Single-step synthesis of N-doped TiO₂ by flame aerosol method and the effect of synthesis parameters

We have established a novel route for the synthesis of N-doped TiO₂ by adopting flame aerosol (FSP) technique and investigated the effect of water content on the physico-chemical properties of the as-synthesized nanoparticles. The key characteristics of the developed method are to modify the precursor solution in order to incorporate nitrogen atoms into the TiO₂ lattice without altering the FSP set-up. The reduction of the flame enthalpy resulting in N-incorporation into the TiO₂ and the N-doping can be greatly enhanced further by the addition of secondary N-source (urea). Our XRD results reveal a shift of the (101) plane anatase diffraction peak to lower angles in our N-doped TiO₂ compared to undoped TiO_2, which suggest the distortion and strain in the crystal lattice prompted by the incorporation of the nitrogen atoms. The growth or expansion of crystal lattice can be attributed to the larger atomic radius of respective nitrogen atoms (r = 1.7 Å) compared to oxygen (r = 1.40 Å). Our XPS and EDX spectroscopy results elucidate that the nitrogen was effectively doped into the crystal lattice of TiO₂ in our as-synthesized N-TiO₂ catalysts predominantly in the form of interstitial nitrogen (Ti−O−N). The nitrogen atoms incorporation into the crystal lattice of titania modifies the electronic band structure of TiO₂, resulting in a new mid-gap energy state N 2p band formed above O 2p valence band. This occurrence narrows the band gap of TiO₂ (from 3.12 to ∼2.51 eV) in our N-doped TiO₂ and shifts the optical absorption to the visible region.

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