Ulises Martinez

Self-Supported PdxBi Catalysts for the Electrooxidation of Glycerol in Alkaline Media

Highly active self-supported PdxBi catalysts are synthesized by the sacrificial support method. Self-supported PdxBi catalysts have a porous nanostructured morphology with high surface areas (in the range from 75 to 100 m(2) g(-1)), making PdxBi a state-of-the-art catalyst. Pd4Bi displays the highest activity toward glycerol oxidation. In situ Fourier transform infrared spectroscopy highlights the unique catalytic behavior of self-supported PdxBi materials due to their particular structure and morphology. The confinement of reactants and intermediates in pores acting as nanoreactors is responsible for the high selectivity as a function of the electrode potential: aldehyde and ketone at low potentials, hydroxypyruvate at moderate potentials, and CO2 at high potentials. Moreover, the selectivity depends on the electrode history: it is different for the positive potential scan direction than for the reverse direction, where the catalyst becomes selective toward the production of carboxylates.

Investigation of the nanomechanical and tribological properties of dental materials

This study utilises nanoindentation and nanoscratch for testing the human enamel and dentine and three biocompatible dental filling materials: epoxy nanocomposite, glass ionomer, and silver amalgam. Nanoindentation gave hardness and Youngs modulus. Nano-scratch gave critical load in the scratch test, and resistance to sliding wear. The results show that the silver amalgam filling has a higher modulus of elasticity, hardness and wear resistance than the nanocomposite. These relatively nondestructive mechanical characterisation techniques may assist in better understanding the mechanical behaviour of the dental fillers and thus facilitate the design of robust fillers with excellent mechanical properties.

Large-scale protein arrays generated with interferometric lithography for spatial control of cell-material interactions

Understanding cellular interactions with material surfaces at the micro- and nanometer scale is essential for the development of the next generation of biomaterials. Several techniques have been used to create micro- and nanopatterned surfaces as a means of studying cellular interactions with a surface. Herein, we report the novel use of interference lithography to create a large (4 cm2) array of 33nm deep channels in a gold surface, to expose an antireflective coating on a silicon wafer at the bottom of the gold channels. The fabricated pores had a diameter of 140-350nm separated by an average pitch of 304-750 nm, depending on the fabrication conditions. The gold surface was treated with 2-(2-(2-(11-mercaptoundecyloxy)ethoxy)ethoxy)ethanol to create protein-resistant areas. Fibronectin was selectively adsorbed onto the exposed antireflective coating creating nanometer-scale cell adhesive domains. A murine osteoblast cell line (MC3T3-E1) was seeded onto the surfaces and was shown to attach to the fibronectin domains and spread across the material surface.

Pt7Sn3 catalysts for ethanol electro-oxidation: correlation between surface structure and catalytic activity

Ethanol electro-oxidation has attracted great attention in the fuel cell technology for direct ethanol fuel cells (DEFCs). Active and inexpensive electrocatalysts are required to efficiently break C-C bond and completely convert ethanol to CO2. Recent studies showed that PtxSn1-x catalysts have promising catalytic activity for ethanol electro-oxidation in both acidic and alkaline solutions [1, 2]. Despite the numerous studies on PtSn catalysts, several issues regarding their catalytic activity and stability remain to be addressed. Surface composition and chemistry of bimetallic catalyst is complex and may be influenced by several parameters, e.g., synthesis method, particle size, catalyst structure, surface chemistry, therefore investigation of the surface structure of bimetallic catalysts and its correlation to the catalytic performance is an important task. In the present work PtSn nanostructured catalysts with the atomic ratio of Pt to Sn of 70:30 at. % were synthesized and tested for ethanol electro-oxidation in alkaline and acidic solutions. X-ray photoelectron spectroscopy has been chosen to study the surface chemistry of carbon-supported Pt7Sn3 catalysts and correlate it with electrocatalytic activity. The ability to discriminate between different chemical environments, not just elemental compositions, is one of the primary advantages of XPS in the characterization of catalysts. Synthesis of the bimetallic Pt7Sn3 catalysts supported on carbon (Vulcan XC-72) is described in details elsewhere [4]. Table 1 summarizes the synthesis conditions and some characteristics of Pt7Sn3 nanoparticles. Carbon-supported Pt7Sn3 catalysts were analyzed by KRATOS Axis Ultra DLD X-ray Photoelectron Spectrometer. The XPS analysis was conducted at 140 W and at pass energy of 20 eV. The peak positions were corrected for sample charging by setting the maximum of C 1s peak to binding energy of 284.7 eV. Data analysis and quantification was performed using CasaXPS software. Correlation of XPS structural information with catalytic performance for ethanol electro-oxidation in acidic and alkaline solutions, particle size and structural characteristics is accomplished by application of Multivariate statistical methods of data analysis (MVA). [3] Principal Component Analysis (PCA) and Partial Least Squares Discriminant Analysis (PLSDA) are used herein as an analysis tools to find samples which are globally correlated or anti-correlated, and to facilitate visualization of the variables responsible for the correlations and to highlight differences between two categories of structures of catalysts obtained. Several observations were found from the structureto-property correlations for the carbon-supported Pt7Sn3 catalysts : 1. Best performing catalysts for ethanol electrooxidation in acidic solution do not have largest absolute amounts of Pt and Sn on the surface, whereas samples with largest amount of total Pt and Sn have the worst catalytic activity (current density, i) and largest electrochemical active surface area (EASA). 2. Relative distribution of types of Pt and Sn is more important than the absolute amounts. Best performing samples have small amounts of both metals, but have largest relative amount of both metallic Pt and metallic Sn. The same best performing samples have fewest amounts of all types of oxides, i.e. PtO, PtO2 and SnOx. Ongoing electrochemical evaluations of Pt7Sn3 catalysts for ethanol oxidation in alkaline media will be correlated to XPS structural information and discussed along with their catalytic activities.

Investigation of the Nanomechanical and Tribological Properties of Tooth-Fillings Materials

This study utilizes novel characterization techniques nanoindentation and nanoscratch for testing both the human enamel and dentine together with two biocompatible dental filling materials; epoxy nanocomposite and silver amalgam. Nanoindentation tests were performed to obtain accurate hardness and reduced modulus values for the enamel, dentin and two different fillers. We utilized Nano-scratch tests to obtain critical load in scratch test and resistance to sliding wear. Testing showed the silver amalgam filling has a higher modulus of elasticity, hardness and wear resistance compared to the nanocomposite. The novel mechanical characterization techniques utilized might assist in better understanding the mechanical behavior of the dental fillers and thus facilitate the design of robust fillers with excellent mechanical properties.Copyright