Hana Tarábková

Nanobubble-assisted formation of carbon nanostructures on basal plane highly ordered pyrolytic graphite exposed to aqueous media.

Ambient gas nanobubbles of size approximately 10(1)-10(2) nm occupying the hydrophobic surface of basal plane highly ordered pyrolytic graphite (HOPG) immersed in aqueous media at room temperature cause exfoliation of the top graphene layers, as revealed by both in situ and ex situ atomic force microscope (AFM) imaging. The formation of nanoparticles composed mostly from graphene-based nanoscrolls, nanohorn-like and onion-like nanostructures was resolved by high resolution transmission electron microscopy (TEM) and examined by diffraction and x-ray photoelectron spectroscopy (XPS) analyses. The diameter of nanostructures varied from about 5 nm for single-layered scrolls to tens of nanometres for multishells. Raman spectroscopy confirmed the structural rearrangement of the HOPG basal plane after the above-mentioned treatment. The implications for nanobubble interfacial forces are discussed.

Bovine serum albumin film as a template for controlled nanopancake and nanobubble formation: in situ atomic force microscopy and nanolithography study.

Air nanobubbles and nanopancakes were investigated in situ by both tapping mode atomic force microscopy (TM AFM) and atomic force nanolithography techniques employing bovine serum albumin (BSA) film supported by highly oriented pyrolytic graphite (HOPG). The BSA denaturation induced by the water-to-ethanol exchange served for conservation of nanobubble and nanopancake sites appearing as imprints in BSA film left by gaseous cavities formerly present on the interface in the aqueous environment. Once the BSA film was gently removed by the nanoshaving technique applied in ethanol, a clean basal plane HOPG area with well-defined dimensions was regenerated. The subsequent reverse ethanol-to-water exchange led to the re-formation of nanopancakes specifically at the nanoshaved area. Our approach paves the way for the study of gaseous nanostructures with defined dimensions, formed at solid-liquid interface under controlled conditions.

Surface rearrangement of water-immersed hydrophobic solids by gaseous nanobubbles.

Interactions of gaseous (ambient) nanobubbles (10-100 nm diameter) with different hydrophobic materials-Teflon, polystyrene, paraffin, and basal plane highly ordered pyrolytic graphite (HOPG)-are studied by AFM in situ and ex situ. Exactly identical surface locations are examined before and after exposure to ambient gas nanobubbles in deionized water and compared for nanomorphological changes. While freely flooded/immersed surfaces, regularly occupied by nanobubbles, do not exhibit resolvable alterations, significant surface rearrangement is found on whole flooded area after mild pressure drop (10 kPa) applied on the solid-liquid interface. Nanopattern and its characteristic dimension appear to be material specific and solely reflect surface-nanobubble interaction. Mild, nonswelling, noncorrosive conditions (20 °C, deionized water) prevent intervention of chemical reaction and high-energy-demanding processes. Experimental results, in accordance with the presented model, indicate that the mild pressure drop triggers expansion of pinned nanobubbles, imposing local tensile stress on the solid surface. Consequently, nanobubbles should be considered as large-area nanoscale patterning elements.

Nickel-cobalt hydroxide nanosheets: Synthesis, morphology and electrochemical properties

This paper reports the synthesis, characterization, and electrochemical performance of nickel-cobalt hydroxide nanosheets. The hydroxide nanosheets of approximately 0.7nm thickness were prepared by delamination of layered nickel-cobalt hydroxide lactate in water and formed transparent colloids that were stable for months. The nanosheets were deposited on highly oriented pyrolytic graphite by spin coating, and their electrochemical behavior was investigated by cyclic voltammetry in potassium hydroxide electrolyte. Our method of electrode preparation allows for studying the electrochemistry of nanosheets where the majority of the active centers can participate in the charge transfer reaction. The observed electrochemical response was ascribed to mutual compensation of the cobalt and nickel response via electron sharing between these metals in the hydroxide nanosheets, a process that differentiates the behavior of nickel-cobalt hydroxide nanosheets from single nickel hydroxide or cobalt hydroxide nanosheets or their physical mixture. The presence of cobalt in the nickel-cobalt hydroxide nanosheets apparently decreases the time of electrochemical activation of the nanosheet layer, which for the nickel hydroxide nanosheets alone requires more potential sweeps.

Versatile cell for in-situ spectroelectrochemical and ex-situ nanomorphological characterization of both water soluble and insoluble phthalocyanine compounds

A novel cell for complex spectroelectrochemical and nanomorphological characterization of phthalocyanine has been developed. The applicability and universality of the cell allows performing both in-situ and ex-situ characterization of the same sample, in solid and solution state, respectively, which was demonstrated on tetramethyltetra-3,4-pyridine-porphyrazino cobalt as water soluble and tetraneopentoxyphthalocyanine cobalt as water insoluble phthalocyanine based compound. The cell is composed of a planar freely replaceable bottom formed by a basal plane of highly ordered pyrolytic graphite. It allows complete characterization of modified electrode on same electrode, from spectral observation of modification process via atomic force microscopy to spectroelectrochemical characterization of redox and catalytic behavior. The relatively inert HOPG electrode serves as a substrate for phthalocyanine compounds and also as a backscattering mirror for in-situ reflection spectroscopy. This makes the cell suitable for spectroelectrochemical studies of phthalocyanine both as HOPG-supported thin film and in the solution. Moreover, the cell can take the advantage of optional utilization of supported thin layer interface of two immiscible electrolyte solutions allowing spectroelectrochemical analysis of sub-microgram quantities of water insoluble compounds.Graphical abstract.

Interface of Two Immiscible Electrolytes as a Potentiometric Sensor for Flow Analysis

ABSTRACT An interface of two immiscible electrolyte solutions (dual ITIES) was investigated for application as a biomimetic sensor for potentiometric flow analysis. The dual ITIES was formed by a water/ortho–dichlorobenzene/water interface in free-standing and nanoporous membrane-supported arrangements. One aqueous phase served as the mobile and second aqueous phase as the stationary phase. The nonaqueous (ortho-dichlorbenzene) phase contained dissolved phthalocyanine as a redox mediator, whereas tetrabutylammonium perchlorate acted as a phase transfer agent. The sensing mechanism utilized ambient oxygen for regeneration of the redox mediator; the sensor thus operates under air conditions where oxygen serves to partially establish the equilibrium interface potential. The free-standing and nanoporous membrane-supported arrangements provided fast and reproducible response for flow analysis with sulfide serving as a model analyte. Good stability, fast recovery, and high resistance to saturation were found. The signal-to-noise ratio was discussed with respect to electrolyte concentration and gaseous bubbles trapped on the membrane.