Characterization of the stability of Ag nanoparticles during its incorporation into TiO2 coatings and its photocatalytic activity

ESTANISLAO PORTA; MARÍA VIRGINIA ROLDÁN; NORA S. PELLEGRI

Santa Fe

Conferencia; VI San Luis Conference; 2018

INTEC, IFIS

Self-cleaning surfaces have received an increasing interest in the last years. The modification of surfaces by deposition of metal oxides thin films is a very effective strategy for granting self-cleaning properties to a wide variety of materials1. Nowadays TiO2 is recognized as one of the most interesting photocatalysts due to its photo-stability, chemical inertness, low cost and nontoxicity2. TiO2 may exist as three possible crystalline structures: anatase, rutile or brookite; being the first one the most efficient as a photocatalyst. However, when sunlight is used to activate the photochemical processes, the yield is bounded by the band-gap energy (3.2 eV for anatase-structured TiO2). This delimits the useful radiation only to the UV part of the spectrum, which represents barely 3 to 5% of the total electromagnetic radiation. For that reason, there is an increasing interest in tayloring materials to broaden the activation range towards the visible part of the spectrum, which represent almost 43% of the incident radiation. A useful strategy for achieving this is doping the material with metallic nanoparticles. Among these, Ag nanoparticles have gained a lot of attention due to their high extinction coefficient, good chemical stability, relatively low cost as well as exhibiting enhanced photocatalytic behavior of Ag NP doped TiO2 materials, due to a better harnessing of solar radiation3. To obtain these composite materials, Sol-gel techniques are specially useful because they allow the deposition of metal oxide films onto different substrates, such as stainless steel, ceramic or glass, among others, with good control of their composition and nano-architecture. In this work, we present the synthesis and characterization of TiO2 thin films doped with Ag nanoparticles obtained by a Sol-gel method. A TiO2 sol was obtained from hydrolysis and condensation reactions of Titanium iso propoxide. Separately, Ag NPs were synthesized from a bottom-up method and they were added to the colloidal solution that acted as a precursor. Due to the nanometric size of the silver nanoparticles, their chemical reactivity is largely enhanced in relation to the bulk material, therefore characterization of the solution?s stability during all the stages is of great importance. Thus, different acids where used as catalysts or chelating agents of the Sol-gel processes and stability over time of the Ag-TiO2 sols were monitored. This was made through studying the viscosity and absorption coefficient in the UV-Vis spectra. Subsequently, coatings on glasses and Si waffers were obtained through dip-coating techniques. The thin-films were thermally treated in a conventional furnace and, because Ag NPs may undergo oxidation and melting processes, different gaseous atmospheres were studied. To understand the structural evolution of the composite material during thermal treatment, differential thermo-gravimetric analysis, FT-IR and XRD studies were performed. The photocatalytic properties of the composite materials was studied through the degradation of methyl orange under UV irradiation of the Ag NP doped TiO2 thin films, using different doping concentrations.