Nanoparticle synthesis and characterization

The interest for the synthesis processes of nanostructured materials, such as nanoparticles, nanotubes and nanolayers, is due to both scientific and technological motivations. The study of nanomaterials allows to investigate totally new phenomena, while their assembly in nanostructures offers the possibility of many applications in numerous technological fields.

Numerous processes are utilized for the synthesis of nanostructured materials and in particular for nanoparticle production. These processes can be divided in three main categories. The mechanical methods obtain a reduction of the particle dimensions through mechanical systems such as the “ball milling” technique. The liquid-chemical methods rely on the precipitation of a solid in a solution or the chemical conversion of colloidal dispersions in a gel (“sol-gel technique”). The high temperature methods for the synthesis are numerous and include evaporation/condensation techniques, aerosol techniques and flame synthesis. The high temperature synthesis offers several advantages for nanoparticle production in terms of both purity of materials and size control of the particles. For the flame synthesis process there are two main ways to inject the precursor in the flame: in homogenous phase, through an evaporation system at controlled temperature, or through a spray system, in liquid phase. This last method offers a greater flexibility in term of type of precursors to be utilized and flow control determining the amount of produced material. Moreover the easy scaling-up of the experimental equipment allow the production of nanopowders in sufficient quantities to be used for the realization of prototypes by other research groups.

Our research group developed two types of burners for nanoparticle synthesis of several oxides such as TiO₂, SiO₂, V₂O₃.

The burner (fig. 1) consists of a porous plug and a premixing chamber for producing a lean premixed methane-air flame. On the axis of the flame the evaporated precursor is injected trough a capillary. The precursor in general diluted with Nitrogen. A diffusion flame within the premixed flame is obtained . By varying the precursor, the flow and the stoichiometry of the flames nanoparticles of different composition and size can be obtained.

For the utilization of an appropriate synthesis system a crucial issue is the development of a collecting system. Figure 2 shows the experimental apparatus and two collecting systems. In particular a cooled sucking probe, CSP, can be employed. With this technique nanopowders are sucked and dispersed in an appropriate liquid, mainly water. A second system consists of an expansion and cooling duct and a filter for nanopowders collection. An electrostatic precipitator will be also realized in the near future.

The FPS technique is based on the use of a spray flame generated by an oxygen assisted injector coaxial of a pilot flame. Figure 3 shows the nozzle for the spray. A capillary (Φin.= 0.3 mm, Φout.= 0.8 mm) is inserted in the nozzle (Φ= 1 mm) in order to form an annular gap. The liquid precursor and fuel are mixed and injected through the capillary. An oxygen flow exits from the gap generating a spray. The spray is burning within the pilot flame. The spray shape and the droplet size play a major role in determining the morphological and functional characteristic of the synthesized nanoparticles.

The collected nanoparticles will be characterized by TEM, SEM, XRD and FT-IR techniques. In such a way the size, morphology, the crystal structure and the composition of the nanomaterials will be determined. A special apparatus for the determination of the photo-electrochemical properties of the nanoparticles can be also used.

Current research activities are:

• Flames and synthesis processes characterization
• Hybrid flame structure
• Oxides synthesis in hybrid burner
• Experimental correlation between particle size and laser-induced incandescence (LII) time decay in TiO₂ flame synthesis
• Design and characterization of an experimental apparatus for nanoparticles synthesis
• Nanopowder characterization

Selection of published papers

• F. Cignoli, C. Bellomunno, S. Maffi, G. Angella, G. Zizak, Use of a hybrid burner for flame synthesis of oxide nanopowders, 3rd European Combustion Meeting, Chania, Crete, April 11-13, 2007
• S. Maffi, F. Cignoli, C. Bellomunno, S. De Iuliis, G. Zizak, Spectral effects in laser induced incandescence application to flame-made titania nanoparticles, Spectrochim. Acta B 63, 202-209 (2008)
• F. Cignoli, S. Maffi, R. Dondè, G. Zizak, G.Solero, I. Brescia, S. Alberti, Design and preliminary characterization o fan experimental set-up for nanoparticles synthesis through flame spray pyrolysis, 32 Annual Meeting of the Combustion Institute, Napoli, April 26-28, 2009
• G. Solero, F. Cignoli, R. Dondè, S. Maffi, G. Zizak, S. Alberti, I. Brescia, Flame spray pyrolysis for sintesi of nanoparticles, XX AIDAA Congress, Milano, June29-July 3, 2009
• F. Cignoli, C. Bellomunno, S. Maffi, G, Zizak, Laser-induced incandescence of titania nanoparticles synthesized in a flame, Appl. Phys. B 96, 593-599 (2009)

Contracts

• Commessa “Advanced diagnostics for innovative materials and combustion systems” of Dipartimento Energia e Trasporti del CNR
• IEA (International Energy Agency) Implementing Agreement on Energy Conservation and Emission Reduction in Combustion” in the collaborative task “Nanoparticle Diagnostics”
• GDRE “Energetic and Safety of Hydrogen”
• In the past the research activities have been financed by the project FIRB RBAU01K749
• A PRIN project is under evaluation

Contacts

• Dr. Silvana De Iuliis, phone +39 02 66173 297
• Dr. Silvia Maffi, phone +39 02 66173 303
• Dr. Francesca Migliorini, phone +39 02 66173 384
• Dr. Barbara Vercelli, phone +39 02 66173 314
• Enio Fantin, phone +39 02 66173 221
• Dr. Giorgio Zizak (associate), phone +39 02 66173 304