Microwave-assisted synthesis of various gallium oxyhydroxide nanorods and their controllable conversion into different g
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Lizhi Zhanga) Key Laboratory of Pesticide and Chemical Biology of Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079, China
Huimin Jia and Zhi Zhengb) Institute of Surface Micro and Nano Materials, Xuchang University, Xuchang, Henan 461000, China (Received 25 August 2008; accepted 27 October 2008)
Various a-GaOOH nanorods were synthesized through a microwave-assisted method at 80 C. In the synthesis, Ga(NO3)3 was used as the gallium source, and urea, L-cysteine, and EDTA disodium salt were used as the additives. The thermal decomposition of the as-prepared a-GaOOH nanorods could selectively produce a-, b-, and e-Ga2O3 nanorods. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and cathodoluminescence were used to characterize the resulting samples. On the basis of characterization results, the possible growth mechanisms of these various GaOOH nanorods were proposed. This study provides a controllable method to prepare various gallium oxyhydroxide and gallium oxide nanorods.
I. INTRODUCTION
In recent years, one-dimensional (1D) nanostructured semiconductor oxides (TiO2, ZnO, In2O3, and Ga2O3) have received much attention because of their potential applications in electronic/optical nanodevices and functional materials.1,2 Among them, gallium oxide (Ga2O3) with a wide band gap of 4.9 eV is of great importance due to its varieties of potential applications including transparent conducting oxide,3–5 optical emitter for UV,6 gas sensors,7,8 and photocatalysis.9 It is well known that gallium oxide is a polymorphic compound with different crystalline phases (a-, b-, g-, d-, and e-Ga2O3).10 Among these polymorphs, b-Ga2O3 has been studied most widely.11,12 So far, the synthesis and characterization of 1Dnanostructured b-Ga2O3 such as nanowires13,14 and nanorods15–17 have been extensively studied. Various methods including hydrothermal synthesis,15,16 hydrolysis,18 laser ablation,13 and carbon-thermal reduction19 have been developed to synthesize b-Ga2O3. Previous studies indicated that gallium oxides prepared under reducing conditions have oxygen vacancies, which resulted Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2009.0280 2268
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J. Mater. Res., Vol. 24, No. 7, Jul 2009 Downloaded: 17 Mar 2015
in the remarkable conduction and luminescence characteristics6 because of the formation of n-type semiconductor. More recently, scientists have found that b-Ga2O3 prepared under nonreducing conditions could also exhibit remarkable luminescence characteristics.20 In addition to the b-Ga2O3, the fabrication of other Ga2O3 polymorphs has also been attracting much attention in recent years because of their interesting photocatalytic and luminescence properties.9,16 For example, Hou and Wu reported a-, b-, and g-Ga2O3 could be used for the photocatalytic decomposition of volatile aro
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