Milena Zorko

Zinc-decorated silica-coated magnetic nanoparticles for protein binding and controlled release.

The aim of this study was to be able to reversibly bind histidine-rich proteins to the surface of maghemite magnetic nanoparticles via coordinative bonding using Zn ions as the anchoring points. We showed that in order to adsorb Zn ions on the maghemite, the surface of the latter needs to be modified. As silica is known to strongly adsorb zinc ions, we chose to modify the maghemite nanoparticles with a nanometre-thick silica layer. This layer appeared to be thin enough for the maghemite nanoparticles to preserve their superparamagnetic nature. As a model the histidine-rich protein bovine serum albumin (BSA) was used. The release of the BSA bound to Zn-decorated silica-coated maghemite nanoparticles was analysed using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). We demonstrated that the bonding of the BSA to such modified magnetic nanoparticles is highly reversible and can be controlled by an appropriate change of the external conditions, such as a pH decrease or the presence/supply of other chelating compounds.

Time Evolution of the Stability and Oxygen Reduction Reaction Activity of PtCu/C Nanoparticles

Crystalline Cu3Pt nanoparticles supported on graphitized carbon are synthesized by using a modified sol–gel method, and subsequent thermal annealing leads to alloying of Pt with Cu and formation of a partially ordered Pm

SEM method for direct visual tracking of nanoscale morphological changes of platinum based electrocatalysts on fixed locations upon electrochemical or thermal treatments

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Electrochemical Dissolution of Iridium and Iridium Oxide Particles in Acidic Media: Transmission Electron Microscopy, Electrochemical Flow Cell Coupled to Inductively Coupled Plasma Mass Spectrometry, and X-ray Absorption Spectroscopy Study

m structure. Electrochemical dealloying under potentiodynamic conditions (potential cycling) induces not only changes from rather spherical high‐index faceted to more cuboctahedral low‐index faceted core–shell structures for particles in a size range of 10–20 nm but also percolation for some particles larger than 20 nm. In contrast, during dealloying under potentiostatic conditions (potential hold) the semispherical shape of small particles is completely retained and extensive porosity is formed on all particles larger than 20 nm. Other degradation processes are not observed on performing an additional accelerated aging test; hence, the high specific and mass activity of the catalyst decreases only slightly, mainly owing to continuing Cu leaching. The difference in dealloying protocols and their effect on the structure of the catalysts as well as their activities, considering the promising porosity formation, are discussed and indicate future directions for a rational design of active and stable oxygen reduction reaction catalysts.

TEM Study of Heavily Twinned Cu3Pt Nanoparticles

A general method for tracking morphological surface changes on a nanometer scale with scanning electron microscopy (SEM) is introduced. We exemplify the usefulness of the method by showing consecutive SEM images of an identical location before and after the electrochemical and thermal treatments of platinum-based nanoparticles deposited on a high surface area carbon. Observations reveal an insight into platinum based catalyst degradation occurring during potential cycling treatment. The presence of chloride clearly increases the rate of degradation. At these conditions the dominant degradation mechanism seems to be the platinum dissolution with some subsequent redeposition on the top of the catalyst film. By contrast, at the temperature of 60°C, under potentiostatic conditions some carbon corrosion and particle aggregation was observed. Temperature treatment simulating the annealing step of the synthesis reveals sintering of small platinum based composite aggregates into uniform spherical particles. The method provides a direct proof of induced surface phenomena occurring on a chosen location without the usual statistical uncertainty in usual, random SEM observations across relatively large surface areas.

In-situ TEM and Atomic-Resolution STEM Study of Highly Active Partially Ordered Cu 3 Pt Nanoparticles used as PEM-Fuel Cells Catalyst

Iridium-based particles, regarded as the most promising proton exchange membrane electrolyzer electrocatalysts, were investigated by transmission electron microscopy and by coupling of an electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometry. Additionally, studies using a thin-film rotating disc electrode, identical location transmission and scanning electron microscopy, as well as X-ray absorption spectroscopy have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that Ir particles dissolve well below oxygen evolution reaction (OER) potentials, presumably induced by Ir surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile-type IrO2 particles are substantially more stable and less active in comparison to as-prepared metallic and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER-relevant conditions, E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism, where the formation of unstable Ir(>IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low-temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyzer.

New Insights into Corrosion of Ruthenium and Ruthenium Oxide Nanoparticles in Acidic Media

The efficiency of proton exchange membrane fuel cells (PEM-FC) is mainly limited by the activity of the cathode catalyst for oxygen reducing reaction (ORR). Various materials based on Pt – transition metal alloys are used for such application [1, 2] where it was found that electrocatalytic activity can be substantially increased through the formation of ordered intermetallic compound (like Cu3Pt) and the formation of core-shell structure [3]. The physicochemical properties of metal nanoparticles strongly depend on their size, shape and the internal crystal structure. Nanocrystals with twinned structures can exhibit different properties comparing to single-crystal counterparts, due to a large defect-to-volume ratio. The lattice strain caused by twin defects could have a significant impact on the electronic structure of metal nanocrystals influencing the interatomic distances and thus the energy levels of bonding electrons, which in turn determines the catalytic, electrical and optical properties [4]. It was reported, that in the case of the parallel twined structure of platinum nanoparticles, the conductivity is increased significantly, up to 6 times compared to pure (defect free) Pt. [5] Some particles could exist as single twin (just one twin defect) or as multiple twin particles. Two types of multiple (repeated) twinning are known in metal nanoparticles: lamellar and cyclic. Lamellar twinning is characterized by parallel contact twins repeating continuously one after another while cyclic twinning requires nonparallel coplanar composition planes forming decahedron and icosahedron morphologies.

Nanocomposites containing embedded superparamagnetic iron oxide nanoparticles and rhodamine 6G

The efficiency of harvesting the energy in proton exchange membrane fuel cells (PEM-FC), like in all other types of fuel-cells, is mainly limited by the activity of the cathode catalyst for oxygen reducing reaction (ORR). Various catalysts, such as noble metals, intermetallic alloys, carbon-based supports, metal chalcogenides and carbides, are used to reduce the ORR temperature and achieve maximum reaction efficiency [1]. The main problem is slow adsorption and reaction kinetics, so searching for more efficient catalysts is one of the main challenges in the field of fuel cells. Among the most promising materials are C-supported Pt-based catalysts [2, 3]. In order to reduce the price of the material, Pt has been alloyed with various transition metal elements. In many cases not only the expected mass activity of the catalyst is improved, but also its specific activity is enhanced due to crystal lattice strains and the ligand effects through the d-band center shift induced by the transition elements [4, 5]. In the case of C-supported CoPt3 particles it has been recently shown that the electrocatalytic activity can be radically increased through core-shell structural ordering of intermetallic nanoparticles [5].