Pacheco-Londoño, Leonardo C.
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Publication Recognition of 2,4-DNT, RDX and TATP in various matrices by FTIR-partial least squares - discriminant analysis and kinetics of surface sublimation(2005) Pacheco-Londoño, Leonardo C.; Hernandez-Rivera, Samuel P.; College of Arts and Sciencies - Sciences; Mina-Camilde, Nairmen; Cortés-Figueroa, José E.; Department of Chemistry; Walker, Uroyoán R.A methodology useful for processing spectroscopic information using pattern recognition was designed, developed and implemented in detection of energetic materials at trace level in air, sand and surfaces. Partial Least Squares-1 (PLS) was used to generate vectors to be used with pattern recognition. These vectors were then coupled to Discriminant Analysis by adjusting to a discriminating function. Fourier Transform Infrared (FTIR) spectra of traces of 2,4-dinitro-toluene (2,4-DNT) in air, triacetone triperoxide (TATP) in air and air free of those explosives were recorded and used for generated the vectors. Short wave infrared (Near IR) and Long wave infrared (Mid IR) regions were studied and used for the model. Two vectors were necessary for good discrimination for TATP and four vectors for 2,4-DNT; but, when the regions were weighted from the response of detector, the model was improved and less vectors were needed for all discrimination in the prediction of new samples. Traces of 2,2,4,4,6,6-hexa-hydro-1,3,5-trinitro-1,3,5-triazine (RDX) in sand were detected for microscopy FT-IR. By means of the methodologies PLS and Discriminant analysis, we are found that spectra infrared of the sand can be affected by the presence of traces of RDX. The traces of RDX is created perturbation or patter in the spectra of sand, and this patter is utilized for the detection of RDX. In addition, the kinetics of surface sublimation for 4 explosives was studied. For TATP two minutes were necessary for the half of the explosive on the surface be to transported to air. For 2,4-DNT one hour were necessary. RDX and TNT was not good candidate for detection in gas phase, specially RDX, because its half life is very long, approximately 2 years.Publication Laser-Induced growth of nanoparticles and nanostructures(2011) Pacheco-Londoño, Leonardo C.; Hernández Rivera, Samuel P.; College of Arts and Sciences - Sciences; Mina Camilde, Nairmen; Fernández, Félix E.; Souto Bachiller, Fernando A.; De Jesús, Marco A.; Briano Peralta, Julio G.; Department of Chemistry; Mehta, Narinder K.The preparation of nanostructures assisted by laser action was studied and successfully accomplished from solution and on surfaces. The synthesized nanostructures were characterized by several microscopy techniques. Silver, gold, copper and platinum nanoparticles were grown on surfaces in the form of patterns by the exposure of laser radiation onto droplets of metal ion solutions and the aid of a reducing agent. The generation of patterns from metallic nanoparticles (NPs) was achieved by combining induced growth of nanoparticles and nanostructures by laser incidence directly on surfaces (LIDS) and optical image formation techniques for transferring the patterns. Near-ultraviolet (363.8 nm) and visible (532 nm) laser wavelengths were used for the laser induced growth of NPs into microstructures on glass, quartz, stainless steel, silicon and gold-on-silicon substrates. The sizes of the patterns formed were on the micrometer scale and the sizes of the transferred patterns were on the millimeter scale. The patterns formed were generated by optical transference of image and interference of laser beams. Ag and Au substrates were highly active in surface enhanced Raman spectroscopy (SERS). The enhanced Raman activity was measured for SERS probe molecules: 9H-purin-6-amine (adenine) and 1,2-bis(4-pyridyl)-ethane (BPE) analytes on Ag and Au substrates, respectively. The enhancement factor obtained were 1.8×105 and 6.2×106 respectively. The growth Ag nanoparticles in solution and their conversion to nanoprisms induced by laser radiation action were studied and the kinetics of growth and conversion processes was measured. A mechanism for the growth and conversion from nanoparticle seeds to nanostructures consisting of two processes was proposed. The kinetics for the two processes was measured and the dependence of rate of growth and conversion with laser power was obtained. The quantum efficiency for the processes was also measured. The first process consisting of agglomeration was found to depend on the probability of excitation of plasmon the initial nanoparticles (seeds). This first process is necessary for the second process (growth process) to occur and controls it in an indirect way. Nucleation and crystallization of nanoprisms and the growth of crystal are produced by the NP excited by light. The size of the crystals obtained is controlled by the wavelength of the incident light in the second process. The growth begins by an agglomeration process followed by fusion of the nanoparticles to produce small crystals and finally the growth of relatively large crystals. SERS activity was measured for three different analytes, several types of nanoprisms and various Raman excitation lines. Enhanced Raman activity was measured for nanoprisms in aqueous suspensions and on surfaces. The activity SERS for the nanoprisms is better when those are on substrate surfaces. It is possible have a considerable repeatability when a gold surface is treated with a solution of S2− anions.