Continuous Crystallization of ZnO Nanoparticles by Spray Flash Evaporation versus Batch Synthesis

Significance Statement

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.

Continuous Crystallization of ZnO Nanoparticles by Spray Flash Evaporation versus Batch Synthesis. Advances In Engineering
















Journal Reference

Chemical Engineering & Technology, Volume 38, Issue 8, pages 1477–1484, August, 2015. 

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.

Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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About The Author

Martin Klaumünzer is a chemist who has been working as scientist within “The Cluster of Excellence – Engineering of Advanced Materials” at the University of Erlangen-Nuremberg.

Currently, he is conducting some research and development activities as a responsible scientist within a joint venture of the Ministére de la Défense (France) and the Bundesministerium der Verteidigung (Germany) at the Institute of Saint-Louis (ISL). ISL is actively supporting the NS3E (Nanomatériaux pour les Systèmes Sous Solicitations Extrêmes) joint laboratory including the Centre National de la Recherche Scientifique (CNRS) and the University of Strasbourg (UNISTRA). Here his focus lies on the continuous (nano-) crystallization of semiconductors for sensors, pharmaceuticals (co-crystallization), and insensitive explosives. Further motivation is the detection of explosives for security reasons (anti-terror) and secure demilitarization of contaminated area.


About The Author

Laurent Schlur (Dr.) is a scientist who made his PhD at the University Louis Pasteur of Strasbourg. He developed a synthesis allowing the growth of ZnO nanorods for hybrid solar cells applications.

By now, he is working since three years at the Institute of Saint-Louis (ISL) where he is involved in different projects and topics for the purposes of the detection of secondary explosives. His work consists in functionalization of sensors like cantilevers with advanced CuO or ZnO nanostructures in order to decrease the detection limit of frequently used explosives like TNT, RDX or PETN. Finally his research activities aim for issues of civil security and countermeasures against terrorism encountered both at home and during overseas military operations.


About The Author

Fabien Schnell is an expert technician of the French Centre National de la Recherche Scientifique (CNRS). Specialized on scientific instrumentation, he has worked in various laboratories at CNRS and at the University of Strasbourg (UNISTRA), where he was responsible for operating analytical devices and for developing adapted protocols for research. His main field of experience focus on X-Ray Diffraction (XRD), Small-angle X-ray scattering (SAXS) and Scanning Electron Microscope (SEM), for innovative materials research and for the characterization at the nanoscale. He is also in charge of health and safety organization for pyrotechnical activities in laboratory environment. He is co-author of more than 20 articles and 30 communications in both peer reviewed international journals and large recognized international conferences.



About The Author

Denis Spitzer (Dr. Habil. Ing.) is a confirmed scientist and the founding-director of the NS3E laboratory (Nanomatériaux pour les Systèmes Sous Solicitations Extrêmes). He received his PhD. in chemistry from the University Louis Pasteur of Strasbourg in 1993. His main research activity is the continuous nanocrystallization of explosives and pharmaceuticals. He patented several processes, the investigation of ultra-sensitive explosive detection systems, and imaging of energetic materials with high resolution microscopy (STM and AFM). He is author of more than a hundred publications within peer-reviewed journals and technical reports. Moreover, he is author of 15 patents and more than 50 abstracts presented on national and international conferences. In 2013 he obtained the first price of “Strategic Thinking” on bio-inspired explosive detection, that he received from the former French Minister of Interior, Manuel Valls. For his main results on nanocrystallization, synthesis by detonation and also detection studies he recently (2015) received the “Grand Prix Lazare Carnot” from the French “Académie des Sciences”.