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A stable film of zinc hexacyanoferrate is deposited on a GC (glassy carbon) substrate following a specific electrochemical protocol. The electrode maintains its characteristic even after dry and wet processes. SEM characterization confirms the cubic morphology of the materials and the IR suggests the presence of the FeII-C-N-ZnII structural unit. The electrochemical characterization indicates a very good stability of the film, thus opening application in ion exchange system. The focus is on monovalent, divalent, and trivalent ions. These results, the zinc low toxicity, and cost make zinc hexacyanoferrate films a promising candidate for many electrochemical applications.

Aqueous rechargeable Zinc-ion batteries (ARZIBs) have attracted extensive attention as one of the most promising post-lithium ion battery candidates for large-scale electrochemical applications, because of their low cost, intrinsic safety, and environmental friendliness. The metallic zinc, as an ideal anode material shows high theoretical gravimetric and volumetric capacity of 820 mAh g-1 and 5855 mAh cm-3, low electrochemical potential (-0.76 V vs. SHE) and high abundance.[1,2] Manganese hexacyanoferrate (MnHCF), one of the Prussian blue analogues (PBAs), has attracted widely attention as promising cathode material for Li-ion and post-Li ion batteries. MnHCF is composed of only highly abundant metals and displays large capacity and high discharge potential owning to the two-redox active sites [3-4]. Here, the electrochemical performance of MnHCF was studied in 3 M ZnSO4 aqueous electrolyte with Zn sheet as anode. The battery exhibits high specific capacity (176 mAhg-1) at C/20, and around 61% capacity retention after 50 cycles at C/5. In order to explain the capacity fading problems during cycling, the local geometric, electronic structures, as well as the framework structure change of MnHCF electrode were studied by means of ex-situ X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (XRD). Based on XAS data, no obvious change was observed at the Fe K-edge during cycling, and this indicates that there is no apparent change of the local Fe structural environment. However, the XAS spectra of Mn K-edge exhibit an apparent change after 10 cycles. The Zn K-edge shows a typical -Zn-NC-Fe- structural framework in the cycled samples that resembles the one of zinc hexacyanoferrate (ZnHCF), providing evidence for Zn-Mn partially replacement upon cycling, resulting in dissolution the Mn ion [5]. From the ex-situ XRD data, we found that this phase changes mainly concerns early cycles, because the XRD patterns of the 2nd and 10th cycle are almost identical. ZnHCF phase formed even during the first charge process. The more detailed phase transformation process is still under studying. By combing the ex-situ XAS and XRD data, the charge/discharge mechanism of MnHCF in aqueous Zn-ion battery can be more clearly illustrated. Trócoli, F. La Mantia, ChemSusChem. 8, 2015, 481–485. Tang, L. Shan, S. Liang, J. Zhou, Energy Environ. Sci. 12, 2019, 3288–3304. Mullaliu, J. Asenbauer, G. Aquilanti, S. Passerini, M. Giorgetti. Small Methods, 2019, 1900529. Mullaliu, M. Gaboardi, J. R. Plaisier, S. Passerini, and M. Giorgetti, ACS Applied Energy Materials 3, 2020, 5728. Li, R. Sciacca, M. Maisuradze, G. Aquilanti, J. Plaisier, M. Berrettoni, M. Giorgetti, Electrochim. Acta. 400 ,2021.

The paper reports a detailed study about the influence of the electrolyte composition in nickel-hexacyanoferrate (NiHCF) electrochemical behavior. Shapes and positions of the CV waves are strongly related to the cation of the supporting electrolyte, which undergoes intercalation/de-intercalation during the redox process. The electrochemical behavior of NiHCF has been characterized in different electrolyte solutions containing either pure monovalent or trivalent metal nitrates. Nickel-hexacyanoferrate permits the reversible insertion of a wide variety of monovalent, divalent and trivalent ions in aqueous solution; the characteristic potential Ep of the cathodic process depends upon the nature of the intercalated cation. Electrochemical measurements demonstrate the unprecedented fast kinetics of trivalent ion insertion associated with this material. The reported findings represent the first systematic step toward understanding the principles of multivalent charge screening and provide a novel cation intercalation mechanism in NiHCF, assisted by both water molecules and ferrocyanide vacancies. The synergistic mechanism can reduce the electrostatic repulsion and provide a preferential path for the rapid cation intercalation.

In February 2016, 47 ingots were found in the seabed of Contrada Bulala (Gela, CL, Italy) near the site where 40 ingots had previously been recovered. The ingots composition was determined to be a Cu - Zn alloy, dated by the archaeologist to the VI century B.C. This specific alloy was then known as Orichalcum. From an archaeological point of view, the first question raised about the new discovery was whether the ingots of the first and the second excavations belonged to the same shipwreck. Following the previous study, an elemental analysis was performed on the ingots from the second finding by using ICP-OS and ICP-MS techniques. The chemometric treatment of the analytical results obtained on both sets, i.e. ingots from first and second discovery, confirms their similarity. Therefore, the two findings can be considered to belong to the same naval load. The lead isotopic ratios were determined on selected/representative ingots to improve the knowledge about this treasure. Results can provide information about probable location of the lead sources, that could be very useful for the reconstruction of the ancient trade routes in the Mediterranean Sea.

Manganese hexacyanoferrate (MnHCF) has attracted much attention as promising cathode material for Li and Na ion batteries, owning to its low cost, environmental friendliness, high specific capacity and voltage plateau. Here, the electrochemical performance and electronic structure information of MnHCF were studied in aqueous Zn-ion batteries (ZIBs). Based on the cyclic voltammetry and galvanostatic charge/discharge results, an activation of Fe-sites during beginning cycles was observed, and the capacity contribution of Fe-sites increases from 30% to 86% at C/20 during the first 10 cycles. The local geometric and electronic structure information of MnHCF was investigated by X-ray absorption spectroscopy (XAS) in a set of ex-situ electrodes. From Fe K-edge spectra, it shows a consistent oxidation and reduced state in charged and discharged electrodes, and this indicates that there is no apparent change for the local Fe-sites environment. However, the XAS spectra of Mn K-edge show apparent change after 10 cycles. Compared to the rhombohedral phase of Zinc hexacyanoferrate (ZnHCF), a -Zn-CN-Fe- structural framework was detected in the cycled MnHCF samples, and this indicates that a part of Zn replaced Mn-sites, because of the dissolution of the Mn-sites. The gradual activation of Fe-sites at the beginning cycles can be attributed to the alleviation spatial resistance with the dissolution of Mn-sites, and the replacement of Zn for Mn explains the decreasing capacity during cycling.

Alternative energy sources are currently worldwide under development to contribute to the increasing energy demand. Along with the introduction of new technologies, heavy metals, such as radionuclides from nuclear power plant leaks, might be released into the environment and contaminate waters, air, and soil. Among the investigated methods, the use of adsorbents has been proven the most suitable one, able to extensively remove heavy metals, e.g., radioactive 137Cs+. Prussian blue analogs (PBAs) have been demonstrated to be effective adsorbents toward the sequestration of a variety of heavy metals, including the recovery and valorization of rare earth elements. Here, we point out the structure-property link of PBAs: the large channels and cavities are able to accommodate a variety of ions, ranging from monovalent to multivalent ones, while the ion exchange may be either diffusion-controlled or electrochemically driven. While distribution coefficients are shown to be key parameters in the diffusion driven process, resulting in high affinities of PBAs toward metals such as Cs+, Tl+, Cu2+, and Zn2+, electrochemical ion exchange is considered to be promising due to the effectiveness in the removal of metals and the possibility to reversibly restore the adsorbent to its initial state. Related examples concerning the capture of Cs+ from wastewaters and the recovery of rare earth elements are herein presented and commented.

Geopolymers obtained by mixing metakaolin powder with tannery wastewater and NaOH pellets are proposed as 3D aluminosilicate network to chemically entrap Cr(III) species. X-ray Absorption Spectroscopy studies show the absence of toxic Cr(VI). The analysis of EXAFS also reveals a Cr(III) first coordination shell formed by 6 oxygens and a second shell of 7/8 Al or Si atoms, indicating strong bonding with the aluminosilicate network.

A combined X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) methodology is here presented on a series of partially and fully reduced Au(III) samples. This allows monitoring the relative fraction of Au(III) and Au(0) in the studied samples, displaying a consistent and independent outcome. The strategy followed is based, for the first time, on two structural models that can be fitted simultaneously, and it evaluates the correlation among strongly correlated parameters such as coordination number and the Debye-Waller factor. The results of the present EXAFS and XANES approach can be extended to studies based on X-ray absorption spectroscopy experiments for the in situ monitoring of the formation of gold nanoclusters.

Nanopowders of yttrium aluminum garnet (YAG, Y3Al5O12) have been prepared by thermal treatment of hydroxides obtained by synthesis in a confined environment constituted by water/Cetyltrimethylammonium bromide (CTAB)/1-butanol/n-heptane. The phase behavior of the above system has been investigated on varying the water/CTAB molar ratio (R) at constant 1-butanol/CTAB and heptane/CTAB molar ratio. The dispersed aqueous phases were constituted by solutions of ammonia and of yttrium and aluminum nitrates, respectively. Measures of Kinematic Viscosity, Electrical Conductivity and Small Angle X-ray Scattering have been carried out. It was found that, on increasing the ammonia solution content the system evolves from a water in oil microemulsion to a bicontinuous one to a lamellar system and then it return to be bicontinuous, the yttrium and aluminum nitrate solution stabilizes the bicontinuous phase preventing the formation of the lamellar phase. The precursor synthesis was performed by mixing two microemulsions containing reactants at the same R, 20 and 70, respectively. The YAG nanopowders obtained from precursor calcination have been characterized by means of Wide Angle X-ray Scattering and Transmission Electron Microscopy. The obtained nanopowders were constituted by nanoparticles showing strong differences in terms of size and aggregation that depend on the microemulsion structure.

Cobalt hexacyanoferrate (CoHCF) was electrodeposited into an organically modified silica (ormosil) film with a nanoarray of parallel, cylindrical channels, which were obtained using 20-nm poly(styrene sulfonate), PSS, beads as a templating agent. The PSS was bound to the electrode surface with 3-aminopropyltriethoxysilane, APTES. Methoxytrimethylsilane was the ormosil precursor. Electrochemically assisted processing at a positive potential where the hydrogen ion catalyst was generated was used to deposit the ormosil film. Subsequently, the PSS and APTES were removed to provide the pores. The CoHCF was deposited in the 20-nm channels by cyclic voltammetry of a freshly prepared K3Fe(CN)6, CoCl2 mixture with 1.0 mol dm−3 KCl as the supporting electrolyte. Limiting the number of electrodeposition cycles to 10–20 resulted in CoHCF nanorods in the pores, whereas with 50 cycles bulk-form CoHCF spilled over the outer ormosil surface. Electrocatalytic oxidation of cysteine was successfully performed on these nanorod arrays, which showed greater catalytic activity than bulk-form CoHCF.

International audience; 57 Fe Mössbauer spectroscopy was used to highlight a charge transfer mechanism in cobalt hexacyanoferrate (CoHCF) when synthetized in the presence of anatase TiO2. The electron transfer in TiO2–CoHCF composites along the Co–NC–Fe–CN–Co chain is confirmed by the unequivocal evolution of the typical quadrupole doublet of Fe(II) and Fe(III) in pristine CoHCF into the single line spectrum of the Fe(II) species when CoHCF is nanodispersed on TiO2 anatase. Parallel galvanostatic measurements also confirm the electron transfer mechanism induced by TiO2. To the best of our knowledge, this is one of the first examples of the triggering of spin-crossover phenomena in metal-hexacyanoferrate based-molecular solids by an external stimulus other than photoexcitation and most of all one of the first studies in which a completely pure low-spin Fe(II) is obtained starting from a mix of low-spin Fe(II) and Fe(III).

The policies of curbing CO 2 emissions have worked poorly on a global scale and an economically sound proposal of bringing electric power to Europe from an Algerian solar hub has just been dismissed. With reference to the Algerian – European relationships, we analyze the broad context where an environmental policy benefitting both developing and developed countries can be put in place. We then discuss the connection between anthropogenic CO 2 emissions and acidification of Oceans along with a geo-engineering proposal aimed at solving these pressing problems with large-scale solar-powered chloralkali plants. While the cost of sequestering a ton of CO 2 with dedicated chloralkali plants is unacceptably high, it is economically and environmentally sound to replace an existing European Cl 2 plant (consuming fossils) with a solar-powered plant in Algeria. If the Algerian plant uses a new, more efficient chloralkali process, it will be competitive with existing European plants even at the current low market value of the carbon emission credits. We finally explore the possibility of coupling Cl 2 production with CO 2 reuse and syngas production through a novel electrochemical process.

This paper deals with the synthesis and characterization of iron-hexacyanocobaltate (FeHCC) and its antibacterial properties. The nanoparticles were prepared by a facile co-precipitation technique. Crystal structure, particle morphology, and elemental composition were determined using X-ray Powder Diffraction, X-ray fluorescence spectroscopy, Transmission Electron Microscopy (TEM), and Infrared Spectroscopy (IR). The antibacterial activity of the FeHCC nanoparticles was tested against Escherichia coli and Staphylococcus aureus as models for Gram-negative and Gram-positive bacteria, respectively, by bacterial counting method and microscopic visualization (TEM, FEG-SEM, and fluorescence microscopy). The results showed that the FeHCC nanoparticles bind to the bacterial cells, inhibit bacterial growth in a dose- and time-dependent manner, inducing a loss of the membrane potential, the production of reactive oxygen species and the release of macromolecules (nucleic acids and proteins) in the extracellular environment. To the best of our knowledge, this is the first study reporting the antimicrobial effects of metal-hexacyanometallates suggesting practical uses of these materials in different areas, such as self-cleaning surfaces or food packaging.

In this work a careful ICP-OES and ICP-MS investigation of 38 ancient ingots has been performed to determine both major components and trace elements content to find a correlation between the observed different features and the composition. The ingots, recovered in an underwater archaeological site of various finds near Gela (CL, Italy), were previously investigated by X-Ray Fluorescence (XRF) spectroscopy to know the composition of the alloy and it was found that the major elements were copper and zinc, in a ratio compatible with the famous orichalcum similar to the contemporary brass that was considered a precious metal in ancient times. The discovery of huge amount this alloy is extraordinary. Following a chemometric approach at first, the use of Principal Component Analysis (PCA) and Cluster Analysis (CA) allowed us to highlight three well-defined groups of ingots and to point out three ingots that appeared outlier with respect to the whole sample set. Linear Discriminant Analysis (LDA) and Soft Independent Modeling of Class Analogy (SIMCA) enabled us to confirm the difference between the hypothesized groups. The prediction power of the variables computed by SIMCA allowed us pointing out some elements able to differentiate each group. The three well-defined groups of ingots resulting from the chemometric analysis were in agreement with the observations of some morphological parameters such as ingot shape, width, and length and weight and by the presence of different kind of patina. The appearance of three distinctive families of ingots can indicate different geographical location of the furnace, different technology stages and/or different raw material used in melting process and the morphology is indicative of cast diverse technologies. These findings can signify the starting point for giving important insights in the archaeometric study of the orichalcum ingots regarding the provenience and the manufacture technologies.

Nanoparticles of yttrium aluminum garnet (YAG, Y 3 Al 5 O 12 ) have been obtained by thermal treatments, at several temperature in the range 400–950 °C, of the precursors synthetized via co-precipitation in water in oil microemulsion. The obtained nanoparticles have been characterized by means of X-ray Diffraction and Transmission Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (EDS) and Select Area Electron Diffraction (SAED). Results show the phase evolution occurring to obtain not aggregated nanoparticles of YAG phase. A possible growth mechanism of YAG nanoparticles is discussed on the basis of observed particle microstructure and morphology. The results indicate that, applying this sequence of thermal treatments, the formation of the garnet phase takes place with the formation of yttria nuclei that grow preferentially in one direction. The growth takes place via two processes: at low temperature the nuclei evolve to the garnet phase by following the oriented attachment mechanism, at higher temperatures by the Kirkendall effect accounting for the morphological modification. The proposed synthesis and thermal treatments, by favoring one or the other growth mechanisms, allowed attaining a fine control on nanoparticles features thus making it useful for similar mixed oxides preparations.

The paper describes the synthesis and characterization of novel TiO2–metal hexacyanometallates (MHCMs) composite materials. The starting material, TiO2, was modified by addition of cobalt-hexacyanoferrate (CoHCF) or iron-hexacyanocobaltate (FeHCC) at various concentrations. The resulting composites were characterized as follows: cyclic voltammetry (CV) followed the formation of TiO2–MHCM clusters, TEM micrographs studied their morphology, XAS and XPS data indicated that MHCM bonds to TiO2 through the nitrogen atom of its –CN group and modifies the environment of Ti compared to that of pure anatase. As expected, and confirmed by UV-Vis and XP-valence band data, the electronic properties of TiO2 were substantially modified: the edge in the composite materials shifted by about −2.0 eV relative to TiO2.

Electrochemically assisted deposition of an ormosil film at a potential where hydrogen ion is generated as the catalyst yields insulating films on electrodes. When the base electrode is modified with 20-nm poly (styrene sulfonate), PSS, beads bound to the surface with 3-aminopropyltriethoxysilane (APTES), and using (CH3) 3SiOCH3 as the precursor, the resulting film of organically modified silica (ormosil) has cylindrical channels that reflect both the diameter of the PSS and the distribution of the APTES-PSS on the electrode. At an electrode modified by a 20-min immersion in 0.5 mmol dm−3 APTES followed by a 30-s immersion in PSS, a 20-min electrolysis at 1.5 V in acidified (CH3) 3SiOCH3 resulted in an ormosil film with 20-nm pores separated by 100 nm. Cyclic voltammetry of Ru (CN) 6 4− at scan rates above 5 mV s−1 yielded currents controlled primarily by linear diffusion. Below 5 mV s−1, convection rather than the expected factor, radial diffusion, apparently limited the current. © 2014, Springer-Verlag Berlin Heidelberg.

A short review on the fundamental and technological issues relevant to water electrolysis in alkaline and proton exchange membrane (PEM) devices is given. Due to price and limited availability of the platinum group metal (PGM) catalysts they currently employ, PEM electrolyzers have scant possibilities of being employed in large-scale hydrogen production. The importance and recent advancements in the development of catalysts without PGMs are poised to benefit more the field of alkaline electrolysis rather than that of PEM devices. This paper presents our original data which demonstrate that an advanced alkaline electrolyzer with performances rivaling those of PEM electrolyzers can be made without PGM and with catalysts of high stability and durability. Studies on the advantages/limitations of electrolyzers with different architectures do show how a judicious application of pressure differentials in a recirculating electrolyte scheme helps reduce mass transport limitations, increasing efficiency and power density. © 2012 Elsevier Ltd. All rights reserved.

In this paper we investigate the electrochemical behavior of iron hexacyanocobaltate (FeHCC) in comparison to the cobalt hexacyanoferrate (CoHCF). The best results were achieved on electrochemical synthesized film of FeHCC on the TiO2 modified electrodes. The chemical and physical characterizations confirm the formation of the FeHCC with the classical cubic crystal structure of the Prussian blue analogs, with cell parameter a very close to 10 A, as well as the formation of micro aggregates of TiO2 covered by FeHCC. The synthesis was performed on various substrates such as glassy carbon (GC), graphite foil (GF) and indium tin oxide (ITO) in order to develop new technological applications.

X-ray absorption spectroscopy (XAS) has been used to monitor the local geometry of Fe and Cu sites of copper hexacyanoferrates (CuHCF)-modified electrodes which find application in the electrochemical detection of hydrogen peroxide. The XAS approach has permitted to check the nature of the Cu and Fe sites and to investigate their local structure around about 500 pm from the metal centres. The measurements have been done on electrodes prior and after the addition of known quantities of hydrogen peroxide at two different concentration ranges, following a protocol consisting of H2O2 addition, applied potential, and rest period. For the CuHCF-modified electrode, this protocol leads to the increasing conversion to an already present “inactive” component, which limits the usability of the sensor; whereas the electrode modified with the Cu2+-loaded CuHCF displays a better resistance to this unavoidable process. In particular, the formation of the “inactive” component takes place more slowly, confirming the capability, at molecular scale, of such Cu-enriched CuHCF used as electrode modifier to detect more efficiently hydrogen peroxide, as recently demonstrated in our previous paper.

The paper describes the time-dependent evolution of the electrochemical deposition of cobalt hexacyanoferrate (CoHCFe) on graphite foil electrode modified with electrochemically formed sol–gel film doped with β-cyclodextrin to impart porosity. With short-time electrodeposition, cyclic voltammetry (CV) shows a single redox couple typical of nano-sized clusters of CoHCFe, while at longer deposition times the CV’s shape evolves to the classical form of a bulk compound in which there are present two redox couples. The electrode modified with β-cyclodextrin (CD) included in the sol–gel film has an active surface that corresponds to pores created by CD stacks normal to the surface. Hence, the electrochemical formation of CoHCFe starts in these conductive pores; only at long deposition times do the clusters overlap to form moieties with the voltammetric characteristics of bulk CoHCFe.

The oxidation of 5-hydroxytryptophan (5-HTPP) yielded a passivating polymeric film at an indium tin oxide (ITO) electrode. Coating ITO with a nanoscale sol-gel film with a mesoporous structure was shown to change the pathway of the chemical reaction coupled to the electron transfer. The sol-gel film was deposited by an electrochemically assisted process, and the mesoporosity was imparted by including generation-4 poly(amidoamine) dendrimer in the precursor solution. The dendrimer was removed subsequently with an atmospheric oxygen plasma. This electrode remained active during cyclic voltammetry and controlled potential electrolysis of 5-HTPP, which was attributed to dimer, rather than polymer, formation from the oxidation product. Mass spectrometry confirmed this hypothesis. The anodic current was limited by the electron-transfer kinetics. Modification of the sol-gel film by inclusion of cobalt hexacyanoferrate, which catalyzes the oxidation, resulted in a diffusion-limited current. Determination of 5-HTPP by flow-injection amperometry had a detection limit of 17 nM.

The preparation of cobalt hexacyanoferrate nanoparticles–poly(methyl methacrylate) (CoHCF–PMMA) composites are described together with their characterization and thermochromic properties. CoHCF nanoparticles – investigated by dynamic light scattering – were prepared by optimizing solvent composition and temperature to obtain nanoparticles with a reduced degree of aggregation. The nanoparticles were embedded in a PMMA matrix to obtain a transparent coloured composite which was studied by transmission electron microscopy. The nanoparticle chromic features, enhanced by their reduced sizes, were investigated by UV–vis and FT-IR spectroscopy.

X-ray Absorption Spectroscopy (XAS) has been used to probe the local structure of doped vanadium pentoxide materials prepared through sol-gel processes. The doped samples have been analyzed at the vanadium k-edge as well as at the doping metal K-edge (copper and zinc). The presence of two metals sites gives two independent absorption signals, even if we are investigating the same compound, for this reason the reliability of the analysis is enhanced. The strategy in determining the local structure will be discussed. The local structural modifications resulting from low to high doping concentration in the best performing copper doped - V2O5 aerogel like material is reported. Similar measurements were done using zinc as doping metal, in both aerogel-like and xerogel form. The EXAFS analysis shows that the vanadium atomic environment is not altered by the doping metal insertion and that the doping metals (Cu and Zn) are found to be in the same site. Copper and zinc are 4-fold coordinated by almost coplanar oxygens in both xerogel and aerogel-like oxide hosts. The use of the metal-metal interaction while analyzing data concerning sample of high doping level played a key role in the determination of the preferred metal sites.

The paper characterizes electrochemical properties of indium hexacyanoferrates (Inhcf). The cyclic voltammetric response in the presence of different metal alkali cations of divalent cations and of hydronium has been investigated. The Inhcf can exchange reversibly with all of these cations. This feature makes the Inhcf a good candidate for many electrochemical applications where a source or sink of metal cations is needed, e.g., electrochromic and energy storage devices. A prototype electrochromic system based on an Inhcf and Cohcf couple has been assembled and tested.

A charge transfer between Fe and Co in cobalt hexacyanoferrate has been observed for the first time by anatase doping. The charge transfer, which involves a spin transition at the Co site, is supported by high-resolution XANES spectra. EXAFS evidenced a consistent change (10%) of the Co-N first shell.

A Ni, Al hydrotalcite-like compound (Htlc) has been proven an useful host material for an alternative synthesis of a K{sup +}-free mixed hexacyanoferrate Ni{sub 1.5}Fe{sup III}(CN){sub 6}, which is very difficult to obtain in bulk. The first stage of the procedure consists in the intercalation of hexacyanoferrate(III) inside the Htlc structure. The intercalated Htlc has been treated with a NiNO{sub 3} solution. The obtained material has been characterized by XRD, XAS Raman and FT-IR spectroscopy. The voltammetric response of the compound obtained after the complete solubilization of the Htlc host shows a typical fingerprint of nickel hexacyanoferrate material with a very low level of potassium. Elemental analysis confirmed the absence of K{sup +} and thus the occurrence of K{sup +}-free nickel hexacyanoferrate (14% yield). - Graphical abstract: A new synthetic route is proposed to prepare a K{sup +}-free nickel hexacyanoferrate by using a Ni, Al LDH, intercalated with Fe(CN){sub 6} {sup 3-}, as host material. The different host-guest solubility allowed us to synthesize, with a quite good yield, a pure mixed hexacyanoferrate, which is very difficult to obtain. Elemental analysis and cyclic voltammetry confirmed the absence of K{sup +}.

The solid-state electrochemistry and thermochromism of cobalt hexacyanoferrate (CoHCF) in a composite matrix comprising silica sol–gel and generation-4 poly(amidoamine) dendrimer was investigated and compared to analogous studies of CoHCF powders. The thermochromic behaviour over the range, 25–85 °C, of the reduced form in the sol–gel matrix differed from that of the powder. The results suggested that even in the presence of KCl in this matrix, the dominate form of the reduced CoHCF was Co 2 II Fe II (CN) 6 rather than K 2 Co II Fe II (CN) 6 . In contrast, the thermochromic behaviour of the oxidized form of CoHCF was the same as that reported for the powders. The observed cyclic voltammetric behaviour of CoHCF in the sol–gel composite matrix was the same as that of powders in terms of the electrode processes, but the influence of scan rate on the current was dependent upon the cell configuration. With the CoHCF-doped composite contacted to a solution phase, this behaviour was consistent with anion intercalation/de-intercalation control, but in a solid-state cell, a transition from a surface-controlled to a mass-transport controlled current was observed.

Pt electrodes, modified with a directly electrosynthesised film of Ni/Al-NO3 hydrotalcite were evaluated as amperometric sensors for oxidizable substrates in flow systems. The optimization of the operative parameters has been carried out using EtOH as test analyte, NaOH as carrier electrolyte and applying a constant potential. Analytical results in terms of linear range, limit of detection and precision were much satisfactory. The sensors are simple and rapid to prepare, and the coatings obtained by electrosynthesis are reproducible and stable from a mechanical point of view. The detector response was stable: a very good repeatability was observed during 12 h of flow experiments (R.S.D. < 2.6%).

The intercalation of hexacyanoferrate(II) ions inside the interlayer of a Ni,Al hydrotalcite has been carried out by anionic exchange of the originally existing chloride ions. The best exchange reaction conditions have been established in order to use the intercalated hydrotalcite as a microreactor to synthesise the compound Ni2IIFeII(CN)6, i.e., a mixed hexacyanoferrate not containing structural potassium. All the samples have been characterised by elemental chemical analysis, powder X-ray diffraction, FTIR and X-ray absorption spectroscopies and cyclic voltammetry. It has been found that, after destroying the intercalated structure by keeping it in contact with a Ni2+ solution, the desired compound Ni2IIFeII(CN)6 is not obtained, since the Fe(CN)64− ion is not exchanged as such but as the ion pair with potassium. Moreover, it has been demonstrated by X-ray absorption spectroscopy that no partial oxidation of Fe(CN)64− occurs during the intercalation inside the hydrotalcite structure.

Electrochemical properties of thin films and microcrystalline precipitates of nickel(II) hexacyanoferrate(II, III), NiHCNFe, are strongly dependent on the method of their preparation and experimental conditions of their investigation. The films have been generated on both inert (gold) and parent metal (nickel) substrates. Interpretation of voltammetric responses of nickel hexacyanoferrate microstructures on electrodes is supported with the data of elemental analysis estimations obtained using atomic absorption and surface examination based on X-ray energy dispersive spectroscopy. Both electrodeposited films and mechanically-attached precipitates of nickel hexacyanoferrate constitute mixed structures in which the relative ratios of K and Ni to Fe reflect composition of a solution for modification, choice of the deposition potential and time, and the time and potential limits of exposure of the system to voltammetric potential cycling in potassium salt supporting electrolyte. We demonstrate here that the more positive set of peaks of nickel hexacyanoferrate is related to the electroactivity of the form containing relatively larger amount of potassium and smaller of nickel. On the other hand, the more negative set of the system’s peaks shall be attributed to the form that is largely potassium depleted and containing more nickel relative to iron. In this context, the use of the previously proposed approximate formulas, K 2 Ni[Fe II (CN) 6 ] and KNi 1.5 [Fe II (CN) 6 ], for the predominant nickel hexacyanoferrate (reduced) forms is justified.

The electrocatalytic oxidation of mannitol at a nickel oxide electrode was investigated. The experimental conditions for determining mannitol concentrations have been optimised taking into account the involved electrochemistry. Unlike what previously reported in the literature, our findings lead to the conclusion that both the electrochemical reaction involving the Ni(II)/Ni(III) couple and the chemical reaction between mannitol and Ni(III) are effective in determining the overall kinetics of the electrocatalytic process. The calibration line for mannitol was linear up to 20.0 mmol l-1. Mannitol determination with the nickel oxide electrode was performed in a liquid culture medium selective for Staphylococcus aureus in order to make an indirect calibration of bacterial viable cells, but the results were not satisfactory.

Vanadium pentoxide materials prepared through sol–gel processes (xerogel, aerogel and aerogel-like) act as excellent intercalation hosts for lithium as well as for polyvalent cations. The large lithium insertion capacity of these materials makes them attractive for use as cathodes in high capacity lithium batteries. This paper describes the utility of X-Ray absorption spectroscopy (XAS) for the investigation of gel-based V2O5 materials. In particular, X-ray near edge structure (XANES) and polarized EXAFS experiments are highlighted.

Some ‘conductive’ hydrotalcites containing nickel as divalent cation and Cl − , SO 4 2− or CO 3 2− as interlayer anion, have been synthesised and membranised with different types of polymeric matrices to modify glassy carbon electrodes. The mechanism responsible of the conductive properties has been deeply investigated by voltammetric techniques using both a stationary and a rotating disk electrode, demonstrating that the interlayer anion does not affect significantly the electrochemical behaviour of the material. The electrocatalytic properties have been also studied pointing out the key role of the steric hindrance of the oxidisable substrate. In particular, mono- and polyhydric compounds have been taken into account. As to the electrocatalytic efficiency, the nature of the interlayer anion and, hence, the dimension of the interlayer spacing, is important in determining the sensitivity of the measurement since it can affect the analyte diffusion inside the hydrotalcite structure.

An ion-selective electrode (ISE) for sulfate based on a dispersion of hydrotalcite particles into a polymeric membrane using coated-wire (CW) configuration is described. Membranes, based both on poly(vinyl chloride) (PVC) containing different plasticizers and poly(dimethylsiloxane) (PDMS) were studied. The best performance in terms of slope (−29.6±0.8 mV per decade) and response time ( −5 to 4.0×10 −2 M) was practically the same for all the developed ISEs. The interference of hydrophobic inorganic anions was very low in comparison with the conventional ion-exchanger based electrodes, as shown by the selectivity coefficients determined by the matched potential method (MPM). The selectivity was also good towards the most common univalent and divalent anions and improved in the presence of 2-[4-(2-Hydroxyethyl)-1-piperarazinyl]ethanesulfonic acid (HEPES). The potentiometric response was practically constant in the pH range 4–7. A successful application of sulfate determination in commercial mineral waters, using direct potentiometry, is presented.