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Adsorption: Journal of the International Adsorption Society (v.14, #1)
Characterization of two single-wall carbon nanotubes samples by Ar and Kr adsorption isotherms by V. Goudon; J. C. Lasjaunias (pp. 1-9).
We investigated by Ar and Kr adsorption isotherm techniques for two kinds of carbon single-wall nanotube bundles prepared by different synthesis methods. Despite the difference in the adsorption capacity in the two samples, the adsorption mechanisms are similar, which indicates that the same adsorption sites are involved for Ar and Kr. We have already measured a similar difference in the adsorbed amount in these samples studied by a low-temperature heat-capacity technique, i.e., for the case of 4He as adsorbate. These results cannot be easily explained by only taking into account the topology of the bundles if all tubes are closed-ended. A larger spread of effective surface areas among different sources of samples is reported in the literature data.
Keywords: Carbon nanotubes; Adsorption isotherms; Adsorption sites
Effect of temperature, particle size and percentage deacetylation on the adsorption of acid dyes on chitosan by Y. C. Wong; Y. S. Szeto; W. H. Cheung; G. McKay (pp. 11-20).
The adsorption of five acidic dyes on chitosan—a by-product from waste crustacean shell—has been studied. The equilibrium data have been studied using Langmuir, Freundlich and Redlich-Peterson equations. The best correlations are obtained using the Langmuir isotherm suggesting the mechanism involves one process step of dyes complexing with the free amino group. The effect of chitosan particle size was investigated and showed an increase in adsorption capacity with decreasing particle size indicating that the available external surface was an important factor. Increasing solution temperature resulted in an increase in adsorption capacity indicating an exothermic process with a negative ΔH. Finally, the effect of varying the percentage degree of deacetylation showed that from 52% to 97% resulted in decrease in the dye adsorption capacity suggesting that more amorphisation may cause changes in the internal structure of chitosan and reduce the capacity.
Keywords: Acid dyes; Chitosan; Equilibrium; Temperature; Particle size; Deacetylation
Heavy metal removal using SiO2-TiO2 binary oxide: experimental design approach by Adel A. Ismail; Ayman A. El-Midany; Ibrahim A. Ibrahim; Hideyuki Matsunaga (pp. 21-29).
Sorption of Ni2+ and Cd2+ as heavy metals ions at the interface of the binary oxide TiO2-SiO2 was investigated. In addition, physical properties of TiO2-SiO2 matrices such as BET surface area, X-ray diffraction, and point of zero charge (pHPZC) were measured. Statistical design of experiments was applied to find the conditions of sorption at which the maximum heavy metal removal was achieved. A second order polynomial function was used to correlate the independent variables (pH, metal ion concentration, and shaking time) and response (heavy metal removal). Values of regression parameters were determined by the computer program, Design expert® (Stat-Ease Inc.). The quality of fit of the polynomial model equation was expressed by the regression coefficient R 2. The sorption results showed that the pH is the most significant factor. In turn, the sorbed percentage reached 100% at high initial concentration and long shaking times due to formation of hydroxyl compounds between the ions and TiO2-SiO2 matrices. The results show that there is a Gaussian (normal) distribution of residuals (squared differences between experimentally observed and predicted values from the model), and also that the differences between observed and predicted values are in the range of ±5%. These indicate that experiments were well-conducted and the results have no significant error.
Keywords: TiO2-SiO2 ; Sorption; Heavy metals; Ni2+ ; Cd2+ ; Statistical design
Extraction of cobalt (II) and nickel (II) by a solvent impregnated resin containing bis(2,4,4-trimethylpentyl)monothiophosphinic acid by F. T. Mu; Q. Jia; Y. M. Tian; Q. K. Shang (pp. 31-36).
In the present work, studies have been conducted on the equilibrium distribution of cobalt (II) and nickel (II) between aqueous hydrochloric solution and macromolecular resin impregnated with bis(2,4,4-trimethylpentyl)monothiophosphinic acid (Cyanex302, HL). Effects of extraction time, pH values, metal ion concentration, and temperature were investigated. Analysis of the results shows that the extraction of the two metal ions can be explained assuming the formation of metal complexes in the resin phase with a general composition ML 2. An extraction reaction is proposed and the equilibrium constants of the complexes were determined. The Freundlich isotherm and thermodynamic quantities, i.e., ΔG, ΔH and ΔS were also obtained. Both of the extraction reactions of cobalt (II) and nickel (II) are endothermic ones. The efficiency of the resin in the separation of cobalt (II) and nickel (II) is provided according to the separation factors. Under the experimental conditions employed, pH50 values for cobalt (II) and nickel (II) are 3.76, 5.01, respectively. The logarithmic value of separation factor was calculated as 2.50.
Keywords: Extraction; Cobalt; Nickel; Solvent impregnated resin; Bis(2,4,4-trimethylpentyl)monothiophosphinic acid
Application of the LBET class models to describe the structure of microporous activated carbons on the basis of argon and benzene adsorption isotherms by Mirosław Kwiatkowski (pp. 37-53).
The reported research is concerned with the properties of the new LBET class models designed to describe the heterogeneous adsorption on microporous carbonaceous materials. In particular, the new adsorption models were applied to a computer analysis of the microporous structure of two active carbons on the basis of argon and benzene adsorption isotherms. This paper provides for more thorough information on the properties of the proposed models and identification technique presented in the earlier papers.
Keywords: Adsorption; Modeling; Activated carbon; Micropores; Adsorption isotherms
Adsorption of metal anions of vanadium(V) and chromium(VI) on Zr(IV)-impregnated collagen fiber by Xue-Pin Liao; Wei Tang; Rong-Qing Zhou; Bi Shi (pp. 55-64).
The metal anions of vanadium (V) and chromium (VI) in aqueous solution can be effectively adsorbed by Zr(IV)-impregnated collagen fiber (ZrICF). The maximum adsorption capacity of V(V) takes place within the pH range of 5.0 to 8.0, while that of Cr(VI) is within the pH range of 6.0 to 9.0. When the initial concentration of metal ions was 2.00 mmol L−1 and the temperature was 303 K, the adsorption capacity of V(V) on Zr-ICF was 1.92 mmol g−1 at pH 5.0, and the adsorption capacity of Cr(VI) was 0.53 mmol g−1 at pH 7.0. As temperature increased, the adsorption capacity of V(V) increased, while that of Cr(VI) was almost unchanged. The adsorption isotherms of the anionic species of V(V) and Cr(VI) can be fit by the Langmuir equation. The adsorption rate of V(V) follows the pseudo-first-order rate model, while the adsorption rate of Cr(VI) follows the pseudo-second-order rate model. Furthermore, ZrICF shows high adsorption selectivity to V(V) in the mixture solution of V(V) and Cr(VI). Practical applications of ZrICF could be expected in consideration of its performance in adsorption of V(V) and Cr(VI).
Keywords: Zr(IV); Collagen fiber; Adsorbent; Vanadium(V); Chromium(VI); Metal anion; Adsorption
Synthesis and characterization of superparamagnetic poly(urea-formaldehyde) adsorbents and their use for adsorption of flavonoids from Glycyrrhiza uralensis Fisch by B. Zhang; J. M. Xing; H. Z. Liu (pp. 65-72).
Superparamagnetic spherical poly(urea-formaldehyde) (PUF) adsorbents were synthesized and their selective adsorption for licorice flavonoids was investigated in this paper. The magnetite (Fe3O4) nanoparticles were prepared by co-precipitation of ferrous and ferric salts. Then the magnetic adsorbents with PUF shell were synthesized by reversed phase suspension polymerization. The spherical adsorbents have an average diameter of 50 μm and exhibit superparamagnetic characteristics. The saturation magnetization of the adsorbents was 15.1 emu/g. The sorption and desorption properties of licorice flavonoids on the adsorbents were studied. The result shows that the adsorbents have high adsorption capacity (about 16.7 mg/g (adsorbent)). The adsorption data of flavonoids generally obeys the Langmuir isotherm equation. The adsorption can reach equilibrium rapidly and depends strongly on the pH of the feed solution. The concentration of licorice flavonoids after desorption can reach 25.12% in the desorbed fraction with 75% ethanol solution, which is higher than the 21.9% of commercial macroporous resin XDA-1. HPLC showed that liquiritin, one of main flavonoids in the licorice, was retained in this fraction, while glycyrrhizic acid (GA) can be almost removed from this fraction.
Keywords: Superparamagnetic adsorbent; Poly(urea-formaldehyde); Glycyrrhiza uralensis Fisch; Flavonoids; Liquiritin; Glycyrrhizic acid; Adsorption; Desorption
Adsorption kinetics for arsenic removal from aqueous solutions by untreated powdered eggshell by I. A. Oke; N. O. Olarinoye; S. R. A. Adewusi (pp. 73-83).
The batch removal of arsenic from aqueous solution using low-cost adsorbent (powdered eggshell) under the influences of initial arsenic ion concentrations (0.50 to 1.50 mg/L), pH (3.2 to 11.5) and particle size of eggshells (63 to 150 μm) were investigated. Eggshells were collected from Obafemi Awolowo University, Ile-Ife, washed with distilled water, air dried, ground into powder and sieved into different sieve sizes using British standard sieve. Powdered eggshells were stored in a desiccator for use. Adsorption isotherms and dynamics of arsenic onto PES were studied. The study revealed that there was a slight reduction in the rate of adsorption of arsenic ion onto the larger particle size, but adsorption capacity and parameters were unaffected. Powdered eggshell with particle size of 63 μm removed up to 99.6% of the 1.5 mg/L of arsenic ion in synthetic water within the first 6 hours but decreased to 98.4% and 97.4% when the powdered eggshell particle sizes were increased to 75 and 150 μm respectively. The pH optimum for arsenic removal was 7.2. The adsorption isotherms and adsorption dynamic kinetic studied through the use of graphical method revealed that Freundlich, activated sludge adsorption and pseudo second-order kinetic models correlate significantly with the experimental data with correlation coefficient of not less than 0.964.
Keywords: Arsenic; Adsorption kinetics; Low-cost adsorbents; Solution; Adsorption isotherms
Adsorption of Cr(VI) using activated neem leaves: kinetic studies by B. V. Babu; S. Gupta (pp. 85-92).
In the present study, adsorbent is prepared from neem leaves and used for Cr(VI) removal from aqueous solutions. Neem leaves are activated by giving heat treatment and with the use of concentrated hydrochloric acid (36.5 wt%). The activated neem leaves are further treated with 100 mmol of copper solution. Batch adsorption studies demonstrate that the adsorbent prepared from neem leaves has a significant capacity for adsorption of Cr(VI) from aqueous solution. The parameters investigated in this study include pH, contact time, initial Cr(VI) concentration and adsorbent dosage. The adsorption of Cr(VI) is found to be maximum (99%) at low values of pH in the range of 1-3. A small amount of the neem leaves adsorbent (10 g/l) could remove as much as 99% of Cr(VI) from a solution of initial concentration 50 mg/l. The adsorption process of Cr(VI) is tested with Langmuir isotherm model. Application of the Langmuir isotherm to the system yielded maximum adsorption capacity of 62.97 mg/g. The dimensionless equilibrium parameter, R L, signifies a favorable adsorption of Cr(VI) on neem leaves adsorbent and is found to be between 0.0155 and 0.888 (0<R L<1). The adsorption process follows second order kinetics and the corresponding rate constant is found to be 0.00137 g/(mg) (min).
Keywords: Adsorption; Batch studies; Neem leaves; Kinetics; Isotherms
Modification of activated carbon porosity by pyrolysis under pressure of organic compounds by Juan Alcañiz-Monge; M. José Illán-Gómez (pp. 93-100).
Co-pyrolysis at relatively low temperature (673 K) and high pressure (10 MPa), using three organic compounds, was used to modify the porosity of the two ACs. The co-pyrolysis is effective for the modification of the porosity of an AC, and the efficiency depends on the organic compound used. The differences found are consequence of the chemical composition of the organic precursor. High pressure pyrolysis produces beneficial results when an organic compound that volatilizes during the preparation is used. Conducting pyrolysis at low temperature permits improved control of the porosity because the rate of gasification can be more tightly controlled.
Keywords: Activated carbon; Microporosity
Theoretical analysis of the adsorption of metal ions to the surface of melanin particles by Maria Grazia Bridelli; Pier Raimondo Crippa (pp. 101-109).
We have re-examined the problem of the interaction of melanins with metal ions. Metal ions are normal constituents of the pigment, but in some cases they can be related to pathologies, mainly at the level of the skin (Cu2+ and Fe3+) and of the central nervous system (Fe2+ and Mn2+). Our approach has been based on the mechanisms of adsorption on the particle surface, by the use of theoretical adsorption isotherms and kinetic models. Although this analysis doesn’t give detailed information on the specific sites involved, it is useful to better characterize the surface behaviour of the colloidal melanin. The results obtained demonstrate that the affinity of melanin for metal ions is very high, comparable to the most efficient materials employed in decontamination and recovery techniques. Moreover, our results demonstrate that three-parameters models, such as Langmuir-Freundlich, Redlich-Peterson and Tóth equations, fit the experimental data with great accuracy and that the adsorption follows pseudo-second-order kinetics.
Keywords: Synthetic melanins; Adsorption isotherms; Adsorption kinetics; Surface structure; Microporosity
Adsorption of Cr (VI) by treated weed Salvinia cucullata: kinetics and mechanism by Saroj S. Baral; Surendra N. Das; Gautam Roy Chaudhury; Pradip Rath (pp. 111-121).
In the present study a new low cost, easily available and environmentally friendly adsorbent was used for removal of Cr (VI). The Cr (VI) removal efficiency of the adsorbent was studied as a function of contact time, pH, adsorbent dose, adsorbate concentration, temperature and stirring speed. Different adsorption model equations for kinetics, isotherm and rate mechanism of the process were used to find the best model, which fit well to the experimental data. A full factorial design of nk type was used to find a mathematical relation between the percentage of adsorption and variables affecting the adsorption process such as time, pH, adsorbate concentration and temperature. Using the Students ‘t’ test, the significance of each term of the derived equation was tested. The insignificant terms were removed from the derived equation. The adequacy of the equation after removing the insignificant terms was tested using the Fisher adequacy test. From the factorial design analysis it is found that pH has the most pronounced effect followed by time, temperature and the adsorbate concentration. A column study was performed using the optimum operating conditions.
Keywords: Cr (VI) removal; Waste water treatment; Kinetics; Isotherm; Rate mechanism; Factorial design; Column studies
The kinetics of ethanol adsorption from the aqueous phase onto zeolite NaZSM-5 by B. Adnađević; Z. Mojović; A. Abu Rabi (pp. 123-131).
The kinetics of the isothermal adsorption of ethanol from an aqueous solution onto a hydrophobic zeolite of the NaZSM-5 type in the temperature range 298–333 K was investigated. Specific shape parameters of the adsorption degree curves were determined. The changes in the specific shape parameters of the adsorption degree curves with temperature were determined. The kinetic parameters of ethanol adsorption (Ea,ln A) were determined by the initial rate, the saturation rate and the maximum rate methods as well as from the Johnson, Mehl and Avramy equation. The kinetic model of ethanol adsorption kt=[1−(1−α)1/3] was determined by the “model fitting” method. Ethanol adsorption from aqueous solution onto NaZSM-5 is a kinetically controlled process limited by the rate of three-dimensional movement of the boundary layer of the adsorption phase. A model for the mechanism of ethanol adsorption onto NaZSM-5 is suggested on the basis of the kinetic model. Ethanol molecules in aqueous solution are associated in clusters. The activation energy of the adsorption process corresponds to the energy required for the detachment of an ethanol molecule from a cluster and its adsorption onto the zeolite.
Keywords: Kinetics; Ethanol; Aqueous phase; NaZSM-5
Near-critical adsorption of CO2 on 13X zeolite and N2O on silica gel: lack of evidence of critical phenomena by Ronny Pini; Stefan Ottiger; Arvind Rajendran; Giuseppe Storti; Marco Mazzotti (pp. 133-141).
The excess adsorption of CO2 on 13X zeolite and of N2O on silica gel has been studied at high pressure using a magnetic suspension balance, i.e. a gravimetric method. Recently, a detailed study on the density distribution in the measuring cell of the magnetic suspension balance showed that a proper approach to thermostatting the unit should be used in order to obtain reliable and accurate excess adsorption measurements. This is particularly important in the vicinity of the critical point of the fluid, where the density is strongly dependent on pressure and temperature. In the past, several effects were observed in our laboratory when measuring near-critical adsorption on 13X zeolite and on silica gel, namely critical adsorption and critical depletion. In the present study, these effects have been checked using the balance in the new thermostatting configuration, and the conclusion can be drawn that the accuracy of the measurement is not sufficient to prove that they indeed occur. More accurate adsorption data for the two systems have been measured and reported.
Keywords: Supercritical adsorption; Gravimetric method; Carbon dioxide; Nitrous oxide; 13X zeolite; Silica gel
Binary chromatographic retention times from perturbations in flowrate and composition by Mark J. Heslop; Bryan A. Buffham; Geoffrey Mason (pp. 143-155).
This work is a theoretical and experimental investigation of the binary retention time (t step) when the disturbance is made to a chromatographic system by adding a small flow of one of the pure components. The established theory is for addition of a pulse: in this case, the retention time (t pulse) depends on the two binary isotherm gradients, and should be independent of the choice of pulse gas. From the column material balance, the value of t step also depends on the column pressure drop and perturbation gas—the value of t step should always be greater for the more-adsorbed component. The theory has been validated from results on the nitrogen–argon–5A zeolite system at 25, 54 and 81 °C. For a 50% mixture at 25 °C with a column pressure drop of 0.1 bar, the values of t step are 257 and 254 seconds for the nitrogen and argon perturbations. The values of t step are different because addition of the perturbation flow causes a very small increase in average column pressure (about 0.5 mbar), which causes the binary isotherm gradients to be measured in (slightly) different directions along the isotherm surface. The intention is to determine the value of t step for the case of a zero change in the average column pressure: experimentally, this would require a column with a zero pressure drop. The material balance shows that t step for a column with a zero pressure drop is obtained from a simple weighted function of the values of t step for the two pure-component perturbations. Accurate determination is essential because the “zero pressure drop” values are used to determine binary adsorption isotherms which are, of course, at a fixed pressure.
Keywords: Binary adsorption; Retention time; 5A zeolite; Column pressure drop