Combined Surface Science and DFT Study of the Adsorption of Dinitrotoluene (2,4-DNT) on Rutile TiO2(110): Molecular Scale Insight into Sensing of Explosives

摘要

Dinitrotoluene (2,4-DNT) is a decomposition product of TNT with a higher vapor pressure and thus has been used for detecting explosives. In particular, solid-state gas sensors based on TiO2 have shown promising properties for sensing DNT. However, the adsorption of DNT on TiO2 has not been understood well at the molecular level before. Here we investigate the adsorption of 2,4-DNT on TiO2(110) by scanning tunneling microscopy, X-ray photoemission spec- troscopy, and density functional theory (DFT) simulations. We find that DNT chemisorbs molecularly intact in a bridge bidentate configuration with two oxygen atoms of one nitro group binding to two neighboring five-fold coordinated titanium atoms at the surface. At saturation coverage, half a monolayer with an ordered 2×1 structure is observed. The DFT calculations corrected by London dispersion force showed that the intermolecular interactions are the determining factor for the formation of ordered adsorption structures under both low and high DNT coverages. DNT remains adsorbed on the surface up to 250-300 °C when it partially desorbs or reacts with excess Ti atoms from the substrate. Furthermore, we show that DNT can be desorbed from the surface through UV-light-induced photoreactions.