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

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 O2 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 Hg0 removal under the visible light circumstance was confirmed. Hg0 removal by the TiO2−x nanoparticles was enhanced by increasing the O2 concentration. However, moisture reduced Hg0 capture, especially when light irradiation was applied. The reduction in Hg0 capture may be resulted from the competitive adsorption of H2O on the active sites of TiO2−x with Hg0 and transformed Hg2+.