Smart Biopolymer-Based Nanocomposite Materials Containing pH-Sensing Colorimetric Indicators for Food Freshness Monitoring

Nanocomposite biopolymer materials containing colorimetric pH-responsive indicators were prepared from gelatin and chitosan nanofibers. Plant-based extracts from barberry and saffron, which both contained anthocyanins, were used as pH indicators. Incorporation of the anthocyanins into the biopolymer films increased their mechanical, water-barrier, and light-screening properties. Infrared spectroscopy and scanning electron microscopy analysis indicated that a uniform biopolymer matrix was formed, with the anthocyanins distributed evenly throughout them. The anthocyanins in the composite films changed color in response to alterations in pH or ammonia gas levels, which was used to monitor changes in the freshness of packaged fish during storage. The anthocyanins also exhibited antioxidant and antimicrobial activity, which meant that they could also be used to slow down the degradation of the fish. Thus, natural anthocyanins could be used as both freshness indicators and preservatives in biopolymer-based nanocomposite packaging materials. These novel materials may therefore be useful alternatives to synthetic plastics for some food packaging applications, thereby improving the environmental friendliness and sustainability of the food supply.     

Determination of H2S,COS, CS2 and SO2 by an aluminium nitride nanocluster: DFT studies

ABSTRACT

Density functional theory calculations were used to investigate the potential application of an AlN nanocluster in the detection of H₂S, COS, CS₂ and SO₂ gases. In overall, the order of strength of interaction of these gases with the nanocluster is as follows: SO₂ (E_ad?=??17.6?kcal/mol)?>?H₂S (E_ad?=??14.0?kcal/mol)?>?COS (E_ad?=??8.4?kcal/mol)?>?CS₂ (E_ad?=??4.5?kcal/mol). This indicates that by increasing the electric dipole moment, the adsorption energy becomes more negative. We found that the Al₁₂N₁₂ nanocluster may be a promising work function-type sensor for SO₂ gas among the studied gases. Also, it is an electronic sensor for both SO₂ and CS₂ gases but selectively acts between them because of their different effects on the electrical conductivity. It is neither work function-type nor electronic sensor for H₂S and COS gases. The AlN nanocluster benefits from a short recovery time about 7.7?s and 18.0?ms for desorption of SO₂ and CS₂ gases from its surface at room temperature, respectively. It is also concluded that this cluster can work at a humid environment.     

Cu/Ni-doped sulfated zirconium oxide immobilized on CdFe2O4 NPs: a cheap,sustainable and magnetically recyclable inorgano-catalyst for the efficient preparation of α-aminonitriles in aqueous media

Research on Chemical Intermediates - A new multifunctional bimetallic nanocatalyst was prepared by immobilization of Cu/Ni-doped sulfated zirconium oxide on magnetic cadmium ferrite...     

Exact arithmetic on the Stern–Brocot tree

In this paper we present the Stern–Brocot tree as a basis for performing exact arithmetic on rational numbers. There exists an elegant binary representation for positive rational numbers based on this tree [Graham et al., Concrete Mathematics, 1994]. We will study this representation by investigating various algorithms to perform exact rational arithmetic using an adaptation of the homographic and the quadratic algorithms that were first proposed by Gosper for computing with continued fractions. We will show generalisations of homographic and quadratic algorithms to multilinear forms in n variables. Finally, we show an application of the algorithms for evaluating polynomials.     

Three-dimensional Pd/Pt bimetallic nanodendrites on a highly porous copper foam fiber for headspace solid-phase microextraction of BTEX prior to their quantification by GC-FID

The preparation of bimetallic Pd/Pt nanofoam for use in fiber based solid-phase microextraction (SPME) is described. First, a highly porous copper foam was prepared on the surface of an unbreakable copper wire by an electrochemical method. Then, the substrate was covered with metallic Pd and Pt using galvanic replacement of the Cu nanofoam substrate by applying a mixture of Pd(II) and Pt(IV) ions. The procedure provided an efficient route to modify Pd/Pt nanofoams with large specific surface and low loading with expensive noble metals. The fiber was applied to headspace SPME of benzene, toluene, ethylbenzene and xylene (BTEX) (as the model compounds) in various spiked water and wastewater samples. It was followed by gas chromatography-flame ionization detection (GC-FID). A Plackett-Burman design was performed for screening the experimental factors prior to Box-Behnken design. Compared with the commercial PDMS SPME fiber (100 μm), it had higher extraction efficiency for BTEX. Under the optimum conditions, the method has low limits of detection (0.16–0.35 μg L^?1), a wide linear range (1–200 μg L^?1), relative standard deviations between 5.8 and 10.5%, and good recoveries (>85% from spiked samples).

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Graphical abstract Schematic presentation of a three-dimensional Pd/Pt bimetallic nanodendrites supported on a highly porous copper foam fiber for use in headspace solid phase microextraction of BTEX. They were then quantified by gas chromatography–flame ionization detector.

     

Numerical investigation of mixed convection heat transfer of a nanofluid in a circular enclosure with a rotating inner cylinder

Journal of Thermal Analysis and Calorimetry - In the present paper, mixed convection heat transfer of water–Al2O3 nanofluid in the space between two cylinders is investigated numerically. The...     

Temperature-controlled 'breathing' of carbon dioxide bubbles

We report a microfluidic (MF) approach to studies of temperature mediated carbon dioxide (CO(2)) transfer between the gas and the liquid phases. Micrometre-diameter CO(2) bubbles with a narrow size distribution were generated in an aqueous or organic liquid and subsequently were subjected to temperature changes in the downstream channel. In response to the cooling-heating-cooling cycle the bubbles underwent corresponding contraction-expansion-contraction transitions, which we term 'bubble breathing'. We examined temperature-controlled dissolution of CO(2) in four exemplary liquid systems: deionized water, a 0.7 M aqueous solution of NaCl, ocean water extracted from Bermuda coastal waters, and dimethyl ether of poly(ethylene glycol), a solvent used in industry for absorption of CO(2). The MF approach can be extended to studies of other gases with a distinct, temperature-dependent solubility in liquids.     

Synthesis of titanium dioxide nano-powder via sol–gel method at ambient temperature

Titanium dioxide is a semiconductor with excellent photo catalytic properties and an important material with high regarded in nanotechnology. In this study, titanium dioxide nanoparticles was successfully synthesized via sol–gel method using tetra-n-butyl orthotitanate, hydrochloric acid and ammonia. Tetra-n-butyl orthotitanate was used as precursor. The ingredients were mixed at ambient temperature for 9 h on a magnetic stirring, sol was formed and converted to gel by adding ammonia. X-ray diffraction analysis clearly showed anatase and rutile phases so that, with increasing calcination temperature anatase converts to the rutile. Scanning electron microscopy was used for agglomerate observations. Energy-dispersive detector analysis was carried out and confirmed the formation of titanium dioxide. The influences of calcination temperature and pH value on particles size were studied. The results indicate that synthesis at room temperature reduced the particle size to 15 nm.     

Efficient RuIII-catalyzed synthesis of 9-aryl-9H-xanthene-3,6-diols as precursors to fluorones

Efficient condensation of resorcinol and various aromatic aldehydes in the presence of RuCl₃nH₂O as a homogeneous catalyst under reflux conditions was investigated.It was found that a very simple method afforded good to excellent yields of the desired products.     

Automated microfluidic platform for studies of carbon dioxide dissolution and solubility in physical solvents

We present an automated microfluidic (MF) approach for the systematic and rapid investigation of carbon dioxide (CO(2)) mass transfer and solubility in physical solvents. Uniformly sized bubbles of CO(2) with lengths exceeding the width of the microchannel (plugs) were isothermally generated in a co-flowing physical solvent within a gas-impermeable, silicon-based MF platform that is compatible with a wide range of solvents, temperatures and pressures. We dynamically determined the volume reduction of the plugs from images that were accommodated within a single field of view, six different downstream locations of the microchannel at any given flow condition. Evaluating plug sizes in real time allowed our automated strategy to suitably select inlet pressures and solvent flow rates such that otherwise dynamically self-selecting parameters (e.g., the plug size, the solvent segment size, and the plug velocity) could be either kept constant or systematically altered. Specifically, if a constant slug length was imposed, the volumetric dissolution rate of CO(2) could be deduced from the measured rate of plug shrinkage. The solubility of CO(2) in the physical solvent was obtained from a comparison between the terminal and the initial plug sizes. Solubility data were acquired every 5 min and were within 2-5% accuracy as compared to literature data. A parameter space consisting of the plug length, solvent slug length and plug velocity at the microchannel inlet was established for different CO(2)-solvent pairs with high and low gas solubilities. In a case study, we selected the gas-liquid pair CO(2)-dimethyl carbonate (DMC) and volumetric mass transfer coefficients 4-30 s(-1) (translating into mass transfer times between 0.25 s and 0.03 s), and Henry's constants, within the range of 6-12 MPa.