International audienceRecently, the photocatalytic conversion of glucose appeared as an environmentally friendly route to produce valuable molecules. However, the potential of this new route in comparison with the usual hydrothermal catalytic process remained questionable. In this paper, we compared the two routes using three commercial TiO 2 as catalysts in the same reactor. The TiO 2 superficial acidity and basicity were determined by calorimetry and FTIR of CO 2 , NH 3 and pyridine adsorption. Relationships between the acid-base properties, the TiO 2 glucose adsorption capacities measured in water and their photocatalytic or hydrothermal performances were proposed: while the photocatalytic performances could be linked to the catalysts' Lewis acid sites density and their glucose adsorption capacities, the hydrothermal performances were dependent of the catalysts' basic/acid sites balance. We highlighted that the conversion of glucose over TiO 2 was as efficient with the photocatalytic process at ambient temperature as with the hydrothermal process at 120°C. This underlines the potential of the photocatalytic route at the lab scale as regards to the milder experimental conditions involved

Photocatalytic activity of TiO2 films immobilized on aluminum foam by atomic layer deposition technique

International audienceThe aim of the this work was to study feasibility of titanium dioxide thin films prepared by atomic layer deposition (ALD) technique on aluminum foam substrates for photocatalysis and compare performance of thin films with commercially available AEROXIDE® TiO2. Formic acid and phenol photocatalytic decomposition was monitored using high-pressure liquid chromatography (HPLC). The morphology and thickness of TiO2 films were characterized by scanning electron microscopy (SEM) and their structure was determined by X-ray diffraction (XRD). Surface of the thin films was characterized with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The amount of TiO2 deposited on aluminum foam was measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). It was observed that initial rates of formic acid and phenol degradation were 0.007 and 0.001 mmol L−1 min−1, respectively. The apparent quantum yields for formic acid using immobilized and reference TiO2 powder (AEROXIDE® TiO2 P25, Evonik) were 2.2 and 2.7%, correspondingly. While for phenol apparent quantum yield was equal to 0.4% when TiO2 thin film was used and 0.7% in the case of reference powder. A decrease of the photocatalytic activity of TiO2 films deposited on aluminum foam was observed after the first cycle for both model compounds. It was suggested from this study that suppression of activity occurs due to detachment of TiO2 from the surface of thin film

Influence of the Micro-Nanostructuring of Titanium Dioxide Films on the Photocatalytic Degradation of Formic Acid under UV Illumination

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Influence of the Micro-Nanostructuring of Titanium Dioxide Films on the Photocatalytic Degradation of Formic Acid under UV Illumination

International audienc

Pickering emulsions of fluorinated TiO2: a new route for intensification of photocatalytic degradation of nitrobenzene

International audienceFluorination of the TiO2 surface has been often reported as a tool to increase the photocatalytic efficiency due to the beneficial effects in terms of production of oxidizing radicals. Moreover, it is shown that the unique amphiphilic properties of the fluorinated TiO2 (TiO2-F) surface allow one to use this material as a stabilizer for the formulation of Pickering emulsions of poorly soluble pollutants such as nitrobenzene (NB) in water. The emulsions have been characterized in terms of size of the droplets, type of emulsion, possibility of phase inversion, contact angle measurements, and optical microscopy. The emulsified system presents micrometer-sized droplets of pollutant surrounded by the TiO2-F photocatalyst. Consequently, the system can be considered to be composed of microreactors for the degradation of the pollutant, which maximize the contact area between the photocatalyst and substrate. The enhanced photocatalytic activity of TiO2-F was confirmed in the present paper as the apparent rate constants of NB photodegradation were 16 × 10–3 and 12 × 10–3 min–1 for fluorinated and bare TiO2, respectively. At NB concentrations largely exceeding its solubility, the rate constant was 0.04 × 10–3 min–1 in the presence of both TiO2 and TiO2-F. However, unlike TiO2, TiO2-F stabilized NB/water emulsions and, under these conditions, the efficiency of NB photocatalytic degradation in the emulsified system was ca. 18 times higher than in the nonemulsified one. This result is relevant also in terms of practical applications because it opens the route to one-pot treatments of biphasic polluted streams without the need of preliminary physical separation treatments

Correlation between Photocatalytic Properties of ZnO and Generation of Hydrogen Peroxide—Impact of Composite ZnO/TiO₂ Rutile and Anatase

The generation of hydrogen peroxide on commercial and synthesized ZnO from different precursors was studied using two model molecules, formic acid (FA) and phenol (Ph), as well as phenolic intermediates, hydroquinone (HQ), benzoquinone (BQ), and catechol (CAT). The samples were characterized using X-ray Diffraction (XRD), Transmission Electronic Microscopy (TEM), RAMAN, and Electron Paramagnetic Resonance (EPR) before evaluating their photocatalytic properties. We found that the improved efficiency is accompanied by a high level of H2O2 production, fewer oxygen vacancies, and that the number of moles of H2O2 formed per number of carbon atoms removed is similar to the degradation of FA and Ph with a factor of 1. Moreover, a comparative study on the formation of H2O2 was carried out in the presence of TiO2 rutile and TiO2 anatase, with commercial ZnO. Our results exhibit the impact of the presence of TiO2 on the decomposition of hydrogen peroxide and the formation of phenolic intermediates, which are much lower than those of ZnO only, which is in agreement with the formation of hydroxyl radicals °OH and superoxide O2°− degrading significantly hydroquinone (HQ), benzoquinone (BQ), and cathecol (CAT)

Correlation between Photocatalytic Properties of ZnO and Generation of Hydrogen Peroxide—Impact of Composite ZnO/TiO2 Rutile and Anatase

The generation of hydrogen peroxide on commercial and synthesized ZnO from different precursors was studied using two model molecules, formic acid (FA) and phenol (Ph), as well as phenolic intermediates, hydroquinone (HQ), benzoquinone (BQ), and catechol (CAT). The samples were characterized using X-ray Diffraction (XRD), Transmission Electronic Microscopy (TEM), RAMAN, and Electron Paramagnetic Resonance (EPR) before evaluating their photocatalytic properties. We found that the improved efficiency is accompanied by a high level of H2O2 production, fewer oxygen vacancies, and that the number of moles of H2O2 formed per number of carbon atoms removed is similar to the degradation of FA and Ph with a factor of 1. Moreover, a comparative study on the formation of H2O2 was carried out in the presence of TiO2 rutile and TiO2 anatase, with commercial ZnO. Our results exhibit the impact of the presence of TiO2 on the decomposition of hydrogen peroxide and the formation of phenolic intermediates, which are much lower than those of ZnO only, which is in agreement with the formation of hydroxyl radicals °OH and superoxide O2°− degrading significantly hydroquinone (HQ), benzoquinone (BQ), and cathecol (CAT)