The paper addresses laboratory preparation and antibacterial activity testing of kaolinite/nanoTiO2 composite in respect of the daylight irradiation time. Kaolinite/nanoTiO2 composites with 20 and 40 wt% of TiO2 were laboratory prepared, dried at 105 °C and calcined at 600 °C. The calcination caused transformation of kaolinite to metakaolinite and origination of the metakaolinite/nanoTiO2 composite. X-ray powder diffraction, Raman and FTIR spectroscopic methods revealed titanium dioxide only in the form of anatase in all evaluated samples (non-calcined and calcined) and also transformation of kaolinite to metakaolinite after the calcination treatment. Scanning electron microscopy was used as a method for characterization of morphology and elemental composition of the studied samples. A standard microdilution test was used to determine the antibacterial activity using four human pathogenic bacterial strains (Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa). A lamp with a wide spectrum bulb simulating daylight was used for induction of photocatalysis. The antibacterial assays found all the KATI samples to have antibacterial potency with different onset of the activity when calcined samples exhibited antibacterial activity earlier than the non-calcined. Significant difference in antibacterial activity of KATI samples for different bacterial strains was not observed.

• Klíčová slova
• Antibacterial activity, FTIR, Kaolinite/TiO(2) composites, Raman spectroscopy, Staphylococcus aureus, XRD,
• MeSH
• antibakteriální látky chemie   farmakologie   účinky záření   MeSH
• Bacteria účinky léků   MeSH
• časové faktory MeSH
• kaolin chemie   účinky záření   MeSH
• katalýza účinky záření   MeSH
• nanočástice chemie   účinky záření   MeSH
• nanokompozity chemie   účinky záření   MeSH
• povrchové vlastnosti MeSH
• světlo * MeSH
• titan chemie   účinky záření   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• antibakteriální látky MeSH
• kaolin MeSH
• titan MeSH
• titanium dioxide MeSH Prohlížeč

The aim of this study was to prepare self-supporting homogeneous nano/microfibrous layers with a content of the clay mineral kaolinite and kaolinite modified with the antibacterial agent chlorhexidine (CH). Fibers were made of hydrophobic polymers-polyurethane and polycaprolactone. Polymer suspensions for electrospinning contained 2, 5, and 8 wt % (relative to the total weight of the suspension) of kaolinite or CH/kaolinite and were electrospun using 4SPIN LAB. The morphology of prepared fibrous layers was characterized using scanning electron microscopy; energy-dispersive X-ray spectroscopy mapping and Raman spectroscopy were used to confirm the presence and distribution of kaolinite in the layers. Fiber diameters decreased after adding kaolinite or CH/kaolinite and ranged from 600 nm to 5 μm. Antibacterial CH was found in kaolinite itself as well as separately in the fibers (result of imperfect bonding of CH onto the surface of kaolinite). The encapsulation efficiency of all samples exceeded 64%, and the highest efficiency was observed in samples with 2 wt % CH/kaolinite. Samples containing CH exhibited good antibacterial activity against Staphylococcus aureus, and the effectiveness of which was affected by the concentration of the antibacterial agent. The release of CH was very slow, and there was no initial burst release. Overall, no more than 5% of the CH was released over a course of 168 h. The Korsmeyer-Peppas model revealed that CH is released by a diffusion mechanism.

• Klíčová slova
• antibacterial, chlorhexidine, electrospinning, kaolinite, microfibers, nanofibers,
• Publikační typ
• časopisecké články MeSH

The importance of studies on photoactive zinc oxide nanoparticles (ZnO NPs) increases with increasing environmental pollution. Since the ZnO NPs (and NPs in general) also pose an environmental risk, and since an understanding of the risk is still not sufficient, it is important to prevent their spread into the environment. Anchoring on phyllosilicate particles of micrometric size is considered to be a useful way to address this problem, however, so far mainly on the basis of leaching tests in pure water. In the present study, the phytotoxicity of kaolinite/ZnO NP (10, 30, and 50 wt.%) nanocomposites in concentrations 10, 100, and 1000 mg/dm3 tested on white mustard (Sinapis alba) seedlings was found to be higher (relative lengths of roots are ~ 1.4 times lower) compared with seedlings treated with pristine ZnO NPs. The amount of Zn accumulated from the nanocomposites in white mustard tissues was ~ 2 times higher than can be expected based on the ZnO content in the nanocomposites compared with the ZnO content (100 wt.%) in pristine ZnO NPs. For the false fox-sedge (Carex otrubae) plants, the amount of Zn accumulated in roots and leaves was ~ 2.25 times higher and ~ 2.85 times higher, respectively, compared with that of the pristine ZnO NPs (with respect to the ZnO content). Increased phytotoxicity of the nanocomposites and higher uptake of Zn by plants from the nanocomposites in comparison with pristine ZnO NPs suggest that the immobilization of ZnO NPs on the kaolinite does not reduce the environmental risk.

• Klíčová slova
• Anchoring, Kaolinite, Nanocomposite, Phytotoxicity, Scanning electron microscopy, Zinc oxide,
• MeSH
• kaolin MeSH
• kořeny rostlin MeSH
• listy rostlin MeSH
• nanočástice toxicita   MeSH
• nanokompozity toxicita   MeSH
• oxid zinečnatý toxicita   MeSH
• rostliny účinky léků   MeSH
• semenáček MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• kaolin MeSH
• oxid zinečnatý MeSH

Preparation of nanocomposite kaolinite/TiO(2), using hydrolysis of titanyl sulfate in the presence of kaolin was addressed. A variable (kaolin)/(titanyl sulfate) ratio has been used in order to achieve the desired TiO(2) content in prepared nanocomposites. Calcination of the composites at 600 °C led to the transformation of the kaolinite to metakaolinite and to origination of metakaolinite/TiO(2) composites. The prepared samples were investigated using X-ray fluorescence spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry and diffuse reflectance spectroscopy in the UV-VIS region. Structural ordering of TiO(2) on the kaolinite particle surface was modeled using empirical force field atomistic simulations in the Material Studio modeling environment. Photodegradation activity of the composites prepared was evaluated by the discoloration of Acid Orange 7 aqueous solution.

• MeSH
• azosloučeniny chemie   účinky záření   MeSH
• barvicí látky chemie   účinky záření   MeSH
• benzensulfonáty chemie   účinky záření   MeSH
• fotolýza * MeSH
• kaolin chemie   MeSH
• látky znečišťující životní prostředí chemie   účinky záření   MeSH
• nanokompozity chemie   MeSH
• počítačová simulace MeSH
• povrchové vlastnosti MeSH
• průmyslový odpad prevence a kontrola   MeSH
• titan chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• 2-naphthol orange MeSH Prohlížeč
• azosloučeniny MeSH
• barvicí látky MeSH
• benzensulfonáty MeSH
• kaolin MeSH
• látky znečišťující životní prostředí MeSH
• průmyslový odpad MeSH
• titan MeSH
• titanium dioxide MeSH Prohlížeč

The adhesion of TiO(2) (anatase structure) nanoparticles to kaolinite substrate was investigated using molecular modeling. Universal force field computation, density function theory computation, and a combination of both two approaches were used. This study enabled the adhesion energy for the TiO(2)/kaolinite nanocomposite to be estimated, and revealed the preferred orientation of the TiO(2) nanoparticles on the kaolinite substrate. The results of all three levels of computation were compared in order to show that the accuracy of universal force field computations is sufficient in this context. The role of nanoparticle size and the importance of the nanoparticle-substrate bonding contribution are presented here and discussed. A comparison of the molecular modeling results with scanning electron microscopy observations showed that the results of the modeling were consistent with the experimental data, and that this approach can be used to help characterize nanocomposites of the nanoparticle/phyllosilicate substrate type.

• MeSH
• kaolin chemie   MeSH
• krystalografie MeSH
• kvantová teorie MeSH
• molekulární konformace MeSH
• molekulární modely * MeSH
• nanočástice chemie   ultrastruktura   MeSH
• nanokompozity chemie   ultrastruktura   MeSH
• počítačová simulace * MeSH
• povrchové vlastnosti MeSH
• termodynamika MeSH
• titan chemie   MeSH
• velikost částic MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• kaolin MeSH
• titan MeSH
• titanium dioxide MeSH Prohlížeč

A soil not naturally containing montmorillonite (M) was amended with approximately 5, 10 or 20% M or kaolinite (K), maintained in a greenhouse under periodic cultivating and alternate wetting and drying of more than two years, and then used in perfusion studies. The incorporation of M enhanced the rate of both heterotrophic degradation of glycine and subsequent autotrophic nitrification in direct relation to the amounts of M added. In soil amended with K, neither degradation nor nitrification was stimulated. The addition of M shortened the lag phase before nitrification was initiated, increased the pH of both the soil and the perfusates, and increased the rate, but not the extent, of oxidation of ammonium to nitrite and nitrate. The addition of CaCO2 or MgCO3, but not of CaSO4, also enhanced the rate of nitrification. The effects observed may have resulted from the influence of M on the pH, buffering capacity, and other soil conditions necessary for maximum activity of nitrifying microorganisms.

• MeSH
• bentonit farmakologie   MeSH
• biodegradace MeSH
• dusičnany metabolismus   MeSH
• dusitany metabolismus   MeSH
• glycin metabolismus   MeSH
• kaolin farmakologie   MeSH
• koncentrace vodíkových iontů MeSH
• kvartérní amoniové sloučeniny metabolismus   MeSH
• Nitrobacter metabolismus   MeSH
• oxidace-redukce MeSH
• půdní mikrobiologie * MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bentonit MeSH
• dusičnany MeSH
• dusitany MeSH
• glycin MeSH
• kaolin MeSH
• kvartérní amoniové sloučeniny MeSH

Kaolinite is a single 2D layer of kaolin or metakaolin (MK), common clays that can be characterized as layered 3D materials. We show that because of its chemical composition, kaolinite can be converted into an amorphous 3D material by chemical means. This dimensional transformation is possible due to the large surface to volume ratio and chemical reactivity of kaolinite. We investigate the formation and influence of quasi- or nanocrystalline phases in MK-based alkali-activated materials (AAM) that are related to the Si/Al ratio. We analyze the formation of an AAM from a MK precursor, which is a 3D bonded network that preserves the layered structure at the nanometer scale. We also exfoliate the remaining layered phase to examine the effects of the alkali-activation in the final sheet structures embedded within the amorphous network. The final material can be used as a cement with no carbon dioxide produced by the transformation reaction.

• Klíčová slova
• 2D materials, Alkali-activation, Clays, Geopolymer, Metakaolin,
• Publikační typ
• časopisecké články MeSH

Photoactive and non-hazardous kaolinite/ZnO nanocomposite with 50 wt.% of ZnO nanoparticles was prepared using simple and cheap hydrothermal method. The resulting solid phase was separated by decantation, and dried at 105 °C. Calcination of the nanocomposites at 600 °C led to the kaolinite-metakaolinite phase transformation, to further growth of ZnO crystallites, and to significant increase in photodegradation activity. Whereas, for the several applications, e.g., in brake industry, the larger amount of composites is needed, thus, the evaluation of the reproducibility of preparation process is one of the crucial parameter. Prepared nanocomposites were deeply characterized by using X-ray fluorescence spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and Rietveld quantitative phase analysis. Photodegradation activity was evaluated by the discoloration of Acid Orange 7 aqueous solution under UV irradiation. All used analytical techniques and methods confirm the reproducibility of the preparation process and as well that ZnO nanoparticles are anchored tightly on the clay surface which prevents the release to the environment.

• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The recently published method for the structure refinement from three-dimensional precession electron diffraction data using dynamical diffraction theory [Palatinus et al. (2015). Acta Cryst. A71, 235-244] has been applied to a set of experimental data sets from five different samples - Ni2Si, PrVO3, kaolinite, orthopyroxene and mayenite. The data were measured on different instruments and with variable precession angles. For each sample a reliable reference structure was available. A large series of tests revealed that the method provides structure models with an average error in atomic positions typically between 0.01 and 0.02 Å. The obtained structure models are significantly more accurate than models obtained by refinement using kinematical approximation for the calculation of model intensities. The method also allows a reliable determination of site occupancies and determination of absolute structure. Based on the extensive tests, an optimal set of the parameters for the method is proposed.

• Klíčová slova
• dynamical diffraction, electron crystallography, electron diffraction tomography, kaolinite, mayenite, orthopyroxene, precession,
• Publikační typ
• časopisecké články MeSH

Ammonium [Formula: see text] removal from municipal wastewater poses challenges with the commonly used biological processes. Especially at low wastewater temperatures, the process is frequently ineffective and difficult to control. One alternative is to use ion-exchange. In the present study, a novel [Formula: see text] ion-exchanger, metakaolin geopolymer (MK-GP), was prepared, characterised, and tested. Batch experiments with powdered MK-GP indicated that the maximum exchange capacities were 31.79, 28.77, and 17.75 mg/g in synthetic, screened, and pre-sedimented municipal wastewater, respectively, according to the Sips isotherm (R2 ≥ 0.91). Kinetics followed the pseudo-second-order rate equation in all cases (kp2 = 0.04-0.24 g mg-1 min-1, R2 ≥ 0.97) and the equilibrium was reached within 30-90 min. Granulated MK-GP proved to be suitable for a continuous column mode use. Granules were high-strength, porous at the surface and could be regenerated multiple times with NaCl/NaOH. A bench-scale pilot test further confirmed the feasibility of granulated MK-GP in practical conditions at a municipal wastewater treatment plant: consistently <4 mg/L [Formula: see text] could be reached even though wastewater had low temperature (approx. 10°C). The results indicate that powdered or granulated MK-GP might have practical potential for removal and possible recovery of [Formula: see text] from municipal wastewaters. The simple and low-energy preparation method for MK-GP further increases the significance of the results.

• Klíčová slova
• Alkali activation, ammonium, geopolymer, ion exchange, municipal wastewater,
• MeSH
• amoniové sloučeniny analýza   MeSH
• chemické látky znečišťující vodu analýza   MeSH
• kaolin chemie   MeSH
• odpad tekutý - odstraňování metody   MeSH
• odpadní voda chemie   MeSH
• polymery chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• amoniové sloučeniny MeSH
• chemické látky znečišťující vodu MeSH
• kaolin MeSH
• odpadní voda MeSH
• polymery MeSH