Effect of the Nucleation Layer on TiO 2 Nanoflowers Growth via Solvothermal Synthesis
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Effect of the Nucleation Layer on TiO2 Nanoflowers Growth via Solvothermal Synthesis Oscar A. Jaramillo, Reshmi Raman, and Marina E. Rincón* CIE-UNAM, Priv. Xochicalco S/N, Col. Centro, Temixco, Mor. 62580, México. *Contact email: [email protected] ABSTRACT TiO2 nanoflowers were obtained on modified ITO substrates by solvothermal synthesis. Surface modification was achieved with a layer of TiO2 seeds/nucleus obtained by dip-coating at various pH and dip cycles. Field emission scanning electron microscopy results indicated that at all nucleation conditions there was a dual population of TiO2 nanoparticles and nanoflowers. For a particular pH, the effect of increasing the number of dips was to increase the size and number of the nanoflowers, whereas for a fixed number of dips, the increase in pH causes a decrease in nanoflower population. The comparison with solvothermal films obtained on unmodified substrates indicates that TiO2 nanoflowers grew up on the nucleation sites. These microstructural changes determine the active surface area and sensing properties of the solvothermal films. At room temperature, no evidence of superior ethanol sensing properties was found for TiO2 nanoflowers, which show larger resistivity than TiO2 nanoparticles. Keywords: crystal growth, nanostructure, sensor INTRODUCTION Over the past decades, nanostructured materials have emerged as promising materials for fundamental studies and possible technological applications. The reduction in size of functional architectures has been a dominating trend in many fields of science and technology. This size reduction provides unique physical and chemical properties, such as quantum confinement and high electron mobility. In particular, TiO2 nanostructures have received a great deal of attention owing to its outstanding chemical and physical properties and have been extensively used in a wide range of environmental and energy related applications [1-5]. For many of these applications, including gas sensors, it is important to maximize not only the specific surface area of TiO2 nanostructures to increase the device performance, but also to take advantage of new effects associated with particular geometries, such as those found in TiO2 nanotubes and nanowires related to surface reconstruction and surface curvature. Consequently, TiO2 nanoparticles and one-dimensional TiO2 thin films have been widely used as gas sensors in the detection of acetone, ethanol, hydrogen, and carbon monoxide [6-9]. Synthesis of TiO2 nanostructures with confined geometry may be achieved by electrochemical anodic oxidation, sol-gel, chemical vapour deposition, and hydrothermal or solvothermal synthesis [10-15]. Among these methods, hydrothermal/solvothermal synthesis of TiO2 is a promising approach due to its simplicity, fast reaction velocity, and low cost. The advantages of the non-hydrolytic synthesis lie in the suppression of uncontrolled hydrolysis at the beginning of the condensation reaction [15]. Therefore, the solvothermal method has the potential for depositing novel T
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