| Summary: | 博士 === 國立高雄第一科技大學 === 工程科技研究所 === 100 === Oxygen-vacant titanium dioxide (TiO2-x) nanoparticles possessing a narrower band gap were synthesized with a single-step process using N2/He/Ar thermal plasma as a heating source. Samples with diverse characteristics were developed and the elemental mercury (Hg0) removal effectiveness was subsequently evaluated. TiO2 nanoparticles possessing high purity and uniform particle sizes were successfully synthesized using metal titanium and O2 as precursors and Ar as plasmas gas. TiO2-x in anatase phase with a particle size at 5–10 nm was formed at the He/Ar volume ratio of 25/75. Further increasing the He/Ar ratio elevated the plasma temperature, causing the tungsten to melt, vaporize from the cathode, and then dope into the formed TiO2 nanoparticles. The doped W appeared to inhibit the growth of nanoparticles and decrease the crystallinity of formed anatase. In the case of N2 mixed with He and Ar as the plasma gas, sample characterization showed that the formed TiO2-x nanoparticles had a size within 5–40 nm and was in a mixing from of anatase and rutile. An evident absorption red shift to 470 nm wavelength was observed. The deconvolution results of XPS spectra supported the formation of TiO2-x due to the presence of Ti3+2p peaks. The Hg removal efficiency of TiO2-x nanoparticles increased with increasing O2 concentration and in the presence of light irradiation, suggesting an enhancement in Hg0 oxidation. H2O molecules, however, greatly reduced the Hg removal of TiO2-x under visible-light (VL) irradiation. The photoinduced hydrophilicity of TiO2-x under VL irradiation was suspected to amplify the competitive adsorption of H2O that decreased Hg capture. Hg removal performances at 50oC were better than those at 25oC and 100oC, suggesting that both adsorption and catalytic oxidation limit the Hg removal. TiO2-x/ACF composite was also manufactured with thermal plasma evaporation condensation system to confirm TiO2-x effectiveness on Hg0 removal under VL. Resembling results were shown in the test using TiO2-x nanoparticle and TiO2-x/ACF composite. The effectiveness of oxygen-vacant sites on Hg0 removal under the visible light circumstance was thus confirmed. These observations also implicate that the bonding between TiO2-x and adsorbed Hg was weak and adsorption reaction may be reversible.
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