Physicochemical Aspects of Metal Nanoparticle Preparation

Physicochemical properties, including optical properties or catalytic activity, and biological properties of metal nanoparticles are considerably influenced by their diameter. Therefore, a tailored synthesis of metal nanoparticles represents a key topic in the field of nanotechnology, and the number of research papers, concerning this topic, has been annually growing with an arithmetic progression. Metal nanoparticles are most frequently prepared via chemical reduction of metals in ionic form from their solutions. Using this synthetic approach, tailored parameters of the particles can be achieved via the adjustment of numerous factors: difference of potentials of the metal redox system and the reducing agent redox system, pH of the reaction mixture, and its temperature. The influence of these three factors on the diameter of the prepared metal nanoparticles will be discussed in the following chapter with respect to general laws and based on numerous examples from research practice

Thermally Induced Solid-Phase Quasi-Intramolecular Redox Reactions of [Hexakis(urea-O)iron(III)] Permanganate: An Easy Reaction Route to Prepare Potential (Fe,Mn)O x Catalysts for CO2 Hydrogenation

Research on new reaction routes and precursors to prepare catalysts for CO2 hydrogenation has enormous importance. Here, we report on the preparation of the permanganate salt of the urea-coordinated iron(III), [hexakis(urea-O)iron(III)]permanganate ([Fe(urea-O)6](MnO4)3) via an affordable synthesis route and preliminarily demonstrate the catalytic activity of its (Fe,Mn)Ox thermal decomposition products in CO2 hydrogenation. [Fe(urea-O)6](MnO4)3 contains O-coordinated urea ligands in octahedral propeller-like arrangement around the Fe3+ cation. There are extended hydrogen bond interactions between the permanganate ions and the hydrogen atoms of the urea ligands. These hydrogen bonds serve as reaction centers and have unique roles in the solid-phase quasi-intramolecular redox reaction of the urea ligand and the permanganate anion below the temperature of ligand loss of the complex cation. The decomposition mechanism of the urea ligand (ammonia elimination with the formation of isocyanuric acid and biuret) has been clarified. In an inert atmosphere, the final thermal decomposition product was manganese-containing wuestite, (Fe,Mn)O, at 800 °C, whereas in ambient air, two types of bixbyite (Fe,Mn)2O3 as well as jacobsite (Fe,Mn)T-4(Fe,Mn)OC-62O4), with overall Fe to Mn stoichiometry of 1:3, were formed. These final products were obtained regardless of the different atmospheres applied during thermal treatments up to 350 °C. Disordered bixbyite formed first with inhomogeneous Fe and Mn distribution and double-size supercell and then transformed gradually into common bixbyite with regular structure (and with 1:3 Fe to Mn ratio) upon increasing the temperature and heating time. The (Fe,Mn)Ox intermediates formed under various conditions showed catalytic effect in the CO2 hydrogenation reaction with <57.6% CO2 conversions and <39.3% hydrocarbon yields. As a mild solid-phase oxidant, hexakis(urea-O)iron(III) permanganate, was found to be selective in the transformation of (un)substituted benzylic alcohols into benzaldehydes and benzonitriles

Comparative Study of Antimicrobial Activity of AgBr and Ag Nanoparticles (NPs)

<div><p>The diverse mechanism of antimicrobial activity of Ag and AgBr nanoparticles against gram-positive and gram-negative bacteria and also against several strains of candida was explored in this study. The AgBr nanoparticles (NPs) were prepared by simple precipitation of silver nitrate by potassium bromide in the presence of stabilizing polymers. The used polymers (PEG, PVP, PVA, and HEC) influence significantly the size of the prepared AgBr NPs dependently on the mode of interaction of polymer with Ag⁺ ions. Small NPs (diameter of about 60–70 nm) were formed in the presence of the polymer with low interaction as are PEG and HEC, the polymers which interact with Ag⁺ strongly produce nearly two times bigger NPs (120–130 nm). The prepared AgBr NPs were transformed to Ag NPs by the reduction using NaBH₄. The sizes of the produced Ag NPs followed the same trends – the smallest NPs were produced in the presence of PEG and HEC polymers. Prepared AgBr and Ag NPs dispersions were tested for their biological activity. The obtained results of antimicrobial activity of AgBr and Ag NPs are discussed in terms of possible mechanism of the action of these NPs against tested microbial strains. The AgBr NPs are more effective against gram-negative bacteria and tested yeast strains while Ag NPs show the best antibacterial action against gram-positive bacteria strains.</p></div

Average values of AgNP diameter determined from DLS measurements and from TEM images.

<p>*¹determined from DLS;</p><p>*²determined from TEM.</p><p>AgNPs were prepared via a modified Tollens process using various reducing agents in the presence of gelatin.</p

TEM images and distribution diagrams of Ag NPs prepared in the presence of a) PEG, b) PVP, c) PVA and d) HEC.

<p>TEM images and distribution diagrams of Ag NPs prepared in the presence of a) PEG, b) PVP, c) PVA and d) HEC.</p

UV-Vis spectra of ten times diluted Ag NPs in aqueous dispersions prepared by the reduction of AgBr NPs by NaBH₄ in the presence of a) PEG, b) PVP, c) PVA and d) HEC.

<p>UV-Vis spectra of ten times diluted Ag NPs in aqueous dispersions prepared by the reduction of AgBr NPs by NaBH₄ in the presence of a) PEG, b) PVP, c) PVA and d) HEC.</p

Minimum inhibitory concentrations (mg/L) of silver bromide nanoparticles, silver nanoparticles and ionic silver against gram-positive (+) and gram-negative (-) bacteria and against yeast pathogens recalculated on total silver concentration prepared in the presence of selected polymers.

<p>Minimum inhibitory concentrations (mg/L) of silver bromide nanoparticles, silver nanoparticles and ionic silver against gram-positive (+) and gram-negative (-) bacteria and against yeast pathogens recalculated on total silver concentration prepared in the presence of selected polymers.</p

TEM images and corresponding particle size distribution histograms of AgNPs reduced by maltose (a), ascorbic acid (b), and sodium borohydride (c) in the presence of gelatin.

<p>The concentration of gelatin was 0.025% (w/w).</p