Marianna Hundáková

ZnO/graphite composites and its antibacterial activity at different conditions

The paper reports laboratory preparation, characterization and in vitro evaluation of antibacterial activity of ZnO/graphite nanocomposites. Zinc chloride and sodium carbonate served as precursors for synthesis of zinc oxide, while micromilled and natural graphite were used as the matrix for ZnO nanoparticles anchoring. During the reaction of ZnCl2 with saturated aqueous solution of Na2CO3a new compound is created. During the calcination at the temperature of 500 °C this new precursors decomposes and ZnO nanoparticles are formed. Composites ZnO/graphite with 50 wt.% of ZnO particles were prepared. X-ray powder diffraction and Raman microspectroscopy served as phase-analytical methods. Scanning electron microscopy technique was used for morphology characterization of the prepared samples and EDS mapping for visualization of elemental distribution. A developed modification of the standard microdilution test was used for in vitro evaluation of daylight induced antibacterial activity and antibacterial activity at dark conditions. Common human pathogens served as microorganism for antibacterial assay. Antibacterial activity of ZnO/graphite composites could be based on photocatalytic reaction; however there is a role of Zn(2+) ions on the resulting antibacterial activity which proved the experiments in dark condition. There is synergistic effect between Zn(2+) caused and reactive oxygen species caused antibacterial activity.

Vermiculite as efficient sorbent of CeIII and CeIV

Environmental context Cerium, a Technology Critical Element with many technical, agricultural, and medicinal applications, is increasingly being discharged to the environment. One of the best ways to remove cerium from wastes is its fixation into inexpensive bulk material such as vermiculite. This paper investigates the mechanism of CeIII and CeIV uptake and capture by vermiculite in neutral and acidic aqueous solutions. Abstract This study focussed on the mechanism of CeIII and CeIV uptake on vermiculite (Ver), which has been studied sporadically. Chemical equilibrium and leaching experiments in acid solutions were evaluated using batch experiments and changes of mineral composition were monitored by X-ray powder diffraction analysis. The concentrations of Ce, Na, K, Ca, Mg, Al and Si were determined by atomic emission spectroscopy coupled with inductively coupled plasma (AES-ICP). The data for CeIII uptake on Ver in neutral aqueous solution were fitted both with adsorption and ion-exchange models. The latter, with a calculated selectivity constant =14.30 (L mmol–1)k–1, showed a better fit with experimental data than adsorption models. The uptake of CeIII on Ver at pH 2 was also controlled by intensive leaching of cations from 2:1 layers and therefore these data were not fitted. A much higher uptake of CeIV on Ver (~6 mequiv. g–1, i.e. ~210mgg–1) at pH 2 and 6 in comparison with the cation-exchange capacity of original vermiculite (1.28 mequiv. g–1) was found and explained. With regard to the different rate of CeIV species fixation on Ver, their different CeIV solubility in NaCl solution, aqueous acid solution (pH 2), and 3M H2SO4, three species of CeIV bonded on vermiculite are proposed. They are ion-exchanged CeIV, CeIV–complex 1 and CeIV–complex 2. The CeIV species uptake on Ver was quantitatively determined both for pH 2 and 6. The new findings show a very effective method of cerium uptake, especially from acidic aqueous solutions.

Decoration of Inorganic Substrates with Metallic Nanoparticles and Their Application as Antimicrobial Agents

Effect on antimicrobial activity observed for several types of hybrid materials is described in our chapter. The substrates for functional antimicrobial particles are natural clay minerals and carbon materials for this review limited to graphite/graphene and carbon nanoparticles (nanotubes and fullerenes). Short description of substrate materials and their properties is followed by discussion of the effect of selected most popular antimicrobial metals (silver, copper) and several oxides (zinc, titanium and copper oxides) and it is conferred for Gram positive and Gram negative bacterial strains. The methods for preparation of such particles may vary but the most used are intercalation and decoration methods from solution for the clay minerals. Nanoparticles (NPs) of metals and metal oxides on carbon and nanocarbon materials are prepared using physico-chemical approach. The research confirmed that the shape and size of functional NPs can depend on used substrate, preparation conditions and used method. Interestingly, it was found that Ag-clay sample was as effective as the free Ag+ions. Generally, it was found the size of active surface area, mobility and availability of potential active particles (ions or nanoparticles) and chemical state of them plays an important role in antimicrobial activity.

Vermiculite With Ag and Cu Used as an Antibacterial Nanofiller in Polyethylene/ Vermikulit S Ag A Cu Použitý Jako Antibakteriální Nanoplnivo V Polyethylenu

Abstract Vermiculite (Ver) enriched with silver and copper was used as nanofiller to the polyethylene (PE) matrix. Specifically, the low density polyethylene (LDPE) was chosen as a matrix. The samples Ver-Ag,Cu were prepared by shaking of Ver with the aqueous solutions of silver and copper nitrate. The mixtures of the Ver nanofillers and PE were homogenized by melt compounding technique and further thin plates were pressed from stiff matter of PE with Ver nanofiller. The exfoliation of the powdery Ver nanofillers in PE matrix was characterized by the X-ray diffraction analysis of thin plates. Distribution of Ver nanofiller in PE matrix was observed by Light microscopy. The reinforcing effect of nanofillers onto PE matrix was studied by creep experiment. Antibacterial activity of powder Ver-Ag,Cu samples and surfaces of PE/Ver-Ag,Cu samples was tested on the Gram-positive bacteria Enterococcus faecalis. All tested PE/Ver-Ag,Cu surfaces showed good antibacterial behaviour after 24 h in comparison to pure PE. The number of colonies decreased from the countless number to several hundred colonies. Abstrakt Vermikulit (Ver) obohacený stříbrem a mědí byl použit jako nanoplnivo v polyethylenové (PE) matrici. Konkrétně byl jako matrice vybrán nízko hustotní polyethylen (LDPE). Vzorky Ver-Ag,Cu byly připraveny mícháním Ver s vodnými roztoky dusičnanu stříbrného a měďnatého. Směsi Ver nanoplniv a PE byly homogenizovány postupem míchání taveniny a následně byly ze ztuhnuté směsi PE s Ver nanoplnivem vylisovány tenké destičky. Exfoliace práškového Ver nanoplniva v PE matrici byla hodnocena pomocí Rentgenové difrakční analýzy tenkých destiček. Distribuce Ver nanoplniva v PE matrici byla studována Světelnou mikroskopií. Vyztužující efekt nanoplniv na PE matrici byl studován pomocí krípového experimentu. Antibakteriální působení práškových vzorků Ver-Ag,Cu a povrchů vzorků PE/Ver-Ag,Cu bylo testováno na grampozitivní bakterii Enterococcus faecalis. Všechny testované povrchy PE/Ver-Ag,Cu vykazovaly dobré antibakteriální působení po 24 h oproti povrchu čistého PE. Počet kolonií poklesl z nespočetného množství na několik stovek kolonií.

Preparation of calcium-deficient hydroxyapatite particles on vermiculite by precipitation and sonication

Ca-deficient hydroxyapatite (CDH) is biocompatible, cheap material used in implants and non-biological applications. Due to similarity of CDH with human hard tissues, it is suitable for manufacturing of bone substituents. Clay minerals are suitable natural and non-toxic materials used as substrates for the growth of nanoparticles. Combination of non-toxic nature of the clay minerals with CDH is possible to achieve nanocomposites with properties advantageous for medical or catalytic applications. The aim of the study was to prepare CDH on the surface of a monoionic Na/Mg form of original vermiculites (Vs) from Brazil and Bulgaria. The CDH was prepared by precipitation under constant mixing or sonication conditions. XRD analysis confirmed that CDH was successfully prepared on the V surfaces, and the type of V did not influence CDH creation. Basal reflections of vermiculites do not show changes indicating an interaction between vermiculites and CDH. No interactions between V and CDH were observed in FTIR measurement and fitting analysis. Scanning electron microscopy shows creation of CDH particles and coherent layer on the V surface. The results showed that V serves as a support for CDH particles and probably does not influence the chemistry of CDH.