tailieunhanh - Báo cáo hóa học: " Formation of tungsten oxide nanostructures by laser pyrolysis: stars, fibres and spheres"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Formation of tungsten oxide nanostructures by laser pyrolysis: stars, fibres and spheres | Govender et al. Nanoscale Research Letters 2011 6 166 http content 6 1 166 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Formation of tungsten oxide nanostructures by laser pyrolysis stars fibres and spheres 1 Malcolm Govender 1 Lerato Shikwambana 1 Bonex Wakufwa Mwakikunga Elias Sideras-Haddad Rudolph Marthinus Erasmus2 Andrew Forbes1 4 Abstract In this letter the production of multi-phase WO3 and WO3-x where x could vary between and nanostructures synthesized by CO2-laser pyrolysis technique at varying laser wavelengths mm and power densities 17-110 W cm2 is reported. The average spherical particle sizes for the wavelength variation samples ranged between 113 and 560 nm and the average spherical particle sizes for power density variation samples ranged between 108 and 205 nm. Synthesis of W18O49 stars by this method is reported for the first time at a power density and wavelength of kW cm2 and am respectively. It was found that more concentrated starting precursors result in the growth of hierarchical structures such as stars whereas dilute starting precursors result in the growth of simpler structures such as wires. Introduction Tungsten trioxide is known as a smart material because it exhibits excellent electrochromic photochromic and gasochromic properties. Nano-sized tungsten trioxide has been applied in many nano-photonic devices for applications such as photo-electro-chromic windows 1 sensor devices 2 3 and optical modulation devices 4 . Many techniques for synthesizing nano-sized tungsten trioxide have been reported 5-8 and this article concerns with laser pyrolysis. Laser pyrolysis is more advantageous than most methods because the experimental orientation does not allow the reactants to make contact with any side-walls so that the products are of high quality and purity 9 . Laser pyrolysis is based on photon-induced chemical reactions which is believed