Use of X-Ray Photoelectron Spectroscopy as an analytical tool for the study of contamination by Teflon in the synthesis of Mo(VI)Cl2O2Bipy/ TiO2 catalysts

The preparation of catalysts can involve various sources of contamination, which can seriously affect the quality of the prepared materials. In the present work, a case of fluorine contamination in a set of catalyst samples was studied, in which using the X-Ray Photoelectron Spectroscopy (XPS) technique, it was evidenced by the F 1s signal that this element was present in the form of Teflon, since its binding energy corresponded mainly to the CF2 species. Furthermore, using the C 1s signal, it was also possible to corroborate the presence of the CF2 group, which is associated with the main component of the Teflon carbon chains. The use of this information made it possible to identify that the solvent dehydration procedure (previous step to obtaining the catalysts) could lead to contamination with Teflon since it involved various accessories with Teflon, organic solvents and high temperature; the Teflon tape and the magnetic stirrer being the possible sources of contamination.

La preparación de catalizadores puede contener diversas fuentes de contaminación, las cuales pueden afectar seriamente las propiedades de los materiales preparados. En este artículo se estudió un caso de contaminación con flúor en una serie de muestras de catalizadores. Empleando la técnica de espectroscopia fotoelectrónica de rayos X (XPS) se evidenció la presencia de flúor en la superficie de los materiales, el cual estaba asociado al polímero teflón, ya que su energía de enlace correspondía principalmente con la de la especie CF2. Además, empleando la señal C 1s, se logró corroborar la presencia de la especie CF2, el cual está asociado al componente principal de las cadenas carbonadas de teflón. El uso de la información obtenida por XPS permitió determinar que durante la deshidratación del solvente (paso previo para la obtención de los catalizadores en el cual se emplean solventes orgánicos y alta temperatura) se podría estar llevando a cabo la contaminación con teflón, ya que este componente está presente en diversos accesorios empleados en el proceso de deshidratación, siendo la cinta de teflón y el agitador magnético las posibles fuentes de contaminación.

A preparação de catalisadores pode conter diversas fontes de contaminação, as quais podem afeitar seriamente as propriedades dos materiais preparados. No presente trabalho estudou-se um caso de contaminação com flúor numa série de amostras de catalisadores. Usando a técnica da espectroscopia fotoeletrônica de raios X (XPS), evidenciou-se a presença de flúor na superfície dos materiais, o qual estava associado ao polímero Teflon, já que sua energia de ligação correspondia principalmente à da espécie CF2. Além disso, usando a sinal C 1s, foi possível corroborar a presença do grupo CF2, o qual está associado ao componente principal das cadeias carbônicas do Teflon. O uso da informação obtida por XPS permitiu determinar que durante a desidratação do solvente (passo prévio para a obtenção dos catalisadores no qual são usados solventes orgânicos e alta temperatura) tem-se a contaminação com Teflon, já que este componente está presente em diversos acessórios utilizados no processo de desidratação, sendo a fita do Teflon e o agitador magnético as possíveis fontes da contaminação.

XPS of carbon nanostructures obtained by underwater arc discharge of graphite electrodes / XPS de nanoestructuras de carbono obtenidas por descarga de arco de electrodos de grafito sumergidos en agua

Abstract Carbon nanostructures, obtained by underwater arc discharge of graphite electrodes, were studied by X-Ray Photoelectron Spectroscopy (XPS). It was observed that the spectra of the samples taken from the floating part of the synthesis products, composed basically by Carbon nano-onions (CNO), present differences with those obtained from the precipitate, which contains a mixture of CNOs and multi-walled Carbon Nanotubes (MWCNT). These differences are related with the presence of atoms of carbon located in orbitals with different degree of hybridization (sp2-sp3), which in turn is related to the diverse grade of curvature of the planes of carbon in the nanostructures present in the samples. The obtained results indicate that XPS can be an important element in the characterization of the products obtained by the above-mentioned method of synthesis.

Resumen Se utilizó la Espectroscopia Fotoelectrónica de Rayos X (XPS) para estudiar nanoestructuras de carbono obtenidas por descarga de arco de electrodos de grafito sumergidos en agua. Se observó que los espectros de las muestras tomadas de la fracción flotante de los productos de la síntesis, compuestas básicamente por nano-cebollas de carbono (CNO), presentan diferencias con los de las muestras obtenidas del precipitado, que contiene una mezcla de CNOs y nano-tubos de carbono de capas múltiples (MWCNT). Estas diferencias están asociadas con la presencia de átomos de carbono localizados en orbitales con diferente grado de hibridación (sp2-sp3), lo que a su vez se relaciona con las diferentes curvaturas de los planos de carbono en las nanoestructuras presentes en la muestras. Los resultados obtenidos indican que XPS puede ser un elemento importante en la caracterización de los productos obtenidos por el citado método de síntesis.

Physicochemical and Biological Investigation of Different Structures of Carbon Coatings Deposited onto Polyurethane

The aim of this study was to examine the thrombogenic properties of polyurethane that was surface modified with carbon coatings. Physicochemical properties of manufactured coatings were investigated using transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy and contact angle measurement methods. Samples were examined by the Impact-R method evaluating the level of platelets activation and adhesion of particular blood cell elements. The analysis of antimicrobial resistance against E. coli colonization and viability of endothelial cells showed that polyurethane modified with use of carbon layers constituted an interesting solution for biomedical application.

Effect of Mutans Streptococcus on Corrosion Resistance of Ni-Cr Alloy / 上海第二医科大学学报

Objective To study the effect of Mutans Streptococcus(S.Mutans) on the corrosion resistance of Ni-Cr alloy. Methods S.Mutans were isolated in TSB,and then 10~(5)10~6 CFU/mL of bacterial population was reached.The self-corrosion electrical current density and the corrosion electrical current potential of Ni-Cr alloy were found from polarization curves under the condition with or without media plus S.Mutans.The surface of Ni-Cr alloy after bacterial corrosion was examined with X-ray photoelectron spectroscopy(XPS) to find out different element contents.(Results)From polarization curves,it could be found that the self-corrosion electrical current density and the corrosion electrical current potential of Ni-Cr alloy without S.Mutans were 53.5 ?A/cm~(2)and-62 mV,and those with S.Mutans were 75.7 ?A/cm~(2)and-220 mV.Examination of XPS showed that besides Ni and Cr,the element of chlorine(Cl),sulphur(S),calcium(Ca) could be found on the surface of Ni-Cr alloy after bacterial corrosion.(Conclusion Because of) the metabolism of S.Mutans,an oxide film could be destroyed and a biofilm be formed on the surface of Ni-Cr alloy.Bacterial corrosion could lower the corrosion resistance performance of Ni-Cr alloy.