Cleavage of alumina cells in organic acid solutions during high voltage anodization.

The split effect of porous alumina cells with the formation of nanotubular films has been reported in several papers, however, many unclear aspects of such growth still remain. In this study, the possible mechanism of alumina nanotube formation in an aqueous solution of tartaric acid was proposed. According to SEM, EDX, and XPS studies, entrapment of carbonaceous species in large amounts, especially at the back-side, proceeds due to cleavage of the barrier layer at extremely high current density. The transport of anions through these gaps to the metal|film interface and reduction therein leads to the formation of a composite film with alumina/carbon/graphene oxide nanoplatelet caps.

Investigation of BiVO4-based advanced oxidation system for decomposition of organic compounds and production of reactive sulfate species.

Growth of population and expansion of industries lead to increasing contamination of environment with various organic pollutants. If not properly cleaned, wastewater contaminates freshwater resources, aquatic environment and has huge negative impact on ecosystems, quality of drinking water and human health, therefore new and effective purification systems are in demand. In this work bismuth vanadate-based advanced oxidation system (AOS) for the decomposition of organic compounds and production of reactive sulfate species (RSS) was investigated. Pure and Mo-doped BiVO4 coatings were synthesized using sol-gel process. Composition and morphology of coatings were characterized using X-ray diffraction and scanning electron microscopy techniques. Optical properties were analyzed using UV-vis spectrometry. Photoelectrochemical performance was studied using linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy. It was shown that increase in Mo content affects the morphology of BiVO4 films, reduces charge transfer resistance and enhances the photocurrent in the solutions of sodium borate buffer (with and without glucose) and Na2SO4. Mo-doping of 5-10 at.% leads to 2- to 3-fold increase in photocurrents. Faradaic efficiencies of RSS formation ranged between 70 and 90 % for all samples irrespective of Mo content. All studied coatings demonstrated high stability in long-lasting photoelectrolysis. In addition, effective light-assisted bactericidal performance of the films in deactivation of Gram positive Bacillus sp. bacteria was demonstrated. Advanced oxidation system designed in this work can be applied in sustainable and environmentally friendly water purification systems.

Antimicrobial particles based on Cu2ZnSnS4 monograins.

In this research, Cu2ZnSnS4 (CZTS) particles were successfully fabricated via the molten salt approach from the copper, zinc and tin sulphides as raw precursors. SEM analysis revealed that CZTS particles are tetragonal-shaped with sharp edges, smooth flat plane morphology, and crystal size varying from 10.8 to 28.7 µm. The phase and crystalline structure of synthesized powders were investigated using XRD analysis, which confirms the presence of a tetragonal crystal structure kesterite phase. The chemical composition of CZTS particles was evaluated by EDX spectroscopy, which identified the nearly stoichiometric composition with an averaged formula of Cu1.88Zn1.04SnS3.97. The TG/DTA-MS and ICP-OES analysis showed the possible decomposition pathways and predicted their degradation rate in aqueous solutions. The CZTS particles possessed highly effective concentration and time-dependent antimicrobial properties against medically relevant bacteria and yeast strains. The CZTS particles (1 g L-1) exhibited over 95.7 ± 1.9% killing efficiency towards M. luteus. In contrast, higher dosages (3.5 and 5 g L-1) led to its complete inactivation and reduced the P. aeruginosa cell viability to 43.2 ± 3.2% and 4.1 ± 1.1%, respectively. Moreover, the CZTS particles (0.5 g L-1) are responsible for causing 54.8 ± 1.8% of C. krusei and 89.7 ± 2.1% of C. parapsilosis yeasts death within the 24 h of exposure, which expanded to almost 100% when yeasts were treated with two times higher CZTS concentration (1.0 g L-1). The mechanism of action has been proposed and evidenced by monitoring the 2',7'-dichlorofluorescein (DCF) fluorescence, which revealed that the overproduction of reactive oxygen species (ROS) is responsible for microorganism death.

Designing red-fluorescent superparamagnetic nanoparticles by conjugation with gold clusters.

Photoluminescent (PL) metal and metal oxide nanoclusters (NCs), with a size of just several nanometers, are a separate class of nanomaterials abundant with new attractive optical, physical, and chemical properties and biocompatibility. However, the synthesis of PL magnetic NCs via attachment of PL NCs to iron oxide-based nanoparticles (NPs) is still problematic. Motivated by this, herein, we report the development of a microwave-driven conjugation approach of red-fluorescent gold nanoclusters (BSA@AuNCs) to superparamagnetic NPs. Synthesized CoFe2O4@AuNCs possess strong photoluminescence in water and ethanol media as well as good colloidal and optical stability, and magnetization response. High-resolution transmission electron microscopy (HRTEM), steady-state and time-resolved photoluminescence spectroscopy, X-ray powder diffraction (XRD), and magnetic measurements from ambient to cryogenic temperatures were applied for structural characterization and evaluation of optical and magnetic properties of the synthesized species.

Highly efficient antimicrobial agents based on sulfur-enriched, hydrophilic molybdenum disulfide nano/microparticles and coatings functionalized with palladium nanoparticles.

In this research the molybdenum disulfide (MoS2)-based nano/microparticles and coatings were synthesized through a simple, one-step hydrothermal approach without any other additives. Composition, structure, and morphology of the synthesized MoS2-based materials were investigated using ultraviolet-visible spectroscopy (UV-Vis), inductively coupled plasma optical emission spectrometry (ICP-OES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) techniques. The fabricated materials exhibited relatively small (Δθ = 18.7 ± 2.5°) contact angle and prominent hydrophilic properties, which are attributable to sulfur-enriched MoS2 composite as evidenced by simultaneous thermal analysis (STA) coupled with mass spectrometric (MS) analysis of evolving gaseous species (TG/DTA-MS) analysis. Such nanostructures exhibit a better adhesion of biomolecules, thus facilitating the interaction between them, as confirmed by highly effective antimicrobial action. The present study examines antimicrobial properties of hydrophilic, sulfur-enriched MoS2 nano/microparticles as well as MoS2-based coatings against various humans' pathogenic bacteria such as Salmonella enterica, Pseudomonas aeruginosa, Escherichia coli, methicillin-resistant Staphylococcus aureus (MRSA), Micrococcus luteus, and two Candida yeast strains (C. parapsilosis, C. krusei). The MoS2-ns (40 µg mL-1) showed over 90% killing efficiency against S. aureus MRSA bacteria and both Candida yeast when exposed for 24 h. Petal-like MoS2 microstructures and heterostructured MoS2/Ti and Pd/MoS2/Ti coatings also possessed high antimicrobial potential and are considered as a promising antimicrobial agent. The MoS2-induced production of intracellular reactive oxygen species (ROS) was evidenced by measuring the standard DCF dye fluorescence.

Interaction of lead(II) with beta-cyclodextrin in alkaline solutions.

Polarographic and UV-spectrophotometric investigations of Pb(II) complex formation with beta-cyclodextrin have showed that the complexation of Pb(II) ions begins at pH >10. The formation of lead(II) 1:1 complex with the beta-cyclodextrin anion was observed at pH 10-11.5. The logarithm of the stability constant of this complex compound is 15.9+/-0.3 (20 degrees C, ionic strength 1.0), and the molar extinction coefficient value is ca. 5500 (lambda(max)=260 nm). With further increase in solution pH the Pb-beta-cyclodextrin complex decomposes and converts to Pb(OH)(2) or Pb(OH)(3)(-) hydroxy-complexes. This process occurs with a decrease in Pb(II) complexation degree. The latter result could be explained by a decrease in the beta-cyclodextrin anion activity. Neither Pb(OH)(2) nor Pb(OH)(3)(-) encapsulation into beta-CD cavity was observed.

Interaction of beta-cyclodextrin with cadmium(II) ions.

Reduction of Cd(II) on a dropping mercury electrode was used to study interaction of beta-cyclodextrin with Cd(II) ions. It was found that Cd(II) forms Cdbeta-CD(OH)(2)(2-) hydroxy-complex with the anion of beta-cyclodextrin in alkaline solutions (pH>11), the logarithm of stability constant being 10.4+/-0.1 (20 degrees C; I=1.0). The calculated value of the diffusion coefficient equal to 1.0x10(-6)cm(2)/s shows a large size Cd(II) complex species formation in alkaline solutions containing beta-CD.

Deprotonation of beta-cyclodextrin in alkaline solutions.

Variable pH (13)C NMR and (1)H NMR spectroscopic studies of the beta-cyclodextrin (beta-CD) in alkaline aqueous solutions revealed that beta-CD does not deprotonate at pH<12.0. Further increase in solution pH results in the deprotonation of OH-groups adjacent to C-2 and C-3 carbon atoms of beta-CD glucopyranose units, whereas the deprotonation of OH-groups adjacent to C-6 carbon atoms is expressed less markedly. The pK(a) values for beta-CD OH-groups adjacent to C-2 and C-3 carbon atoms are rather close, pK(a1,2) being 13.5+/-0.2 (22.5 degrees C).