Influence of ZnO nanoparticles on slow release of essential oil from polimeric matrix

Biopolymer emulsions were processed in the form of thin films for application in active food packaging. Active packaging is defined as material designed to release active components into food or absorb them from food in order to extend durability or to maintain/improve packaging conditions and extend shelf-life of food. We synthesized emulsion based on biodegradable polymers (pectin, gelatin, chitosan) with addition of active components -essential oils and ZnO nanoparticles (NPs). By introducing essential oils in the polymer matrix, with the addition of certain emulsifiers, it comes to encapsulation of oil droplets and the formation of a homogeneous emulsion. Thin films were fabricated by mold casting or spraying of the emulsions on a substrate. The slow release of an essential oil from the polymeric matrix was determined by UV-vis spectrophotometry. It was shown that polymers with addition of nanoparticles provided a prolonged action of active components. Surface morphology of the films was characterized by atomic force microscopy (AFM), and it was noticed that nanoparticles were mainly accumulated around oil droplets, which additionally contributed to a slow release of the active components

Visible-light photocatalytic degradation of mordant blue 9 by BiVO4 nanopowder

The photocatalytic degradation of highly toxic azo dye Mordant Blue 9 (MB 9) was investigated using single-phase monoclinic BiVO4 nanopowder as a photocatalyst under the simulated solar irradiation. The photodegradation process as a function of different pH values of aqueous dye solution (pH = 1 – 13) and irradiation time was investigated, and the complete degradation mechanism was proposed. MB 9 was resistant to direct photolysis and the BiVO4 nanoparticles exhibited higher photocatalytic activity in a basic medium than in neutral and acid media. Photodegradation of the dye molecules occurred primarily due to a reaction with the photo-generated holes and OH– anions forming ∙OH radicals. The alkaline pH range favors the formation of more ∙OH radicals through the oxidation of hydroxide ions existing at the BiVO4 surface, thus the effectiveness of the photocatalytic process significantly increased. BiVO4 photocatalyst was stable and active under simulated solar irradiation over four consecutive cycles, which confirms its good photocatalytic properties

6. Effect of Cu dopping on microstructural, thermoelectric and mechanical properties of NaCoCuO4 ceramics

Ceramic samples of NaCo2-xCuxO4 (x = 0, 0.01, 0.03, 0.05) were obtained after calcination of powder precursors synthesized by a mechanochemically assisted solid-state reaction method (MASSR) and a citric acid complex method (CAC). Effects of small concentrations of Cu doping and the above-mentioned syntheses procedures on the microstructural, thermoelectric and mechanical properties were observed. The electrical resistivity (ρ), the thermal conductivity (κ) and the Seebeck coefficient (S) were measured simultaneously in the temperature gradient (ΔT) between hot and cold side of the sample, and the figure of merit (ZT) was subsequently calculated. ZT of the CAC samples was higher compared with the MASSR samples. The highest ZT value of 0.061 at ΔT = 473 K was obtained for the sample with 5 mol% of Cu prepared by the CAC method, and it was 1.7 times higher than the highest value obtained for the MASSR sample with 3 mol% of Cu (ZT = 0.036 at ΔT = 473 K). The CAC samples showed better mechanical properties compared to the MASSR samples due to the higher hardness of the CAC samples which is a consequence of homogeneous microstructure and higher density obtained after sintering of these samples. The results confirmed that, besides the concentration of Cu, the synthesis procedure considerably affected the microstructural, thermoelectric and mechanical properties of NaCo2O4 ceramics

CHITOSAN- AND PECTIN-BASED COATINGS WITH INCORPORATED ACTIVE COMPONENTS FOR APPLICATION IN ACTIVE FOOD PACKAGING

The subject of this research was the development of biodegradable and eco-friendly material based on natural biopolymers from renewable sources, with the addition of active components for application in active food packaging. The main principle was the incorporation of the active components (lemongrass (Cymbopogon citratus L.) essential oil, ZnO nanoparticles, or Zn(CH3COO)2∙2H2O) with antimicrobial activity in the polymer matrix (chitosan, pectin, and gelatin), and their slow release during the time. All of the used components are listed as GRAS (Generally Recognized as Safe) by the U.S. Food and Drug Administration. Different formulations of emulsions and dispersions were processed for mutual comparison. The stability of chitosan and pectin emulsions was determined by using laser diffraction methods. Chitosan emulsions exhibited higher stability during 30 days of storage. The chitosan emulsions and dispersions exhibited a higher antibacterial effect in vitro against Escherichia coli, Bacillus subtilis, and Staphylococcus aureus. Biopolymer coatings were formed by the spraying of emulsions on existing packaging. The effects of biopolymer coatings on the development of microorganisms on fresh raspberries (Rubus idaeus L.) were performed in vivo during eight days of raspberry storage at refrigerator temperature. The tested coatings extended the shelf life of stored raspberries from four to eight days. The synergistic effect between lemongrass essential oil and ZnO nanoparticles or Zn(CH3COO)2∙2H2O was observed both in vivo and in vitro

Ultrasonic synthesis and characterization of mesoporous monoclinic BiVO4 nanopowder

The BiVO4 sample was successfully synthesized from a mixture of ammonium vanadate, bismuth(III) nitrate, and nitric acid exposed to ultrasound irradiation. Structure, microstructure and optical properties of the obtained BiVO4 nanopowder were investigated. X-ray diffraction (XRD) analysis confirmed single phase monoclinic lattice system with average crystallite size of 50 nm in diameter. Scanning electron microscopy (SEM) micrographs revealed the tendency of crystallites to agglomerate forming larger irregular sub-micron spheres. Brunauer-Emmett-Teller (BET) method was used to estimate the specific surface area of the sample and determine pore shape and size. UV–vis spectroscopy measurements have revealed favorably high absorbance of the visible light with the calculated band-gap value of 2.48 eV. Calculated values of valence and conducting band energies are +2.77 eV and +0.29 eV respectively, suggested that BiVO4 can be used for photocatalytic degradation under sunlight irradiation as evident from the UV–vis spectrum

COMPARISON OF SENSING PROPERTIES OF SnO2/KIT-5 AND SnO2 HUMIDITY SENSORS

In this work, two different syntheses approaches – nanocasting and sol-gel technique were employed for the preparation of SnO2 powders for humidity sensors. Stock solution of SnCl2 in ethanol (0.5 M) was used as a Sn-precursor for both syntheses. In the first procedure, this solution was infiltrated by wet impregnation method into the hydrothermally prepared KIT-5 used as silica template. Mesoporous SnO2/KIT-5 hybrid was obtained after two step loading/calcination process. Calcination was performed at 550 C for 5 h. In the second procedure, silica template was excluded from synthetic path. Ethanol solution of SnCl2 was slowly heated to form the gel which was later submitted to the same calcination conditions resulting in the preparation of SnO2 nanopowder. By dispersing the as prepared powders in the ethyl-cellulose/α-terpineol solution and adding a few drops of acetic acid in the mixture, viscous pastes were prepared and further homogenized for 24 h with magnetic stirrer. Using doctor blade applicator a few micron thick films were deposited onto alumina substrates provided with interdigitated Pt/Ag electrodes. Sensors’ characteristics were compared by measuring the change of the complex impedance of the samples exposed to a humid climate chamber environment at different temperatures and RH values from 40 % to 90 % at 25 °C and from 30 % to 90 % at 50 °C. The value of impedance measured at 42 Hz and within the RH range of 40 % to 90 %, changes 53 times at 25 °C, and 96 times at 50 °C. In contrast, for the sensor prepared from chemically derived SnO2, the impedance changes in a moderate way – 8 times at 25 °C and 3 times at 50 °C. Fast response/recovery time of the SnO2/KIT-5 hybrid sensor exposed to humidity change from 40 % – 90 % at room temperature, confirmed superior potentials of this material for humidity sensing over the SnO2

Structural, optical and photocatalytic properties of BiFeO3 nanoparticles

BiFeO3 (BFO) precursor powder was synthesized by ultrasound asissted sol–gel route at relatively low temperature, starting from Bi-nitrate, Fe-nitrate, and ethylene glycol. Structural, optical, and photocatalytic properties of the obtained powder were investigated. X-ray diffraction analysis confirmed that thermal treatment of precursor powder at 500 °C led to formation of pure phase BiFeO3. BFO is p-type semiconductor where determined band gap was 2.20 eV, indicating its potential application as visible-light-response photocatalyst. Mott-Schottky measurements were performed to determine flat band potential and position of valence and conduction bands. Obtained BFO powder is used for photocatalytic degradation of typical organic azo dye Mordant Blue 9 in concentration of 50 mg/l. Measurements were performed for different times of irradiation and pH of the dye solution. Photodegradation products were analyzied by HPLC technique, and mechanism of photocatalytic degradation of organic dye was proposed

Temperature dependence of fractal dimension of grain boundary region in SnO2 based ceramics

Fractal dimensions of grain boundary region in doped SnO2 ceramics were determined based on previously derived fractal model. This model considers fractal dimension as a measure of homogeneity of distribution of charge carriers. Application of the derived fractal model enables calculation of fractal dimension using results of impedance spectroscopy. The model was verified by experimentally determined temperature dependence of the fractal dimension of SnO2 ceramics. Obtained results confirm that the non-Debye response of the grain boundary region is connected with distribution of defects and consequently with a homogeneity of a distribution of the charge carriers. Also, it was found that C-T-1 function has maximum at temperature at which the change in dominant type of defects takes place. This effect could be considered as a third-order transition

Evaluation of stability and functionality of BaCe1-xInxO3-delta electrolyte in a wider range of indium concentration

The properties of BaCe1-xInxO3-delta (x = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, and 0.40) as proton conducting electrolyte are examined. The dense electrolyte is formed after sintering at 1300 degrees C for 5 h in air. The samples with In content > 25 mol% contain In2O3 as a secondary phase. The highest total conductivity is around 5x10(-3) S/cm for BaCe0.75In0.25O3-delta in the wet hydrogen atmosphere at 700 degrees C. After exposure to pure CO2 atmosphere at 700 degrees C for 5 h, the concentrations of at least 15 mol% In can completely suppress degradation of the electrolyte. The power density of Ni-BaCe0.75In0.25O3-delta/BaCe0.75In0.25O3-delta/LSCF-BaCe0.75In0.25O3-delta fuel cell tested in wet hydrogen atmosphere reaches 264 mW/cm(2) at 700 degrees C. This result is an indication of stability and functionality of this electrolyte and its versatility in respect to type of fuel and performing environment

Lipase catalyzed synthesis of flavor esters in non-aqueous media: Optimization of the yield of pentyl 2-methylpropanoate by statistical analysis

In this study, the synthesis of pentyl 2-methylpropanoate employing a commercial lipase from Candida rugosa was investigated, the emphasis being placed on analyzing the effects of various process conditions on the yield of ester. The response surface methodology (RSM) and five-level-five-factor central composite rotatable design (CCRD) were used to evaluate the effects of variables, namely the initial water content, 0.0–2.0 % (w/v), the reaction temperature, 35–75 °C, the enzyme concentration, 1.0–5.0 g dm-3, the acid/alcohol mole ratio, 1:2–5:2, and the reaction time, 4–48 h, on the yield (%) of ester. The production of pentyl 2-methylpropanoate was optimized and an ester yield response equation was obtained, enabling the prediction of ester yields from known values of the five main factors. It seems that the enzyme concentration, reaction time and acid/alcohol mole ratio predominantly determine the conversion process, while the amount of added water amount had no significant influence on the ester yield. Conversion of around 92 % of the substrate to ester could be realized using a concentration of lipase as low as 4.0 g dm-3 and in a relatively short time (26 h) at 35 °C, when a high substrate mole ratio of 2.5 was used