Phase transformations of Fe(ІІ)-Fe(III) layered dоuble hydroxides of corrosion origin in the aqueous solutions of platinum and palladium

Abstract

One of the urgent scientific problems is the development of new or alternative to the well-known methods оf the synthesis of biocompatible substances and composites with unique complexes of physicochemical properties (optical, magnetic, catalytic, electrical, bactericidal). Promising substances for the production of compounds of this class are Fe (II)-Fe (III) layered double hydroxides (LDHs) or Green Rust.At present, Green Rust suspensions are already used as nanoreactors for the one stage reduction of precious metal particles (gold and silver), the production of magnetite doped with precious metals and the synthesis of shell nanocomposites. The advantages of using Fe(II)-Fe(III) LNG structures as a reducing agent are the absence of the need to introduce into the system foreign components, such as anions of iron salts, organic substances, including surfactants, as well as the simplicity of the synthesis procedure, carried out without the use of expensive equipment.While the processes of formation of shell nanocomposites Fe3O4&Ag0 and Fe3O4&Au0 in Green Rust suspensions, their physicochemical properties, experience and prospects for practical use in biomedical research are covered in the literature in detail, the lack of comprehensive data on the structure and properties of shell composites based on particles of magnetite of corrosion origin and clusters of platinum and palladium, or magnetite doped with platinum group metals, still remain an unsolved part of this scientific problem.Therefore, the aim of this study was to determine the composition and physicochemical properties of the products of phase transformations of hydroxycarbonate Green Rust of corrosion origin in its contact with aqua forms of platinum and palladium under conditions of free air in the reaction zone.To obtain the primary phase of hydroxycarbonate Green Rust, a disk device was used, the working part of which is made of steel 3. During the synthesis procedure, the steel disk was alternately in contact with aqueous solution and air. Before the start of each experiment, the disk was treated mechanically and chemically to remove the oxide layer and activate the surface of the carbon alloy. The build-up of the GR(CO3)2- layer was performed under conditions of contact of the steel surface with distilled water for an hour, after which the dispersion medium was changed to aqueous solutions of noble metals.Six aqueous sodium chlorine platinate Na2[PtCl6] ‧ 6H2O in the concentration range (Pt 4+) from 0.5 to 10 mg/dm3 was used to obtain platinum-containing solutions, and H2[PdCl4] and PdCl2 with concentrations (Pd 2+) from 0.1 to 10 mg/dm3 were selected to obtain palladium-containing solutions, respectively. The synthesis was performed before the transition of the system to a steady state (70 hours). The studies were based on the following methods: X-ray phase analysis and X-ray fluorescence spectroscopy (X-ray diffraction), thermogravimetry (TG-DTA), photocolorimetry, electrokinetic studies, scanning electron microscopy (SEM), magnetic field and force microscopy, magnetometry.As a result of the conducted experiments, the processes of phase transformations of Fe(II)-Fe(III) LNG of hydroxycarbonate composition of corrosion origin in the presence of aquaforms of platinum and palladium were investigated. The formation of nanosized particles of magnetite on the surface of steel and oxyhydroxides of iron, relics of Fe(II)-Fe(III) LNG and particles of reduced noble metals - in the film of its near-surface layer have been established. It is determined that the phase formation in the system is accompanied by the activation of electrode processes on the steel surface, which lead to the accumulation of Fe2 + cations and hydroxyl anions in the dispersion medium. The typical course of exogenous oxidation of iron-containing compounds is elucidated by thermogravimetry. It is shown that the entry of platinum and palladium cations into the structure of magnetite significantly affects the value of its electrokinetic potential. The method of magnetometry proved that the particles of platinum-doped magnetite have nanometer sizes and belong to superparamagnetic, which opens up prospects for their practical use in biomedicine.