Spinning disk reactor technology in photocatalysis: nanostructured catalysts intensified production and applications

The use of photocatalysis in environmental remediation processes has become more important in the last decade, mainly due to the notable efforts made by researchers in this field. The photocatalytic process requires a semiconductor material (photocatalyst), usually a metal oxide, which can be activated through the energy transported by ultraviolet light or visible light waves. The activated photocatalyst generates active compounds, such as hydroxyl radicals and superoxide ion, able to degrade very recalcitrant and non-biodegradable compounds present on the catalyst surface or in the liquid medium. The efficiency of the pollutant removal process is affected by various factors related to the employed photocatalyst, such as mean dimension, size distribution, physical structure and energy required for the activation. The photocatalyst characteristics are strongly dependent on the production process, and several researchers have developed new intensified production nanostructured catalysts in a continuous Spinning Disk Reactor is discussed. The main features of Spinning Disk Reactor technology are reported and analysed, i.e. rotational velocity, disk diameter, disk surface material and roughness, focusing on the production of nanoparticles to be used in the photocatalytic application, in view of the process intensification of photocatalysis application in the field of environmental remediation. A general overview about process intensification and its application to chemical engineering is presented, and the advantages offered by Spinning Disk Reactor technology, in terms of an increase of process efficiency due to the misinformation of operative conditions in reactors, are illustrated. Basing on the Spinning Disk Reactor characteristics and operative conditions, nanoparticle production by Spinning Disk Reactor compared to conventional technologies and the current application of this technology to selected nanoparticles (titania, magnetite, MgO and hydroxyapatite), synthesis is discussed. Spinning Disk Reactor technology allows to produce active semiconductor particles, characterized by a mean size significantly below 100 nm and with a narrow unimodal distribution, improving the quality of these products in comparison with those produced through conventional processes and equipment. Finally, the application of vertical and horizontal Spinning Disk Reactor configuration to the degradation of refractory compounds by photocatalysis is reviewed, aiming at evaluating process efficiency and the produced nanoparticle characteristics, to assess the key parameters and the limiting factors of the technology.