Metal-organic frameworks as template for synthesis of Mn3+/Mn4+ mixed valence manganese cobaltites electrocatalysts for oxygen evolution reaction.

Cobalt-based oxides are among the most promising electrocatalysts for oxygen evolution reactions (OER). In this context, this work reports the synthesis of manganese-doped cobaltites using the Zeolitic-Imidazolate Frameworks 67 (ZIF-67) as template. The incorporation of manganese ions into ZIF-67 structure was evaluated in ethanol and methanol, in order to obtain the best synthetic route. Non-doped (ZIF-67C) and Mn-doped cobaltites (Mn/ZIF-67C(E) and Mn/ZIF-67C(M)) were obtained after thermal treatment at 350 °C. Structural and morphological properties were investigated and presence of Mn3+ and Mn4+ was confirmed by X-ray photoelectron spectroscopy (XPS) data and magnetization curves. The electrocatalytic activity in OER was investigated in alkaline medium for manganese cobaltites, and compared to the ZIF-67C. Overpotentials to generate a current of 10 mA cm-2 were 338 mV and 356 mV for Mn/ZIF-67C(E) and Mn/ZIF-67C(M), respectively. These results are superior to those found for similar materials in the literature. The material obtained in methanol (Mn/ZIF-67C(M)) presents lower overpotential, however, shows superior electrocatalytic performance for current density above 100 mA cm-2, therefore being an efficient electrode for commercial electrolysers.

The Effect of Microstructural Changes on Mechanical and Electrochemical Corrosion Properties of Duplex Stainless Steel Aged for Short Periods.

This work reports the effects of microstructural changes due to the secondary phases, in particular sigma (σ), on the mechanical properties and electrochemical behavior of thermally aged duplex stainless steel (DSS). Structural, morphological, mechanical, and electrochemical characterizations were performed. Sigma phase content increased with increasing aging treatment time. It had a net-like shape, as observed by electron backscatter diffractometry (EBSD). Its presence directly damaged mechanical properties. The corrosion assessment included electrochemical impedance spectroscopy (EIS) in 1 M NaCl solution at temperatures of 25, 40, and 65 °C. EIS results demonstrate that an increase in the σ phase content decreased the corrosion resistance (21.1-0.8, 3.5-0.3, and 3.1-0.2 kΩ cm2 at 25, 40, and 60 °C, respectively).

Improved mechanical performance of self-adhesive resin cement filled with hybrid nanofibers-embedded with niobium pentoxide.

OBJECTIVES: In this study hybrid nanofibers embedded with niobium pentoxide (Nb2O5) were synthesized, incorporated in self-adhesive resin cement, and their influence on physical-properties was evaluated. METHODS: Poly(D,L-lactide), PDLLA cotton-wool-like nanofibers with and without silica-based sol-gel precursors were formulated and spun into submicron fibers via solution blow spinning, a rapid fiber forming technology. The morphology, chemical composition and thermal properties of the spun fibers were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC), respectively. Produced fibers were combined with a self-adhesive resin cement (RelyX U200, 3M ESPE) in four formulations: (1) U200 resin cement (control); (2) U200+1wt.% PDLLA fibers; (3) U200+1wt.% Nb2O5-filled PDLLA composite fibers and (4) U200+1wt.% Nb2O5/SiO2-filled PDLLA inorganic-organic hybrid fibers. Physical properties were assessed in flexure by 3-point bending (n=10), Knoop microhardness (n=5) and degree of conversion (n=3). Data were analyzed with One-way ANOVA and Tukey's HSD (α=5%). RESULTS: Composite fibers formed of PDLLA-Nb2O5 exhibited an average diameter of ∼250nm, and hybrid PDLLA+Nb2O5/SiO2 fibers were slightly larger, ∼300nm in diameter. There were significant differences among formulations for hardness and flexural strength (p<0.05). Degree of conversion of resin cement was not affected for all groups, except for Group 4 (p<0.05). SIGNIFICANCE: Hybrid reinforcement nanofibers are promising as fillers for dental materials. The self-adhesive resin cement with PDLLA+Nb2O5 and PDLLA+Nb2O5/SiO2 presented superior mechanical performance than the control group.

1D hollow MFe2O4 (M = Cu, Co, Ni) fibers by Solution Blow Spinning for oxygen evolution reaction.

The development of low-cost transition metal electrocatalysts for the oxygen evolution reaction (OER) has been the focus of intense research. Herein, we report for the first time the synthesis of one dimensional (1D) hollow MFe2O4 (M = Cu, Co and Ni) fibers by the Solution Blow Spinning (SBS) technique and their performance towards OER in alkaline medium. The formation mechanism of the hollow structure and the influence of the fibrillar morphology on the performance of electrocatalysts were discussed. Electrocatalytic performance to generate 10 mA cm-2 with low overpotential followed the sequence: CuFe2O4 > CoFe2O4 > NiFe2O4. The improved OER performance of hollow CuFe2O4 fibers is due to a superior number of active sites exposed to surface reactions, confirmed by a remarkable electrochemically active surface area (ECSA) of 225 cm2. Solution blow spun hollow ferrite fibers showed better electrocatalytic activity towards OER than 1D, 2D and 3D ferrite-based nanostructures reported in the literature.

Evidence for the dissolution of molybdenum during tribocorrosion of CoCrMo hip implants in the presence of serum protein.

We have characterized CoCrMo, Metal-on-Metal (MoM) implant, wear debris particles and their dissolution following cycling in a hip simulator, and have related the results to the tribocorrosion of synthetic wear debris produced by milling CoCrMo powders in solutions representative of environments in the human body. Importantly, we have employed a modified ICP-MS sample preparation procedure to measure the release of ions from CoCrMo alloys during wear simulation in different media; this involved use of nano-porous ultrafilters which allowed complete separation of particles from free ions and complexes in solution. As a result, we present a new perspective on the release of metal ions and formation of metal complexes from CoCrMo implants. The new methodology enables the mass balance of ions relative to complexes and particles during tribocorrosion in hip simulators to be determined. A much higher release of molybdenum ions relative to cobalt and chromium has been measured. The molybdenum dissolution was enhanced by the presence of bovine serum albumin (BSA), possibly due to the formation of metal-protein complexes. Overall, we believe that the results could have significant implications for the analysis and interpretation of metal ion levels in fluids extracted from hip arthroplasty patients; we suggest that metal levels, including molybdenum, be analysed in these fluids using the protocol described here. STATEMENT OF SIGNIFICANCE: We have developed an important new protocol for the analysis of metal ion levels in fluids extracted from hip implant patients and also hip simulators. Using this procedure, we present a new perspective on the release of metal ions from CoCrMo alloy implants, revealing significantly lower levels of metal ion release during tribocorrosion in hip simulators than previously thought, combined with the release of much higher percentages of molybdenum ions relative to cobalt and chromium. This work is of relevance, both from the perspective of the fundamental science and study of metal-protein interactions, enabling understanding of the ongoing problem associated with the biotribocorrosion and the link to inflammation associated with Metal-on-Metal (MoM) hip implants made from CoCrMo alloys.