By Wissanu Charerntanom
Year 2016
Abstract
Titanium dioxide (TiO2) and the TiO2-based materials have been deployed in a wide variety of applications, e.g. in dye-sensitized solar cells, water purification and treatment, photocatalytic water splitting, and gas sensors. Moreover, nanosheets are of special interest because of its transformability into various two-dimensional (2D) functional nanostructures. It has large surface area with high chemical activity and quantum confinement effect. The purposes of this research are a) to investigate the prepared nanosheets from Thai magnetic leucoxene mineral using hydrothermal method, b) to study of the nanosheets properties such as size, shape and crystal structure, and c) to know the application of nanosheets on photocatalytic activity and electromagnetic wave absorber application.
This research has experimentally synthesized the nanosheets from the natural magnetic leucoxene mineral under the hydrothermal synthesis condition of 105ºC for 24 hours. Magnetic leucoxene was utilized as the starting material due to its high TiO2 content (70-80%) and inexpensiveness. The characterization of the synthesized nanosheets was subsequently carried out as follows: crystalline structure, chemical composition, shape, size and specific surface area using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) specific surface area analysis. The said characterization was used to determine the applications of nanosheets on photocatalytic activity and electromagnetic wave absorber applications.
The results indicated that at the beginning, the magnetic leucoxene was of rutile phase while the synthesized nanosheets were of titanate structure (H2TixO2x+1). After the calcination at the temperature range of 300 and 400 ºC, the calcined samples demonstrated TiO2 (B). At 500 and 600 ºC, the calcined nanosheets revealed a bi-crystalline mixture consisting of TiO2 (B) and anatase TiO2. At 700–1000 ºC, the
crystalline structure showed anatase and rutile phase. At 1100 ºC, the prepared samples consisted of a mixture of anatase, rutile phase of TiO2, and Fe2O3 phase. The synthesized product also exhibited the flower-like morphology with 2-5μm in diameter, and the nanosheets structure was slightly curved, with 100nm–2μm in width and 1-3nm in thickness. At 100–200 ºC, the product showed sheets–like structure. At 300–1100 ºC, the calcined nanosheets became unstable and began to decompose and transform into
nanoparticles. The increasing size of nanoparticle decreased the specific surface area of the nanosheets caused by increasing calcination temperature. Furthermore, the BET specific surface area of the nanosheets was approximately 279.8 m2/g. More importantly, the synthesized nanosheets achieved the higher photocatalytic activity under UV and visible light than the commercial TiO2 nanoparticles (JRC-01, JRC-03, ST-01 and P-25). The electromagnetic wave absorber coin with nanosheets and the commercial TiO2 nanoparticles (P-25) can absorb electromagnetic wave in gamma (γ) ray and x-ray region were 96.57 and 89.88 % of the initial intensity, respectively. The electromagnetic wave absorber plates made from the as-synthesized nanosheets and recycled high density polyethylene (HDPE) composite could be used for the electromagnetic wave absorption activities in gamma (γ) ray and x-ray region. This synthesis method provided a simple route to prepared nanostructure materials from low-cost Thai mineral with high potential for energy and environment applications.