Reactions of hydrazoic acid on TiO 2 nanoparticles: An experimental and computational study

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Abstract

This article reports the results of a computational and experimental study on the reaction of hydrazoic acid, HN 3, adsorbed on 15-20 nm TiO 2 particle films. Experimentally, FTIR spectra of HN 3(a) have been measured by varying HN 3 dosage, UV irradiation time and surface annealing temperature. Three sharp peaks, related to v a(NNN) of HN 3(a) and N 3(a) with different configurations in the 2000-2200 cm -1 region, and a broad band absorption, related to associated and isolated HN(a) and HO(a) adsorptions in the 3000-3800 cm -1 region, have been detected. Computationally, molecular structures, vibrational frequencies and adsorption energies of possible adsorbates including HN 3 and its derivatives, N 3, N 2, NH, and H, have been predicted by first-principles calculations based on the density functional theory (DFT) and the pseudopotential method. On the basis of the experimental and computational results, the peak appeared at 2075 cm -1, which increases at a faster rate with HN 3 exposure time, is attributed to a stable adsorbate, N3-Ti(a), with the predicted adsorption energy, E ads = 13 kcal/mol. The peak at 2118 cm -1, which survives at the highest surface temperature in the heating experiment, is attributable to the most stable adsorbate, Ti-N 2N(H)-O(a) with E ads = 36 kcal/mol. The peak at 2170 cm -1, which vanishes most readily in all of the aforementioned experiments, is related to less stable molecular adsorbates, end-on HN 3-Ti(a) with E ads = 5 kcal/mol and side-on HN(N 2)-Ti(a) with E ads = 8 kcal/mol. A potential energy diagram for the formation of various absorbates with their transition states has been established for the HN 3/TiO 2 system. On the basis of the predicted desorption energies, the four most stable products of the HN 3 reaction on TiO 2 are H-O(a), 118 kcal/mol; HN-O(a), 85 kcal/ mol; Ti-N 2N(H)-O(a), 36 kcal/mol; and N 3-O(a), 19 kcal/mol.

Original languageEnglish
Pages (from-to)5133-5142
Number of pages10
JournalJournal of Physical Chemistry B
Volume109
Issue number11
DOIs
Publication statusPublished - 2005 Mar 24

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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