Synthesis and characterization of nanostructures for catalysis

Santini, Alessandra (2012) Synthesis and characterization of nanostructures for catalysis. PhD thesis, University of Trento.

PDF - Doctoral Thesis


Catalysts are of great importance in many different fields, including the energy and the environmental sectors. It is important to produce them with simple preparation technique and to enhance the catalysts surface-to-volume ratio. The work undertaken in this thesis concerns the synthesis of nanostructures by Pulsed Laser Deposition (PLD) and R.F. sputtering deposition and the tailoring of their structures by varying deposition parameters. We synthesized Cobalt oxide nanoparticles (NPs) by PLD and studied the influence of the deposition parameters (i.e. substrate temperature, target-to-substrate distance and partial pressure of Oxygen in the chamber) on the final structure and crystalline phase of the NPs. The deposited NPs can be divided in two main categories: small NPs having a diameter of about 5 nm, and big NPs of size ranging from 50 to 400 nm. Depending on the value chosen for the deposition parameters, small NPs have CoO- or Co3O4 crystalline phase, and NPs can have a core/shell structure. The phase composition of the core and of the shell also vary according to the deposition conditions. We synthesized thin film of Co-B NPs by PLD. Depending on the energy density, the laser process is able to produce well-dispersed spherical Co NPs partially embedded within B-based film matrix in a single-step deposition. The small size, the polycrystalline nature of Co NPs, and the presence of Boron matrix is important for catalytic performance of the Co-B film. The catalytic activity of the Co-B has been tested in hydrolysis of chemical hydrides (ammonia borane and sodium borohydride). PLD deposition of C-film, to serve as support for Co-B NPs, was performed at different Ar pressures (from 10 to 50 Pa) to tailor film roughness in order to investigate the role of porous and irregular C- surface on supporting Co-B NPs acting as catalysts. The measured hydrogen generation rate attained with C-supported Co-B catalyst film is higher than both unsupported-Co-B film and conventional Co-B powder. Multilayer ITO/Cr-doped-TiO2 thin films have been synthesized by radiofrequency magnetron sputtering in order to sensitize TiO2 in visible light and to lower the charge recombination rate in the Cr-doped-TiO2. When the multilayer films were exposed to visible light, we observed that the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/Cr-doped- TiO2. The superior photocatalytic efficiency of the 6-bilayers film implies higher hydrogen production rate through water-splitting. Spontaneous growth of Lead nanowires (NWs) have been observed in composite Al-Pb film deposited by R.F. sputtering deposition. The parameters of deposition and the storage of the Al-Pb films after deposition has been changed in order to understand the growth process of NWs. Evolution of NWs growth was also observed inside a SEM chamber. We propose that a stress-driven mechanism and the corrosion occurring on the films surface in environment atmosphere are the cause of NWs growth.

Item Type:Doctoral Thesis (PhD)
Doctoral School:Physics
PhD Cycle:XXV
Subjects:Area 02 - Scienze fisiche > FIS/01 FISICA SPERIMENTALE
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