Marta Valášková

Study of silver adsorption on montmorillonite

Neste trabalho foi estudada a adsorcao de Ag+ sobre montmorilonita (MMT) do tipo Wyoming rica em Na+. Os dados de adsorcao foram ajustados de acordo com varias isotermas comuns, mas os melhores parâmetros de regressao foram obtidos pelo modelo de Langmuir, indicando que Ag+ foi adsorvido na superficie de MMT formando monocamadas. A adsorcao de pequenas quantidades de Ag+ promoveu o aumento da area superficial especifica (SSA) de micro (r = 0.4-0.5 nm) a mesoporos (r = 1.5-3 nm). A intercalacao de Ag+ em MMT foi observada por difracao de raios-X (XRD). Com o aumento da concentracao de solucoes de nitrato de prata, a quantidade de Ag+ em MMT tambem aumentou e a estrutura em camadas gradualmente sofreu colapso e esfoliacao. As amostras de MTT saturadas com Ag+ foram tratadas com solucao de boro hidreto de sodio para produzir Ag0. Foi estimado um tamanho medio de L111 = 8.5(1) nm dos cristalitos de Ag0. As nanoparticulas de prata metalica ficaram localizadas na superficie e nas bordas dos cristais de MMT.

Preparation of novel organovermiculites with antibacterial activity using chlorhexidine diacetate.

The novel antibacterial organovermiculites with different mass ratios of chlorhexidine diacetate (CA) were successfully prepared by ion exchange reactions. The resultant organovermiculites were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal properties of prepared organovermiculites were investigated by simultaneous thermogravimetry (TG) and differential thermal analysis (DTA). The antibacterial activity of prepared organovermiculites against Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa was evaluated by finding minimum inhibitory concentration (MIC). Antibacterial studies showed that the organovermiculites strongly inhibited the growth of variety of microorganisms.

INTERCALATION AND GRAFTING OF VERMICULITE WITH OCTADECYLAMINE USING LOW-TEMPERATURE MELTING

Octadecylamine (ODA) was used to intercalate a fine-grained and a coarse-grained fraction of natural Mg-vermiculite (VER) using a low-temperature melting procedure. Mixtures of Mg-vermiculite fractions and powdered ODA in the molar ratios of 2:1, 1:1, 1:2 and 1:6 were homogenized and heated for 1, 3, 15 and 30 h at 80°C to prepare intercalated samples. X-ray powder diffraction analysis of intercalated samples was combined with molecular modeling to investigate their interlayer structure. Significant amounts of non-intercalated vermiculite and diffuse peaks with very low intensity and basal spacings close to 29 Å were identified when the lowest concentration (molar ratio VER:ODA = 2:1) was used. According to molecular modeling, this indicates the initial stage of a one-layer arrangement of distorted ODA molecules in the interlayer. If the concentration of ODA molecules and treatment time were increased, a two-layer arrangement of ODA molecules with a different ODA chain-disorder and interlayer-space saturation was identified. Interlayer ODA molecules were inclined to the vermiculite basal plane with an inclination angle for two-layer arrangements that ranged from 76 to 95°. Experimental basal spacings with these two-layer arrangements varied from 52 to 58 Å and were in agreement with molecular modeling results. A fully-saturated 58 Å two-layer ODA arrangement was identified when higher ODA concentrations (VER:ODA = 1:2 and 1:6) and 15 and 30 h treatment times were used. There was no significant difference between ODA-intercalated samples prepared using fine-grained and coarse-grained Mg-vermiculite fractions. A grafted ODA-chain nano-layer with a 49.6(2.1) Å average height was observed on the surface of thin ODA-intercalated micro-flakes using atomic force microscopy. Grafted ODA chains not only created an homogeneous surface nano-layer, but also variable-width channels between the ODA molecules.

Vermiculite: Structural Properties and Examples of the Use

The effort to clarify the meanings of the terms ‘clay’, ‘clays’, and ‘clay minerals‘ was the subject of the joint nomenclature committees (JNCs) of the Association Internationale pour l’Etude des Argiles (AIPEA) and the Clay Minerals Society (CMS). The JNCs have proposed the term a class of hydrated phyllosilicates forming the fine-grained fraction of rocks, sediments, and soils and have defined ‘clay’ as ‘‘a naturally occurring material composed primarily of fine-grained minerals, which is generally plastic at appropriate water contents and will harden when dried or fired’’ [1]. According to this definition synthetic clays and clay-like materials are not regarded as clay even though they may be fine grained, and display the attributes of plasticity and hardening on drying and firing.

Antibacterial efficiency of vermiculite/chlorhexidine nanocomposites and results of the in vivo test of harmlessness of vermiculite

Clay minerals have been proposed as very useful materials for modulating drug delivery. These are the commonly used materials in pharmaceutical production both as inorganic carriers or active agents. We focused on the development of suitable long-acting material for local treatment of oral infection where clay minerals act as inorganic drug carriers. Organovermiculites with antibacterial activity were prepared by ion exchange reactions using different concentrations of chlorhexidine diacetate. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal analysis (TGA). The antibacterial activity was evaluated by finding the minimum inhibitory concentration (MIC). All studied organoclays possessed good antibacterial activity after 24h exposure against Escherichia coli, Enterococcus faecalis and particularly against Staphylococcus aureus. Pseudomonas aeruginosa however proved very resistant as only the sample with the highest concentration of CA that successfully inhibited bacterial growth. Furthermore, clay mineral vermiculite was subjected to in vivo toxicological analysis and its influence on gastrointestinal tract during its oral application was investigated. Tissue samples from buccal mucosa, tongue, esophagus, stomach, terminal duodenum, small intestine, caecum, distal colon and liver were subjected to histological examination, both macroscopically and microscopically. Neither systemic nor local reactions were observed. Therefore the toxicity of vermiculite to a mammal model organism can be excluded.

Preparation and characterization of porous cordierite for potential use in cellular ceramics

Cordierite porous ceramics Z, X, and K were prepared using three mixtures of clay minerals: Z from kaolinite, talc, and aluminum hydroxide, X from kaolinite, talc, vermiculite, and aluminum hydroxide, and K from kaolinite, talc, and magnesium oxide. Ceramics were different in porosity, specific surface area, cordierite polymorphs, and secondary crystalline phases. Vermiculite influenced textural architecture of calcined cordierite ceramics X and predestinated crystallization of the high-temperature hexagonal α-cordierite with secondary minerals enstatite, spinel and corundum. Ceramics Z contained low-temperature orthorhombic β-cordierite, enstatite, and corundum, K was diphase of β-cordierite and forsterite. Total pore area (TPA) and specific surface area (SSA) of X, in spite of the higher porosity and the pore size distribution in the range of 300–1000 nm, were smaller in comparison with TPA and SSA of Z. Ceramics K retained high porosity, two maxima at 300–1000 nm and 50–200 nm in the pores size distribution, and the highest TPA and SSA compared to those observed in ceramics Z and X.

Molecular modeling of surface modification of Wyoming and Cheto montmorillonite by methylene blue

The surface area of various types of montmorillonites (MMT) with different values of layer charge plays a very important role in surface arrangement of methylene blue cations (MB). Photoluminescence measurements can be strongly or partially influenced by this surface arrangement of cations. For these reasons and on the basis of our previous results, molecular simulations were performed for various types of montmorillonites covered with methylene blue cations. Adsorption of methylene blue cations on Na-Wyoming MMT surface is different from Ca-Cheto MMT. In the case of Wyoming with a lower layer charge, MB cations lie parallel to the silicate layer for all investigated samples. On the other hand, Cheto surface is covered with a higher amount of MB cations. The results obtained from molecular modeling indicate that MB lies parallel to low loading case and become tilted with respect to layer for a higher loading. Moreover, a higher amount of MB cations covering the silicate layer are much less energy-stable. A higher loading of MB cations leads to aggregates but at low loading MB cations degrade to monomers.

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.

Infrared and Raman spectroscopy of three commercial vermiculites doped with cerium dioxide nanoparticles

Three commercial vermiculites and these vermiculites doped with cerium dioxide nanoparticles were investigated by infrared and Raman spectroscopy. Infrared spectroscopy in middle infrared region (4000-400 cm-1) was supplemented by separation of overlapped spectral bands in the region of stretching vibration of hydroxyl groups. Detailed structural properties of vermiculites were completed based on the Raman spectroscopy in the spectral region between 800 and 100 cm-1 and X-ray diffraction analysis. Raman spectroscopy provided evidence of trioctahedral-dioctahedral vermiculite-mica in original vermiculite and trioctahedral phyllosilicate structures in vermiculites after precipitation procedure of cerium dioxide nanoparticles. The wavenumber shifts of the Raman bands at about 670 cm-1 and 190 cm-1 in spectra of vermiculites showed strong trend with increasing Fe3+ and Al substitution in tetrahedra and octahedra, respectively.