Birabar Ranjit Kumar Nanda

Adsorption and functional transformation of 2,4,6-trinitrotoluene (TNT) are highly desirable to create a safer environment. Using first principles electronic structure calculations and MD simulations, we have examined the adsorption and catalytic conversion of TNT on the rutile(r) TiO2 (110) surface. TNT is found to remain adsorbed in its molecular form on the pristine r-(110) surface; however, the presence of water and oxygen results in a degradation of TNT to 2,4,6-trinitrobenzoic acid and trinitrobenzaldehyde, while for the latter slightly lower energy barrier is required. Furthermore, the TNT adsorption is dependent on the vacancy concentration. The molecule remains adsorbed on single vacancy reduced surface, while in the presence of double vacancy, the nitro group forms a bond either with the vacant oxygen site or at the five-fold coordinated Ti-site.

Understanding the mechanism of NO2 interaction on semiconductor surfaces such as TiO2 is a key step in designing the catalytic processes for conversion of NO2 to useful products. In the present work, through density functional theory calculations and NEB simulations, we have performed a comprehensive electronic structure study and established the reaction steps for efficient conversion of NO2 to HONO on TiO2 surface in the presence of water vapor. We predict the dimerization of NO2 to form a metastable N2O4. The latter's dissociation to NO+and NO3- complexes occurs in two pathways: (i) direct disproportionation reaction and (ii) through formation of NO2+and NO2- intermediates followed by O transfer. The introduction of H2O on a NO2 chemisorbed surface leads to the formation of nitrous acid through the interaction of NO+ with the water. The reaction pathways leading to formation of nitrous and nitric acids are formulated.