Papers by Stéphanie Lambert
Processes
This study presents the development of a method for the washcoating of Ni/boehmite gels, prepared... more This study presents the development of a method for the washcoating of Ni/boehmite gels, prepared by the sol–gel process, onto the surface of a commercial ceramic monolith. Indeed, a cordierite monolith in a honeycomb shape was used as the substrate for the Ni/Al2O3 deposition. An experimental assembly was made in order to apply the coating on the cordierite surface. Different suspensions were used with various viscosities, and multiple coating parameters were tested as the withdrawal speed, or the number of impregnations. It was observed that the simple deposition of the Ni/boehmite gel led to the formation of coating. Different morphologies were observed, and defects were highlighted as cracks, coating-free areas or aggregates. Among the various parameters studied, the pH of the sol appeared to play a role even more important than the viscosity. Indeed, the sol acidified with nitric acid showed a coating which was almost free of cracks or of large aggregates. Moreover, the use of ...
Catalysts
Since the beginning of the industrial era, various human activities have steadily increased, lead... more Since the beginning of the industrial era, various human activities have steadily increased, leading to rapid technological developments and high population growth [...]
Catalysts, 2022
Raw clays, extracted from Bana, west Cameroon, were modified with semiconductors (TiO2 and ZnO) i... more Raw clays, extracted from Bana, west Cameroon, were modified with semiconductors (TiO2 and ZnO) in order to improve their depollution properties with the addition of photocatalytic properties. Cu2+ ions were also added to the clay by ionic exchange to increase the specific surface area. This insertion of Cu was confirmed by ICP-AES. The presence of TiO2 and ZnO was confirmed by the detection of anatase and wurzite, respectively, using X-ray diffraction. The composite clays showed increased specific surface areas. The adsorption property of the raw clays was evaluated on two pollutants, i.e., fluorescein (FL) and p-nitrophenol (PNP). The experiments showed that the raw clays can adsorb FL but are not efficient for PNP. To demonstrate the photocatalytic property given by the added semiconductors, photocatalytic experiments were performed under UVA light on PNP. These experiments showed degradation up to 90% after 8 h of exposure with the best ZnO-modified clay. The proposed treatment ...
The objective of this work is to improve the efficiency of TiO2 photocatalysts by activation trea... more The objective of this work is to improve the efficiency of TiO2 photocatalysts by activation treatments and by modification with palladium nanoparticles and doping with SiO2. The influence of the additive loading was explored, and two activation treatments were performed: UV exposition and H2 reduction. TiO2/SiO2/Pd photocatalysts were synthesized by an original cogelation method: a modified silicon alkoxide, i.e., [3-(2-aminoethyl)aminopropyl]trimethoxysilane (EDAS), was used to complex the palladium ions, thanks to the ethylenediamine group, while the alkoxide groups reacted with TiO2 precursors. Pure TiO2 was also synthesized by the sol–gel process for comparison. X-ray diffraction evidenced that the crystallographic structure of TiO2 was anatase and that Pd was present, either in its oxidized form after calcination, or in its reduced form after reduction. The specific surface area of the samples varied from 5 to 145 m2 g-1. Transmission electron microscopy allowed us to observe ...
Catalysts, 2021
This work reviews an eco-friendly process for producing TiO2 via colloidal aqueous sol–gel synthe... more This work reviews an eco-friendly process for producing TiO2 via colloidal aqueous sol–gel synthesis, resulting in crystalline materials without a calcination step. Three types of colloidal aqueous TiO2 are reviewed: the as-synthesized type obtained directly after synthesis, without any specific treatment; the calcined, obtained after a subsequent calcination step; and the hydrothermal, obtained after a specific autoclave treatment. This eco-friendly process is based on the hydrolysis of a Ti precursor in excess of water, followed by the peptization of the precipitated TiO2. Compared to classical TiO2 synthesis, this method results in crystalline TiO2 nanoparticles without any thermal treatment and uses only small amounts of organic chemicals. Depending on the synthesis parameters, the three crystalline phases of TiO2 (anatase, brookite, and rutile) can be obtained. The morphology of the nanoparticles can also be tailored by the synthesis parameters. The most important parameter is ...
Molecules, 2021
Photocatalytic nanomaterials, using only light as the source of excitation, have been developed f... more Photocatalytic nanomaterials, using only light as the source of excitation, have been developed for the breakdown of volatile organic compounds (VOCs) in air for a long time. It is a tough challenge to immobilize these powder photocatalysts and prevent their entrainment with the gas stream. Conventional methods for making stable films typically require expensive deposition equipment and only allow the deposition of very thin layers with limited photocatalytic performance. The present work presents an alternative approach, using the combination of commercially available photocatalytic nanopowders and a polymer or inorganic sol–gel-based matrix. Analysis of the photocatalytic degradation of ethanol was studied for these layers on metallic substrates, proving a difference in photocatalytic activity for different types of stable layers. The sol–gel-based TiO2 layers showed an improved photocatalytic activity of the nanomaterials compared with the polymer TiO2 layers. In addition, the us...
Catalysts, 2020
An eco-friendly photocatalytic coating, active under a cost-effective near-visible LED system, wa... more An eco-friendly photocatalytic coating, active under a cost-effective near-visible LED system, was synthesized without any calcination step for the removal of organic pollutants. Three types of doping (Fe, N and Fe + N), with different dopant/Ti molar ratios, were investigated and compared with undoped TiO2 and the commercial P25 photocatalyst. Nano-crystalline anatase-brookite particles were successfully produced with the aqueous sol-gel process, also at a larger scale. All samples displayed a higher visible absorption and specific surface area than P25. Photoactivity of the catalyst powders was evaluated through the degradation of p-nitrophenol in water under visible light (>400 nm). As intended, all samples were more performant than P25. The N-doping, the Fe-doping and their combination promoted the activity under visible light. Films, coated on three different substrates, were then compared. Finally, the photoactivity of a film, produced from the optimal N-Fe co-doped colloid...
Nanomaterials, 2019
A screening study on seven photocatalysts was performed to identify the best candidate for pharma... more A screening study on seven photocatalysts was performed to identify the best candidate for pharmaceutical products degradation in water. Photocatalysts were deposited as thin films through a sol-gel process and subsequent dip-coating on glass slides. The efficiency of each photocatalyst was assessed through the degradation of methylene blue first, and then, through the degradation of 15 different pharmaceutical products. Two main types of synthesis methods were considered: aqueous syntheses, where the reaction takes place in water, and organic syntheses, where reactions take place in an organic solvent and only a stoichiometric amount of water is added to the reaction medium. Photocatalysts synthesized via aqueous sol-gel routes showed relatively lower degradation efficiencies; however, the organic route required a calcination step at high temperature to form the photoactive crystalline phase, while the aqueous route did not. The best performances for the degradation of pharmaceutic...
Materials (Basel, Switzerland), Jan 10, 2018
In this paper, TiO₂ prepared with an aqueous sol-gel synthesis by peptization process is doped wi... more 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. 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 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 -nitrophenol show a marked improvement for all doped catalysts under visibl...
Environnement, Ingénierie & Développement, 2015
In this work, the effect of iron oxide particles Fe2O3 and iron nanoparticles encapsulated in a p... more In this work, the effect of iron oxide particles Fe2O3 and iron nanoparticles encapsulated in a porous silica matrix (xerogel Fe/SiO2) was investigated on biphenyl biodegradation by the strain Rhodococcus erythropolis T902.1. After 18 days of incubation biodegradation yields of 75% and 85% were achieved respectively in presence of non-autoclaved or autoclaved xerogel Fe/SiO2at 10-5 M iron. These results are 42 and 60% higher than in standard conditions without nanoparticles. They suggest that the autoclave procedure lead to the release of some iron less anchored in the silica matrix. This study highlights that siderophore production byRhodococcus erythropolis T902.1 would be related to the presence of iron nanoparticles in the culture. It suggests that the production of these strong chelating compounds decreases with increase of iron release from xerogel Fe/SiO2. Moreover, most of the surfactants synthesized by Rhodococcus erythropolis T902.1 which are glycolipids containing trehalo...
Decrease of degradation efficiency with time Due to polymers deposition on biocatalysts Challenge... more Decrease of degradation efficiency with time Due to polymers deposition on biocatalysts Challenge: Understanding the polymerization kinetics Experiments & modelisation Reduction of polymer formation to enhance the performance of the reactor PEMFC are promising candidates for applications in mobile devices and transportations Nanostructured carbons : improve the mass transport in catalytic layers Objective: elaboration of catalytic layers based on carbon xerogels : Synthesis and grinding of carbon xerogels Coatings and characterizations
Crystallized pure SnO 2 powders were prepared by the sol-gel process, and were used as photocatal... more Crystallized pure SnO 2 powders were prepared by the sol-gel process, and were used as photocatalyst for the degradation of phenol under UV light at pH 6.5 and a temperature of 20 C. The physical properties of photocatalyst were characterized by X-ray di raction, Scanning Electron Microscopy, nitrogen adsorption-desorption and Ultravioletvisible di use re ectance spectroscopy. The in uences of di erent operating variables, such as the pH, the photocatalyst loading, and the initial concentration of phenol, were studied to improve the e ciency of phenol degradation.
The catalytic layers used in Proton exchange membrane fuel cell (PEMFC) are classically based on ... more The catalytic layers used in Proton exchange membrane fuel cell (PEMFC) are classically based on Pt particles supported on carbon black (Pt/C). The structure of these catalytic layer is however not optimal, resulting in incomplete utilization of the mass of Pt loaded onto the carbon support [1]. In order to reduce the cost of the catalytic layer without decreasing its performance, two parameters can be improved: the support and the synthesis of the Pt particles. With respect to the support, commonly used carbon blacks do not display optimal properties for electrocatalysis: they may contain high amount of chemical impurities, and the final structure of the electrodes is hardly tuneable [2]. A possible solution to these drawbacks is to use synthetic nanostructured materials with a controllable, reproducible texture and with a pure, known and constant chemical composition; carbon xerogels exhibit such properties [3]. With respect to the synthesis of the Pt particles, highly dispersed Pt/carbon xerogel catalysts can be prepared by the Strong Electrostatic Adsorption (SEA) method [4, 5]. This technique consists in impregnating the support, e.g. carbon xerogel, with a solution of metal precursor, e.g. hexachloroplatinic acid (H2PtCl6), under pH control (2.4-2.5 for the impregnation of carbon xerogels by hexachloroplatinic acid [6]). After impregnation by the precursor, the impregnated support is dried and submitted to reduction treatment under H 2 flow. The impregnation-reduction step was repeated up to five times to increase the Pt loading. The five resulting catalysts were then characterized by physicochemical and electrochemical methods.
Synthesis, 2004
The synthesis of a new series of trimethoxysilyl-tethered N-substituted 3,5-dialkylpyrazolylpyrid... more The synthesis of a new series of trimethoxysilyl-tethered N-substituted 3,5-dialkylpyrazolylpyridines is reported. The silyl spacers allow the grafting of ligands onto silica via formation of covalent bonds as well as the synthesis of xerogels.
Chemical Engineering Journal, 2012
TiO 2 thin films have been produced by a dip-coating process using a non-aqueous sol-gel method. ... more TiO 2 thin films have been produced by a dip-coating process using a non-aqueous sol-gel method. This study investigated the influence of the operating variables such as nature of the substrate, sol concentration, withdrawing speed of the dip-coater and number of layers on the physico-chemical properties of the films using XRD, GIXRD, UV-Vis spectroscopy, profilometry, spectroscopic ellipsometry and SEM. Photocatalytic activity of the films was
Bioresource Technology, 2013
This paper investigated the enhancement effect of nanometre-sized metallic (Pd, Ag and Cu) or met... more This paper investigated the enhancement effect of nanometre-sized metallic (Pd, Ag and Cu) or metallic oxide (Fe x O y) nanoparticles on fermentative hydrogen production from glucose by a Clostridium butyricum strain. These nanoparticles (NP) of about 2-3 nm were encapsulated in porous silica (SiO 2) and were added at very low concentration (10-6 mol•L-1) in batch hydrogen production test. The cultures containing iron oxide NP produced 38% more hydrogen with a higher maximum H 2 production rate (HPR) of 58% than those without NP or with silica particles only. The iron oxide NP were used in a 2.5 L sequencing-batch reactor and showed no significant effect on the yields (established at 2.2 mol hydrogen •mol glucose-1) but an improvement of the HPR (+ 113%, reaching a maximum HPR of 86 mL hydrogen •L-1 •h-1). These results suggest an improvement of the electron transfers trough some combinations between enzymatic activity and inorganic materials.
The design of efficient catalytic layers of proton exchange membrane fuel cells (PEMFCs) requires... more The design of efficient catalytic layers of proton exchange membrane fuel cells (PEMFCs) requires the preparation of highly-loaded and highly-dispersed Pt/C catalysts. During the last few years, our work focused on the preparation of Pt/carbon xerogel electrocatalysts, starting from simple impregnation techniques that were further optimized via the strong electrostatic adsorption (SEA) method to reach high dispersion and a high metal weight fraction. The SEA method, which consists of the optimization of the precursor/support electrostatic impregnation through an adequate choice of the impregnation pH with regard to the support surface chemistry, leads to very well-dispersed Pt/C samples with a maximum 8 wt.% Pt after drying and reduction under H2. To increase the metal loading, the impregnation-drying-reduction cycle of the SEA method can be repeated several times, either with fresh Pt precursor solution or with the solution recycled from the previous cycle. In each case, a high dispersion (Pt particle size ~3 nm) is obtained. Finally, the procedure can be simplified by combination of the SEA technique with dry impregnation, leading to no Pt loss during the procedure.
We study algebraic dynamical systems (and, more generally, σvarieties) Φ : A n C → A n C given by... more We study algebraic dynamical systems (and, more generally, σvarieties) Φ : A n C → A n C given by coordinatewise univariate polynomials, Φ(x 1 ,. .. , xn) = (f 1 (x 1),. .. , fn(xn)) by refining an old theorem of Ritt on compositional identities amongst polynomials. Our main result is an explicit description of the skew-invariant varieties, that is, those algebraic varieties X ⊆ A n C for which there is a field automorphism σ : C → C with Φ(X) = X σ. As consequences, we deduce a variant of a conjecture of Zhang on the existence of rational points with Zariski dense forward orbits and a strong form of the dynamical Manin-Mumford conjecture for liftings of the Frobenius. We also show that in models of ACFA 0 , a trivial set defined by σ(x) = f (x) for f a polynomial has Morley rank 1 and is usually strongly minimal, that the induced structure on this set is ℵ 0-categorical unless f is defined over a fixed field of a power of σ, and that nonorthogonality between two such sets is definable in families if f is defined over a fixed field of a power of σ.
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Papers by Stéphanie Lambert