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91.
The adsorption by a coal-based mesoporous activated carbon of humic acids (HAs) isolated from two Polish lignites was studied. For comparison, a commercial Aldrich humic acid was also included into this study. The differences in chemical structure and functional groups of HAs were determined by elemental analysis and infrared spectroscopy DRIFT. Two activated carbons used differed in terms of mesopore volume, mesopore size distribution, and chemical properties of the surface. The kinetics of adsorption of HAs have been discussed using three kinetic models, i.e., the first-order Lagergren model, the pseudo-second-order model, and the intraparticle diffusion model. It was found that the adsorption of HAs from alkaline solution on mesoporous activated carbon proceeds according to the pseudo-second-order model. The correlation coefficients were close to 1. The intraparticle diffusion of HA molecules within the carbon particle was identified to be the rate-limiting step. Comparing the two activated carbons, the carbon with a higher volume of pores with widths of 10-50 nm showed a greater removal efficiency of HA. An increase in the Freundlich adsorption capacity with decreasing carbon content of HA was observed. Among the HAs studied, S-HA shows characteristics indicating the highest contribution of small-size fraction. The S-HA was removed by both activated carbons to the highest extent. The effect of pH solution on the adsorption of HA was examined over the range pH 5.4-12.2. It was found that the extent of adsorption decreased with decreasing pH of the solution.  相似文献   
92.
A new cadmium(II)-imprinted polymer based on cadmium(II) 2,2′-{ethane-1,2-diylbis[nitrilo(E)methylylidene]} diphenolate-4-vinylpyridine complex was obtained via suspension polymerization. The beads were used as a minicolumn packing for flow-injection-flame atomic absorption spectrometry (FI-FAAS) determination of cadmium(II) in water samples. Sorption effectiveness was optimal within pH range of 6.6-7.7. Nitric acid, 0.5% (v/v) was used as eluent. Fast cadmium(II) sorption by the proposed material enabled to apply sample flow rates up to 10 mL min−1 without loss in sorption effectiveness. Enrichment factor (EF), concentration efficiency (CE) and limit of detection (LOD, 3σ) found for 120-s sorption time were 117, 39.1 min−1 and 0.11 μg L−1, respectively. Sorbent stability was proved for at least 100 preconcentration cycles (RSD = 2.9%). When compared to non-imprinted polymer the new Cd(II)-imprinted polymer exhibited improved selectivity towards cadmium(II) against other heavy metal ions, especially Cu(II) and Pb(II), as well as light metal ions. Accuracy of the method was tested for ground water and waste water certified reference materials and fortified water. The method was applied to Cd(II) determination in natural water samples.  相似文献   
93.
The Diels-Alder reaction between cyclopentadiene and dienophiles in deanol derivatives containing bis(trifluoromethylsulfonyl)imide anion as media have been studied. The effect of the substituents attached to the cation on the endo:exo selectivity as well as the reaction yield have been evaluated in the absence and presence of Lewis acid catalyst - Y(OTf)3. Catalytic activity of metal triflates and the recycling of chosen catalytic systems have also been investigated   相似文献   
94.

Nanosized carbon black (CB) was introduced into polypropylene/maleic anhydride-grafted polyolefin elastomer/intumescent flame retardant (PP/POE-MA/IFR) system to investigate the effect of nanofiller as synergist on thermal, electrical and mechanical properties of polymer composites. With 5 mass% CB into PP/POE-MA/IFR system (POFC5), the Tmax (corresponded to the temperature at the maximum mass loss rate) under air was increased by 122.4 °C; its limited oxygen index was as high as 31.4%; its vertical burning rating (UL-94) reached V0, and the peak value of heat release rate was decreased to only 19% of neat PP in cone calorimeter testing. Moreover, PP composites exhibited good electrical conductivity with more than 1.6 mass% CB, which is a low loading level to reach the critical percolation concentration. In addition, a good balance on stiffness and toughness of PP composites was achieved; especially, Young’s moduli and impact strength of POFC5 were increased to 1.26 and 2.5 times in comparison with that of neat PP, respectively. These results indicated that CB was an effective synergist in multi-component PP composites to simultaneously improve thermal, electrical and mechanical properties.

  相似文献   
95.
The paper presents a study of the effect of a constant magnetic field (CMF) on the basic processes of quercetin electrochemical reactions. According to the observation made in previous studies, the presence of a double bond in the C-ring of quercetin enhances the antioxidant properties of that compound, whereas the presence of −OH groups also affects the antioxidant properties. Using cyclic voltammetry it was found that the constant magnetic field improves the efficiency of quercetin electrooxidation, especially of the third stage of the process, i. e. the stage in which the oxidation of the OH groups in the A-ring is the most difficult. The use of HPLC confirmed the electrochemical measurements and the results of cyclic voltammetry studies. The beneficial effect of the magnetic field on the efficiency of quercetin oxidation was confirmed by the results of impedance spectroscopy measurements.  相似文献   
96.
In the solvent-free oxidation of benzyl alcohol to benzaldehyde using supported gold-palladium nanoparticles as catalysts, two pathways have been identified as the sources of the principal product, benzaldehyde. One is the direct catalytic oxidation of benzyl alcohol to benzaldehyde by O(2), whereas the second is the disproportionation of two molecules of benzyl alcohol to give equal amounts of benzaldehyde and toluene. Herein we report that by changing the metal oxide used to support the metal-nanoparticles catalyst from titania or niobium oxide to magnesium oxide or zinc oxide, it is possible to switch off the disproportionation reaction and thereby completely stop the toluene formation. It has been observed that the presence of O(2) increases the turnover number of this disproportionation reaction as compared to reactions in a helium atmosphere, implying that there are two catalytic pathways leading to toluene.  相似文献   
97.
The synthesis of novel mono- and di(substituted)-1,2,4-triazine derivatives containing thiophene and furan rings are described. Heteroaromatic rings were provided using palladium-catalyzed cross-coupling reaction between 3-alkylsulfanyl-5-acyl-1,2,4-triazines or 5-cyano-3-alkylsulfanyl-1,2,4-triazines and heteroaromatic tin compounds. New compounds bearing masked acyl groups were also obtained. These reactions were optimized to determine the scope and limitations of this methodology and were used for preparation of oligothiophenes bearing terminal heterocyclic ring.  相似文献   
98.
An artificial neural network model of supported liquid membrane extraction process with a stagnant acceptor phase is proposed. Triazine herbicides and phenolic compounds were used as model compounds. The model is able to predict the compound extraction efficiency within the same family based on the octanol–water partition coefficient, water solubility, molecular mass and ionisation constant of the compound. The network uses the back‐propagation algorithm for evaluating the connection strengths representing the correlations between inputs (octanol–water partition coefficients logP, acid dissociation constant pKa, water solubility and molecular weight) and outputs (extraction efficiency in dihexyl ether and undecane as organic solvents). The model predicted results in good agreement with the experimental data and the average deviations for all the cases are found to be smaller than ±3%. Moreover, standard statistical methods were applied for exploration of relationships between studied parameters.  相似文献   
99.
The formal potentials of the Hg2+/Hg 2 2+ , Hg 2 2+ /Hg and Hg2+/Hg redox couples and the apparent equilibrium constants of the reaction Hg2+ + Hg ∝ Hg 2 2+ in conc. aqueous solutions of Mg(ClO4)2 and Ca(ClO4)2 have been determined from emf measurements performed using cells with liquid junction. Based on these data, the hydration numbers of the Hg2+ and Hg 2 2+ ions were estimated.  相似文献   
100.
Abstract

Polymerization of methyl methacrylate and styrene can be effectively photoinitiated by a binary photoinitiator system consisting of cyclopentadienyl(iron)arene hexafluorophosphonate salt and bis(p-N, N-dimethylaminobenzylidene)cyclopentanone in the spectral range of 400–500 nm. The amine-type radical formed from the exciplex of the binary photoinitiator system is probably responsible for the radical polymerization of vinyl monomers. A probable mechanism of initiation of polymerization is discussed.  相似文献   
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