This study proposes preparing N-doped TiO2 nanoparticles that exhibit a narrow bandgap by calcinating a mixture of Degussa P-25 TiO2 and NH4CI at a temperature of 400 degrees C under airtight conditions to remove gaseous elemental mercury (Hg-0). Sample characterization performed using X-ray photoelectron spectroscopy and ultraviolet-visible spectra indicated that the presence of Ti3+ caused by oxygen vacancy and molecular-state N may be incorporated into a TiO2 lattice; this result was supported by an observation of the Ti-N group conducted using Fourier transform infrared spectroscopy. The formed nanoparticles exhibited a size of 32.4 nm and were in a mixed form of anatase and rutile according to the X-ray diffraction spectra. The low Hg removal of TiO2 nanoparticles under the 0% O-2 dark condition indicated that photocatalytic oxidation limited Hg adsorption. The reemission of adsorbed Hg caused by H2O competition for active sites can be markedly inhibited by N modification, which may be caused by strong bonding between Hg, N, and 0 groups. In addition, TiOxNy underwent less adsorption competition from humidity at an elevated temperature than an untreated sample did. NO exhibited substantial competition for the adsorption sites on the TiO2 surface. By contrast, under dark conditions, both SO2 and HCl slightly enhanced Hg adsorption; under ultraviolet and visible-light irradiation, both SO2 and HC1 markedly reduced Hg removal. SO2 and HC1 may substantially consume O-2(-) and (OH)-O-center dot free radicals during light irradiation and subsequently reduce the transformation of Hg-0 into HgO. (C) 2014 Elsevier B.V. All rights reserved.