66 research outputs found
Intrinsic photoanode band engineering: enhanced solar water splitting efficiency mediated by surface segregation in Ti-doped hematite nanorods
Band engineering is thoroughly employed nowadays targeting technologically
scalable photoanodes for solar water splitting applications. Most often complex
and costly recipes are necessary, for average performances. Here we report very
simple photoanode growth and thermal annealing, with effective band engineering
results. Strongly enhanced photocurrent, of more than 200 %, is measured for
Ti-doped hematite nanorods grown from aqueous solutions and annealed under
Nitrogen atmosphere, compared to air annealed ones. Oxidized surface states and
increased density of charge carriers are found responsible for the enhanced
photoelectrochemical activity, as shown by electrochemical impedance
spectroscopy and synchrotron X-rays spectromicroscopies. They are found related
to oxygen vacancies, acting as n-dopants, and the formation of pseudo- brookite
clusters by surface Ti segregation. Spectro-ptychography is used for the first
time at Ti L3 absorption edge to isolate Ti chemical coordination arising from
pseudo-brookite clusters contribution. Correlated with electron microscopy
investigation and Density Functional Theory (DFT) calculations, our data
unambiguously prove the origin of the enhanced photoelectrochemical activity of
N2-annealed Ti-doped hematite nanorods. Finally, we present here a handy and
cheap surface engineering method beyond the known oxygen vacancy doping,
allowing a net gain in the photoelectrochemical activity for the hematite-based
photoanodes.Comment: 2 parts: first main manuscript with 39 pages, second supplementary
informations with 14 page
Spin State As a Probe of Vesicle Self-Assembly
International audienceA novel system of paramagnetic vesicles was designed using ion pairs of iron-containing surfactants. Unilamellar vesicles (diameter approximate to 200 nm) formed spontaneously and were characterized by cryogenic transmission electron microscopy, nanoparticle tracking, analysis, and light and small-angle neutron scattering. Moreover, for the first time, it is shown that magnetization measurements can be used to investigate self-assembly of such functionalized systems, giving information on the vesicle compositions and distribution Of surfactants between the bilayers and the aqueous bulk
A compact photoreactor for automated H2 photoproduction: Revisiting the (Pd, Pt, Au)/TiO2 (P25) Schottky junctions
The configuration and geometry of chemical reactors underpins the accuracy of performance evaluation for photocatalytic materials and, accordingly, the development and validation of thermodynamic and kinetic model reactions. The lack of accurate photonic, mass, and heat transport profiles for photochemical reactors hinder standardization, scale-up, and ultimately comparison between different experiments. This work proposes two contributions at the interface between engineering of chemical process and materials science: (A) an automated compact stainless-steel photoreactor with 40 cm3 and 65 cm2 of volume and area, respectively, for hydrogen photoproduction as a model reaction and (B) the synthesis, characterization, and performance of TiO2 Schottky junctions, using Pd, Pt, or Au nanoparticles (ca. 0.5, 1, 2 wt% loadings each) to validate the operation of the reactor. A photonic profile methodology is implemented to the studied reactor to obtain the local light absorption profile, opening up for evaluation of the local quantum yield calculation for the selected materials. A combination of transmission electron microscopy, (X-ray/ultraviolet) photoelectron/electron, energy loss/infrared spectroscopies, X-ray scattering, inductively coupled plasma atomic emission spectroscopy, and ultraviolet–visible spectrophotometry is employed to determine the distinctive surface and bulk properties to build structure–function correlations. The (Pd, Pt, Au)/TiO2 Schottky junction exhibits H2 production rates slightly higher than previous studies, with quantum yields almost 2-fold higher than reported values. These results, demonstrate that the proposed novel geometry of the photoreactor improves the photonic, heat, and mass profiles. An in-depth analysis of the Au plasmon was investigated coupling electron energy loss spectroscopy, UV–vis, and transmission electron microscope, resulting in insightful information about the Au NP mode at the TiO2 interface
Optical and structural properties of Nd doped SnO2 powder fabricated by the sol-gel method
We report on the structural and optical properties of undoped and neodymium doped SnO2 powders (0, 1, 3, and 5 at% of Nd) synthesized by the sol-gel method. SEM and TEM microscopy techniques reveal a nanometric scale of the powders. We show that the tetragonal rutile phase is achieved after annealing at 700 degrees C. The crystallite size of the doped SnO2 is found to decrease gradually with the increase of Nd content without changing the SnO2 structure. A strong decrease in the intensity of the Raman peaks is noted for doped powders, which can be attributed to the location of Nd3+ ions at the Sn sites indicating Nd incorporation into the host matrix. For the first time the optical properties were studied by UV-VisNIR spectroscopy and revealed Nd related absorption bands in the SnO2 matrix. The investigation of the photoluminescence properties shows broad emission centred around 550-650 nm originating from defects present in the SnO2 host matrix. Under 325 nm laser excitation, a strong photoluminescence of trivalent Nd is observed in the infrared region and shows Nd related emission peaks at 885, 1065, and 1336 nm. Such a strong PL signal under laser excitation indicates that Nd3+ is optically active. The excitation dependent PL (PLE) recorded in the 450-700 nm range confirms the presence of active Nd3+ successfully inserted into the SnO2 host matrix
Mimicking the chemistry of natural eumelanin synthesis: the ke sequence in polypeptides and in proteins allows for a specific control of nanosized functional polydopamine formation
The oxidation of dopamine and of other catecholamines leads to the formation of conformal films on the surface of all known materials and to the formation of a precipitate in solution. In some cases, it has been shown that the addition of additives in the dopamine solution, like certain surfactants or polymers, polyelectrolytes, and certain proteins, allows to get polydopamine nanoparticles of controlled size and the concomitant decrease, in an additive/dopamine dependent manner, in film formation on the surface of the reaction beaker. However, the mechanism behind this controlled oxidation and self-assembly of catecholamines is not known. In this article, it is shown that a specific diad of amino acids in proteins, namely KE, allows for specific control in the oxidation-self-assembly of dopamine to obtain polydopamine@protein core–shell nanoparticles which are biocompatible. The interactions between dopamine and the adjacent KE amino acids potentially responsible for the size control of polydopamine aggregates was investigated by molecular dynamics simulations. The obtained core– shell nanoparticles display the biological activity of the protein used to control the self- assembly of PDA. The photon to heat conversion ability of PDA is conserved in the PDA@protein particles
Two dimensional dipolar coupling in monolayers of silver and gold nanoparticles on a dielectric substrate
The dimensionality of assembled nanoparticles plays an important role in their optical and magnetic properties, via dipolar effects and the interaction with their environment. In this work we develop a methodology for distinguishing between two (2D) and three (3D) dimensional collective interactions on the surface plasmon resonance of assembled metal nanoparticles. Towards that goal, we elaborate different sets of Au and Ag nanoparticles as suspensions, random 3D arrangements and well organized 2D arrays. Then we model their scattering cross-section using effective field methods in dimension n, including interparticle as well as particle-substrate dipolar interactions. For this modelling, two effective field medium approaches are employed, taking into account the filling factors of the assemblies. Our results are important for realizing photonic amplifier devices
Study by advanced transmission electron microscopy techniques fragile materials
Le travail présenté dans ce manuscrit a montré l’importance du développement méthodologique et technique pour identifier et débloquer les verrous empêchant l’analyse de matériaux hybrides et complexes qui se dégradent sous irradiation par un faisceau d’électrons. Nous avons mis en évidence que des dégâts sur l’échantillon produits par les électrons n’apparaissent qu’au-dessus d'un certain seuil de densité de courant électronique qui dépend de la nature du matériau et de ses caractéristiques morphologiques et structurales. Ces développements couplés à la Cryo-EM, nous ont permis de mettre en évidence l’architecture des matériaux hybrides à base de carbone, la variation de la distance lamellaire dans une pérovskite en fonction de la molécule insérée et le positionnement du métal, d’identifier les interactions à l’interface entre deux cristaux moléculaires et la quantification 3D de la fonctionnalisation d’un MOF. Dans la dernière partie, nous avons mis en évidence les processus de nucléation et de croissance d’oxyde de fer par MET in-situ en phase liquide.The present manuscript shows the importance of methodological and technical development to identify and to unblock locks preventing the analysis of hybrid and complex materials that undergo degradation under electron beam irradiation. We have shown that beam-induced damage to the sample only appears above some specific threshold of current density. Such a threshold depends on the nature of the material and on its morphological and structural characteristics. These developments in synergy with the use of Cryo-EM, allowed us to expose the architecture of carbon-based hybrid materials, measure the variation of the lamellar distance in a perovskite according to the molecular spacer and to the positioning of the metal, identify the interactions at the interface between two molecular crystals, and the 3D quantification of the functionalization within a MOF. Lastly, we brought to light the processes of nucleation and growth of iron oxide by in-situ liquid phase TEM
Etude par les techniques avancées de microscopie électronique en transmission de matériaux fragiles
The present manuscript shows the importance of methodological and technical development to identify and to unblock locks preventing the analysis of hybrid and complex materials that undergo degradation under electron beam irradiation. We have shown that beam-induced damage to the sample only appears above some specific threshold of current density. Such a threshold depends on the nature of the material and on its morphological and structural characteristics. These developments in synergy with the use of Cryo-EM, allowed us to expose the architecture of carbon-based hybrid materials, measure the variation of the lamellar distance in a perovskite according to the molecular spacer and to the positioning of the metal, identify the interactions at the interface between two molecular crystals, and the 3D quantification of the functionalization within a MOF. Lastly, we brought to light the processes of nucleation and growth of iron oxide by in-situ liquid phase TEM.Le travail présenté dans ce manuscrit a montré l’importance du développement méthodologique et technique pour identifier et débloquer les verrous empêchant l’analyse de matériaux hybrides et complexes qui se dégradent sous irradiation par un faisceau d’électrons. Nous avons mis en évidence que des dégâts sur l’échantillon produits par les électrons n’apparaissent qu’au-dessus d'un certain seuil de densité de courant électronique qui dépend de la nature du matériau et de ses caractéristiques morphologiques et structurales. Ces développements couplés à la Cryo-EM, nous ont permis de mettre en évidence l’architecture des matériaux hybrides à base de carbone, la variation de la distance lamellaire dans une pérovskite en fonction de la molécule insérée et le positionnement du métal, d’identifier les interactions à l’interface entre deux cristaux moléculaires et la quantification 3D de la fonctionnalisation d’un MOF. Dans la dernière partie, nous avons mis en évidence les processus de nucléation et de croissance d’oxyde de fer par MET in-situ en phase liquide
Study by advanced transmission electron microscopy techniques fragile materials
Le travail présenté dans ce manuscrit a montré l’importance du développement méthodologique et technique pour identifier et débloquer les verrous empêchant l’analyse de matériaux hybrides et complexes qui se dégradent sous irradiation par un faisceau d’électrons. Nous avons mis en évidence que des dégâts sur l’échantillon produits par les électrons n’apparaissent qu’au-dessus d'un certain seuil de densité de courant électronique qui dépend de la nature du matériau et de ses caractéristiques morphologiques et structurales. Ces développements couplés à la Cryo-EM, nous ont permis de mettre en évidence l’architecture des matériaux hybrides à base de carbone, la variation de la distance lamellaire dans une pérovskite en fonction de la molécule insérée et le positionnement du métal, d’identifier les interactions à l’interface entre deux cristaux moléculaires et la quantification 3D de la fonctionnalisation d’un MOF. Dans la dernière partie, nous avons mis en évidence les processus de nucléation et de croissance d’oxyde de fer par MET in-situ en phase liquide.The present manuscript shows the importance of methodological and technical development to identify and to unblock locks preventing the analysis of hybrid and complex materials that undergo degradation under electron beam irradiation. We have shown that beam-induced damage to the sample only appears above some specific threshold of current density. Such a threshold depends on the nature of the material and on its morphological and structural characteristics. These developments in synergy with the use of Cryo-EM, allowed us to expose the architecture of carbon-based hybrid materials, measure the variation of the lamellar distance in a perovskite according to the molecular spacer and to the positioning of the metal, identify the interactions at the interface between two molecular crystals, and the 3D quantification of the functionalization within a MOF. Lastly, we brought to light the processes of nucleation and growth of iron oxide by in-situ liquid phase TEM
Enzymatically Active Polydopamine @ Alkaline Phosphatase Nanoparticles Produced by NaIO<sub>4</sub> Oxidation of Dopamine
Polydopamine (PDA) deposition, obtained from the oxidation of dopamine and other catecholamines, is a universal way to coat all known materials with a conformal coating which can subsequently be functionalized at will. The structural analogies between polydopamine and eumelanin, the black-brown pigment of the skin, were incited to produce stable polydopamine nanoparticles in solution, instead of amorphous precipitates obtained from the oxidation of dopamine. Herein, we demonstrate that size-controlled and colloidally stable PDA-based nanoparticles can be obtained in acidic conditions, where spontaneous auto-oxidation of dopamine is suppressed, using sodium periodate as the oxidant and a protein, like alkaline phosphatase (ALP), as a templating agent. The size of the PDA@ALP nanoparticles depends on the dopamine/enzyme ratio and the obtained particles display enzymatic activity of alkaline phosphatase, with an activity extending up to two weeks after particle synthesis. The PDA@ALP nanoparticles can be engineered in polyelectrolyte multilayered films to potentially design model biosensors
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