Pavel Janda

Layered zinc hydroxide salts: delamination, preferred orientation of hydroxide lamellae, and formation of ZnO nanodiscs.

Delamination of layered zinc hydroxide salts (LZH) into hydroxide layers provides nanobuilding blocs of a two-dimensional anisotropy. The methodology, extent of delamination, the size and stability of hydroxide lamellae are described in detail. The ability of lamellae to restack to form oriented hydroxide films depends on the solvent, original LZH salt, and conditions used for delamination. The most interesting results were obtained using LZH intercalated with dodecyl sulfate anions and LZH nitrate delaminated in butanol at 60 °C and in formamide at room temperature, respectively. The former method produces hydroxide lamellae of a lateral size of ca. 10-20 nm. The inner structure of the hydroxide layers is conserved and separated lamellae restack to the original layered structure of LZH dodecyl sulfate. The latter method yields lamellae with a size decreasing from 73.3 nm to 10 nm after a 2-week aging, while their thickness is nearly constant (2.6-3.8 nm). However, the use of formamide is complicated by the formation of Zn(II) formate. The major part of LZH intercalated with dodecyl sulfate anions is transformed during the delamination procedure to anisotropic ZnO nanoparticles, either needle-like particles prolonged in the [0 0 1] direction or disc-like particles flattened along the (0 0 1) plane.

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.

Electrochemical nanostructuring of fullerene films—spectroscopic evidence for C60 polymer formation and hydrogenation

Electrochemical reduction of ordered C60 fullerene films in aqueous solution was studied by AFM, FTIR and Raman spectroscopy, mass spectrometry and elastic recoil detection analysis. During the irreversible reduction process the film morphology changed from a heteroepitaxial (111) surface to a nanostructured array with clusters of 20 to 50 nm lateral size on average. On the molecular level the initial C60 underwent electrochemical reactions to form C60 polymers and hydrogenated C60. Chemical follow-up reactions of electrochemically formed C60- with water are responsible for the different reduction behaviour of C60 films in aqueous solution compared to C60 reduction in organic solvents and to C60 doping with alkali metals. Based on the spectroscopic analysis a reaction scheme accounting for the chemical processes at the C60 / aqueous electrolyte interface is presented.

Nickel hydroxide ultrathin nanosheets as building blocks for electrochemically active layers

Layered nickel hydroxides (LNHs), intercalated with lactate and nitrate anions, were synthesised using controlled precipitation and anion exchange methods. The present study reports a novel approach for the delamination of LNHs in water into nickel hydroxide nanosheets. The thickness of a single nanosheet varied between 0.7 and 1.0 nm with a lateral dimension between 50 and 80 nm. The nanosheets formed colloidal solutions or gels, retained the original hydroxide structure of LNHs, and were stable for weeks. The nanosheets were re-assembled into large-scale, well-oriented films with adjustable thickness using drop casting and spin coating techniques. The prepared nanostructured films were electrochemically active with stable and reproducible charge–discharge properties in an alkaline electrolyte. These results suggest that the nickel hydroxide nanosheets, prepared by the present methods, have potential as building blocks in the design of nanocomposite materials for energy applications.

Rotating cell for in situ Raman spectroelectrochemical studies of photosensitive redox systems.

A recently developed rotating spectroelectrochemical cell for in situ Raman spectroscopic studies of photoreactive compounds without marked decomposition of the sample is presented. Photochemically and thermally sensitive redox systems are difficult to be studied under stationary conditions by in situ spectroelectrochemistry using laser excitation as in Raman spectroscopy. A rotating spectroelectrochemical cell can circumvent these difficulties. It can be used for any type of a planar electrode and for all electrode materials in contact with aqueous or nonaqueous solutions as well as with ionic liquids. The innovative technical solution consists of the precession movement of the spectroelectrochemical cell using an eccentric drive. This precession movement allows a fixed electrical connection to be applied for interfacing the electrochemical cell to a potentiostat. Hence, any electrical imperfections and noise, which would be produced by sliding contacts, are removed. A further advantage of the rotating cell is a dramatic decrease of the thermal load of the electrochemical system. The size of the spectroelectrochemical cell is variable and dependent on the thickness of the cuvettes used ranging up to approximately 10 mm. The larger measuring area causes a higher sensitivity in the spectroscopic studies. The as constructed spectroelectrochemical cell is easy to handle. The performance of the cell is demonstrated for ordered fullerene C(60) layers and the spectroelectrochemical behavior of nanostructured fullerenes. Here the charge transfer at highly ordered fullerene C(60) films was studied by in situ Raman spectroelectrochemistry under appropriate laser power and accumulation time without marked photodecomposition of the sample.

Nickel nanoparticle assembly on single-crystal support: formation, composition and stability

A nickel nanoparticle assembly was formed by vapour deposition on various single-crystal supports. The nanoparticle structure, distribution, composition and charge transfer properties were examined simultaneously by atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), mass spectroscopy (MS) and electrochemistry. The data obtained by applied analytical techniques were correlated. X-ray photoelectron spectroscopy (XPS) of nanoparticle assemblies deposited at ambient temperature revealed the Ni(II) oxidation state, while metallic Ni was found in nanoparticles grown at 300??C. The amount of nickel deposited on highly ordered pyrolytic graphite (HOPG) estimated by AFM was found to be an order of magnitude higher than that obtained from XPS analysis, while AFM and XPS data for silicon agree well. The discrepancy was discussed in terms of differences in support elastic properties and AFM-tip/surface interactions. Current?potential measurements of nanoparticle charge transfer reaction point to the high stability and low resistant Ohmic character of the nanoparticle/HOPG interface.

Raman Spectroelectrochemistry of Ordered C60 Fullerene Layers

Abstract Electrochemical nanostructuring of ordered C60 fullerene layers in aqueous solution was studied by in situ Raman spectroelectrochemistry. A completely changed molecular film structure was found for nanostructured films. C60 polymers/oligomers and hydrogenated C60 were identified as the main fullerene structures after nanostructuring. No significant contributions of AxC60 fullerides (A=alkaline metal; x=1, 3, 6) were found.

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.