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941.
Vassileios M. Matsis 《Chemical engineering science》2008,63(3):609-621
The macroscopic adsorption behavior of dissolved oxygen on a coconut shell-derived granular activated carbon has been studied in batch mode at 301 and 313 K for initial dissolved oxygen concentrations of 10-30 mg/l and oxygen/carbon ratios of 2-180 mg/g. BET (Brunauer, Emmett, and Teller) surface area, micropore volume, and pore size distribution were determined from N2 isotherm data for fresh and used samples of carbon. The surface groups were characterized using Boehm titrations, potentiometric titrations, and FTIR study. The material is characterized by its high specific surface area , microporocity (micropore volume ), its basic character ( total basic groups) and its high iron content (15,480 ppm Fe). BET n-layer isotherm describes adsorption equilibrium suggesting cooperative adsorption and important adsorbate-adsorbate interactions. Kinetic data suggest a process dependent on surface coverage. At low coverage a Fickian, intraparticle diffusion rate model assuming a local equilibrium isotherm (oxygen dissociation reaction) adequately describes the process. The calculated diffusion coefficients (D) vary between and for initial oxygen concentration of 10 and 20 mg/l, respectively. Sensitivity analysis shows that the oxygen dissociation equilibrium constant determines the equilibrium concentration, whereas the diffusion coefficient controls the kinetic rate of the adsorption process having no effect at the final equilibrium concentration. A combined kinetic mass transfer model with concentration-dependent diffusion (parabolic form) has been developed and successfully applied on the dissolved oxygen adsorption system at high surface coverage. For equilibrium uptake of the estimated mean mass transfer coefficient and adsorption rate constant are and , respectively. 相似文献
942.
Single component and competitive adsorption of propane, carbon dioxide and butane on Vycor glass 总被引:1,自引:0,他引:1
Equilibrium of gas phase adsorption on Vycor glass has been investigated. Adsorption isotherms for propane, carbon dioxide and butane as pure gases, binary mixtures and ternary mixtures were determined experimentally as a function of temperature using a volumetric method. The single-component isotherms were described with the Langmuir and Freundlich equations. Additionally, a second order isotherm based on statistical thermodynamics and an isotherm equation based on vacancy solution theory taking into account real phase behavior were used for fitting single-component equilibrium data. In order to describe the measured partial isotherms for binary mixtures, at first simple extensions of the single-component isotherm models were used, i.e., the conventional competitive Langmuir model and a multi-Freundlich equation based on the ideal adsorbed solution theory (IAS). Since these two simple isotherm models failed to represent the unusual competitive behavior observed, three model extensions using additional mixture parameters were applied, i.e., two modified multi-Langmuir equations based on: (a) statistical thermodynamics and (b) vacancy solution theory and a modified multi-Freundlich IAS model correcting spreading pressure uncertainties. These three model equations were found to be capable to describe the observed behavior better. Finally, the measured partial adsorption equilibrium data of the ternary system were correlated based on the extended equations using the determined additional binary parameters. The results obtained reveal the difficulty to predict accurately multi-component adsorption equilibria. 相似文献
943.
Treatment of aniline hypersaline wastewater with a combined physical–biological method was investigated in this study. This method consisted of the physical adsorption of aniline from hypersaline effluents by resins and the biodegradation of the adsorbate and the regeneration of the adsorbent in the subsequent stage. The XDA-1 resin, selected from five commercial products, could separate aniline from salt effectively. The adsorption rate increased with the increase of salinity. Biodegradation of the aniline desorbed from the exhausted resin could be realized easily without salt interference. During the repetitive six combined operations, the percentage regeneration (PR) and NaCl separation efficiency (SE) of XDA-1 were 92.3% and 98.3%, respectively. No obvious difference could be found in pore size distribution between virgin XDA-1 and samples repeated six regeneration cycles. The PR of specific surface area and total pore volume of the bio-regenerated XDA-1 resin were 94.5% and 97.2%, respectively. It was indicated that XDA-1 could be bio-regenerated successfully and the regenerated resin could be re-utilized. 相似文献
944.
N.A. Oladoja C.O. Aboluwoye Y.B. Oladimeji A.O. Ashogbon I.O. Otemuyiwa 《Desalination》2008,227(1-3):190-203
The potentialities of castor seed shell (CSS), a waste agricultural by-product, in the remediation of water, contaminated with Methylene Blue (MB), a basic dye, were investigated in the present study. The CSS was ground and washed, thoroughly, to remove any water extractable constituents. The dried CSS was reground, sieved and used in series of agitated batch adsorption experiments. The experiments were conducted to assess the effect of two process variables i.e. initial MB concentration and CSS dosage on the sorption process. The equilibrium sorption isotherm was studied using the two widely used isotherm models (i.e. Freundlich and Langmuir isotherm models). The results from the isotherm studies showed that the process of sorption of MB occurred on a heterogeneous surface of the CSS. The sorption capacity of the CSS, as obtained from the Langmuir plot was 158 mg/g. The mass transfer property of the sorption process was studied using Lagergren pseudo-first-order and chemisorptions pseudo-secondorder kinetic models. The sorption process obeyed the pseudo-second-order kinetic model more than the pseudo-first order; hence the mechanism of the sorption process was analysed further using this kinetic model. The application of the intraparticle diffusion model to determine the rate limiting step showed that intraparticle diffusion is not the singular rate limiting step in the sorption of MB onto CSS. The role of chemisorptions in the mechanism of sorption was established by an empirical relationship between the pseudo-second-order rate constant, K, and the initial MB concentration. The results of this relationship showed that pseudo-second-order chemisorptions are important in the sorption process. 相似文献
945.
The inhibition effect of 2-mercaptothiazoline (2MT) on the corrosion behavior of mild steel (MS) in 0.5 M HCl solution was studied in both short and long immersion times (120 h) using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. For long-term tests, hydrogen gas evolution (VH2−t) and the change of the open circuit potential with immersion time (Eocp − t) were also measured in addition to the former three techniques. The surface morphology of the MS after its exposure to 0.5 M HCl solution with and without 1.0 × 10−2 M 2MT with the different immersion times was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermal stability of the inhibitor film was investigated by thermogravimetric analysis (TGA). The value of activation energy (Ea) for the MS corrosion and the thermodynamic parameters such as adsorption equilibrium constant (Kads), free energy of adsorption (ΔGads), adsorption heat (ΔHads) and adsorption entropy (ΔSads) values were calculated and discussed. The potential of zero charge (PZC) of the MS in inhibited solution was studied by the EIS method, and a mechanism for the adsorption process was proposed. The results showed that 2MT performed excellent inhibiting effect for the corrosion of the MS. Finally, the high inhibition efficiency was discussed in terms of adsorption of inhibitor molecules and protective film formation on the metal surface. TGA results also indicated that the inhibitor film on the surface had a relatively good thermal stability. 相似文献
946.
Gintaras Baltrūnas Aušra Valiūnienė Justas Vienožinskis Ernestas Gaidamauskas Teofilis Jankauskas Žana Margarian 《Journal of Applied Electrochemistry》2008,38(11):1519-1526
Electrochemical gold deposition from sulfite solutions was studied by means of voltammetry, EIS and EQCM. A gold film electrode
was used for polyaniline layer formation by electrochemical oxidation of aniline. The standard electrochemical reduction potential
of the reaction [Au(SO3)2]3− + e− = Au + 2 SO32− was determined, and is equal to 0.116 V (vs. NHE). Both solution stirring and temperature increase accelerate the electrochemical
reduction of gold, when the electrode potential is below −0.55 V. When the potential is above −0.55 V the electrochemical
reduction proceeds via passive layer formation. Our study suggests that the passive layer consists of chemically adsorbed
sulfite ions and sulfur. The gold film deposited from sulfite solution is a high quality substrate suitable for conducting
polymer layer formation. This technique, where a polymer layer electrode is prepared by thin gold film deposition onto a metal
surface and by subsequent polymer layer formation, can be applied in sensor research and technology. 相似文献
947.
Nickel–Co nanocrystalline coatings were electrodeposited onto a carbon steel substrate with and without saccharin addition.
In the absence of saccharin, current density and adsorption of hydrogen complexes and/or intermediate components were distinguished
as two effective parameters causing nanocrystalline electrodeposits. In the latter case, the growth active sites can be blocked
easily at low current densities. By increasing the current density, a lower degree of adsorption was associated by a significant
increase in surface diffusion of adions resulting in grain growth. Although, the nucleation rate is expected to increase with
current density, it seems that the Ni–Co grain size is not reduced by the nucleation rate. Adsorption of saccharin molecules
and/or decomposed sulfide species occurred in the saccharin contained bath, resulting in slow surface diffusion of adions.
Therefore, finer grains were obtained which produced a smooth morphology instead of the pyramidal forms obtained in the absence
of saccharin. 相似文献
948.
949.
Masaru KuboKeisuke Ishiyama Atsushi ShimojimaTatsuya Okubo 《Microporous and mesoporous materials》2012,147(1):194-199
We investigate the hydrogen adsorption properties of periodic mesoporous organosilicas (PMOs) and focus, in particular, on how these properties are affected by diverse organic groups embedded in the walls. PMOs with π electrons on the pore surface adsorb more hydrogen molecules per unit area and have a higher isosteric heat of hydrogen adsorption (Qst). The number of adsorbed hydrogen molecules per unit area correlates well with the density of organic groups on the pore surface. We attribute the high Qst to the high polarizability of organic groups with π electrons, which enhances the dispersion force. The molecular order of organic groups affects the adsorption-site affinity to hydrogen molecules as well as the location of adsorption sites. For phenylene-bridged PMOs with crystal-like pore walls, Qst decreases rapidly with increasing hydrogen loading, which indicates two types of adsorption sites with different affinities to hydrogen molecules: one is an exposed CH bond and the other is a siloxane bond. However, Qst for phenylene-bridged PMOs with amorphous pore walls exhibits a moderate slope, which might be caused by the random order of organic groups; this results in several types of adsorption sites with various affinities. 相似文献
950.
F. BenalioucheY. Boucheffa F. Thibault-Starzyk 《Microporous and mesoporous materials》2012,147(1):10-16
Ag- and Cu-exchanged forms of HY zeolite are prepared by the solid-state ion exchange (SSIE) technique. Samples with different metal loadings ranging from low to high exchange are obtained. Both compositional and structural investigations of the exchanged zeolites are performed by elemental analysis, powder X-ray diffraction (XRD), and nitrogen adsorption porosimetry. The acidity investigation is carried out by using the Fourier transform infrared spectroscopy (FTIR) of pyridine adsorption. Propene adsorption over the Ag- and Cu-exchanged zeolites is studied at room temperature by using in situ FTIR spectroscopy. XRD analysis shows good conservation of the zeolitic structure after ionic exchange even at high exchange degree. Porosity measurements indicate that the increase of Ag and Cu exchange degrees leads to a decrease of the porous volumes and the specific surface areas, which is more pronounced for Ag-exchanged zeolites. The acidity evaluation for both exchanged metals shows an important decrease of Brønsted acidity and a slight increase of Lewis acidity, which are more noticeable at high degree of exchange. Instantaneous oligomerization of propene on HY zeolite at room temperature is favored by the relatively high amount of Brønsted acid sites. The propene molecules interact more strongly with Cu2+ than with Ag+. The shape of the CC stretching band of the FTIR spectra involves at least two overlapping bands indicating that the propene CC bond may interact with several kinds of Ag+, Cu2+ and Cu+ sites of various propene bonding. 相似文献