Search

SSCI-VIDE+CARE:ECI2D+MHM:GBE:FDA:CGU:HKO; International audience; The influence of polyhydroxyfullerene (PHF) on the photocatalytic properties of calcined hydrogenotitanate nanotubes (HNT) were evaluated in the present study. PHF-HNT nanocomposites were first characterized by N-2 adsorption-desorption measurements, X-ray diffraction, X-ray photoelectron, electron paramagnetic resonance and UV vis diffuse reflectance spectroscopies, transmission electron microscopy, photoluminescence, and photocurrent experiments. Correlation was then established with the photocatalytic properties of PHF-HNT nanocomposites during the photodegradation of formic acid. (C) 2017 Elsevier B.V. All rights reserved.

This paper builds on previous literature showing the interesting adsorptive properties of TiO2 nanotubes. It further explores the positive effect of β-cyclodextrin on these properties. Hence, β-cyclodextrin modified TiO2 nanotubes were successfully prepared and characterized by XRD, N2 physisorption at 77 K, Raman, FTIR-ATR, 1H NMR, TEM and EPR. The adsorptive interaction of Cu(II) with materials was investigated in aqueous solution at pH 9.25 (NH4+/NH3). The main conclusion is that copper(II)-ammonia complexation equilibria play an important role in the adsorption process. The β-cyclodextrin was found to improve the Cu(NH3)42+ adsorption mainly by retarding its precipitation to high concentrations values (>400 mg L−1). Adsorption experimental data showed good fit with the pseudo-second-order model and the Langmuir isotherm model.

Selective adsorption of La, Ce, Y and Nd rare earth elements (REEs) from aqueous solution was performed using TiO2 nanotubes. Kinetic study reveals that REEs adsorption on TiO2 nanotubes is highly enhanced at pH 5 (acetate buffer). The experimental parameters keys such as pH, eluent concentration and flow rate are investigated. The desorption of REEs prior to ICP analysis is also studied. From thermodynamic study, the adsorption heats, are REEs atomic radius dependent, which opens a new route for the selective separation. An engineered packed column with TiO2 nanotubes was used under continuous flow for the REEs extraction. Our method yields excellent recovery (> 98%) of REEs, and the column can be regenerated up to 20 cycles.

AIR:EAU:RAFFINAGE:MATERIAUX+ATR:HKO:CGU:GBE; The influence of the sodium content on thermal stability and photocatalytic activity of calcined titanate nanotubes (TNT) was herein evaluated by preparing different samples through hydrothermal treatment of TiO2 powder (P25) in a concentrated NaOH solution (11.25 M) at 130 degrees C during 20 h followed by acid washing steps. Titanate nanotubes samples with sodium (Na-TNT) and sodium-free (H-TNT) were then obtained using different concentrations of HCI aqueous solutions namely 0.1 M and 1 M respectively. As synthesized nanomaterials with different Na percentages were then calcined at temperatures varying between 400 degrees C and 700 degrees C. Samples were characterized by means of nitrogen adsorption-desorption isotherms at 77 K, thermal analysis (DTA, TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and diffuse reflectance spectroscopy (DRS). The photocatalytic activities of Na-TNT and H-TNT derived nanomaterials were then evaluated through the photocatalytic degradation of formic acid (FA). Results show that the presence of sodium retards the dehydration process during the transformation of titanate into TiO2 shifting the formation of anatase phase to higher temperatures. However, sodium is not necessary to preserve the nanotubular morphology. The presence of sodium after calcination strongly impacts negatively the photocatalytic properties. If sodium is completely removed from the initial titanate orthorhombic phase, calcination leads to TiO2 anatase materials with enhanced photocatalytic properties compared to P25 in the degradation of formic acid, particularly if nanotubular morphology is preserved. The highest activity was therefore achieved for the H-TNT sample calcined at 400 degrees C. The photodegradation activity of formic acid depends on the specific surface areas and TiO2 crystallinity. In pure anatase nanoparticles the activity strongly decreases with coherent crystallographic domains >= 10 nm. (c) 2013 Elsevier B.V. All rights reserved.

Titanium dioxide nanotubes were prepared via a hydrothermal treatment of TiO 2 powder (Degussa P25). Obtained samples were analyzed by various techniques, such as transmission electron microscopy (TEM) and X-ray diffraction (XRD), which revealed that the crystal structure of the obtained materials was similar to that of H 2 Ti 2 O 5 ·H 2 O nanotubes, and were about 50 nm in length and 20 nm in diameter. Nitrogen adsorption–desorption isotherms indicated that synthesized solids are mesoporous materials with a multi-walled nanotubular structure and high specific surface area. The methanol oxidation reaction was investigated on platinum nanoparticles supported TiO 2 nanotubes (XC72). The electrocatalytic activity of the catalyst was measured by cyclic voltammetry. CO stripping voltammetry in acidic solutions was investigated to study the reaction of the catalysts towards poisoning by carbonyl compounds. The results demonstrated that Pt/TiO 2 nanotubes catalyst exhibits the best activity for methanol oxidation and were favorable for improving the tolerance to poisoning species.

A thioresistant NOx trap based on CuO supported on sulphated zirconia mixed with a solid base is described. The rate of adsorption of NO at constant temperature and the amount of NO retained from a feed containing 750 ppm NO, 10% O2 and 5% water in nitrogen were measured. On badly dispersed CuO, the capacity for NOx adsorption does not decrease but slightly increases in the presence of 25 ppm SO2 in the feed. By contrast, a well dispersed Cu catalyst is irreversibly poisoned. The surface nitrates can be decomposed in air at 623 K. In a mixture, Ar + 1% H2, the nitrate is partly reduced to N2 at about 630 K, even after operation in the presence of SO2. The catalyst does not lose adsorption capacity after 10 cycles of adsorption–desorption and can be used in the temperature range 473–773 K. The resistance to SO2 depends also in part of the properties of the solid base.

Oxidation of primary hydroxyl groups of potato starch to the corresponding carboxylic acids was performed in a fluidized bed using N2-diluted NO2 as oxidant. FT-IR spectrum of the oxidized starch show the presence of two absorption bands at 1743 and 1379 cm−1. The absorption at 1743 cm−1 which normally attributed to carbonyl absorption vanishes after washing the oxidized starch by water. Then two new absorption bands appeared at 1650 and 1400 cm−1 corresponding to the ionized carboxyl groups. The presence of nitrate favor the un-ionized form of carboxyl groups and then the band at 1743 cm−1 can be observed. Furthermore, the ionized carboxyl absorption (1600, 1400 cm−1) are replaced by carbonyl absorption at 1743 cm−1 by adding DCl. By means of 13C NMR analysis, oxidized starch, show a band around 200 ppm attributed to carboxylic acid, no formic acid was detected indicating that no cleavage took place under the applied reactions conditions.

Primary hydroxyl groups were oxidized regioselectively to carboxylic acid using organic nitrosonium salts generated on supported silver catalysts, which promote disproportionation of 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) in aqueous solution. The oxidation reactions were performed at pH 9.5 in a batch reactor at room temperture using heterogeneous silver catalysts and peroxides as primary co-oxidants; e.g., 99 mol% selectivity to methyl-α-D-glucopyrasiduronic acid was obtained at 90% conversion of the pyranoside using a silver carbonate–celite catalyst . The efficiency of the system was increased by adding carbonates to the silver catalyst. This result is explained by the increase of the electron charge deficiency on silver in the presence of carbonate, which accelerates the nucleophilic attack of hydroxyls and/or TEMPO. In the case of the Ag–Al2O3 catalyst, this result was proved by temperature-programmed desorption measurements using ammonia. With primary/secondary polyols, the selectivity for the primary hydroxyl groups is high. In addition, primary hydroxyl groups, as in the case of pyranosides, were oxidized more selectively than those of the furanosides. The observed regioselectivity is due to the sterical hindrance caused by the four methyl groups in TEMPO.

Hydrophobic mesoporous titano-silicates (HyMTS) have been prepared at ambient temperature by a sol–gel technique using hexadecyl-trimethyl-ammonium chloride in acid medium as templating surfactant. The gellation time increases for low reaction temperatures and low H + /Si ratios. The amorphous materials thus obtained at long gellation times show hydrophobic properties and a lower number of OH bearing Si atoms as determined from 29 Si MAS NMR. In the epoxidation of norbornene with H 2 O 2 or of cyclohexene with tert-butyl hydroperoxide, HyMTS reaches selectivities for the epoxide of 95% or higher. The epoxidation of cyclohexene by H 2 O 2 also gives better selectivities to the epoxide on these hydrophobic samples, compared to hydrophilic solids. It is suggested that hydrophobicity results from the slow kinetics of gellation.