Crystalline ZnO photocatalysts with different morphologies prepared at ambient temperature

peer reviewe

N2-H2 capacitively coupled radio-frequency discharges at low pressure. Part I. Experimental results: Effect of the H2 amount on electrons, positive ions and ammonia formation

The mixing of N2 with H2 leads to very different plasmas from pure N2 and H2 plasma discharges. Numerous issues are therefore raised involving the processes leading to ammonia (NH3) formation. The aim of this work is to better characterize capacitively-coupled radiofrequency plasma discharges in N2 with few percents of H2 (up to 5%), at low pressure (0.3-1 mbar) and low coupled power (3-13 W). Both experimental measurements and numerical simulations are performed. For clarity, we separated the results in two complementary parts. The actual one (first part), presents the details on the experimental measurements, while the second focuses on the simulation, a hybrid model combining a 2D fluid module and a 0D kinetic module. Electron density is measured by a resonant cavity method. It varies from 0.4 to 5 109 cm-3, corresponding to ionization degrees from 2 10-8 to 4 10-7. Ammonia density is quantified by combining IR absorption and mass spectrometry. It increases linearly with the amount of H2 (up to 3 1013 cm-3 at 5% H2). On the contrary, it is constant with pressure, which suggests the dominance of surface processes on the formation of ammonia. Positive ions are measured by mass spectrometry. Nitrogen-bearing ions are hydrogenated by the injection of H2, N2H+ being the major ion as soon as the amount of H2 is >1%. The increase of pressure leads to an increase of secondary ions formed by ion/radical-neutral collisions (ex: N2H+, NH4 +, H3 +), while an increase of the coupled power favours ions formed by direct ionization (ex: N2 +, NH3 +, H2 +).N. Carrasco acknowledges the financial support of the European Research Council (ERC Starting Grant PRIMCHEM, Grant agreement no. 636829). A. Chatain acknowledges ENS Paris-Saclay Doctoral Program. A. Chatain is grateful to Gilles Cartry and Thomas Gautier for fruitful discussions on the MS calibration. L.L. Alves acknowledges the financial support of the Portuguese Foundation for Science and Technology (FCT) through the project UID/FIS/50010/2019. L. Marques and M. J. Redondo acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2019

Photocatalysts heterogenization on silica nanoparticles for the photosensitization of oxygen and photoredox applications

Within the last decades, solar energy has attracted much attention as the supply of clean, secure, and sustainable energy and chemicals which is of paramount importance for the future. Chemists therefore try to use light activation to conduct organic transformations through photocatalysis. Ruthenium and iridium polypyridyl complexes dominate this field but their use is limited due to their price, scarcity, and strong ecological impact. Organic dyes and copper complexes have been investigated to replace them, but their low photostability still hamper their implementation. In this context, the strategy of homogeneous silica-supported photocatalysis triggered our attention to design more efficient, photostable, and recyclable photoactive systems. Firstly, we investigated the impact of the morphology of silica nanoparticles onto the photocatalytic generation of singlet oxygen by Rose Bengal that was non-covalently bound to the solids surface. We identified that a Core-shell nanostructure was the best to employ in terms of photophysical properties, activity and recycling of the surface-bound molecules. Next, we designed a covalent anchoring strategy between a benzophenazine and the silica surface, which requires the derivatization of the considered photocatalyst. To determine the best way to anchor it without perturbing its photophysical properties and photoactivity in singlet oxygen generation, we established a structure-activity relationship to identify the best route for immobilization and successfully devised photoactive grafted organic dyes. Finally, heteroleptic and homoleptic copper(I) complexes were anchored onto silica to increase their photostability by limiting their ligand exchange likelihoods. Grafted homoleptic complexes were competent for excited-state electron transfers to diazonium derivatives which generated the corresponding Cu(II) analogue that persisted on the millisecond timescale. Such long-lived analog is promising for photoredox applications.(SC - Sciences) -- UCL, 202

Approche anthropo-didactique du Moringue en Créole: vers une interculturalité de l'EPS à l'école primaire Réunionnaise

International audienc

Assessment of circulating dickkopf-1 with a new two-site immunoassay in healthy subjects and women with breast cancer and bone metastases

The aim of our study was to investigate the sex- and age-related changes of serum Dickkopf-1 (Dkk-1), a soluble inhibitor of the Wnt signaling pathway, in healthy individuals and in patients with breast cancer (BC) and bone metastases (BM) using a new ELISA. Association of serum Dkk-1 with markers of bone turnover was also investigated. Serum Dkk-1 measurements were performed using a commercial sandwich ELISA in 150 healthy men, 175 healthy pre- and postmenopausal women (20-65 years), 22 women with BC and BM (mean age 63 years), and 16 women with BC and metastases at sites other than bone (mean age 53 years). Intra- and interassay coefficients of variation were below 7% and 12%, respectively. The detection limit was determined to be 0.018 microg/L. In healthy women and men, Dkk-1 did not change with age. Serum Dkk-1 modestly correlated with serum bone alkaline phosphatase (r = 0.19, P = 0.013) and serum C-terminal cross-linking telopeptide of type I collagen (r = 0.19, P = 0.014) in women but not in men. Dkk-1 levels were higher in women with BC and BM (5.57 +/- 5.50 microg/L) than in healthy age-matched controls (3.47 +/- 1.47 microg/L, P < 0.0001) and women with metastases at sites other than bone (3.57 +/- 1.66 microg/L, P = 0.0003). In conclusion, serum Dkk-1 is stable with age in healthy women and men and increases in patients with BC and BM. Measurements of circulating Dkk-1 with this new ELISA may be useful for the clinical investigation of patients with malignant bone diseases.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Impact of silica nanoparticles architectures on the photosensitization of O2 by immobilized Rose Bengal

Transforming light into chemical energy has been widely studied to design ecofriendly, cost-effective and sustainable synthetic approaches. The heterogenization of organic photocatalysts is a well-known strategy providing efficient solid supported catalysts. One of the most suitable solid as support is silica nanoparticles (NPs). This research note highlights the impact of silica nanoparticles morphology on a representative photochemical process that is the photooxidation of citronellol, involving oxygen sensitization. Three architectures of silica NPs were investigated: Nanospheres (NS), Core-Shell (CS) and Urchins (U). Their surfaces were functionalized with ammonium moieties allowing the immobilization of Rose Bengal (RB) by electrostatic interactions. The heterogenized RB on the various supports displayed different activities in the production of singlet oxygen, CS being the best support in terms of activity, recyclability and dye immobilization rate

Photo‐catalyzed α‐arylation of enol acetate using recyclable silica‐supported heteroleptic and homoleptic copper(I) photosensitizers

Earth‐abundant photosensitizers are highly sought after for light‐mediated applications, such as photoredox catalysis, depollution and energy conversion schemes. Homoleptic and heteroleptic copper(I) complexes are promising candidates in this field, as copper is abundant and the corresponding complexes are easily obtained in smooth conditions. However, some heteroleptic copper(I) complexes suffer from low (photo)stability that leads to the gradual formation of the corresponding homoleptic complex. Such degradation pathways are detrimental, especially when recyclability is desired. In here, we report a novel approach for the heterogenization of homoleptic and heteroleptic Cu complexes on silica nanoparticles. In both cases, the photophysical properties upon surface immobilization were only slightly affected. Excited‐state quenching with aryl diazonium derivatives occurred efficiently (108‐1010 M–1 s–1) with heterogeneous and homogeneous photosensitizers. Moderate but almost identical yields were obtained for the a‐arylation of enol acetate using the homoleptic complex in homogeneous or heterogeneous conditions. Importantly, the silica‐supported photocatalysts were recycled with moderate loss in photoactivity over multiple experiments. Transient absorption spectroscopy confirmed that excited‐state electron transfer occurred from the homogeneous and heterogeneous homoleptic copper(I) complexes to aryl diazonium derivatives, generating the corresponding copper(II) center that persisted for several hundreds of microseconds, compatible with photoredox catalysis applications.info:eu-repo/semantics/publishe

Photo‐Catalyzed α‐Arylation of Enol Acetate Using Recyclable Silica‐Supported Heteroleptic and Homoleptic Copper(I) Photosensitizers

Earth-abundant photosensitizers are highly sought after for light-mediated applications, such as photoredox catalysis, depollution and energy conversion schemes. Homoleptic and heteroleptic copper(I) complexes are promising candidates in this field, as copper is abundant and the corresponding complexes are easily obtained in smooth conditions. However, some heteroleptic copper(I) complexes suffer from low (photo)stability that leads to the gradual formation of the corresponding homoleptic complex. Such degradation pathways are detrimental, especially when recyclability is desired. This study reports a novel approach for the heterogenization of homoleptic and heteroleptic Cu complexes on silica nanoparticles. In both cases, the photophysical properties upon surface immobilization were only slightly affected. Excited-state quenching with aryl diazonium derivatives occurred efficiently (108–1010 M−1 s−1) with heterogeneous and homogeneous photosensitizers. Moderate but almost identical yields were obtained for the α-arylation of enol acetate using the homoleptic complex in homogeneous or heterogeneous conditions. Importantly, the silica-supported photocatalysts were recycled with moderate loss in photoactivity over multiple experiments. Transient absorption spectroscopy confirmed that excited-state electron transfer occurred from the homogeneous and heterogeneous homoleptic copper(I) complexes to aryl diazonium derivatives, generating the corresponding copper(II) center that persisted for several hundreds of microseconds, compatible with photoredox catalysis applications