Flame Spray Pyrolysis for oxides nanoparticles synthesis

Flame spray pyrolysis (FSP) process is considered as a powerful method to produce nanoparticles oxides with different properties. In particular, the ability to change the experimental conditions in the flame can be very helpful for the synthesis of single- and multi-component nanoparticles with specific and tailored characteristics. Properties such as crystallite size, crystalline phase, degree of aggregation and agglomeration, surface area and porosity can be very challenging in different applications including catalysis, gas sensors as well as energy storage. The flame spray pyrolysis apparatus developed in CNR Milano laboratory consists of an oxygen-assisted spray used to inject the liquid precursor, which is normally feed by a syringe pump. A pilot flame, positioned coaxially to the flame spray, allows starting combustion reactions. The apparatus has been designed and developed in order to produce nanoparticles in powder as well as in film. The availability of powder supported deposits is very useful for catalytic applications (e.g. air and water treatment), to overcome several problems of process design and implementation. During the synthesis, the powder is collected on a filter, whilst the nanoparticles deposition is obtained by orthogonal impingement on a cooled (100°C) substrate holder (alumina or stainless steel) positioned at 30 cm height above the burner. A pneumatically operated mechanical shutter placed above the target substrate allows the control of the exposure time of the aerosol-generated powder deposition. Temperature measurements along the synthesis process is properly changed and monitored in order to obtain nanoparticles of particular chemical and physical characteristics. After synthesis, an annealing process of the film is performed in order to improve film-substrate adhesion. Synthesis of TiO2 are performed with this method and then characterised by means of XRD, STEM and FT-IR analysis. In particular, size and phase of the nanoparticles and the related deposits have been investigated changing the experimental conditions of the reactor. Moreover, as for the titania films, the photocatalytic activity has been evaluated by measuring the degradation of toluene in air at typical environment concentration using a stirred flow photoreactor operated at constant concentration under UV-A irradiation.