Mass transport on an anionic clay-modified electrode as studied by a quartz crystal microbalance

Tuning Redox State and Ionic Transfers of Mg/Fe-Layered Double Hydroxide Nanosheets by Electrochemical and Electrogravimetric Methods

Studying the electrogravimetric behavior of Mg/Fe-layered double hydroxide (LDH) nanoparticles with an electrochemical quartz crystal microbalance demonstrates its pseudocapacitance properties of mix cation and anion exchanger. The electrochemical control of the oxidation state of iron constituting the layered sheets allowed anion intercalation/deintercalation into the LDH interlayer space. Concomitantly, in agreement with the pH of zero point of net charge of the Mg/Fe-LDH, the interfacial pH increase via catalyzed hydrogen evolution reaction allows cation electroadsorption onto the external surfaces of the nanoplatelets.

Layered-double-hydroxide-modified electrodes: electroanalytical applications

Two-dimensional inorganic solids, such as layered double hydroxides (LDHs), also defined as anionic clays, have open structures and unique anion-exchange properties which make them very appropriate materials for the immobilization of anions and biomolecules that often bear an overall negative charge. This review aims to describe the important aspects and new developments of electrochemical sensors and biosensors based on LDHs, evidencing the research from our own laboratory and other groups. It is intended to provide an overview of the various types of chemically modified electrodes that have been developed with these 2D layered materials, along with the significant advances made over the last several years. In particular, we report the main methods used for the deposition of LDH films on different substrates, the conductive properties of these materials, the possibility to use them in the development of membranes for potentiometric anion analysis, the early analytical applications of chemically modified electrodes based on the ability of LDHs to preconcentrate redox-active anions and finally the most recent applications exploiting their electrocatalytic properties. Another promising application field of LDHs, when they are employed as host structures for enzymes, is biosensing, which is described considering glucose as an example.

Intercalation of Iron(III) Hexacyano Complex in a Ni,Al Hydrotalcite-like Compound

The product obtained by the intercalation of hexacyanoferrate(III) inside a Ni, Al hydrotalcite-like compound (Htlc) has been characterized using XRD, FT-IR, Raman, and XAS spectroscopy. The intercalation was carried out by anionic exchange of the originally existing chloride ions. The combined use of those techniques gave more insight on the insertion chemistry of Htlcs. Extended X-ray absorption fine structure spectra of the intercalated Htlc demonstrated that the native structure was stable during the iron complex insertion, whereas the exchange process occurred with a partial reduction of hexacyanoferrate(III). Both Raman and FT-IR spectroscopy pointed out the concomitant formation of K(2)NiFe(II)(CN)(6) and KNiFe(III)(CN)(6). The effect of aging on the intercalated product is also addressed.