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The study deals with the catalytic cyclocarbonation of epoxides to produce monomers used in the synthesis of polyurethane. A benchmark study of the textural properties of silica-based, doped or not, supports enabling the identification and optimization of the key parameters affecting the catalytic activity is reported. The results reveal that ammonium catalysts immobilized onto mesostructured supports with high surface area and low aggregation show better catalytic performances than analogue catalysts grafted onto microstuctured ones. While a high external surface area favours the grafting of ammonium salt, pore size must be large enough to enhance the accessibility of both carbon dioxide and epoxides to the catalytic sites. The activity of heterogeneous catalysts was evaluated for a model coupling reaction between carbon dioxide and propylene glycol diglycidylether. Using appropriated supports, cyclocarbonation yields are found to be higher in the presence of the heterogeneous catalyst in comparison with the homogeneous one. These results allow to confirm the beneficial effect of the presence of residual OH silanol groups at the surface of the support, which activate epoxide through forming of hydrogen bonds.

Different types of heterogeneous catalysts designed for a cyclocarbonation reaction between an epoxidized source and CO2 under supercritical conditions have been synthesized. The process implied a quaternization step where a (haloalkyl)trimethoxysilane reacted with tributylamine leading to a tributyl(trimethoxysilylalkyl)ammonium halide, with iodine and bromine as halogens. Then, a grafting step onto commercial fumed silica through condensation reaction between the silane part and Si OH surficial groups provided the immobilized catalyst. The efficiency of grafting has been validated by liquid 1H NMR, solid 29Si NMR and TG-DSC-MS analyzes. The benchmark cyclocarbonation reaction of polyethylene glycol diglycidylether at 80 °C and 100 bar during 4 h showed that the best immobilized catalyst was tributylpropylammonium iodide (IC3Q-EH5). It has also been shown that immobilization provided -surprisingly!- better conversions than the corresponding homogeneous catalyst’s: this phenomenon has been explained through an epoxide-ring-opening activating effect thanks to Si−OH surficial groups. Furthermore, kinetic studies performed by in situ Raman spectroscopy on IC3Q-EH5 showed that temperature had a strong influence on the yield of the reaction while CO2 pressure had only a small effect. Recycling of the catalyst has also been considered, but no precise conclusions could be conducted because of the high catalyst dispersion. Finally, the addition of a fluorinated alcohol co-catalyst allowed obtaining a similar yield but at 80 °C and 55 bar during only 2,5 h with the best candidate.

Zinc was coupled with titanium dioxide using different methods. SiO2 and Zn-SiO2 doped TiO2 films, on the one hand, and Zn doped TiO2 on the other hand, have been produced using controlled sol-gel processes by alcoholic, cogelation and aqueous ways. From these syntheses, films were deposited on soda lime glass. These samples were compared to ZnO samples but also to bilayer samples constituting one layer of TiO2 and one layer of ZnO. The physico-chemical properties of the films were characterized by grazing-incidence X-ray diffraction, profilometry and UV–vis absorption analyses. The photocatalytic activity has been evaluated from the degradation of methylene blue under UV-A light, from the degradation of p-nitrophenol under visible light and from the degradation of H2O2 under halogen light (UV-A + visible light). Superhydrophilicity was evaluated from contact angle measurement after UV exposition and also from hysteresis effects. Finally, a haze measurement was performed to evaluate the impact of the coating on the aesthetic property of the coated glass. Aqueous films have better photocatalytic activity and superhydrophilicity than samples from alcoholic synthesis. The crystallization of the sample appears to be one key factor: alcoholic films required calcination to ensure the crystallization of TiO2, but the alkali migration from the glass support prevents this crystallization, while aqueous synthesis promotes crystallized particles at low temperatures without alkali interference. It appears that the relative activity from one sample to another depends on the nature of the illumination and on the nature of the molecule to be degraded. Nevertheless, the sample with ZnO layer deposited on first TiO2 layer (ZnO 500 Alc/TiO2 100 AQ) composite is found to be the best sample, maintaining a high hydrophilicity similar to TiO2 and a good activity.

An aqueous sol-gel process, previously developed for producing undoped and Cu2+, Ni2+, Zn2+ or Pb2+ doped TiO2 photocatalysts with remarkably high photocatalytic activity without requiring any calcination step, has been adapted to produce Fe3+, Cr3+, La3+ or Eu3+ single-doped TiO2 photocatalysts as well as La3+-Fe3+ and Eu3+-Fe3+ co-doped TiO2 catalysts. The physicochemical properties of the obtained catalysts have been characterized using a suite of complementary techniques, including ICP-AES, XRD, UV-Vis spectroscopy, nitrogen adsorption-desorption and Fe-57 M ssbauer. The active crystalline phase is obtained without requiring any calcination step and all the different catalysts are composed of nanocrystallites of anatase with a size of 6-7 nm and a high specific surface area varying from 181 to 298 m2 g-1. In this study, the effect of the NO3:Ti(IV) mole ratio used to induce the peptisation reaction during the synthesis has been studied and the results revealed that this ratio can influence significantly the textural properties of the resulting catalyst. A screening of the photocatalytic activity of the undoped and Fe3+, Cr3+, La3+ or Eu3+ single-doped and co-doped photocatalysts has been performed by evaluating the degradation of 4-nitrophenol under UV-Visible light (330 nm < < 800 nm). This study suggests that the photocatalyticmore » activity is significantly influenced by the dopant nature and content with an optimal dopant content being observed in the case of Fe3+ or La3+ single-doped as well as in the case of La3+-Fe3+ and Eu3+-Fe3+ co-doped catalysts. In the case of Cr3+ single-doped catalysts, a detrimental effect of the dopant on the photocatalytic degradation of 4-nitrophenol has been observed while no significant influence of the dopant has been detected in the case of Eu3+ single-doped catalysts. In conclusion, the role of the different dopants in modulating the photocatalytic activity is discussed.« less

In this paper, an easy aqueous sol-gel synthesis developed previously by Mahy et al. [1] is adapted to produce highly active TiO2 catalysts doped with Fe3+, Ag+, Cu2+, Zn2+, Cr3+, Al3+, Mn2+, and Co2+ ions and Pt metallic nanoparticles. Samples are characterized by inductively coupled plasma–atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), Mossbauer spectroscopy, transmission electron microscopy (TEM), nitrogen adsorption–desorption measurements and diffuse reflectance spectroscopy measurements. Results show that the samples are composed of anatase-brookite TiO2 nanoparticles with a spherical shape and mean diameter of around 5–8 nm and a surface area of between about 150 − 250 m2 g−1. In each doped sample, the dopant is present in the form added during the synthesis, given that the sample has not undergone any particular treatment. Photoactivity tests show improvement in catalyst activity for Fe3+, Ag+, Cu2+, Zn2+, and Al3+ ion and Pt metallic nanoparticle dopants, while a decrease of activity is obtained for Cr3+, Mn2+ and Co2+ ion dopants. For some dopants, the activity of TiO2 doped with metallic ions and synthesized from the aqueous sol-gel process is equal or superior to the activity of the commercial photocatalyst Degussa P25. Some mechanisms are proposed to explain these modifications of activity with doping. Furthermore, cost comparison at laboratory scale showed that Zn and Cu nitrate salt dopings are clearly less expensive for a halogen light (UV/visible) or low energy light enhanced catalyst and may be considered for industrial applications. Using this method, a large scale Zn-doped TiO2 photocatalyst is synthesized with properties homologous to the lab-scale product. Results show that the aqueous sol-gel synthesis developed previously can be easily adapted for doping in order to produce an up-scalable synthesis.

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.

SiO2 and Ag–SiO2 doped TiO2 films and powders have been produced using a controlled sol–gel process. The dopant has been introduced using an alkoxysilane-functionalized ligand, with or without complexed silver ions. The influence of dopants on physico-chemical properties of the catalysts is studied by XRD, TEM–EDX, DRUV–vis analyses in the case of powders, while GIXRD, XPS, profilometry, UV–vis absorption analyses have been used for thin films. The photocatalytic activity has been evaluated from the degradation of methylene blue under UV-A light in the presence of the different catalysts over a period of 24 h. The detailed comparison between powders and films highlights a surprising positive effect in the case of films due to the presence of the substrate. In the case of photocatalytic powders, the presence of SiO2 or Ag–SiO2 into the TiO2 matrix has a detrimental effect on the photocatalytic activity while the opposite tendency is observed in the case of films, with best activities obtained with Ag–SiO2 doping. Different factors, in particular crystallinity modification between powders and films, have been studied to explain these opposite behaviors. In the case of powders, crystallization is hindered by SiO2 and Ag particles incorporation into the TiO2 matrix, leading to a decrease of the photocatalytic activity. In the case of thin films, probably because of the presence of a substrate, crystallization is not influenced by the presence of SiO2 and Ag particles. Therefore, the latter ones can fully play their role of electron traps leading to an enhanced photocatalytic activity.

Pure and multiwall carbon nanotube (MWCNT)-doped titanium dioxide (TiO2) films, synthesised from two sol–gel routes (alcoholic and aqueous) and deposited by dip-coating on glass, have been developed as conductive, photocatalytic and superhydrophilic materials. While already crystallised in anatase structure at low temperature when synthesised in water, samples prepared in alcohol are amorphous. Their crystallisation in air has been studied at increasing temperatures. Effective incorporation of functionalised MWCNTs is confirmed in both aqueous and alcoholic samples with a closer interaction with TiO2 particles in the case of aqueous synthesis. In alcoholic samples, 400 °C seems to be an optimised calcination temperature since 300 °C does not allow crystallisation into anatase and 500 °C removes MWCNTs through burning. The purpose of MWCNT doping is to obtain coatings that exhibit easy-to-clean or self-cleaning properties. This can be achieved through an optimised combination of electrical conductivity (for antistatic property), photoactivity and superhydrophilicity. These three properties require the crystallisation of TiO2 into anatase. MWCNT doping dramatically increases both conductivity and photocatalytic activity, especially in alcoholic samples for the former and in aqueous samples for the latter. On the other hand, MWCNT introduction does not significantly affect the (super)hydrophilicity of films, which depends solely on the crystallinity of TiO2.

TiO2 films with MWCNTs are produced for anticorrosive applications to increase the lifetime of steel materials. TiO2 has two additional properties, photoactivity and superhydrophilicity. Two TiO2 samples, synthesized in aqueous or alcoholic media, have been doped with MWCNTs. The material which best combines anticorrosive, superhydrophilic and photocatalytic properties, is the one produced in aqueous medium (Aq-TiO2-CNT). Doping with MWCNTs increases the photodegradation of p-nitrophenol from 18% to 50%. MWCNTs allow to reduce the corrosion current and the corrosion potential. The good superhydrophilicity of TiO2 is kept on stainless steel with a contact angle after illumination around 5°.