# On the Micromixing Behavior of a Spinning Disk Reactor for Metallic Cu Nanoparticles Production
## 1 Introduction  
The interest in producing metal nanoparticles is connected to the possibility of employing them in different fields of possible applications with enhanced chemical and physical performances, such as the use in catalysis, in absorption, for chemical and biological sensors, and for photonic and electronic devices [1]. Another advantage is represented by the possibility of using less-noble metals, such as titania or copper, as an alternative to gold or silver with a reduction of relevant material costs. Recently, interest focused on copper nanoparticles production in the framework of the electronic industry, substituting silver in the electroconductive inks, the analytical sensor industry, and aids environmental remediation purposes [2; 3]. In addition to this, copper results appear to be attractive for the preparation of Cu-based nanoparticles due to their extensive range of possible oxidation states (Cu\({}^{0}\), Cu\({}^{1}\), Cu\({}^{1}\) and Cu\({}^{\text{III}}\)), promoting different possible chemical reactions. However, there are some disadvantages in the use of Cu, which are mainly connected to the need to protect the particles from oxidation by the environment during storage and the difficulty to reduce copper ions under mild reaction conditions [4]. Minor difficulties are the tendency to agglomerate and the difficulty to synthesize large quantities of high-quality nanomaterial capable of satisfying the industrial needs.  
Nowadays, the main method to produce metal nanoparticles is to use stirred reactors in batch. However, this method is not capable of producing the growing amounts required by the industry. An alternative to obtain copper nanoparticles is represented by the use of some physical methods, such as thermal decomposition, capable of producing larger quantities in the form of nanopowder but characterized by low purity levels [5]. As a consequence, a great interest by the relevant industry to develop novel routes to produce high quantities of copper nanoparticles of high quality remains [6].  
A promising approach to satisfy these requirements appears to follow the route of the wet chemical synthesis that allows continuous production by employing process intensified equipment with limited investment and operational costs. Possible alternatives are continuous hydrothermal reactors, continuous microwave reactors, tubular flow reactors, T-mixers, and the spinning disk reactor [7]. Each equipment exhibits different capabilities to produce the copper nanoparticles in size and shape.  
In this work, a spinning disk reactor (SDR) was used at different operating conditions by varying the disk velocity, the number and position of the reactants injectors, and the reactant flow rates to study the reaction outcome of copper nanoparticles production in terms of size and purity, and to check if this equipment is capable to reach the requirement targets of the industry. Indeed, the advantages of the SDR are low investment and operations costs compared to other technologies, continuous and high production capacities, and the ease of use of the equipment [8]. Beforehand, the technology was employed for the production of many other materials, such as titania, hydroxyapatite, zero valent iron, and bi-metal nanoparticles [9; 10; 11].