We carried out a complete study (magnetic, electronic, dielectric, dynamic, and elastic properties) of the nickel hydroxide [Ni(OH)2] from first-principles calculations based on density functional theory. No theoretical investigations of these physical properties have been previously reported in literature. Our work supports that Ni(OH)2 is an A-type antiferromagnetic material. In addition, it is negative uniaxial and semiconducting with a direct band gap at the Γ point around 3 eV. By contrast to its electronic dielectric tensor, its static tensor is strongly anisotropic in the plane orthogonal to its optical axis. This anisotropy is mainly governed by a highly polar phonon centered around 510 cm−1 and assigned as a rotational Eu mode. Both Raman and infrared spectra have been computed to clarify the longstanding debate on the assignment of the Ni(OH)2 phonon modes reported in literature. All these theoretical results are fruitfully compared to the experimental ones obtained on large Ni(OH)2 "pseudosingle" crystals when available.

One of the scientific challenges in nanofiltration is to develop nanofilters with both high ion permeability and selectivity, which are often considered as antagonist features. Today, the number of solid state membranes that are readily useable is limited and their performances, i.e. ion permeability and selectivity, are restricted. New materials for nanofiltration are thus clearly requested. On the other hand, it is well known that biological ion-channels insure ionic (Na+, K+…) exchange of living cells and that their properties in terms of ionic permeability and selectivity are extremely high. Unfortunately, the transfer of these properties to artificial set-up whose the mechanical strength is high enough to be useful in many different types of applications has not been achieved yet. So, the idea of combining nanoporous solid-state materials with biological ion channel appears as a scientific and technical challenge that could open new perspectives in nanofiltration. Recently [1], we report the first extremely encouraging results on insertion of the ion channel gramicidin A (gA) inside a nanoporous track-etched membrane. These primary results have demonstrated the feasibility for hybrid bio-inspired membrane made of a biological ion channel and a nanoporous polymer material. The next goal of our project is the enhancement of the hybrid membrane performances in term of ionic selectivity via optimization of the gA confinement inside the nanopores. In this paper, we report the results obtained when the experimental conditions used for the protein insertion are changed : solvent (water/methanol mixture) used for the insertion and temperature. Experimental results on ion diffusion and selectivity through the membrane are interpreted thanks to data obtained from molecular simulation

It is well acknowledged that clay minerals can retain proteins dependently on pH and ionic strength of the aqueous solution in which they are dropped1. However, little is known about the influence of the extra-framework cations (EFC) located into the interlayer space of swelling clays. So, the questions concerning the role plays by EFC on hard or soft proteins regarding their adsorption kinetics and loading, as well as their conformation at the clay outer or inner surface remain posed. In the present study, we investigate the adsorption of different hard and soft proteins (lysozyme, BSA, -chymotrypsin, and trypsin) on a series of homoionic montmorillonite (CMS reference clay SWy-2) exchanged by various monovalent and bivalent EFC, i.e. Li+, Na+, K+, Rb+, Cs+, Ba2+, Ca2+ and Mg2+. Figure 1 shows the lysozyme and BSA loadings at equilibrium under room experimental conditions in two buffer, i.e. Na+ and K+ phosphate, solutions. As expected, it can then be seen that the protein loading is strongly influenced by the buffer solution. However, it can also be observed a protein loading decrease with the EFC radius except for Li+. This result could be correlated to the EFC exchange capacity that is to the EFC hydration2 Nevertheless the particular case of lithium can be explained by its inhibitor effect on protein adsorption3.

Dehydration heat and ionic conductivity of a series of homoionic alkali (Li+, Na+, K+, Rb+, Cs+) and alkali rare-earth (Mg2+, Ca2+, Ba2+) exchanged montmorillonite (ref. CMS: SWy-2) are investigated at low water loading. Dehydration heat is obtained via Van't Hoff's law applied to weight losses measured at several constant temperatures, i.e. treatment temperature (TT), as a function of time by thermo-gravimetric analysis . Dc conductivity is measured at various temperature using Complex Impedance Spectroscopy on samples whose the water loading is fixed by TT . Comparison with the dissociation enthalpy of alkali and alkali rare-earth cation/water complexes shows that dehydration heat montmorillonites results from the competition between opposite energy contributions due to: i) cation solvation, ii) hydration of the silicate interlayer surface and iii) structural swelling. So, depending on the balance between these various energy contributions, different behaviors are observed accordingly to the nature of the extraframework cation (EFC) with a perculiar behavior for K+. Independently on EFC, dc conductivity follows an Arrhenius behavior when the water loading is closed to zero. In contrast, this behavior is no longer observed as long as water molecules are adsorbed and, hence, in interaction with EFC. In that case, the results are well described by the empirical Vogel-Tamman-Fulcher (VTF) form, i.e. , suggesting order/disorder transition in the water/cation sub-network even at low hydration state. This outcome depends on EFC in accordance with dehydration heat. It is then shown that dc conductivity evolution with both temperature and water loading is a significant source of information regarding adsorption in connection with EFC.

On the one hand, one of the scientific challenges in nanofiltration is to develop nanofilters with both high permeability and selectivity, which are often considered as antagonist features. Today, the number of solid state membranes that are readily useable is limited and their performances, i.e. permeability and selectivity, are restricted. New materials for nanofiltration are thus clearly requested. On the other hand, it is well known that ionic bio-channels insure ionic (Na+, K+...) exchange of living cells and that their properties in terms of ionic permeability and selectivity are extremely high. Unfortunately, the transfer of these properties to artificial set-up whose the mechanical strength is high enough to be useful in many different types of applications has not been made, or even proposed, yet. Here, we report the first time extremely encouraging results obtained on a hybrid membrane made of a track-etched polycarbonate thin (thickness=5µm) film whose the nanopores (diameter=15nm) are filled with the ion channel Gramicidin-A (GA). The confinement of GA is checked by means of confocal fluorescence spectroscopy and the effective ion diffusion determined by means of ion diffusion coefficient measurement of various electrolytes, viz. 10-1, 10-2 and 5 10-3 mol.l-1 Na+, K+,Ca2+ and Mg2+ chlorine solution. Comparison with the effective ion diffusion coefficient measured on GA free membranes emphasizes that, when GA is absorbed into the nanopore, the effective ion diffusion significantly increases. Finally, simulations at the atomic level are conducted to confirm the GA insertion into a modeled hydrophobic nanopore, i.e. a carbon nanotube, and to gain some insights into the GA conformations in the pore.

A hybrid nanoporous membrane made of a solid-state polymeric thin film in which an ion channel is confined is realized. The primary and extremely encouraging results obtained by confocal fluorescence spectroscopy and ion diffusion measurement demonstrate respectively that (i) the considered ion channel, that is, Gramicidin-A, can be confined selectively inside the nanopores and (ii) the ionic permeability of the membrane is enhanced. Atomistic molecular simulations are also reported and fruitfully compared to the experimental findings.

The electrochemical properties of â-type nickel (oxy)hydroxides Ni(OH)2 and NiO(OH) are known to depend significantly on their structural features. In this work, these features are investigated by means of inelastic neutron scattering and infrared and Raman spectroscopies. Our experiments probe both inter- and intramolecular (40-4000 cm-1) vibrational ranges and particular attention is paid to the low-frequency (40-300 cm-1) domain, where new features are observed. Namely, the presence of an IR active mode at around 130 cm-1, characteristic of the oxidized â-NiO(OH) phase, is observed for the first time. The effects of temperature (10-300 K) and deuteration are also measured in order to provide deeper insight into the nature of the vibrational states. A detailed comparison of all of the collected data allows us to propose a new assignment of the vibrational features observed in both â-Ni(OH)2 and â-NiO(OH) and to quantify the proton dynamic relevance on the vibrational modes. We show that the interlayer interactions are mostly electrostatic and, hence, do not involve hydrogen bonding. We also point out that, in the oxidized â-phase, protons cannot be localized so that they can be considered as fully labile. To sum up, this investigation emphasizes that proton delocalization and crystalline disorder, which arise concomitantly upon oxidation, are the key factors that explain the evolution of the vibrational features observed between the oxidized and reduced â-type forms.