Sulfate-selective electrodes based on hydrotalcites

Layered Double Hydroxides as the Unique Product of Target Ionic Construction for Energy, Chemical, Foods, Cosmetics, Medicine and Ecology Applications

Layered Double Hydroxide (LDH) is an α-modification of the M-host (M2+ ) hydroxide, in which some part of the M-host cations is replaced by M-guest cations (M3+ or M4+ ). The emerging excess positive charge is compensated by the intercalation of anions into the interlayer space, which also contains water molecules. LDHs exhibit anion exchange properties. Targeted ionic design of LDHs via combining three components (M-host, M-guest cations, intercalated anions) allows the creation of a very wide range of highly efficient electrochemical, electrocatalytic, electrochromic substances, catalysts, ion exchangers, sorbents, color pigments, pharmacological drugs, food, and cosmetic additives. In this review, the structure and areas of application of LDHs are considered from the perspective of the targeted ionic design of a substance for a specific application.

Voltammetric quantitative analysis of vildagliptin in bulk form and spiked human serum at a modified electrode

The electrochemical behavior of Vildagliptin (VILD) was studied using the cyclic voltammetric technique in an aqueous Britton–Robinson (BR) universal buffer solution of various pH levels between 4.0 and 10 at a 5% calcium-montmorillonite clay modified with carbon paste electrode surface (5% Ca-MMT/CPE). The results exhibited an irreversible anodic peak at about 1.238 V versus Ag/AgCl, KCl (3 mol L−1). The anodic peak was found to be diffusion–adsorption controlled. The possible reaction mechanism is estimated taking into consideration of the calculated electrons and protons number transferred on the electrode/electrolyte interface using the cyclic voltammetric technique. VILD was found to adsorb onto the surface of 5% Ca-MMT/CPE in a monolayer surface coverage of 3.0 × 10−12 mol cm−2. A validated square wave voltammetry (SWV) technique for VILD determination was performed. The calibration curve of VILD onto the 5% Ca-MMT/CPE surface was linear in the concentration range of 1.0–110 nmol L−1 with the mean limits of detection and quantification was 0.285 and 0.950 nmol L−1, respectively, in the bulk form. The proposed procedure for the assay of VILD in bulk form, dosage form, and spiked human serum has the advantage of being simple, rapid, sensitive, and inexpensive compared to other analytical methods. The described method showed an excellent performance for the trace determination of VILD in its formulation without interference from excipients.

Graphical abstract

Preparation of Layered Double Hydroxides toward Precisely Designed Hierarchical Organization

Layered double hydroxides (LDHs) are a class of materials with useful properties associated with their anion exchange abilities for a wide range of materials’ applications including adsorbent, catalyst and its support, ceramic precursor, and drug carrier. In order to satisfy the requirements for the detailed characterization and the practical application, the preparation of LDHs with varied composition and particle morphology has been examined extensively. The versatility of the preparation methods led LDHs with varied composition and micro/macroscopic morphology, which makes the application of LDHs more realistic. In the present review article, synthetic methods of LDHs are overviewed in order to highlight the present status of the LDHs for practical application.

Squaramide-based tripodal ionophores for potentiometric sulfate-selective sensors with high selectivity

A class of squaramide-based tripodal molecules was employed as new ionophores for highly sensitive and selective sulfate-selective sensors.

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.

A novel electrochemical sensing platform for anions based on conducting polymer film modified electrodes integrated on paper-based chips

In this paper, conducting polymer film modified electrodes were applied to fabricate paper-based chips (PCs), and different concentrations of chloride ions (Cl(-)) in water can be selectively detected based on the potential response towards Cl(-). The three-electrode system was screen-printed on paper and the polypyrrole (PPy) film doped with Cl(-) was electrochemically polymerized on working electrodes through cyclic voltammetry in aqueous solution. Open circuit potential-time method was used to measure the potential response. Based on such PCs, Cl(-) can be selectively detected in the range of 10(-7)-10(-2)M. Moreover, such PCs were utilized for Cl(-) analysis in real water samples and resulted in good results with recoveries between 113% and 124%. Besides, following the strategy we also employed this method to detect F(-) in water to demonstrate its general applicability. In view of its novelty, simplicity, sensitivity and low price, such PCs will potentially be utilized for the monitoring of anions in the environment, and our method made a start for the application of CMEs to PCs to design electrochemical sensors.

Emission reduction of aluminium anodising industry by production of Mg2+-Al3+-SO4(2-) -hydrotalcite-type compound

The synthesis of Mg(2+)-Al(3+)-SO(4)(2-)-hydrotalcite-type compound from the acid wastewaters of the aluminium anodising industry has been studied as a possible way of reducing the emissions to the environment, recovering simultaneously resource materials as a valuable mineral. The process of synthesis was carried out using rinse wastewater solutions generated from the anodising treatment when a cascade rinsing system is employed. The method of co-precipitation at constant pH was employed for such a process, using MgO as a source of magnesium. The synthesis was studied as a function of precipitation pH (8-10) and flow rate of reagent mixture (5-30 ml min(-1)). High pH of precipitation and low flow rate of reagent mixture (5-15 ml min(-1)) were found optimal to improve the crystallinity of the synthesised product. The mineral characterisation was performed using X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis and differential thermal analysis, all of which indicated characteristics typical of the desired compound. Almost 100% of the aluminium initially present in the acid wastewater solutions was recovered in the form of Mg(2+)-Al(3+)-SO(4)(2-)-hydrotalcite-type compound.

Sulfate-selective Electrode Based on a Complex of Copper

A new sulfate-selective electrode based on the complex N,N'-bis(2-amino-1-oxo-phenelenyl)phenylenediamine copper(II) (CuL) as the membrane carrier was developed. The electrode exhibited a good Nernstian slope of -29.5 +/- 0.5 mV/decade and a linear range of 1.0 x 10(-7) - 1.0 x 10(-1) M for sulfate. The limit of detection was 1.0 x 10(-8) M. It has a fast response time of 10 s and can be used for more than three months. The selective coefficients were determined by the fixed interference method (FIM). The electrode could be used in the pH range 3.5 - 8.0. It was employed as an indicator electrode for direct determination of sulfate in pharmacy and cement samples.

Ionic liquids promote selective responses towards the highly hydrophilic anion sulfate in PVC membrane ion-selective electrodes

A remarkable enhanced response towards the hydrophilic anion sulfate using plasticized PVC membranes containing the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and a polyazacycloalkane derivative as ionophore has been found.