Size-controlled synthesis of ZnO quantum dots in microreactors

International audienceIn this paper, we report on a continuous flow microreactor process to prepare ZnO quantum dots (QDs) with widely tunable particle size and photoluminescence emission wavelengths. X-ray diffraction, electron diffraction, UV-vis, photoluminescence and transmission electron microscopy measurements were used to characterize the synthesized ZnO QDs. By varying operating conditions (temperature, flow rate) or the capping ligand, ZnO QDs with diameters ranging from 3.6 to 5.2 nm and fluorescence maxima from 500 to 560 nm were prepared. Results obtained show that low reaction temperatures (20 or 35 C), high flow rates and the use of propionic acid as a stabilizing agent are favorable for the production of ZnO QDs with high photoluminescence quantum yields (up to 30%)

Metal-organic and covalent organic frameworks as single-site catalysts

[EN] Heterogeneous single-site catalysts consist of isolated, well-defined, active sites that are spatially separated in a given solid and, ideally, structurally identical. In this review, the potential of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) as platforms for the development of heterogeneous single-site catalysts is reviewed thoroughly. In the first part of this article, synthetic strategies and progress in the implementation of such sites in these two classes of materials are discussed. Because these solids are excellent playgrounds to allow a better understanding of catalytic functions, we highlight the most important recent advances in the modelling and spectroscopic characterization of single-site catalysts based on these materials. Finally, we discuss the potential of MOFs as materials in which several single-site catalytic functions can be combined within one framework along with their potential as powerful enzyme-mimicking materials. The review is wrapped up with our personal vision on future research directions.S. M. J. Rogge, J. Hajek, and V. Van Speybroeck acknowledge the Fund for Scientific Research - Flanders (FWO), the Research Board of Ghent University (BOF) and BELSPO in the frame of IAP/7/05 for financial support. V. Van Speybroeck acknowledges funding from the European Union's Horizon 2020 research and innovation programme (consolidator ERC grant agreement no. 647755 - DYNPOR (2015-2020)). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 641887 (project acronym: DEFNET). W. Dewitte and C. Caratelli are acknowledged for technical support with the figures. J. Gascon acknowledges funding from the European Union's 2020 research and innovation programme (ERC grant agreement no. 335746 - CrystEng-MOF-MMM) and from the Dutch Organization for Scientific Research (NWO, VIDI grant agreement 723.012.107 - MetMOFCat).Rogge, SMJ.; Bavykina, A.; Hajek, J.; García Gómez, H.; Olivos-Suarez, AI.; Sepulveda-Escribano, A.; Vimont, A.... (2017). Metal-organic and covalent organic frameworks as single-site catalysts. Chemical Society Reviews. 46(11):3134-3184. https://doi.org/10.1039/c7cs00033bS31343184461