De La Cruz Montoya, Edwin

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2007 - 200912010 - 20131
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    Surface enhanced raman scattering of TNT on TiO2 substrates-photodegradation kinetics of explosives
    (2007) De La Cruz Montoya, Edwin; Hernández Rivera, Samuel P.; College of Arts and Sciences - Sciences; Mina Camilde, Nairmen; Castro Rosario, Miguel E.; Department of Chemistry; Briano Peralta, Julio G.
    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.
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    Synthesis and characterization of bulk and colloidal magnetic polymer nanocomposites
    (2013) De La Cruz Montoya, Edwin; Rinaldi Ramos, Carlos M.; College of Arts and Sciences - Sciences; Hernández Rivera, Samuel P.; Aponte Huertas, María A.; Morell Cruz, Luis A.; Department of Chemistry; Jiménez Cabán, Esbal
    The development of bulk and colloidal latex polymer nanocomposites of poly (methyl methacrylate) (PMMA) with embedded magnetic nanoparticles particles was investigated. The first approach consisted of the preparation of magnetic PMMA nanocomposites using oleic acid coated cobalt ferrite and magnetite nanoparticles for subsequent characterization of their magnetic properties. It was found that the cobalt ferrite nanocomposite had magnetic hysteresis at 2 and 300 K as well as the magnetite nanocomposite had magnetic hysteresis at 2 K and superparamagnetic behavior at 300 K. Both nanofillers had a similar effect in shifting the glass transition temperature from that of the neat polymer. The influence of cobalt ferrite nanofiller surface chemistry on the thermal, mechanical, and magnetic properties of PMMA nanocomposites was also studied by comparing nanofillers coated with oleic acid (OA, which does not covalently bond to the PMMA matrix) and 3-methacryloxypropyltrimethoxysilane (MPS, which covalently bonds to the PMMA matrix). The values of the degradation temperature (Td) and glass transition temperature (Tg) increased relative to the neat amount polymery when the nanofillers were introduced into the nanocomposites. The greater increase in thermal stability of the nanocomposite with MPS-coated nanoparticles was due to chemical bonding between the acrylate group in MPS and the PMMA. The nanocomposite filled with nanoparticles functionalized with OA showed slightly higher values of magnetic saturation and coercivity compared with those grafted with MPS. Magnetic polymer nanospheres of PMMA with embedded CoFe2O4 nanoparticles were synthesized by magnetic miniemulsion polymerization. The average diameter of the CoFe2O4/PMMA nanospheres was controlled by varying the amount of surfactant. Dynamic light scattering analysis (DLS) of the magnetic polymer nanospheres showed that the average hydrodynamic diameter increased from 145 nm to 225 nm due to the increase in the concentration of the surfactant. The magnetic properties of nanospheres were investigated by measuring the magnetization curves and the complex susceptibility. The particles were found to respond to alternating fields by Brownian magnetic relaxation.