Antibacterial Activity of PVA Hydrogels Embedding Oxide Nanostructures Sensitized by Noble Metals and Ruthenium Dye.

Nanostructured oxides (SiO2, TiO2) were synthesized using the sol-gel method and modified with noble metal nanoparticles (Pt, Au) and ruthenium dye to enhance light harvesting and promote the photogeneration of reactive oxygen species, namely singlet oxygen (1O2) and hydroxyl radical (•OH). The resulting nanostructures were embedded in a transparent polyvinyl alcohol (PVA) hydrogel. Morphological and structural characterization of the bare and modified oxides was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Additionally, electrokinetic potential measurements were conducted. Crystallinity data and elemental analysis of the investigated systems were obtained through X-ray diffraction and X-ray fluorescence analyses, while the chemical state of the elements was determined using XPS. The engineered materials, both as simple powders and embedded in the hydrogel, were evaluated for their ability to generate reactive oxygen species (ROS) under visible and simulated solar light irradiation to establish a correlation with their antibacterial activity against Staphylococcus aureus. The generation of singlet oxygen (1O2) by the samples under visible light exposure can be of significant importance for their potential use in biomedical applications.

Titania nanoparticles for photocatalytic degradation of ethanol under simulated solar light.

TiO2 nanoparticles were synthesized by laser pyrolysis from TiCl4 vapor in air in the presence of ethylene as sensitizer at different working pressures (250-850 mbar) with and without further calcination at 450 °C. The obtained powders were analyzed by energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, and transmission electron microscopy. Also, specific surface area and photoluminescence with optical absorbance were evaluated. By varying the synthesis parameters (especially the working pressure), different TiO2 nanopowders were obtained, whose photodegradation properties were tested compared to a commercial Degussa P25 sample. Two series of samples were obtained. Series "a" includes thermally treated TiO2 nanoparticles (to remove impurities) that have different proportions of the anatase phase (41.12-90.74%) mixed with rutile and small crystallite sizes of 11-22 nm. Series "b" series represents nanoparticles with high purity, which did not require thermal treatment after synthesis (ca. 1 atom % of impurities). These nanoparticles show an increased anatase phase content (77.33-87.42%) and crystallite sizes of 23-45 nm. The TEM images showed that in both series small crystallites form spheroidal nanoparticles with dimensions of 40-80 nm, whose number increases with increasing the working pressure. The photocatalytic properties have been investigated regarding the photodegradation of ethanol vapors in Ar with 0.3% O2 using P25 powder as reference under simulated solar light. During the irradiation H2 gas production has been detected for the samples from series "b", whereas the CO2 evolution was observed for all samples from series "a".

Antibacterial Activity of ZnSe, ZnSe-TiO2 and TiO2 Particles Tailored by Lysozyme Loading and Visible Light Irradiation.

ZnSe, ZnSe-TiO2 microspheres and nanostructured TiO2 obtained by hydrothermal and sol-gel methods were tested against Staphylococcus aureus ATCC 25923 and Micrococcus lysodeikticus ATCC 4698 before and after lysozyme (Lys) loading. Morphological characterization of inorganic matrices and hybrid organic-inorganic complexes were performed by microscopy techniques (SEM, AFM and Dark Field Hyperspectral Microscopy). Light absorption properties of ZnSe, ZnSe-TiO2 and TiO2 powders were assessed by UV-visible spectroscopy and their ability to generate reactive oxygen species (•OH and O2•-) under visible light irradiation was investigated. Antibacterial activity of ZnSe, ZnSe-TiO2, TiO2, Lys/ZnSe, Lys/ZnSe-TiO2 and Lys/TiO2 samples under exposure to visible light irradiation (λ > 420 nm) was tested against Staphylococcus aureus and Micrococcus lysodeikticus and correlated with ROS photogeneration.

Bioactive Coatings Based on Nanostructured TiO2 Modified with Noble Metal Nanoparticles and Lysozyme for Ti Dental Implants.

This work presents the synthesis of nanostructured TiO2 modified with noble metal nanoparticles (Au, Ag) and lysozyme and coated on titanium foil. Moreover, the specific structural and functional properties of the resulting inorganic and hybrid materials were explored. The purpose of this study was to identify the key parameters for developing engineered coatings on titanium foil appropriate for efficient dental implants with intrinsic antibacterial activity. TiO2 nanoparticles obtained using the sol-gel method were deposited on Ti foil and modified with Au/Ag nanoparticles. Morphological and structural investigations (scanning electron and atomic force microscopies, X-ray diffraction, photoluminescence, and UV-Vis spectroscopies) were carried out for the characterization of the resulting inorganic coatings. In order to modify their antibacterial activity, which is essential for safe dental implants, the following aspects were investigated: (a) singlet oxygen (1O2) generation by inorganic coatings exposed to visible light irradiation; (b) the antibacterial behavior emphasized by titania-based coatings deposited on titanium foil (TiO2/Ti foil; Au-TiO2/Ti foil, Ag-TiO2/Ti foil); (c) the lysozyme bioactivity on the microbial substrate (Micrococcus lysodeicticus) after its adsorption on inorganic surfaces (Lys/TiO2/Ti foil; Lys/Au-TiO2/Ti foil, Lys/Ag-TiO2/Ti foil); (d) the enzymatic activity of the above-mentioned hybrids materials for the hydrolysis reaction of a synthetic organic substrate usually used for monitoring the lysozyme biocatalytic activity, namely, 4-Methylumbelliferyl ß-D-N,N',N″-triacetylchitotrioside [4-MU-ß- (GlcNAc)3]. This was evaluated by identifying the presence of a fluorescent reaction product, 7-hydroxy-4-metyl coumarin (4-methylumbelliferone).

Tubular and Spherical SiO2 Obtained by Sol Gel Method for Lipase Immobilization and Enzymatic Activity.

A wide range of hybrid biomaterials has been designed in order to sustain bioremediation processes by associating sol-gel SiO2 matrices with various biologically active compounds (enzymes, antibodies). SiO2 is a widespread, chemically stable and non-toxic material; thus, the immobilization of enzymes on silica may lead to improving the efficiency of biocatalysts in terms of endurance and economic costs. Our present work explores the potential of different hybrid morphologies, based on hollow tubes and solid spheres of amorphous SiO2, for enzyme immobilization and the development of competitive biocatalysts. The synthesis protocol and structural characterization of spherical and tubular SiO2 obtained by the sol gel method were fully investigated in connection with the subsequent immobilization of lipase from Rhizopus orizae. The immobilization is conducted at pH 6, lower than the isoelectric point of lipase and higher than the isoelectric point of silica, which is meant to sustain the physical interactions of the enzyme with the SiO2 matrix. The morphological, textural and surface properties of spherical and tubular SiO2 were investigated by SEM, nitrogen sorption, and electrokinetic potential measurements, while the formation and characterization of hybrid organic-inorganic complexes were studied by UV-VIS, FTIR-ATR and fluorescence spectroscopy. The highest degree of enzyme immobilization (as depicted from total organic carbon) was achieved for tubular morphology and the hydrolysis of p-nitrophenyl acetate was used as an enzymatic model reaction conducted in the presence of hybrid lipase⁻SiO2 complex.

The effect of active carbon on the reduction of concentrated nitric acid by HCOOH.

In nuclear industry, removal of nitric acid from solutions is required in the course of chemical separation and waste treatment procedure as well as in chemical conversion steps. The reduction of HNO3 by HCOOH to gaseous products such as nitrogen, nitrogen oxides, and carbon dioxide is an attractive way to accomplish the denitration. A typical problem for the denitration is the existence of the induction period. The induction period has been explained as the time necessary to increase the concentration of HNO2, which is an important reaction intermediate, above a threshold value. In this study, adsorption sites on the surface of active carbon were found to promote HNO2 formation and efficiently suppress the induction period. Induction time was shortened by increasing the amount of active carbon in the solution. When the solution contains 3 M HNO3 and 1 M HCOOH, 10 g/L of active carbon was enough to eliminate the induction period at 50 degrees C. The catalytic effect exhibited by active carbon was similar to that reported for Pt/SiO2. Therefore, on the surface of active carbon, there is a redox cycle, where HNO3 is reduced to HNO2 and then the oxidized surface site will be reduced by HCOOH.

Nitrite reduction on morphologically controlled Pt nanoparticles.

On the surface of morphologically controlled Pt nanoparticles, statistically rich in [100] crystalline facet, nitrite ions were reduced by H2 to N2 with high selectivity.

The catalytic activity of alumina supported Ru nanoparticles for NO/CH4 reaction.

Alumina supported colloidal Ru nanoparticles, with an initial average size of 4.8 nm, show high activity for NO conversion for T > or = 450 degrees C and remarkably high selectivity (approximately 80%) to syngas at 600 degrees C.

Investigation of the morphology-catalytic reactivity relationship for Pt nanoparticles supported on alumina by using the reduction of NO with CH4 as a model reaction.

The morphological evolution of large Pt nanoparticles supported on alumina in reaction conditions has a significant impact on the catalytic behaviour for the NO/CH4 reaction.