Precursors-guided synthesis of upconverting nanomaterials for near-infrared driven photocatalysis

The utilization of solar energy to solve environmental problems such as water detoxification, air purification and hydrogen production has attracted great interest from the scientific community over the last two decades. Solar photocatalysis is an interesting avenue to target all these environmental issues. Currently, technologies do not yet allow for the efficient use of a significant portion of the solar spectrum, namely the infrared, which corresponds to nearly ~48% of the total solar spectrum. This thesis aims at preparing nanocomposite materials that use these low energy solar photons by converting them into high energy UV and visible photons and then using them for classical photocatalysis. To achieve this, two major aspects of the preparation of this modified photocatalyst were emphasized. Firstly, the synthesis of materials that could efficiently convert currently unused photons and secondly, the preparation of their composite with TiO2, the most widely used photocatalyst.This doctoral thesis focuses on an approach based on "upconversion" in order to extend the range of use of the solar spectrum. To achieve this goal, two optimization strategies were addressed. The optimization of the quantum efficiency of upconversion nanoparticles (UCNPs) using new anhydrous precursors and, the preparation of UCNPs-TiO2 nanocatalyst using metallogels and/or core-shell structures. Finally, we test the objective of using low energy infrared solar photons by performing photocatalysis under IR irradiation only using the platform developed in this workL'utilisation de l'énergie solaire pour résoudre des problèmes environnementaux tels que la détoxification de l'eau, la purification de l'air et la production d'hydrogène a suscité un grand intérêt de la part de la communauté scientifique au cours des deux dernières décennies. La photocatalyse solaire est une piste intéressante pour cibler toutes ces questions environnementales. Actuellement, les technologies ne permettent pas encore d'utiliser efficacement une partie importante du spectre solaire, à savoir l'infrarouge, qui correspond à près de ~48 % du spectre solaire total. Cette thèse vise à préparer des matériaux nanocomposites qui utilisent ces photons solaires à faible énergie en les convertissant en photons UV et visibles à haute énergie et en les utilisant ensuite pour la photocatalyse classique. Pour y parvenir, l'accent a été mis sur deux aspects majeurs de la préparation de ce photocatalyseur modifié. Premièrement, la synthèse de matériaux qui pourraient convertir efficacement les photons actuellement inutilisés et deuxièmement, la préparation de leur composite avec TiO2, le photocatalyseur le plus largement utilisé. Cette thèse de doctorat se concentre sur une approche basée sur l’ « upconversion » afin d’étendre la gamme d'utilisation du spectre solaire. Pour atteindre cet objectif, deux stratégies d’optimisation ont été abordée. L’'optimisation du rendement quantique des nanoparticules à upconversion en utilisant de nouveaux précurseurs anhydres et, la préparation de photo-catalyseur nanocomposite UCNPs-TiO2 en utilisant des métallogels et/ou des structures coeur-coquille. Pour finir nous testons l’objectif de l'utilisation des photons solaires infrarouges à faible énergie en réalisant une photocatalyse sous irradiation IR uniquement en utilisant la plate-forme développée dans ce travai

Synthèse guidée par des précurseurs de nanomatériaux à conversion ascendante pour la photocatalyse dans le proche infrarouge

L'utilisation de l'énergie solaire pour résoudre des problèmes environnementaux tels que la détoxification de l'eau, la purification de l'air et la production d'hydrogène a suscité un grand intérêt de la part de la communauté scientifique au cours des deux dernières décennies. La photocatalyse solaire est une piste intéressante pour cibler toutes ces questions environnementales. Actuellement, les technologies ne permettent pas encore d'utiliser efficacement une partie importante du spectre solaire, à savoir l'infrarouge, qui correspond à près de ~48 % du spectre solaire total. Cette thèse vise à préparer des matériaux nanocomposites qui utilisent ces photons solaires à faible énergie en les convertissant en photons UV et visibles à haute énergie et en les utilisant ensuite pour la photocatalyse classique. Pour y parvenir, l'accent a été mis sur deux aspects majeurs de la préparation de ce photocatalyseur modifié. Premièrement, la synthèse de matériaux qui pourraient convertir efficacement les photons actuellement inutilisés et deuxièmement, la préparation de leur composite avec TiO2, le photocatalyseur le plus largement utilisé. Cette thèse de doctorat se concentre sur une approche basée sur l’ « upconversion » afin d’étendre la gamme d'utilisation du spectre solaire. Pour atteindre cet objectif, deux stratégies d’optimisation ont été abordée. L’'optimisation du rendement quantique des nanoparticules à upconversion en utilisant de nouveaux précurseurs anhydres et, la préparation de photo-catalyseur nanocomposite UCNPs-TiO2 en utilisant des métallogels et/ou des structures coeur-coquille. Pour finir nous testons l’objectif de l'utilisation des photons solaires infrarouges à faible énergie en réalisant une photocatalyse sous irradiation IR uniquement en utilisant la plate-forme développée dans ce travailThe utilization of solar energy to solve environmental problems such as water detoxification, air purification and hydrogen production has attracted great interest from the scientific community over the last two decades. Solar photocatalysis is an interesting avenue to target all these environmental issues. Currently, technologies do not yet allow for the efficient use of a significant portion of the solar spectrum, namely the infrared, which corresponds to nearly ~48% of the total solar spectrum. This thesis aims at preparing nanocomposite materials that use these low energy solar photons by converting them into high energy UV and visible photons and then using them for classical photocatalysis. To achieve this, two major aspects of the preparation of this modified photocatalyst were emphasized. Firstly, the synthesis of materials that could efficiently convert currently unused photons and secondly, the preparation of their composite with TiO2, the most widely used photocatalyst.This doctoral thesis focuses on an approach based on "upconversion" in order to extend the range of use of the solar spectrum. To achieve this goal, two optimization strategies were addressed. The optimization of the quantum efficiency of upconversion nanoparticles (UCNPs) using new anhydrous precursors and, the preparation of UCNPs-TiO2 nanocatalyst using metallogels and/or core-shell structures. Finally, we test the objective of using low energy infrared solar photons by performing photocatalysis under IR irradiation only using the platform developed in this wor

Coinage Metal Complexes with Di-tertiary-butyl Sulfide as Precursors with Ultra-Low Decomposition Temperature

International audienceWe report here the synthesis of [Cu2(TFA)4(tBu2S)2] (1), [Ag4(TFA)4(tBu2S)4] (2) and [AuCl(tBu2S)] (3) (TFA=trifluoroacetate), which decompose in solution medium at ultra-low temperature (e. g., in boiling toluene) to afford phase-pure and highly crystalline Cu9S5, Ag2S and metallic Au nanoparticles, respectively. The low decomposition temperature of these precursors is attributed to the facile decomposition mechanism in the di-tertiary-butyl sulfide ligand. These results are a significant step in the direction of establishing a general low-temperature strategy spanning a range of systems including thermodynamically metastable materials and incorporate them in technologies that are sensitive to the harsh conditions

An anhydrous precursor approach to BaYF5-based upconverting nanocrystals

International audienceWith an objective to have easy access to high quality BaYF5 matrix, we report here new anhydrous precursors of barium and yttrium which show a good compatibility in terms of co-thermal decomposition. These complexes not only fill the void of precursors for Ba-based upconverting (UC) nanomaterials but also provide a way to minimize the –OH concentration around these nanocrystals (NCs) to enhance their UC efficiency without requiring the usual core-shell structure. The precursors and the BaYF5 NCs co-doped with Yb3+/Tm3+ ions were thoroughly characterized. The NCs were studied for upconversion properties and preliminary results are presented here. On the basis of these results, a mechanism for the energy transfer in Yb–Tm system is proposed

Simultaneous automated design of structured QFT controller and prefilter using nonlinear programming

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Robust controller and pre-filter design using QFT and interval constraint techniques

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Quest to enhance up-conversion efficiency: a comparison of anhydrous vs. hydrous synthesis of NaGdF4: Yb3+ and Tm3+ nanoparticles

International audienceA major challenge in the field of up-converting (UC) nanomaterials is to enhance their efficiencies. The –OH defects on the surface of the nanoparticles are thought to be the main cause of luminescence quenching, but there are no comparative studies in the literature showing the impact of anhydrous vs. hydrous synthesis on up-conversion efficiency. In this article, we present the synthesis of up-converting NaGdF4: Yb+3, Tm+3 nanoparticles by two different methods: thermal decomposition of single source metal-organic anhydrous precursors [NaLn(TFA)4(diglyme)] (Ln = Gd, Tm, Yb; TFA = trifluoroacetate) and room temperature co-precipitation using hydrated inorganic salts Ln(NO3)3·5H2O (Ln = Gd, Tm, Yb), NaNO3 and NH4F in ethylene glycol. After a detailed study on the influence of solvents and the percentage of lanthanide dopant on the crystal phase of the up-converting nanoparticles (NPs) and their complete characterization, a comparative up-conversion study was carried out which revealed that the uniform nanospheres (av. size ∼13 nm) obtained from the anhydrous SSP had significantly higher up-conversion efficiency than agglomerated nanorods (∼197 nm in length and ∼95 nm in width) produced from hydrated inorganic salts. An enhanced up-conversion quantum yield of 1.8% for the anhydrous sample validates the anhydrous precursor approach as a strategy to obtain small but highly emitting up-converting particles without requiring a silica or undoped matrix surface passivation layer

Multi-color solar absorption as a synergetic UV up-conversion enhancement mechanism in LiYF 4 :Yb 3+ ,Tm 3+ nanocrystals

International audienceMotivated by the technologically important spectral conversion of sunlight for efficient photocatalysis, we present a detailed analysis of the multi-color excitation of LiYF 4 :Yb 3+ ,Tm 3+ nanocrystals leading to UV emission through upconversion. We demonstrate in particular that the combination of blue and IR light for generating upconversion UV emission is a linear mechanism that occurs at rather low density of excitation (a few mW/cm 2). This up-conversion efficiency is fully compatible with

Single source precursor route to nanometric tin chalcogenides

Low-temperature solution phase synthesis of nanomaterials using designed molecular precursors enjoys tremendous advantages over traditional high-temperature solid-state synthesis. These include atomic-level control over stoichiometry, homogeneous elemental dispersion and uniformly distributed nanoparticles. For exploiting these advantages, however, rationally designed molecular complexes having certain properties are usually required. We report here the synthesis and complete characterization of new molecular precursors containing direct Sn-E bonds (E = S or Se), which undergo facile decomposition under different conditions (solid/solution phase, thermal/microwave heating, single/mixed solvents, varying temperatures, etc.) to afford phase-pure or mixed-phase tin chalcogenide nanoflakes with defined ratios