Investigation on Optical and Catalytic Properties of Noble Metallic Nanoparticles in SiO2 and TiO2 Matrix

Sangpour, Parvaneh | 2009

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39215 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Moshfegh, Alireza; Akhavan, Omid
  7. Abstract:
  8. Doping metal or semiconductor nanoparticles in transparent matrix have attracted much attention for practical application in recent years. From fundamental veiw point, limiting the charge carriers and exitons in nanometric scales resulted in new quantum phenomena. In this context, transparent films containing metal nanoparticles shows an absorption peak in visible region of spectrom. Thus, by choosing an appropriate metal and controlling the size and concentration of particles in corresponding matrix, we can provide coatings with a wide rang of colors. Furthermore, thin films containing metal or metal oxide nanoparticles had been considered as nanostructure materials in research and technological fields such as protective coatings, optical filters, optical switches, sensors, catalysts and electronic applications. In this research, we have used RF reactive magnetron cosputtering method to grow SiO2 and TiO2 thin films containing Au, Ag, Cu and their alloy nanoparticles on glass and quartz substrates. After deposition, thin films annealed in Ar(%80)+H2(%20) atmosphere at different temperature (400, 600 and 800 C). The films were analyzed by using UV-Visible specterophotometery, atomic force microscopy (AFM) and X-ray photoelectron spectoroscopy (XPS) methods. According to optical absorption spectra, appearance of an absorption peak at 400, 530 and 562 nm confirmed formation of Ag, Au and Cu nanoparticles in SiO2 matrix, respectively. These peaks were appeared at 424, 552 and 573 nm for Ag, Au and Cu nanoparticles in TiO2 matrix, respectively. In addition, by increasing annealing temperature full width at half maximum (FWHM) of the optical absorption peaks were decreased due to uniformly distributed all size of nanoparticles. Also, optical properties of alloy nanoparticles (Au-Ag), (Au-Cu) and (Ag-Cu) with different concentrations, was investigated. According to results, by increasing annealing temperature and inter diffusion of metal nanoparticles, alloying process was performed and an optical absorption peak of alloy nanoparticles appeared between two absorption peaks of their corresponding pure metal nanoparticles. By increasing concentration of one of the metals, absorption peak shifts toward that metal. Using XPS technique, the results show that, by increasing annealing temperature, surface concentration was increased and their chemical state of nanoparticles were in metallic state. For alloy nanoparticles, a shift in core level binding energy for each of the metal was observed. According to AFM observation, number of the nanoparticles distributed on surface was increased by increasing the annealing temperature and the size of the nanoparticles decresed. After characterization of the metal and alloy nanoparticles in SiO2 and TiO2 thin films, the nanoparticles were for growing ZnO 1D nanostructure as a catalyst nanoparicles. For 1D nanosructure scanning electrn microscopy (SEM) was used. SEM results showed that, by increasing distance from center of the furnance 1D ZnO structure was changed. ZnO nanowires and nanorods were grwon on Au and Ag catalyst nanoparticles, in low temperature and high temperature zone, respectively. However, for Cu catalyst nanoparticle, an opposite behavior was observed. Also, for alloy catalyst nanoparticles, density and length of ZnO nanowires on the surface was increased. We have applied vapor-liquid-solid (VLS) and vapor-solid (VS) mechanism to describe ZnO nanowire growth. Finally, photocatalytic properties of metal and alloy nanoparticles was investigated for decomposition reaction of Methylene Blue (MB). We have found that for Au-Ag:TiO2 thin films the rate of photocatalic decomposition incresed. So, we have concluded that, alloy metal nanoparticles have higher catalytic and photocatalytic properties than corresponding pure metal nanoparticles.
  9. Keywords:
  10. Optical Properties ; Metallic Nanoparticles ; Alloy Nanoparticles ; Catalyst Properties

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