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| Author(s): |
Glauco Meireles Mascarenhas Morandi Lustosa
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Institution: | Universidade Estadual Paulista (Unesp) |
| Defense date: | 2017-08-24 |
| Advisor: | Maria Aparecida Zaghete Bertochi |
| Abstract | |
The objective of this project was to synthesize two tin dioxide (SnO2) systems, one doped with zinc and niobium and one doped with cobalt and niobium, respectively (Zn, Nb)-SnO2 and (Co, Nb)-SnO2, and conduce the appropriate characterizations to verify the potential use of these systems for applications such as varistor, gas sensor and photocatalyst. The polymer precursors (MPP) method was used for the synthesis SnO2-based systems, this method involves the stoichiometric mixture of the reactants, followed by complexation, polymerization and calcination and subsequent submission to the grinding stage to promote the deagglomeration and reduction of the particle size. The nanoparticles were deposited onto Si (100)/SiO2 (10000 A°)/Ti (200 A°)/Pt (1500 A°) substrate for the study of the varistor property and for analysis of the gas sensor property (when in the presence of carbon monoxide - CO) deposited in substrate of alumina with interdigital electrodes. The films were obtained by electrophoresis deposition technique (EPD), with the following conditions: 20 mg of the powder suspended in 20 mL of isopropanol, which was applied at 2 kV voltage, for different times. For the photocatalytic study, the powder was dispersed into the solution under study, and stirring, aeration and submitted to irradiation with ultraviolet light (9 W and 11 W) to promote the electronic excitation and the generation of active oxidation sites (electron- hole, e- / h+ ). The maximum reaction time was 120 minutes. For the study of the gas sensor activity the (Zn, Nb)-SnO2 films were heat treated at 600 °C for 10 minutes and the (Co, Nb)-SnO2 films at 500 °C for 10 minutes. This stage aimed to promote mechanical resistance to the films avoiding the grain growth, maintaining the presence of the pores to increase the surface area for adsorption of the gas. The films analyzed for the varistor properties were sintered at 1000 °C for 40 minutes and 900 °C for 30 minutes for the compositions, (Zn, Nb)-SnO2 and (Co, Nb)-SnO2 respectively. After sintering, the films for evaluation of varistor properties were modified by the deposition of Cr3+ ions by electrophoresis, followed by a 15 minute heat treatment at the same temperature at which they were sintered. The Cr+3 ions act directly in the region of the grain boundary influencing the formation of the potential barrier. The introduction of the chromium ions, after sintering, aims to control their diffusion by heat treatment, in order to promote the increase of the coefficient of nonlinearity (α) and resistivity of the grain boundary, characteristics necessary to a varistor. Both SnO2-based systems presented responses to the properties of interest, and the best result of photocatalytic activity, in the discoloration of the aqueous solution of rhodamine B, of approximately 80% efficiency was for (Zn, Nb)-SnO2 in 90 minutes of analysis. On the other hand, the system (Co, Nb)-SnO2 presented better sensor and varistor response, and for gas sensor the film presented a response of 2.6 in the self-heating system and for the varistor property the sintered film with rich atmosphere in O2 presented better results with coefficient of nonlinearity (α) between 11.4 and 15.1; (VR <242 V) and leakage current (IF ~ 10-8 A/cm²), which indicates a potential for application as low voltage varistor used in electronic devices. (AU) | |
| FAPESP's process: | 14/11314-9 - Multifunctionality of SnO2 nanoparticles and films modified with ZnO, CoO and Nb2O5 |
| Grantee: | Glauco Meireles Mascarenhas Morandi Lustosa |
| Support Opportunities: | Scholarships in Brazil - Doctorate |