We consider the screening of the negative charges (carboxylic acid groups) fixed on the surface of a conical-shaped track-etched nanopore by divalent magnesium (Mg 2+) and trivalent lanthanum (La 3+). The experimental current (I)voltage (V) curves and current rectification ratios allow discussing fundamental questions about the overcompensation of spatially-fixed charges by multivalent ions over nanoscale volumes. The effects of charge inversion or reversal on nanopore transport are discussed in mixtures of asymmetric electrolytes (LaCl 3 and MgCl 2 with KCl). In particular, pore charge inversion is demonstrated for La 3+ as well as for mixtures of this trivalent ion at low concentrations with monovalent potassium (K +) and divalent Mg 2+ ions at biologically relevant concentrations. It is found that small concentrations of multivalent ions can modulate the nanopore rectification and the transport of other majority ions in the solution. We study also the kinetics of the nanopore electrical recovery when the electrolyte solutions bathing the single-pore membrane are changed and show the hysteretic effects observed in the IV curves. Finally, we describe the hysteresis observed in the IV curves of CaCl 2 , MgCl 2, and BaCl 2 and mixtures. We also give a qualitative description of the effects of charge reversal on the pore rectification using the Nernst-Planck flux equations for multivalent ion mixtures.

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The method of electroless plating offers a facile synthesis route to high-aspect ratio metal nanotubes. Despite the simpleness of the method, the traditional approach involves hazardous and toxic chemicals, to change this Green Chemistry comes into play. Since both, nanotechnology and Green Chemistry, have become important research topics, the combination of those offers new opportunities. According to the asset of Green Chemistry, Pd nanotubes were produced by using nonhazardous chemicals. The challenge was to rebuild the sensitisation and activation process of electroless plating and to find green reaction parameters for controlling the auto-catalysed heterogeneous nucleation of Pd. The produced Pd nanotubes were characterised by SEM and EDX. Furthermore TEM characterisation was done for determining the structural properties of Pd NTs. The efficiency of reaction progress was quantified by ICP-OES and XPS measurements. To illustrate that green synthesized nanomaterials can be compared to conventional made catalysts, the Pd nanotubes were tested in a model reaction to determine the catalytic activity. For this purpose the reduction of 4-nitrophenol to 4-aminophenol by NaBH4 was chosen, which finds also application in the synthesis of acetaminophen.

Polymer coatings on cellulosic fibres are widely used to enhance the natural fibre properties by improving, for example, the hydrophobicity and wet strength. Here, we investigate the effects of a terpolymer P(S-co-MABP-co-PyMA) coating on cotton linters and eucalyptus fibres to improve the resistance of cellulose fibres against wetness. Coated and uncoated fibres were characterised by using scanning electron microscopy, contact angle measurements, Raman spectroscopy and atomic force microscopy with the objective of correlating macroscopic properties such as the hydrophobicity of the fleece with microscopic properties such as the coating distribution and local nanomechanics. The scanning electron and fluorescence microscopy results revealed the distribution of the coating on the paper fleeces and fibres. Contact angle measurements proved the hydrophobic character of the coated fleece, which was also confirmed by Raman spectroscopy measurements that investigated the water uptake in single fibres. The water uptake also induced a change in the local mechanical properties, as measured by atomic force microscopy. These results verify the basic functionality of the hydrophobic coating on fibres and paper fleeces but call into question the homogeneity of the coating. Graphic abstract

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