Morphological Studies of Bismuth Nanostructures Prepared by Hydrothermal Microwave Heating
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Morphological Studies of Bismuth Nanostructures Prepared by Hydrothermal Microwave Heating. Oxana V. Kharissova, Mario Osorio, Boris I. Kharisov, Edgar de Casas Ortiz Universidad Autónoma de Nuevo León, Monterrey, México. E-mail [email protected] ABSTRACT Elemental bismuth nanoparticles and nanotubes were obtained via microwave hydrothermal synthesis starting from bismuth oxide (Bi2O3) in the range of temperatures 200-220oC for 10-45 min. The formed nanostructures were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Relationship between reaction parameters and shape of the formed nanostructures is discussed. KEYWORDS: bismuth, nanotubes, truncated nanospheres, microwave hydrothermal synthesis. 1
INTRODUCTION
Metallic bismuth is an important element, having a lot of distinct industrial applications as a component of low-melting alloys, catalysts, for production of polonium in nuclear reactors and tetrafluorhydrazine, among others (Norman, 1997; Cotton et al, 1999). High-purity metal is used, in particular, for measuring super-strong magnetic fields. Bismuth in nanostructurized forms has been mentioned in some monographs (Sergeev, 2006; Koch et al, 2007; Fryxell and Cao, 2007; Asthana and Kumar, 2005; Kharisov et al, 2012), reviews (Soderberg, 2003; Cao and Liu, 2008; Dresselhaus et al, 2003), patents (Penner et al, 2007; Guo, 2006), and a lot of experimental articles. Bismuth nanoparticles, nanopowders, nanowires, nanofilms and other nanostructurized forms have been produced by a host of methods, among which, microwave heating (MW) has been also used to obtain bismuth nanostructures (Kharissova and Kharisov, 2008). Thus, microwave treatment of bulk bismuth in air in a domestic MW-oven (power 800 W and frequency 2.45 GHz) led to formation of bismuth nanoparticles (60-70 nm) with Bi2O3 impurities (Kharissova and Rangel, 2007); similar treatment in vacuum (Kharissova et al, 2007; Kharissova et al, 2010) resulted Bi nanotubes formed for 5-15 min. The optimal MW-heating process time was 60 min; the process was found to be highly reproducible and easy. The objective of this report is the study and comparison of various bismuth nanostructures, observed as a result of the synthesis in the conditions of microwave hydrothermal procedure. 2
EXPERIMENTAL
The reactions were carried out in a Teflon autoclave (equipment MARS-5), using bismuth(III) oxide as a precursor and ethyleneglycol (EG) as a reductant. Due to the necessity to exceed boiling point of EG (187oC) and security limits of the equipment, the syntheses were made in the range 200-220°C, reaching pressure close to 300 psi. The reaction times were 10, 15, 30 and 45 min. The formed nanostructures were studied by scanning electronic microscopy (SEM, equipment Hitachi S-5500) and transmission electronic microscopy (TEM, equipment
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JEOL 2010-F). The samples were prepared by ultrasonic dispersing of formed products and further application of suspension onto a lacey grid (Lacey Formvar/Carbon, 300 mesh, Copper approx. grid
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