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161.
Miguel A. De La Rosa José A. Navarro Mercedes Roncel 《Applied biochemistry and biotechnology》1991,30(1):61-81
The production of chemicals and fuels, or energy-rich compounds, from water by sunlight is described as a particularly attractive
means for the conversion of solar energy to a valuable renewable resource. The redox properties of photoexcited molecules
and the operating mechanism of light-driven systems are first considered. The mechanism of water oxidation carried out by
higher plants and green algae-which is actually one of the most important biochemical reactions—as well as that of artificial
photosystems, up-to-now designed trying to simulate the natural process with higher efficiency and simplicity, are likewise
discussed. A number of biological and chemical light-driven systems are presented as practical ways to solar energy conversion. 相似文献
162.
K. Benmansour 《European Polymer Journal》2003,39(7):1443-1449
In order to determine the counter-anion effect on conductivity of poly[N-(3,6,9-trioxadecyl)-4-vinylpyridinium)] backbone in aqueous solutions, a set of three polyelectrolytes with three different counter-ions: poly[N-(3,6,9-trioxadecyl)-4-vinylpyridinium]bromide P4VP164Br and its chlorate and tosylate derivatives P4VP164ClO4 and P4VP164Ts respectively, were prepared by spontaneous polymerization of 4-vinylpyridine. This method gives a grafted polyelectrolyte having a positive charge on each pyridinic moiety on the backbone. The conductivities of cationic polyelectrolyte aqueous solution were determined in the concentration range from 10−4 to 10−2 M at 25 °C. The variation of the conductivity versus concentration of the investigated system exhibits a typical polyelectrolyte behavior. The polycation mobility was found to be dependent on the counter-anion nature. Thus, the polyelectrolyte conductivity increases with the ion size. This shows that big ions are weakly or not associated to the backbone.In order to confirm this steric hindrance, we have considered the conductivities of these three anions Br−, ClO4− and Ts− in their sodium salts, both alone and in the presence of 3,6,9-trioxadecanol (PEO164) free chains. In the two cases, the conductivities decrease in the order ΛBr>ΛClO4>ΛTs.These results suggest that counter-ion mobility is mainly influenced by steric effect PEO164 grafted chains.Values of the conductivity predicted from Manning rod-like polyelectrolyte model were compared with our experimental results. 相似文献
163.
A method for the determination of methylmercury (MeHg) fluxes across the air–water and air–soil interfaces was developed using an in situ chamber. The MeHg in the air coming out of the chamber was captured by a column containing sulfhydryl cotton fiber adsorbent. MeHg was then desorbed from the column by using 2 mol L–1 HCl. The MeHg in the effluent was extracted with benzene, and determined by gas chromatography with electron capture detection. Finally, the MeHg flux was calculated using the chamber. The method was applied to simulated experiments, and the results showed that the MeHg fluxes in the air–water system were higher than those in the air–soil–water system. The method was also successfully applied to the field measurements of an environment polluted by a chemical factory, and the results showed that the MeHg fluxes across the air–soil and air–water interfaces were 0.21–3.09 and 0.14–0.79 ng m–2 h–1, respectively. The method will be a useful tool in the environmental study of MeHg. 相似文献
164.
Plasticized protein films were prepared by the casting method from water solution of sodium caseinate and plasticizers with the aim to obtain environmentally friendly materials for packaging applications. Mechanical properties (tensile strength, elongation and Young’s modulus) of caseinate based films were determined versus ratio of protein to plasticizer, plasticizer type and relative humidity conditions. Among the different polyol-type plasticizers tested, glycerol (Gly) and triethanolamine (TEA) were the most efficient for the improvement of mechanical properties (high strains for low stresses). Further, chemical crosslinking between formaldehyde (HCHO) and free amino groups (ε-NH2) of sodium caseinate was performed to increase water resistance of TEA plasticized films. Optimal mechanical properties, i.e. elastic modulus of 105 MPa, tensile strength of 8-9 MPa for elongation at break about 110-125% were obtained for HCHO/ε-NH2 ratios higher than 1.35. Protein specific water solubility was determined from a 280 nm absorbance. For convenient crosslinker (HCHO) content sodium caseinate solubility can be lowered to less than 5 wt% after 24 h immersion in water. 相似文献
165.
Summary A simple and sensitive method has been developed for the liquid chromatographic determination of short-chain aliphatic amines
in water. Analytes are retained in solid-phase extraction (SPE) cartridges, and then derivatized by drawing an aliquot of
the fluorogeneic reagent 9-fluorenylmethyl chloroformate (FMOC) through the cartridges. After a certain reaction time the
derivatives formed are desorbed with acetonitrile. The collected extracts are then chromatographed on a LiChrospher 100 RP18 125 mm×4 mm i.d., 5 μm, column using an acetonitrile-water gradient. The influence of experimental conditions (SPE material,
volume of sample, concentration of FMOC, time of reaction and pH) has been investigated. Optimal results have been obtained
with C18 SPE cartridges using a sample volume of 5.0 mL. For derivatization, 0.25 mL aliquots of 25 mM FMOC have been used, the reaction
time being only 2 min. The method has been applied to the quantification of several aliphatic amines: methylamine, ethylamine,
dimethylamine,n-butylamine,n-pentylamine andn-hexylamine. Under the proposed conditions the percentages of analytes retained plus derivatized were of about 54–107% compared
to those obtained with direct solution derivatization. The method provided good reproducibility, linearity and accuracy within
the 0.050–1.0 mg L−1 concentration range. The limits of detection were in the 0.25–5.0 μg L−1 range. The utility of the described approach has been tested by analysing tap water, river water and industrial waste water. 相似文献
166.
The relative stabilities of thiourea in water are investigated computationally by considering thiourea–water complexes containing up to 1–6 water molecules (CS(NH2)2(H2O)n=1–6) using density functional theory and MP2 ab initio molecular orbital theory. The results show that the thiourea complex is stable and has an unusually high affinity for incoming water molecules. The clusters are progressively stabilized by the addition of water molecules, as indicated by the increasing of the binding energy. The binding energy of the cluster to each H2O molecule is about 33 kJ mol−1 for n=1–5.The C–S bond, N–C bond distance, Mulliken populations and binding energy keep approximately constant as the clusters increase in size with an increasing number of H2O molecules. As the solvation progresses, the C–S distance increases monotonically while the Mulliken populations on the C–S bond reduces monotonically with the addition of each H2O molecule, indicating that the C–S bond of the thiourea unit in the clusters is de-stabilized with an increasing number of H2O molecules. Charge transfers for the clusters are mainly found at N, S atoms of the thiourea. 相似文献
167.
Liquid-liquid-liquid phase microextraction (LLLME) coupled with high-performance liquid chromatography (HPLC) for the analysis of some aromatic amines is described. These compounds were extracted from 4.0 mL aqueous sample that adjusted to pH 13 with, NaOH-NaCl buffer solution (donor phase, P1) into an organic phase (P2) 150 μl benzyl alcohol and ethyl acetate (2:1) and then back extracted into a microdrop of aqueous acceptor phase (P3), adjusted at pH 2, with Na2HPO4-H3PO4 buffer solution. The extraction time, T1 (from P1 to P2) was 20 min and T2 (from P2 to P3) was 1 min. Different crown ethers as complexing agents for amines were added to the acceptor phase to improve the extraction time. Factors such as organic solvents, extraction times, and addition of crown ethers to acceptor phase and stirring rate were optimised. The method was applied for determination of aromatic amines in wastewater samples. Enrichment factors ranged from 184.5 to 389.7. The linearity range was from 3 to 1000 ng/ml and the detection limits varied from 0.8 to 1.80 ng/ml. Relative standard deviations (%, n = 5) were found (at S/N 3) in the range of 1.9 to 10.1. All experiments were carried out at room temperature, 22 ± 0.5 °C. 相似文献
168.
169.
《Arabian Journal of Chemistry》2020,13(9):7115-7131
The impregnation of magnetite (Mt) nanoparticle (NPs) onto Musa acuminata peel (MApe), to form a novel magnetic combo (MApe-Mt) for the adsorption of anionic bromophenol blue (BPB) was studied. The SEM, EDX, BET, XRD, FTIR and TGA were used to characterize the adsorbents. The FTIR showed that the OH and CO groups were the major sites for BPB uptake onto the adsorbent materials. The average Mt crystalline size on MApe-Mt was 21.13 nm. SEM analysis revealed that Mt NPs were agglomerated on the surface of the MApe biosorbent, with an average Mt diameter of 25.97 nm. After Mt impregnation, a decrease in BET surface area (14.89 to 3.80 m2/g) and an increase in pore diameter (2.25–3.11 nm), pore volume (0.0052–0.01418 cm3/g) and pH point of zero charge (6.4–7.2) was obtained. The presence of Pb(II) ions in solution significantly decreased the uptake of BPB onto both MApe (66.1–43.8%) and MApe-Mt (80.3–59.1%), compared to other competing ions (Zn(II), Cd(II), Ni(II)) in the solution. Isotherm modeling showed that the Freundlich model best fitted the adsorption data (R2 > 0.994 and SSE < 0.0013). In addition, maximum monolayer uptake was enhanced from 6.04 to 8.12 mg/g after Mt impregnation. Kinetics were well described by the pseudo-first order and liquid film diffusion models. Thermodynamics revealed a physical, endothermic adsorption of BPB onto the adsorbents, with ΔHo values of 15.87–16.49 kJ/mol, corroborated by high desorption (over 90%) of BPB from the loaded materials. The viability of the prepared adsorbents was also revealed in its reusability for BPB uptake. 相似文献
170.
J.F. Fernández-Sánchez C. Cruces-Blanco A. Fernández-Gutiérrez 《Analytica chimica acta》2004,506(1):1-7
We describe here a method for detecting and quantifying the highly carcinogenic polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BaP) in water, based on a flow-trough optical sensor. The technique is fast (response time of 40 s) and simple and at the same time meets the standards of sensitivity and selectivity required by the European Guidelines on Water for Human Consumption. The optosensor is based on the on-line immobilization of BaP on a non-ionic resin (Amberlite XAD-4) solid support in a continuous-flow system. BaP was analyzed in a 15 mM H2PO4−/HPO42− buffer solution with 25% (v/v) 1,4-dioxane at pH 7. Fluorescence intensity was measured at λex/em=392/406 nm. The experimental conditions (reagent phase, pH, type and concentration of buffer solution and organic solvent) and flow-injection values (flow rate and injection volume) were carefully controlled. Under these conditions the optosensor was sensitive to a linear concentration range of between 3.0 and 250.0 ng l−1 with a detection limit of 3.0 ng l−1 and a standard deviation of 1.5% at 150 ng l−1. The optosensor was applied to the quantification of BaP in drinking and waste water samples (95-105% recovery) in presence of the other 15 EPA PAHs at 1000 ng l−1 concentration level. The influence of other fluorescent polycyclic aromatic hydrocarbons and potential interference from ions usually present in water was also evaluated. 相似文献