Determination of Chlorinated Solvent Sorption by Porous Material—Application to Trichloroethene Vapor on Cement Mortar

Experiments have been performed to investigate the sorption of trichloroethene (TCE) vapor by concrete material or, more specifically, the cement mortar component. Gas-flow experiments were conducted using columns packed with small pieces of cement mortar obtained from the grinding of typical concrete material. Transport and retardation of TCE at high vapor concentrations (500 mg L \(^{-1})\) was compared to that of a non-reactive gas tracer (Sulfur Hexafluoride, SF \(_{6})\) . The results show a large magnitude of retardation (retardation factor \(=\) 23) and sorption (sorption coefficient \(=\) 10.6 cm \(^{3}\)  g \(^{-1})\) for TCE, compared to negligible sorption for SF \(_{6}\) . This magnitude of sorption obtained with pollutant vapor is much bigger than the one obtained for aqueous-flow experiments conducted for water-saturated systems. The considerable sorption exhibited for TCE under vapor-flow conditions is attributed to some combination of accumulation at the air-water interface and vapor-phase adsorption, both of which are anticipated to be significant for this system given the large surface area associated with the cement mortar. Transport of both SF \(_{6}\) and TCE was simulated successfully with a two-region physical non-equilibrium model, consistent with the dual-medium structure of the crushed cement mortar. This work emphasizes the importance of taking into account sorption phenomena when modeling transport of volatile organic compounds through concrete material, especially in regard to assessing vapor intrusion.     

Preliminary thermodynamic study for an efficient turbo-blower external combustion Rankine cycle

This research paper presents a preliminary thermodynamic study of an innovative power plant operating under a Rankine cycle fed by an external combustion system with turbo-blower (TB). The power plant comprises an external combustion system for natural gas, where the combustion gases yield their thermal energy, through a heat exchanger, to a carbon dioxide Rankine cycle operating under supercritical conditions and with quasi-critical condensation. The TB exploits the energy from the pressurised exhaust gases for compressing the combustion air. The study is focused on the comparison of the combustion system’s conventional technology with that of the proposed. An energy analysis is carried out and the effect of the flue gas pressure on the efficiency and on the heat transfer in the heat exchanger is studied. The coupling of the TB results in an increase in efficiency and of the convection coefficient of the flue gas with pressure, favouring a reduced volume of the heat exchanger. The proposed innovative system achieves increases in efficiency of around 12 % as well as a decrease in the heat exchanger volume of 3/5 compared with the conventional technology without TB.     

Growth behavior and kinetics of self-assembled silica-carbonate biomorphs

Upon slow crystallization from silica-containing solutions or gels at elevated pH, alkaline-earth carbonates spontaneously self-assemble into remarkable nanocrystalline ultrastructures. These so-called silica biomorphs exhibit curved morphologies beyond crystallographic symmetry and ordered textures reminiscent of the hierarchical design found in many biominerals. The formation of these fascinating materials is thought to be driven by a dynamic coupling of the components' speciations in solution, which causes concerted autocatalytic mineralization of silica-stabilized nanocrystals over hours. In the present work, we have studied the precipitation kinetics of this unique system by determining growth rates of individual aggregates using video microscopy, and correlated the results with time-dependent data on the concentration of metal ions and pH acquired online during crystallization. In this manner, insight to the evolution of chemical conditions during growth was gained. It is shown that crystallization proceeds linearly with time and is essentially reaction controlled, which fits well in the proposed morphogenetic scenario, and thus, indirectly supports it. Measurements of the silica concentration in solution, combined with analyses of crystal aggregates isolated at distinct stages of morphogenesis, further demonstrate that the fraction of silica coprecipitated with carbonate during active growth is rather small. We discuss our findings with respect to the role of silica in the formation of biomorphs, and moreover, prove that the external silica skins that occasionally sheath the aggregates--previously supposed to be involved in the growth mechanism--originate from secondary precipitation after growth is already terminated.     

Nucleic acid templated uncaging of fluorophores using Ru-catalyzed photoreduction with visible light

Hybridization-based reactions have attracted significant attention. The nucleic acid templated photocatalyzed azide reduction using catalytic amounts of a [Ru(bpy)(2)phen](2+) conjugate is reported. The reaction could be performed with as little as 2% of the Ru nucleic acid probe and was shown to productively unquench 7-azido-coumarin as well as uncage a small molecule.     

HF-LPME as a green alternative for the preconcentration of nickel in natural waters

In the last years, some analytical methodologies have been identified as a source of pollution, receiving increasing attention to decrease their impact on the environment. In this sense, the so-called solvent-less methodologies appear as a green alternative to reduce the volume of solvents used in many sample treatment procedures and, consequently, the volume of toxic wastes produced. Among these techniques, analytical methodologies based on liquid-phase microextraction are being continuously developed, although most applications are focused on organic compounds. In this work, a three-phase hollow-fibre liquid-phase microextraction (HF-LPME) system has been developed for the preconcentration of nickel in natural waters, prior to the analysis by atomic absorption spectrometry. Under optimum conditions, the new system allowed an enrichment factor of 29.80 to be obtained after 60 min of experiment, and it was successfully applied to the determination of nickel in both saline and non-saline water samples, at ppb and ppt levels. The results were compared with those obtained using a well-established methodology based on liquid solvent extraction showing no significant differences (α = 0.05) between both values. In addition, the new HF-LPME presents the advantages of a green analytical technique, as its greenness profile shows, with the additional reduction of sample manipulation and time cost.     

Ultrasound-assisted emulsification microextraction coupled with gas chromatography–mass spectrometry using the Taguchi design method for bisphenol migration studies from thermal printer paper, toys and baby utensils

The optimization of a clean procedure based on ultrasound-assisted emulsification liquid-liquid microextraction for the sensitive determination of four bisphenols is presented. The miniaturized technique was coupled with gas chromatography-mass spectrometry after derivatization by in situ acetylation. The Taguchi experimental method, an orthogonal array design, was applied to find the optimal combination of seven factors (each factor at three levels) influencing the emulsification, extraction and collection efficiency, namely acetic anhydride volume, sodium phosphate concentration, carbon tetrachloride volume, aqueous sample volume, sodium chloride concentration and ultrasound power and application time. A second factorial design was applied with four factors and five levels for each factor, 25 experiments being performed in this instance. The matrix effect was evaluated, and it was concluded that sample quantification can be done by calibration with aqueous standards. The detection limits ranged from 0.01 to 0.03 ng mL(-1) depending on the compound. The environmentally friendly sample pretreatment procedure was applied to study the migration of the bisphenols from different types of samples: thermal printer paper, compact discs, digital versatile discs, small tight-fitting waistcoats, baby's bottles, baby bottle nipples of different materials and children's toys.     

Photo-controlled release of zinc metal ions by spiropyran receptors anchored to single-walled carbon nanotubes

Light controllable release of antinflammatory zinc ions by a smart multifunctional material composed of spiropyrans and single walled carbon nanotubes (SWNTs) is demonstrated. The exploitation of a number of complementary characterization techniques allows the investigation of both composition and performance of the multifunctional SP/SWNT nanomaterial developed. Moreover, its suitability for potential applications in bio-systems is suggested by the effective removal of the metal catalyst and the introduction of biocompatible linkers into the SP/SWNT material. The realization of potential photo controllable SP/SWNTs based drug delivery systems (DDSs) is envisaged, where nanotubes act as intracellular carriers of light modulated receptors for bioactive agents.     

Antibody-free reading of the histone code using a simple chemical sensor array

The histone code refers to the complex network of histone post-translational modifications that control gene expression and are of high interest as drivers of a large number of human diseases. We report here on a mix-and-match toolkit of readily available dyes and calixarene host molecules that can be combined to form dye-displacement sensors that respond to a wide variety of cationic peptides. Using the data from only two or three such simple supramolecular sensors as a chemical sensor array produces fingerprints of data that discriminate robustly among many kinds of histone code elements. "Reads" that are accomplished include the discrimination of unmethylated, mono-, di-, and trimethylated lysines on a single histone tail sequence, identification of different modifications and combinations of modifications on a single histone tail sequence, identification of a single modification type in several different sequence contexts, and identification of isomeric dimethylarginine modifications. Reads that are sometimes troublesome for antibodies are achieved. We also report on the ability of the sensor array to report simultaneously on the concentrations and identities of histone modifications. This sensor array discriminates between post-translationally modified analytes without being limited to partners that contain a single, programmed binding interaction.