ZnO is very well known in the field of medical, pharmaceutical, and cosmetic uses (fluorescence-carrier, creams, sun blocker etc.). Moreover its outstanding optoelectronic characteristics, a wide band gap combined with a large exciton binding energy, makes it an attractive material for applications like sensors, light emitting diodes (LEDs), field effect transistors (FETs) and many more. Besides, ZnO provides, due to its semiconducting nature, a band structure that can be altered by material functionalization or downscaling the matter to the nanoscale, or more precise, to the quantum regime. Consequently, an accelerated and up-scaled industrial processing of ZnO with diverse features is of uppermost interest.
Up to now there are only a few continuous production methods known in academic and industrial environment. These methods are mostly based on precipitation processes which are based on batch – or up-scaled batch methods.
In our work we present a pilot plant device for the continuous ZnO nanoparticle production from Zinc acetate in ethanol. Transformation from the precursor to ZnO is driven by a small amount of water. The pilot plant is divided into a high pressure and a low pressure (vacuum) zone. At the interface of these two zones a nozzle is placed which provides a precursor spray into an evacuated reaction chamber. The spray is flash evaporated and subsequent nucleation and crystallization of ZnO occurs. Particles from the aerosol stream are separated by two axial cyclones. Two tanks and two cyclone pathways ensure a continuous production.
To characterize product formation a full-fledged analysis by microscopy, X-ray diffraction and spectroscopy was done. The product of a conservative batch synthesis was compared to the product from the continuous preparation – both starting with the same precursor solution. Main finding from that was a varying surface termination that triggers differences in stabilization, agglomeration, light scattering and absorption behavior of the ZnO nanoparticles.
Finally we present a feasible and effective method for the continuous production of ZnO nanoparticles; that may also be applied to diverse other areas of advanced materials.
Martin Klaumünzer*, Laurent Schlur,Fabien Schnell , Denis Spitzer
NS3E, ISL-CNRS-UNISTRA (Nanomatériaux pour les Systèmes Sous Sollicitations Extrêmes) UMR 3208, French-German Research Institute of Saint-Louis, Saint-Louis, France.
Regarding the scaled up and accelerated processing of ZnO particles, an advanced continuous pilot plant device is used for ZnO nanoparticle production from a zinc acetate dihydrate solution. A qualitative and mechanistic study is presented to show the feasibility of the process with respect to the formation of semiconducting ZnO nanoparticles. In order to evaluate the continuous approach based on the particle characteristics, a laboratory batch synthesis approach is additionally consulted for conventional preparation. In both cases, the precursor solutions are identical, on the basis of ethanol; no alkaline precipitant is added. The main finding in this comparison is the differing surface chemistry of the particles derived from these two approaches which triggers a whole cascade of differences in particle size distribution and spectroscopic and morphological properties of the particles.
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