ZrO 2 Doped with Cobalt Nanoparticles to Detect UV Radiatiion
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ZrO2 Doped with Cobalt Nanoparticles to Detect UV Radiation Gerardo Villa Sánchez1,2, Demetrio Mendoza Anaya1*, Claudia Gutiérrez-Wing1, Pedro R. González Martínez.1 Oscar F. Olea Mejía2 1. Instituto Nacional de Investigaciones Nucleares; Carretera México-Toluca S/N, La Marquesa; Ocoyoacac, Estado de México; C. P. 52750; México. 2. Facultad de Química, Universidad Autónoma del Estado de México, Paseo Colón y Tollocan, Toluca, México 50110, México. E-mail: [email protected] ABSTRACT This paper reports the synthesis and characterization of the ZrO2:Co nanosystem, by incorporation of Co nanoparticles (CoNP) into tetragonal and monoclinic zirconia. ZrO2 was synthesized by a sol-gel process, while cobalt nanoparticles were obtained through a colloidal method by chemical reduction of a metal precursor. CoNP were incorporated by two different approaches: during the synthesis of the ZrO2 and by classical impregnation of CoNP on zirconium oxide. The size of Cobalt nanoparticles was controlled through the concentration of reducing agent (NaBH4) and passivanting agent (1-dodecanethiol). According to SEM and TEM analysis, the diameter of the zirconium oxide particles depends on the CoNP concentration added; the particle size for pure zirconia treated at 500°C is 200 nm and 180 nm for ZrO2:Co. XRay diffraction showed presence of the tetragonal and monoclinic zirconia, but the abundance of each one depends on the Co nanoparticles and thermally treatment. INTRODUCTION Nowadays, there has been an increase in the intensity of ultraviolet (UV) radiation that reaches the Earth's surface, which represents a risk to the health of human beings. For this reason, there is currently a huge interest in developing new materials to detect and measure fields of UV radiation through their thermoluminescent (TL) signal. Reported results indicate an important TL response of the zirconia after being exposed to UV radiation, gamma and x-rays. This TL signal can be analyzed and a relationship between the TL intensity and the radiation dose received can be established [1-5]. In particular, monoclinic ZrO2 has a higher TL signal but it shows a critical disadvantage when it is used as a thermoluminescent device, since a great part of its signal is lost within the first minutes after being exposed to UV radiation [5]. On the other hand, previous results have shown that when nanoparticles are incorporated as impurities during the synthesis process of some materials the TL signal can be increased or stabilized [6]. So, it is expected that the presence of cobalt nanoparticles in ZrO2 might modulate the TL signal for specific applications, such as sensors of UV radiation. EXPERIMENTAL ZrO2 was prepared by the sol-gel method. Zirconium propoxide was mixed with 1propanol (Baker) and ammonium hydroxide, under vigorous stirring, distilled water was added and the temperature of the system was increased up to 84°C. CoNP were also added at a 1:100
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concentration during this process. The gel was dried at room temperature for 24 hours. Finally, the d
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