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11.
ÜMMÜHAN OCAK HALIT KANTEKIN YAŞAR GÖK H. BASIR ŞENTÜRK 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(1-2):87-91
The selective liquid–liquid extraction of various transition metal cations from the aqueous phase to the organic phase was carried out using a 14-membered N2O2S2-macrobicycle. Metal picrates such as Pb2+, Co2+, Zn2+, Ni2+,Cu2+ and Cd2+ were used in this extraction studies. It was found that the ligand showed moderate selectivity towards Pb2+ only among the other metals. The extraction constant (log K
ex) was determined to be 13.8 for Pb2+ complex. 相似文献
12.
Patrícia A. Russo M. Manuela L. Ribeiro Carrott Peter J.M. Carrott 《Colloids and surfaces. A, Physicochemical and engineering aspects》2007,310(1-3):9-19
The effect of hydrothermal treatment of the synthesis gel on the structure, hydrothermal and mechanical stabilities and acidity of MCM-41 and MCM-48 aluminosilicates synthesised at room temperature has been investigated by X-ray diffraction, nitrogen adsorption at 77 K and DRIFTS with pyridine as probe molecule. The influence of the Al content and pore size on the structure of the resulting treated Al-MCM-41 materials has also been studied. For all samples improvement of the structural ordering and increase of the pore size, was observed, with pore wall thickness remaining practically unchanged. For Al-MCM-48 an improvement of the pore size uniformity occurs during the treatment. Only a small loss of pore size uniformity occurred for Al-MCM-41 prepared with hexadecyltrimethylammonium bromide, but with samples prepared with tetra and octadecyltrimethylammonium bromide the treatment generated a bimodal pore size distribution. The pore volume increased (17%) in the case of Al-MCM-48 but decreased (5.5–14%) for Al-MCM-41, suggesting a decrease in surface roughness resulting from increase of the degree of condensation of the pore walls. Both treated and untreated samples presented relatively strong Brønsted sites and increase of the Lewis acidity was found to occur upon treatment. Treated samples were found to be more resistant to refluxing in boiling water and mechanical compaction, which was attributed to more polymerised pore walls, with Al-MCM-41 samples tested demonstrating higher stability than Al-MCM-48. However, the differences in stability of samples prepared with or without hydrothermal treatment were not significant. Both treated and untreated samples presented high hydrothermal stability. Although refluxing in boiling water lead to some loss of structural ordering, only a small decrease of pore volume (3–5.5% for Al-MCM-41 and 8-14% for Al-MCM-48) occurred, with practically no alterations in pore size and wall thickness. Ordered mesopore structure, with narrower pores and thicker walls, was still observed after compression at 590 MPa for most of the samples tested. 相似文献
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14.
C. Lucas I. Eiroa M. R. Nunes P. A. Russo M. M. L. Ribeiro Carrott M. I. da Silva Pereira M. E. Melo Jorge 《Journal of Solid State Electrochemistry》2009,13(6):943-950
The electrochemical properties of Ca1 − x
Ce
x
MnO3 perovskite-type oxide electrode have been investigated by cyclic voltammetry in Na2SO4 aqueous solutions with pH 14. The structural and morphological characterizations have also been investigated and the information
used to interpret the electrochemical behavior. An estimation of the electrode’s capacitance and roughness factor has been
obtained by means of cyclic voltammetry. The specific capacitance and consequently the roughness factor values are affected
by the presence of Ce ions in the oxide. These findings are in agreement with the increase of the oxide-specific surface area
by the introduction of Ce ion. The open-circuit potential and the voltammetric patterns are dependent on the presence of Ce
ion in the electrodes and support that the surface electrochemistry of the perovskite oxide electrodes is governed by the
Mn4+–Mn3+ redox couple. 相似文献
15.
16.
Experimental results on the nuclear spin-lattice and nuclear spin-spin relaxation times in the ferromagnetic EuB6 at temperatures below 4·2 K are presented using the external magnetic field,H
ext, in the range of 0 ⩽H
ext ⩽ 10 kG. Nuclear spin-spin relaxation time computed on the basis of the Suhl-Nakamura process turns out to be 3·2μs, which compares well with the experimental value 11·1μs obtained with the 10 kG magnetic field at 1·7 K. It is found that in the ferromagnetic EuB6,T
1 is approximately 5 × 103 times larger thanT
2 at 1·7 K with the 10 kG magnetic field. Thus the effect ofT
1 onT
2 can be neglected. From the experimental value ofT
2, the value of the homogeneous line broadening is found to be 14 kHz. The corresponding value obtained from the cw method
is 175 kHz. This evidently shows the presence of the inhomogeneous line broadening in the cw NMR. 相似文献
17.
Patrícia A. Russo M. Manuela L. Ribeiro Carrott Peter J. M. Carrott 《Adsorption》2008,14(2-3):367-375
Adsorption-desorption isotherms of toluene, methylcyclohexane and neopentane were determined on a silica MCM-41 material of
pore diameter ∼3.4 nm over the temperature range 258 K to 308 K (278 K for neopentane). The isosteric enthalpies of adsorption
were determined from the isotherms at the various temperatures. It was found that the isotherms of toluene and methylcyclohexane
have a similar variation with the temperature, exhibiting hysteresis at 268 K and at lower temperature, while the adsorption
of neopentane is reversible at all temperatures. The three organic adsorptives interact differently with the silica surface
and the isosteric enthalpies of adsorption indicated that methylcyclohexane has the weakest interaction and toluene the strongest.
A slight increase in the adsorption enthalpy at the beginning of the capillary condensation step is observed with methylcyclohexane
and neopentane but not with toluene. 相似文献
18.
Sans résumé 相似文献
19.
P.J.M. Carrott I.P.P. Cansado M.M.L. Ribeiro Carrott 《Applied Surface Science》2006,252(17):5948-5952
Carbon molecular sieves (CMS) have been made for the first time from PET textile fibres by carbonisation and pore mouth narrowing using CVD of benzene. The diffusion of O2, N2, CO2 and CH4 in these materials, and also in the commercial CMS Takeda 3A, was studied. It was found that the best PET based CMS was obtained after 10 min CVD time and had adsorption capacities and rates of diffusion similar to those of the Takeda 3A. 相似文献
20.
Exclusively microporous activated carbons have been prepared from cork by physical and chemical activation under different conditions. The results show that it is possible to control the pore size of the activated carbons and to obtain materials with narrow micropore size (≥0.69 nm) and high micropore volume (≤0.64 cm3 g−1) equal to or better than the best activated carbon fibres. Higher micropore volumes are generally obtained by chemical activation at higher temperature using dry or potassium hydroxide impregnation. On the other hand, wet or carbonate impregnation, as well as high temperature, or physical activation with CO2 or H2O under appropriate conditions, favours low mean pore widths. 相似文献