TiO2-x nanoparticles synthesized using He/Ar thermal plasma and their effectiveness on low-concentration mercury vapor removal

Abstract

Oxygen-vacant titanium dioxide (TiO2-x ) nanoparticles were synthesized using thermal plasma as a heating source at various applied plasma currents and He/Ar ratios. Samples with diverse characteristics were developed and the mercury removal effectiveness was subsequently evaluated. TiO2 nanoparticles possessing high purity and uniform particle sizes were successfully synthesized using metal titanium and O-2 as precursors and Ar as plasma 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. The effectiveness of oxygen-vacant sites on Hg-0 removal under the visible light circumstance was confirmed. Hg-0 removal by the TiO2-x nanoparticles was enhanced by increasing the O-2 concentration. However, moisture reduced Hg-0 capture, especially when light irradiation was applied. The reduction in Hg-0 capture may be resulted from the competitive adsorption of H2O on the active sites of TiO2-x with Hg-0 and transformed Hg2+.