Surface enhanced Raman scattering of TNT on titanium dioxide substrates: Photodegradation kinetics of explosives

The majority of explosives found in antipersonnel and antitank landmines contain 2,4,6-trinitrotoluene (TNT). 2,4-Dinitrotoluene (DNT) is a common manufacturing byproduct in the synthesis and degradation of TNT. The production, testing and use of high explosives such as TNT and DNT, from the late 19th century to date has extensively contaminated soil and water at a large number of government installations. These high explosives are toxic and mutagenic and have been classified as environmental hazards and as priority pollutants by US EPA. For these reasons, the study of new processes for the detection and degradation of traces of these compounds is of world-wide interest. Nanotechnology is ideally suited to needs in these two areas by providing new materials and methods that can be employed for trace explosive detection and photodegradation. This work focused on modification of nanoscaled colloids of titanium dioxide (anatase), as substrates for use in Surface Enhanced Raman Scattering (SERS) spectroscopy and in photocatalytic degradation of explosives in water, a process assisted by luminous energy with wavelengths capable of electronically exciting a semiconductor.; Metallic oxides were found to give good Raman enhanced signals of target molecules. TNT increased the intensities of the Raman signatures for this technique and was evaluated for excitation sources of 488, 532, and 785 nm. Ultra fine particles of TiO2 were generated by hydrothermally treatment of sol-gel derived hydrous oxide. SERS spectra of nanocrystalline anatase samples prepared with different average size: 38 nm (without acid), 24 nm (without acid), 7 nm (with HCl acid) and with KBr were obtained of mixtures with 0.5mg of TNT. The studies clearly indicated that the anatase crystal size affects the Raman signal of 0.5 mg of TNT.; The percentage decrease in TNT and DNT concentration, resulting from photocatalytic reactions conducted for 140 min, were 70% and 75%, respectively. The reaction rate was found to obey pseudo first order kinetics represented by the Langmuir-Hinshelwood model. Reaction rate constant of 1.67 [mg/L.min] (TNT) and 1.02 [mg/L.min] (DNT) were found.