Synthèse en milieu aqueux de nanocristaux de semi-conducteurs via des procédés microfluidiques

Abstract : In recent years, microfluidics has become an attractive technology for the continuous flow synthesis of colloidal nanocrystals. This technology allows a good control of the synthesis parameters, a good reproducibility and the possibility of the application on a large scale. In a first part, we have developed continuous and ecological syntheses of the ZIF-8 crystals for the large scale, either with a monophasic or a biphasic flow (water/alkane). The microfluidic technology allows the fast synthesis (10 min) of ZIF-8 crystals over a wide size range (from ca. 300 to 900 nm) simply by varying the experimental parameters (flow rates, temperature,…). ZIF-8 crystals with the stable rhombic dodecahedron shape, of sodalite structure and with a high specific surface area (ca. 1700 m2.g-1) were obtained. Next, the catalytic properties of ZIF-8 crystals were evaluated. These particles were demonstrated to be an efficient heterogeneous catalyst for the Knoevenagel synthesis of α,β-unsaturated cyanoesters and of 3-cyanocoumarins using 2-hydroxy aromatic aldehydes and ethyl cyanoacetate as starting materials (yields ranging from 89 to 95%). The ZIF-8 particles can be recycled at least five times with negligible changes in catalytic performances. In the second part, we synthesized the Mn2+ or Cu+-doped CdS QDs coated with a ZnS shell in a tubular microreactor using a monophasic or a biphasic flow (water/alkane). Various experimental parameters (time, temperature, pH, molar ratio, concentration and nature of the starting materials) were evaluated to optimize the optical properties of the dots. The obtained Mn2+ doped CdS QDs exhibited a photoluminescence emission related to the 4T1 → 6A1 transition with quantum yields higher than 10%. The introduction of a ZnS shell with the monophasic flow allows to improve the optical properties and to reduce the surface defects of the 6% Mn:CdS/ZnS QDs (strong emission at 590 nm and quantum yields of ca. 20%). The introduction of a ZnS shell on the surface of Cu doped CdS QDs does not significantly improve the quantum yields. Finally, the synthesis of Mn2+-doped ZnS QDs with monophasic or biphasic flow (water/alkane) was developed. The dots have a photoluminescence quantum yield of 13% if they are prepared in a monophasic water flow
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Oleksii Kolmykov. Synthèse en milieu aqueux de nanocristaux de semi-conducteurs via des procédés microfluidiques. Micro et nanotechnologies/Microélectronique. Université de Lorraine, 2017. Français. ⟨NNT : 2017LORR0090⟩. ⟨tel-01759703⟩

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