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1.
The sorptive potential of sunflower stem (180-300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. The isotherm yields D-R saturation capacity Xm = 1.60 ± 0.23 mmol g−1, β = −0.00654 ± 0.00017 kJ2 mol−2, mean free energy E = 8.74 ± 0.12 kJ mol−1, Freundlich sorption capacity KF = 0.24 ± 0.11 mol g−1, 1/n = 0.90 ± 0.04 and of Langmuir constant KL = 6800 ± 600 dm3 mol−1 and Cm = 120 ± 18 μmol g−1. The variation of sorption with temperature (283-323 K) gives ΔH = −23.3 ± 0.8 kJ mol−1, ΔS = −64.0 ± 2.7 J mol−1 K−1 and ΔG298k = −4.04 ± 0.09 kJ mol−1. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed. 相似文献
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Moosa Gabeleh 《Quaestiones Mathematicae》2016,39(2):203-215
A new class of noncyclic mappings, called generalized noncyclic relatively nonexpansive, is introduced and used to study the existence of best proximity pairs in the setting of uniformly convex Banach spaces. We also obtain a weak convergence theorem for noncyclic relatively nonexpansive mappings in the setting of Hilbert spaces. 相似文献
4.
Moosa Ebadi 《Numerical Algorithms》2018,79(1):179-193
A new class of hybrid BDF-like methods is presented for solving systems of ordinary differential equations (ODEs) by using the second derivative of the solution in the stage equation of class 2 + 1hybrid BDF-like methods to improve the order and stability regions of these methods. An off-step point, together with two step points, has been used in the first derivative of the solution, and the stability domains of the new methods have been obtained by showing that these methods are A-stable for order p, p =?3,4,5,6,7and A(α)-stable for order p, 8 ≤ p ≤?14. The numerical results are also given for four test problems by using variable and fixed step-size implementations. 相似文献
5.
The details of new methods based on backward differentiation formulas (BDF) for the MOL solution of one-dimensional nonlinear time dependent PDEs are presented. In these extended hybrid BDF methods, we say EHBDF, one additional stage point (or off-step point) together with one step point have been used in the first derivative of the solution. All presented methods, of order p, p = 2,3,..., 12, are A(α)-stable whereas they have wide stability regions comparing with those of some known methods such as BDF, extended BDF (EBDF) and modified EBDF (MEBDF) methods. 相似文献
6.
Solid-Phase Microextraction Gas Chromatography for Determination of Some Organophosphorus Pesticides 总被引:1,自引:0,他引:1
A simple and rapid solid-phase microextraction (SPME) method is presented based on activated charcoal–PVC fiber for determination of some organophosphorus pesticides from aqueous samples in direct mode SPME. After optimization of the experimental variables affecting SPME of the target compounds from aqueous solutions, the proposed method was applied to determine pesticides in fruit juice. The analytes in this procedure were preconcentrated for 15 min on the SPME fiber and subsequently desorbed by heating the fiber at 200 °C for 5 min in the GC injection port. Separation was on a capillary column GC followed by flame ionization detection. Recoveries of the pesticides studied in aqueous samples ranged 42%–63% and repeatability for all analytes was < 9% for a single fiber. Fiber-to-fiber reproducibility was < 18%. 相似文献
7.
This paper proves that a difference field (E, ) admits quantifierelimination if and only if E is an algebraically closed field,and is an integer power of the Frobenius automorphism. 1991Mathematics Subject Classification 03C60, 12H10. 相似文献
8.
A series of new poly(amide imide)s was prepared from new diacid containing sulfone, ether, amide and imide groups with various aromatic diamines. The diacid was synthesized via four steps, starting from reaction of 4-aminophenol with 4-nitrobenzoyl chloride in the presence of propylene oxide afforded N-(4-hydroxy phenyl)-4-nitrobenzamide. In the second step, reduction of nitro group resulted in preparation of 4-amino-N-(4-hydroxy phenyl) benzamide. In the next step for the preparation of diamine, the reaction of 4-amino-N-(4-hydroxy phenyl) benzamide with bis-(4-chlorophenyl) sulfone in the presence of K2CO3 was achieved. The prepared sulfone ether amide diamine was reacted with two moles of trimellitic anhydride to synthesize related sulfone ether amide imide diacid. The precursors and final monomer were characterized by FT-IR, H-NMR and elemental analysis. Direct polycondensation reaction of the sulfone ether amide imide diacid with different diamines in the presence of triphenyl phosphite afforded five different poly (sulfone ether amide imide amide)s. The obtained polymers were fully characterized and their physical properties including thermal behavior, thermal stability, solubility, and inherent viscosity were studied. 相似文献
9.
Moosa GABELEH 《数学物理学报(B辑英文版)》2014,(5):1661-1669
We study the existence of best proximity points for single-valued non-self map-pings. Also, we prove a best proximity point theorem for set-valued non-self mappings in metric spaces with an appropriate geometric property. Examples are given to support the usability of our results. 相似文献
10.
Moosa Gabeleh 《Journal of Optimization Theory and Applications》2013,158(2):615-625
In this work, we consider two classes of non-self-mappings, which are called proximal weakly contractive and proximal nonexpansive mappings, and study the existence of solutions of a minimization problem. Existence results of best proximity points for these two classes of non-self-mappings in metric and Banach spaces are also obtained. 相似文献