Samuel Ahoulou - Academia.edu (original) (raw)
Papers by Samuel Ahoulou
Nanomaterials
This paper shows the possibility to detect the presence of grafted molecules on the surface of si... more This paper shows the possibility to detect the presence of grafted molecules on the surface of silicon nanowires with a wireless RF radar approach based on the measurement of the backscattered signal of a resonant structure on which the nanowires are deposited. The measured resonance frequency allows the determination of the intrinsic properties related to temperature and humidity variations, which can be related to the presence of the grafted molecules. Several functionalizations of nanowires have been realized and characterized. For the first time, an RF approach is used to detect significant differences related to the presence of grafted molecules on the surface of nanowires. In addition to detecting their presence, the obtained results show the potential of the radar approach to identify the type of functionalization of nanowires. A set of six different grafted molecules (including octadecyltrichlorosilane, ethynylpyrene, N3) was tested and correctly separated with the proposed ...
Ce travail de thèse porte sur la mise en forme et la caractérisation de complexes à transition de... more Ce travail de thèse porte sur la mise en forme et la caractérisation de complexes à transition de spin immobilisés dans des films minces de silice mésoporeuse, ordonnés et orientés perpendiculairement à l’électrode. De tels films sont obtenus par la méthode d’auto-assemblage assistée électrochimiquement (EASA). L’objectif principal de cette thèse est d’élaborer des nanocomposites à base de silice, dans laquelle des complexes de coordination sont confinés, qui soient à la fois redox et photo actifs c’est à dire dont les propriétés peuvent être contrôlées soit par la lumière, soit par application d’un potentiel. Pour atteindre cet objectif, nous avons suivi différentes approches de confinement à savoir l’encapsulation dite « one pot », l’imprégnation dans les films de silice préformés (non modifiés ou fonctionnalisés par des groupements sulfonate), et enfin en combinant la chimie click à la méthode EASA. Comme prototypes, nous avons utilisé le complexe [Fe(Htrz)3]2+, qui est un polymè...
Molecules
Iron (II) tris(2,2′-bipyridine) complexes, [Fe(bpy)3]2+, have been synthesized and immobilized in... more Iron (II) tris(2,2′-bipyridine) complexes, [Fe(bpy)3]2+, have been synthesized and immobilized in organosulfonate-functionalized nanostructured silica thin films taking advantage of the stabilization of [Fe(H2O)6]2+ species by hydrogen bonds to the anionic sulfonate moieties grafted to the silica nanopores. In a first step, thiol-based silica films have been electrochemically generated on indium tin oxide (ITO) substrates by co-condensation of 3-mercaptopropyltrimethoxysilane (MPTMS) and tetraethoxysilane (TEOS). Secondly, the thiol function has been modified to sulfonate by chemical oxidation using hydrogen peroxide in acidic medium as an oxidizing agent. The immobilization of [Fe(bpy)3]2+ complexes has been performed in situ in two consecutive steps: (i) impregnation of the sulfonate functionalized silica films in an aqueous solution of iron (II) sulfate heptahydrate; (ii) dipping of the iron-containing mesostructures in a solution of bipyridine ligands in acetonitrile. The in sit...
Ce travail de these porte sur la mise en forme et la caracterisation de complexes a transition de... more Ce travail de these porte sur la mise en forme et la caracterisation de complexes a transition de spin immobilises dans des films minces de silice mesoporeuse, ordonnes et orientes perpendiculairement a l’electrode. De tels films sont obtenus par la methode d’auto-assemblage assistee electrochimiquement (EASA). L’objectif principal de cette these est d’elaborer des nanocomposites a base de silice, dans laquelle des complexes de coordination sont confines, qui soient a la fois redox et photo actifs c’est a dire dont les proprietes peuvent etre controlees soit par la lumiere, soit par application d’un potentiel. Pour atteindre cet objectif, nous avons suivi differentes approches de confinement a savoir l’encapsulation dite « one pot », l’impregnation dans les films de silice preformes (non modifies ou fonctionnalises par des groupements sulfonate), et enfin en combinant la chimie click a la methode EASA. Comme prototypes, nous avons utilise le complexe [Fe(Htrz)3]2+, qui est un polyme...
ChemPhysChem, 2021
Supporting information for this article is given via a link at the end of the document.
Electroanalysis, 2019
Mesoporous silica thin films encapsulating a molecular iron-triazole complex, Fe(Htrz)3 (Htrz = 1... more Mesoporous silica thin films encapsulating a molecular iron-triazole complex, Fe(Htrz)3 (Htrz = 1,2,4,-1H-triazole), have been generated by electrochemically assisted self-assembly (EASA) on indium-tin oxide (ITO) electrode. The obtained modified electrodes are characterized by well-defined voltammetric signals corresponding to the Fe II/III centers of the Fe(Htrz)3 species immobilized into the films, indicating fast electron transfer processes and stable operational stability. This is due to the presence of a high density of redox probes in the material (1.610-4 mol g-1 Fe(Htrz)3 in the mesoporous silica film) enabling efficient charge transport by electron hopping. The mesoporous films are uniformly deposited over the whole electrode surface and they are characterized by a thickness of 110 nm and a wormlike mesostructure directed by the template role played by Fe(Htrz)3 species in the EASA process. These species are durably immobilized in the material (they are not removed by solvent extraction). The composite mesoporous material (denoted Fe(Htrz)3@SiO2) is then used for the electrocatalytic detection of hydrogen peroxide, which can be performed by amperometry at an applied potential of-0.4 V versus Ag/AgCl and by flow injection analysis. The organic-inorganic hybrid film electrode displays good sensitivity for H2O2 sensing over a dynamic range from 5 to 300 μM, with a detection limit estimated at 2 μM.
Chemistry of Materials, 2019
While attempting to confine Fe(Htrz)3 (Htrz = 1,2,4,-1H-triazole) into a mesoporous silica matrix... more While attempting to confine Fe(Htrz)3 (Htrz = 1,2,4,-1H-triazole) into a mesoporous silica matrix during its formation by electrochemically assisted self-assembly (EASA), we have discovered that such spin crossover complex is likely to act as the template (in place of the surfactant species) to form in one step a composite mesoporous material (Fe(Htrz)3@SiO2). The EASA method usually leads to the vertical growth of mesoporous silica thin films owing to the electro-induced condensation of silica precursors (i.e., tetraethoxysilane, TEOS) around tubular micelles (i.e., made of cetyltrimethylammonium bromide, CTAB) oriented orthogonally to the underlying support. In the presence of Fe(Htrz)3 in the starting sol (in addition to TEOS and CTAB), two distinct situations can be reached. At low Fe(Htrz)3 concentration (≤ 3 mM), the vertically aligned mesostructure is formed and Fe(Htrz)3 complexes are incorporated along with the surfactant phase, but most of them are released upon surfactant removal. At high Fe(Htrz)3 concentration (typically 5 mM), a wormlike mesoporous film is obtained in which Fe(Htrz)3 species act as a real template for the formation of a mesoporous Fe(Htrz)3@SiO2 film. Interestingly, the iron-triazole 2 complex is strongly entrapped in the silica matrix as it cannot be removed by solvent extraction (contrary to CTAB), as evidenced from X-ray photoelectron spectroscopy (XPS). Even more attractive are the electrochemical properties of the composite Fe(Htrz)3@SiO2 material, exhibiting highly stable operational stability (i.e., identical voltammetric signals upon multiple successive measurements), contrary to Fe(Htrz)3 species incorporated by impregnation of the surfactant phase which are found to leach out in solution upon use. Such in situ elaborated mesoporous composite made of Fe(Htrz)3 template strongly immobilized in a silica host is thus promising for bridging the gap between soft and hard functional organic-inorganic materials, which is briefly illustrated here for the mediated detection of hydrogen peroxide thanks to the electrocatalytic properties of the Fe(Htrz)3 complex, which are maintained even when immobilized in the composite Fe(Htrz)3@SiO2 film.
Nanomaterials, 2021
Silicon nanowires are attractive materials from the point of view of their electrical properties ... more Silicon nanowires are attractive materials from the point of view of their electrical properties or high surface-to-volume ratio, which makes them interesting for sensing applications. However, they can achieve a better performance by adjusting their surface properties with organic/inorganic compounds. This review gives an overview of the main techniques used to modify silicon nanowire surfaces as well as characterization techniques. A comparison was performed with the functionalization method developed, and some applications of modified silicon nanowires and their advantages on those non-modified are subsequently presented. In the final words, the future opportunities of functionalized silicon nanowires for chipless tag radio frequency identification (RFID) have been depicted.
Nanomaterials
This paper shows the possibility to detect the presence of grafted molecules on the surface of si... more This paper shows the possibility to detect the presence of grafted molecules on the surface of silicon nanowires with a wireless RF radar approach based on the measurement of the backscattered signal of a resonant structure on which the nanowires are deposited. The measured resonance frequency allows the determination of the intrinsic properties related to temperature and humidity variations, which can be related to the presence of the grafted molecules. Several functionalizations of nanowires have been realized and characterized. For the first time, an RF approach is used to detect significant differences related to the presence of grafted molecules on the surface of nanowires. In addition to detecting their presence, the obtained results show the potential of the radar approach to identify the type of functionalization of nanowires. A set of six different grafted molecules (including octadecyltrichlorosilane, ethynylpyrene, N3) was tested and correctly separated with the proposed ...
Ce travail de thèse porte sur la mise en forme et la caractérisation de complexes à transition de... more Ce travail de thèse porte sur la mise en forme et la caractérisation de complexes à transition de spin immobilisés dans des films minces de silice mésoporeuse, ordonnés et orientés perpendiculairement à l’électrode. De tels films sont obtenus par la méthode d’auto-assemblage assistée électrochimiquement (EASA). L’objectif principal de cette thèse est d’élaborer des nanocomposites à base de silice, dans laquelle des complexes de coordination sont confinés, qui soient à la fois redox et photo actifs c’est à dire dont les propriétés peuvent être contrôlées soit par la lumière, soit par application d’un potentiel. Pour atteindre cet objectif, nous avons suivi différentes approches de confinement à savoir l’encapsulation dite « one pot », l’imprégnation dans les films de silice préformés (non modifiés ou fonctionnalisés par des groupements sulfonate), et enfin en combinant la chimie click à la méthode EASA. Comme prototypes, nous avons utilisé le complexe [Fe(Htrz)3]2+, qui est un polymè...
Molecules
Iron (II) tris(2,2′-bipyridine) complexes, [Fe(bpy)3]2+, have been synthesized and immobilized in... more Iron (II) tris(2,2′-bipyridine) complexes, [Fe(bpy)3]2+, have been synthesized and immobilized in organosulfonate-functionalized nanostructured silica thin films taking advantage of the stabilization of [Fe(H2O)6]2+ species by hydrogen bonds to the anionic sulfonate moieties grafted to the silica nanopores. In a first step, thiol-based silica films have been electrochemically generated on indium tin oxide (ITO) substrates by co-condensation of 3-mercaptopropyltrimethoxysilane (MPTMS) and tetraethoxysilane (TEOS). Secondly, the thiol function has been modified to sulfonate by chemical oxidation using hydrogen peroxide in acidic medium as an oxidizing agent. The immobilization of [Fe(bpy)3]2+ complexes has been performed in situ in two consecutive steps: (i) impregnation of the sulfonate functionalized silica films in an aqueous solution of iron (II) sulfate heptahydrate; (ii) dipping of the iron-containing mesostructures in a solution of bipyridine ligands in acetonitrile. The in sit...
Ce travail de these porte sur la mise en forme et la caracterisation de complexes a transition de... more Ce travail de these porte sur la mise en forme et la caracterisation de complexes a transition de spin immobilises dans des films minces de silice mesoporeuse, ordonnes et orientes perpendiculairement a l’electrode. De tels films sont obtenus par la methode d’auto-assemblage assistee electrochimiquement (EASA). L’objectif principal de cette these est d’elaborer des nanocomposites a base de silice, dans laquelle des complexes de coordination sont confines, qui soient a la fois redox et photo actifs c’est a dire dont les proprietes peuvent etre controlees soit par la lumiere, soit par application d’un potentiel. Pour atteindre cet objectif, nous avons suivi differentes approches de confinement a savoir l’encapsulation dite « one pot », l’impregnation dans les films de silice preformes (non modifies ou fonctionnalises par des groupements sulfonate), et enfin en combinant la chimie click a la methode EASA. Comme prototypes, nous avons utilise le complexe [Fe(Htrz)3]2+, qui est un polyme...
ChemPhysChem, 2021
Supporting information for this article is given via a link at the end of the document.
Electroanalysis, 2019
Mesoporous silica thin films encapsulating a molecular iron-triazole complex, Fe(Htrz)3 (Htrz = 1... more Mesoporous silica thin films encapsulating a molecular iron-triazole complex, Fe(Htrz)3 (Htrz = 1,2,4,-1H-triazole), have been generated by electrochemically assisted self-assembly (EASA) on indium-tin oxide (ITO) electrode. The obtained modified electrodes are characterized by well-defined voltammetric signals corresponding to the Fe II/III centers of the Fe(Htrz)3 species immobilized into the films, indicating fast electron transfer processes and stable operational stability. This is due to the presence of a high density of redox probes in the material (1.610-4 mol g-1 Fe(Htrz)3 in the mesoporous silica film) enabling efficient charge transport by electron hopping. The mesoporous films are uniformly deposited over the whole electrode surface and they are characterized by a thickness of 110 nm and a wormlike mesostructure directed by the template role played by Fe(Htrz)3 species in the EASA process. These species are durably immobilized in the material (they are not removed by solvent extraction). The composite mesoporous material (denoted Fe(Htrz)3@SiO2) is then used for the electrocatalytic detection of hydrogen peroxide, which can be performed by amperometry at an applied potential of-0.4 V versus Ag/AgCl and by flow injection analysis. The organic-inorganic hybrid film electrode displays good sensitivity for H2O2 sensing over a dynamic range from 5 to 300 μM, with a detection limit estimated at 2 μM.
Chemistry of Materials, 2019
While attempting to confine Fe(Htrz)3 (Htrz = 1,2,4,-1H-triazole) into a mesoporous silica matrix... more While attempting to confine Fe(Htrz)3 (Htrz = 1,2,4,-1H-triazole) into a mesoporous silica matrix during its formation by electrochemically assisted self-assembly (EASA), we have discovered that such spin crossover complex is likely to act as the template (in place of the surfactant species) to form in one step a composite mesoporous material (Fe(Htrz)3@SiO2). The EASA method usually leads to the vertical growth of mesoporous silica thin films owing to the electro-induced condensation of silica precursors (i.e., tetraethoxysilane, TEOS) around tubular micelles (i.e., made of cetyltrimethylammonium bromide, CTAB) oriented orthogonally to the underlying support. In the presence of Fe(Htrz)3 in the starting sol (in addition to TEOS and CTAB), two distinct situations can be reached. At low Fe(Htrz)3 concentration (≤ 3 mM), the vertically aligned mesostructure is formed and Fe(Htrz)3 complexes are incorporated along with the surfactant phase, but most of them are released upon surfactant removal. At high Fe(Htrz)3 concentration (typically 5 mM), a wormlike mesoporous film is obtained in which Fe(Htrz)3 species act as a real template for the formation of a mesoporous Fe(Htrz)3@SiO2 film. Interestingly, the iron-triazole 2 complex is strongly entrapped in the silica matrix as it cannot be removed by solvent extraction (contrary to CTAB), as evidenced from X-ray photoelectron spectroscopy (XPS). Even more attractive are the electrochemical properties of the composite Fe(Htrz)3@SiO2 material, exhibiting highly stable operational stability (i.e., identical voltammetric signals upon multiple successive measurements), contrary to Fe(Htrz)3 species incorporated by impregnation of the surfactant phase which are found to leach out in solution upon use. Such in situ elaborated mesoporous composite made of Fe(Htrz)3 template strongly immobilized in a silica host is thus promising for bridging the gap between soft and hard functional organic-inorganic materials, which is briefly illustrated here for the mediated detection of hydrogen peroxide thanks to the electrocatalytic properties of the Fe(Htrz)3 complex, which are maintained even when immobilized in the composite Fe(Htrz)3@SiO2 film.
Nanomaterials, 2021
Silicon nanowires are attractive materials from the point of view of their electrical properties ... more Silicon nanowires are attractive materials from the point of view of their electrical properties or high surface-to-volume ratio, which makes them interesting for sensing applications. However, they can achieve a better performance by adjusting their surface properties with organic/inorganic compounds. This review gives an overview of the main techniques used to modify silicon nanowire surfaces as well as characterization techniques. A comparison was performed with the functionalization method developed, and some applications of modified silicon nanowires and their advantages on those non-modified are subsequently presented. In the final words, the future opportunities of functionalized silicon nanowires for chipless tag radio frequency identification (RFID) have been depicted.