Synthesis of nanoparticles of iron oxide, silver and gold for photodegradation and detection of 2,4,6-trinitrotoluene

Abstract

Various nano-structured materials were synthesized to be used in the purification and detection of contaminants in water. Iron oxides and extruded polystyrene/TiO2 nanocomposites were synthesized, characterized and evaluated for potential applications as a photocatalyst in water treatment processes in which heterogeneous photocatalysis forms an essential part. Three iron oxides were synthesized and characterized by X-ray diffraction as hematite, magnetite and Au/magnetite. The last oxide consists of magnetite coated with gold nanoparticles to improve its effectiveness in photodegradation treatments. A dye (methylene blue) was chosen as the test molecule to evaluate dye discoloration during the photocatalytic process. Degradation of about 90% was observed at 6 h of exposure to ultraviolet light. Similarly, a decrease of over 90% in orto-nitrophenol concentration was observed at 3 h of treatment. These results suggest that B-Fe3O4 and Au/Fe3O4 can be used as photocatalyst, to remove contaminants present in water. Taking advantage of their magnetic properties, the oxides may be easily removed from water after the proposed application. Also, satisfactory outcomes were obtained for aqueous solutions of 2,4,6-trinitrotoluene (TNT). The results show that at 9 h of the process 2,4 6-trinitrotoluene concentration decreased to 80% of the initial values. During the study, parameters such as pH, irradiation wavelength and addition of H2O2 as oxidant were evaluated. Degradation of solutions of the highly energetic material cyclotrimethylenetrinitramine (commonly known as RDX) was studied at three wavelengths of ultraviolet radiation (240, 254, and 365 nm). The results show that at 240 and 254 nm, the RDX solutions were degraded without the presence of the photocatalyst. At 365 nm the cyclotrimethylenetrinitramine was resistant to degradation without presence of photocatalyst. Degradation of 70% percent of the explosive in solutions was observed in the presence of magnetite. Also, an evaluation of the degradation of TNT at three pH values (pH = 4, 7, and 9) was carried out. Degradation of 43% was obtained over a period of 3 h of treatment at pH 9. Furthermore, when EPS/TiO2 was evaluated as photocatalyst, methylene blue (MB) solutions were efficiently decolorized using ultraviolet radiation at 254 nm and an intensity value of 600 mW/cm2. The results show a 98% discoloration of MB in solution. A higher stability of the polymer was evidenced through of the incorporation of TiO2 using thermal analysis. Finally, gold and silver nanoparticles were prepared by laser ablation, using water as solvent. 4-Aminobenzenethiol was chosen as probe molecule to determine if nanoparticles deposited served to increase vibrational signals in surface enhanced Raman scattering (SERS) experiments. Parameters such as ablation time and pH of the suspensions were evaluated. TNT was used as analyte to probe if metallic nanoparticles can be substrates in SERS experiments. The results demonstrate that gold and silver nanoparticle substrates prepared by the methods developed show favorable results based on the studies conducted and could be the basis for the development of micro sensors.

Varios materiales nanoestructurados se sintetizaron con el fin de usarse en la purificación y la detección de contaminantes en agua. Óxidos de hierro y un nanocompuesto de EPS/TiO2 se prepararon en forma sencilla y posteriormente se caracterizaron y evaluaron en aplicaciones como fotocatalizadores en procesos de tratamiento de aguas llamados Tecnologías de Oxidación Avanzada, dentro de los cuales se encuentra fotocatálisis heterogénea. Tres óxidos de hierro se sintetizaron e identificaron por difracción de rayos x como hematita, magnetita y Au/magnetita. A este último se le agregaron partículas de oro con el fin de mejorar el tratamiento de fotodegradación. El colorante azul de metileno (MB, por siglas en inglés) fue escogido como molécula de prueba para evaluar la descoloración del tinte bajo el proceso de fotocatálisis. Los resultados muestran una degradación de alrededor de 90% a 6 h de exposición a la luz UV. Igualmente, un decrecimiento de más de 90% en la concentración del compuesto ortonitrofenol (ONP por siglas en inglés) se observó a 3h de tratamiento. Esto indica que los óxidos B-Fe3O4 y Au/Fe3O4 podrían ser utilizados como fotocatalizadores, para eliminar contaminantes presentes en el agua. Tomando ventaja de las propiedades magnéticas, los óxidos podrían ser fácilmente retirados del agua. Igualmente, buenos resultados fueron obtenidos cuando 2,4,6-trinitrotolueno (TNT) fue utilizado como compuesto para ser removido del agua y se encontró que a 9 h del proceso, la concentración del explosivo había disminuido en un 80%. Se evaluaron los efectos de pH, longitud de onda de irradiación y adición H2O2 como un agente oxidante.