Julien Mahy

Aqueous sol–gel synthesis and film deposition methods for the large-scale manufacture of coated steel with self-cleaning properties

A process has been developed to enable the large-scale production of pure TiO2 films deposited on 316L stainless steel in order to get an easy-to-clean surface. This large-scale process requires an easy aqueous sol–gel procedure for the synthesis of the TiO2 sol. This synthesis has been simplified to facilitate the extrapolation toward an industrial scale. Results of TEM, photocatalytic properties, film hydrophilicity and texture obtained with the simplified aqueous sol–gel synthesis (IsoP–TiO2 synthesis) show similar properties to those obtained with the standard aqueous sol–gel synthesis of TiO2 (HAc–TiO2 synthesis) developed previously. Only, X-ray diffraction patterns showed differences, with the presence of anatase-brookite phases in IsoP–TiO2 synthesis while anatase phase only was observed in HAc–TiO2 synthesis. Both the aqueous sol–gel synthesis of pure TiO2 and the film deposition on steel by roll-coating have been successfully extrapolated to a larger scale. The photocatalytic activity and the hydrophilicity of the film were found to be unchanged when compared to films produced at a laboratory scale, thus validating the production of an efficient easy-to-clean material. Although some problems are still to be solved, this study is a hopeful first step in the development of a large-scale process for self-cleaning steel production.Graphical Abstract

Highly Efficient Low-Temperature N-Doped TiO2 Catalysts for Visible Light Photocatalytic Applications

In this paper, TiO2 prepared with an aqueous sol-gel synthesis by peptization process is doped with nitrogen precursor to extend its activity towards the visible region. Three N-precursors are used: urea, ethylenediamine and triethylamine. Different molar N/Ti ratios are tested and the synthesis is adapted for each dopant. For urea- and trimethylamine-doped samples, anatase-brookite TiO2 nanoparticles of 6–8 nm are formed, with a specific surface area between 200 and 275 m2·g−1. In ethylenediamine-doped samples, the formation of rutile phase is observed, and TiO2 nanoparticles of 6–8 nm with a specific surface area between 185 and 240 m2·g−1 are obtained. X-ray photoelectron spectroscopy (XPS) and diffuse reflectance measurements show the incorporation of nitrogen in TiO2 materials through Ti–O–N bonds allowing light absorption in the visible region. Photocatalytic tests on the remediation of water polluted with p-nitrophenol show a marked improvement for all doped catalysts under visible light. The optimum doping, taking into account cost, activity and ease of synthesis, is up-scaled to a volume of 5 L and compared to commercial Degussa P25 material. This up-scaled sample shows similar properties compared to the lab-scale sample, i.e., a photoactivity 4 times higher than commercial P25.

Ethylene polymerization and hydrodechlorination of 1,2-dichloroethane mediated by nickel(II) covalently anchored to silica xerogels

Ni/SiO2 cogelled xerogel catalysts have been prepared in ethanol containing nickel acetylacetonate, tetraethoxysilane (TEOS), an aqueous ammonia solution of 0.54 mol L−1 and either a commercial sylilated ligand, 3-(2-aminoethyl)aminopropyltrimethoxysilane (EDAPMS), or a home-made new silylated pyrazolypyridine ligands, respectively 2-[4-[3-(trimethoxysilyl)propyl]-3,5-dimethyl-1H-pyrazol-1-yl]pyridine (MS-PzPy) and 2-[4-[3-(trimethoxysilyl)propyl]-3,5-dimethyl-1H-pyrazol-1-yl]-6-methylpyridine (MS-PzPyMe), able to form a chelate with a metal ion such as Ni2+. All samples form homogeneous and very highly dispersed Ni/SiO2 cogelled xerogel catalysts. The resulting catalysts are composed of nickel nanoparticles with a diameter of about 2.8 nm, located inside primary silica particles exhibiting a monodisperse microporous distribution. The silylated organic ligand has a strong influence on the textural properties of cogelled xerogel catalysts, both before and after calcination and reduction steps. Changing the nature of the silylated ligand permits tailoring textural properties such as pore volume, pore size and surface area. Homogenous nickel complexes synthesized from pyrazolylpyridine derivatives are inactive for ethylene polymerization. In opposite, heterogenous nickel-based catalysts onto silica xerogel synthesized from pyrazolylpyridine derivatives bearing a tethered trialkoxysilyl group allow increasing ethylene polymerization activity. Although nickel nanoparticles are located inside the silica crystallites, their complete accessibility, via the micropore network, has been shown. For 1,2-dichloroethane hydrodechlorination over Ni/SiO2 catalysts, the conversion of 1,2-dichloroethane is high at the temperature of 350 °C and mainly ethane is produced.Graphical Abstract

Acid acting as redispersing agent to form stable colloids from photoactive crystalline aqueous sol–gel TiO2 powder

AbstractIn this work, the redispersion of three nanocrystalline TiO2 colloids is studied: one pure and two Fe-doped titania. These three colloids are produced by an easy aqueous sol–gel synthesis using precipitation-acidic peptization of Ti precursor. For the two Fe-doped TiO2, one is doped during synthesis (primary doping) and the other is doped after the synthesis (secondary doping). The initial colloids are composed of crystalline TiO2 particles around 7 nm with good photocatalytic properties, tested on PNP degradation under visible light (wavelength >390 nm). The powders obtained by air drying of these three colloids are redispersed in water to produce colloids, which are compared to the initial colloid produced. For each colloid, five cycles of drying redispersion are achieved. The colloids are characterized by dynamic light scattering, zeta potential measurements, inductively coupled plasma–atomic emission spectroscopy, X-ray diffraction, nitrogen adsorption–desorption measurements, Mössbauer spectroscopy, diffuse reflectance spectroscopy, and photocatalytic tests. The results show that similar products are obtained between the cycles, maintaining homologous properties of colloids. This property of redispersion is mainly due to the acid (HNO3, HCl, or H2SO4) which protonates the surface of the TiO2 nanoparticle leading to high-surface charges and electrostatic repulsions between aggregates. This property can be very useful for industrial applications of this synthesis, especially as it allows the volume and weight to be reduced for transportation and storage. Moreover, results show that the pure TiO2 powder can be doped during its redispersion step. The redispersion of the TiO2 developed here is possible without surface functionalization or multiple step processes, contrary to commercial Degussa P25. A 2-year stability study of all the produced colloids has been performed by following the evolution of the macroscopic aspect and the physicochemical properties of these sols. This study showed high stability of the produced colloids. HighlightsCrystalline TiO2 colloids synthesized by aqueous sol–gel method.Redispersion cycles of the TiO2 dried powder are studied.Physicochemical and photocatalytic properties are maintained through redispersion.Acid plays the main role as the redispersing agent of the crystalline powder.Redispersion allows reduction of the volume and weight for transportation and storage.