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Adsorption of Ni(II) from Aqueous Solution Using Oxidized Multiwall Carbon Nanotubes


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Adsorption of Ni(II) from Aqueous Solution Using Oxidized Multiwall Carbon Nanotubes
Changlun Chen and Xiangke Wang*
Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei, 230031, Anhui, People's Republic of China

In this work, oxidized multiwall carbon nanotubes (MWCNTs) were used as a novel adsorbent for removing Ni(II) from aqueous solution. The adsorption of Ni(II) onto oxidized MWCNTs was studied as a function of contact time, pH, ionic strength, MWCNT concentration, and temperature. The results showed that Ni(II) adsorption onto MWCNTs is strongly dependent on pH and oxidized MWCNT concentration and, to a lesser extent, ionic strength. Kinetic data indicated that the adsorption process achieved equilibrium within 40 min and follows a pseudo-second-order rate equation. The adsorption data fit the Langmuir model and its linearized form well, together with thermodynamic data indicating the spontaneous and endothermic nature of the process. Results of a desorption study showed that Ni(II) adsorbed onto oxidized MWCNTs could be easily desorbed at pH <2.0. Ion exchange may be the predominant mechanism of Ni(II) adsorption on oxidized MWCNTs. Oxidized MWCNTs may be a promising candidate for concentration of heavy metal ions from industrial wastewater.
1. Introduction Nickel is a toxic metal ion present in wastewater. More than 40% of nickel produced is used in steel factories, in nickel batteries, and in the production of some alloys, which causes an increase in the Ni(II) burden on the ecosystem and deterioration of water quality.1 Wastewater dissolved or dispersed with Ni(II) is harmful, causing vomiting, chest pain, and shortness of breath.2 Various technologies exist for the removal of Ni(II), which include filtration, surface complexation, chemical precipitation, ion exchange, adsorption using activated carbon, electrode position, and membrane processing. Adsorption is considered one of the most attractive processes for Ni(II) removal from solution, since adsorbents are generally easy to handle and can be used for various situations without large apparatus.3 Carbonaceous materials such as activated carbon are the most commonly used adsorbents for water treatment. Increasingly stringent standards regarding the quality of drinking water have stimulated a growing effort in the exploitation of new highly efficient adsorbents. Carbon nanotubes (CNTs),4 a new form of carbon, have come under intense multidisciplinary study because of their unique physical and chemical properties. CNTs include single-wall (SWCNTs) and multiwall (MWCNTs) depending on the number of layers comprising them. Their unique electronic properties and structure have led to interest in their potential application as quantum nanowires, electron field emitters, catalyst supports, chemical sensors,5 and sorbents for hydrogen and other gas storages6-9 because of their highly porous and hollow structure, large specific surface area, light mass density, and strong interaction between carbon and hydrogen molecules. CNTs have been found an efficient adsorbent for dioxin: their sorption capacity is superior to that of activated carbon, which attributed to stronger interactions between dioxins and CNTs.10 Liu et al.11 reported that CNTs filled with gallium can be used as highly sensitive metal vapor sensors and absorbents, and that copper vapor not only can deposit into open CNTs but also can get
* To whom correspondence should be addressed. Fax: +86-5515591310. E-mail: xkwang@ipp.ac.cn.

into closed CNTs containing gallium through the tip caps of the closed CNTs. Li et al.12,13 reported that surface oxidized CNTs showed exceptional sorption capacity and high sorption efficiency for lead and cadmium removal from water. The earlier studies indicated that CNTs may be promising adsorption materials for use in environmental protection regardless of their high cost at present. The objectives of present work are (a) to investigate adsorption kinetics and to analyze experimental data with a pseudosecond-order rate equation; (b) to study the effect of pH, ionic strength, and MWCNT concentration on Ni(II) adsorption onto oxidized MWCNTs; (c) to investigate adsorption thermodynamic and isotherms and to analyze experimental data with the Langmuir and Freundlich models; (d) to study the desorption of Ni(II) from oxidized MWCNTs as a function of pH; and (e) to presume the adsorption mechanism. 2. Experimental Section Preparation and Oxidation of MWCNTs. MWCNTs were prepared by chemical vapor deposition (CVD) of acetylene in hydrogen flow at 760 °C using Ni-Fe nanoparticles as catalysts. (Fe(NO3)2 and Ni(NO3)2 were treated by a sol-gel process and calcinations to get FeO and NiO, and then deoxidized doubly by H2 to get Fe and Ni.14 Oxidized MWCNTs were prepared by oxidization with 3 M HNO3.15 Briefly, 400 mL of 3 M HNO3 including 2 g of MWCNTs was ultrasonically stirred for 24 h, filtered, rinsed with doubly distilled water until the pH reached about 6, dried overnight in an oven at 80 °C, and then calcined at 450 °C for 4 h. The catalyst Ni and Fe in oxidized MWCNTs were measured by ICP-MS, and the results showed that Ni and Fe were less than 0.01% and 0.03%, respectively. Transmission electron microscopy (TEM) showed that oxidized MWCNTs were 1-10 m long and 10-30 nm outer diameter (see Supporting Information, Figure S1). Using the N2-BET method, the specific surface area of the free, dried oxidized MWCNTs was found to be 197 m2g-1. Li et al.12,13 measured the surface area of MWCNTs and found that oxidized MWCNTs with HNO3 had a larger specific surface area than that of nonoxidized MWCNTs. The point of zero

10.1021/ie060791z CCC: $33.50 2006 American Chemical Society Published on Web 11/14/2006

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charge, pHpzc, i.e., the pH above which the total surface of the carbon is negatively charged, was measured at pH < 5. Acidic surface groups were determined by titration using the Boehm method.16 The main physicochemical characteristics of MWCNTs are summarized in Table S1. Preparation of Ni(II) Stock Solution. Ni(II) stock solution, 1000 mgL-1, was prepared as follows: Ni metal powder (purity > 99.9%) was dissolved in 10 mL of 3 M HNO3 and then transferred into a 100 mL vessel. The stock solution was diluted with doubly distilled water to obtain standard solutions with concentrations ranging from 2 to 20 mgL-1. Analysis. The concentration of Ni(II) was measured using an atomic absorption spectrophotometer. The adsorbed amount of Ni(II) was calculated from the difference between the initial concentration and the equilibrium one. Batch Adsorption Experiments. Duplicate batches were examined to prepare adsorption curves and to investigate the characteristics of the adsorption process, and analysis of duplicates indicated a precision better than (5%. First, adsorption kinetics was carried out to achieve the equilibrium time. Experiments were carried out at 291 ( 1 K using 200 mL of 150 mg of oxidized MWCNTs and 0.01 M KNO3 ionic strength and Ni(II) ion solution containing the desired concentration (6, 12, and 20 mgL-1) in a 500 mL conical flask. The preliminary studies indicated that the rate of Ni(II) adsorption onto MWCNTs is very fast and has no obvious effect on Ni(II) adsorption kinetics. A stirring rate of approximately 300 rpm was chosen in order to make MWCNTs homogeneously disperse in solution. At predetermined time intervals, stirring was briefly interrupted while 4 mL volumes of supernatant solutions were pipetted from the conical flask, and samples were filtered using 0.45 m membrane filters. The residual Ni(II) concentration in the aqueous solution was determined. Except when the pH effect was studied, all experiments were carried out at initial pH 6.55 ( 0.02, where the adsorption is significant but below the pH where metal hydroxide precipitation occurs. Speciation diagrams of Ni(II) ion at a concentration of 20 mgL-1 as a function of pH are given in the Supporting Information (Figure S2). Adsorption isotherms were investigated by using batch technique in polyethylene centrifuge tubes under ambient conditions at 291 ( 1, 303 ( 1, 313 ( 1, and 333 ( 1 K, respectively. The effects of pH, ionic strength, and MWCNT concentration were also investigated at 291 ( 1 K. The blank experiments demonstrated that the adsorption of Ni(II) on the test tube walls and membrane filters was neglected. The stock solutions of KNO3 and oxidized MWCNTs were preequilibrated for 2 h before the addition of Ni(II) stock solution. The samples were gently shaken for 24 h (which was enough to achieve equilibrium). The effect of pH on Ni(II) removal was studied from pH 3.5 to 8.5 by adding negligible volumes of 0.1 M HNO3 or KOH. The effect of ionic strength on Ni(II) adsorption was studied for nonfixed ionic strength, 0.01 M, and 0.1 M KNO3 solution. Batch Desorption Experiments. To investigate the desorption ability of adsorbed Ni(II) from oxidized MWCNTs, desorption experiments were carried out as follows: After the adsorption reached equilibrium at initial pH 6.55 and ionic strength 0.01 M KNO3, oxidized MWCNTs sorbing Ni(II) ions were separated from the suspension by using 0.45 m membrane filters and were slightly washed with doubly distilled water to remove unadsorbed Ni(II) ions on oxidized MWCNTs and then dried at 353 K. The achieved oxidized MWCNTs with adsorbed Ni(II) were dispersed in 200 mL of 0.01 M KNO3, and then

Figure 1. Effect of contact time on Ni(II) adsorption rate for various initial Ni(II) concentrations onto oxidized MWCNTs: experimental data and pseudo-second-order rate equation fit (pH 6.55 ( 0.02, I ) 0.01 M KNO3, m/V ) 0.75 gL-1, T ) 291 ( 1 K). Table 1. Kinetic Parameters of Ni(II) Adsorbed on Oxidized MWCNTs at Various Initial Ni(II) Concentrations pseudo-second-order Co(Ni(II)) (mgL-1) 6 12 20 qe 5.32 7.94 8.75 K 0.0561 0.0470 0.0464 R2 0.998 0.999 0.997

each 20 mL of suspension was removed to test tubes. The pH values of the solution were adjusted from 6.2 to 1.6 using 0.1 M HNO3. After 1 day of shaking, the Ni(II) released from oxidized MWCNTs was measured, and the desorption data were then obtained from the concentration of free Ni(II) in supernatant. 3. Results and Discussion Adsorption Kinetics. Figure 1 shows the effects of contact time and initial Ni(II) concentration on Ni(II) adsorption onto oxidized MWCNTs. The equilibrium was reached within 40 min for all concentrations of Ni(II) used in this study. This result was very interesting because equilibrium time is one of the parameters for economical wastewater treatment plant applications. The implication was that the material could be suitable for a continuous flow system. According to the above results, the shaking time was fixed for 24 h for the rest of the batch experiments to make sure that equilibriums were reached. To analyze the adsorption rate of Ni(II) onto oxidized MWCNTs, a pseudo-second-order rate equation was used to simulate the kinetic adsorption:17

t/qt ) 1/(2K′qe2) + t/qe

(1)

where K′ (gmg-1min-1) is the pseudo-second-order rate constant of adsorption, qt (mgg-1 of dry mass) is the amount of Ni(II) adsorbed on the surface of the adsorbent at time t (min), and qe (mgg-1of dry mass) is the equilibrium adsorption capacity. A linear plot of t/qt vs t (given in the Supporting Information, Figure S3) was achieved, and the K′ values calculated from the slopes and intercepts are summarized in Table 1. The correlation coefficients of the pseudo-second-order rate equation for the linear plots are very close to 1, which suggests that kinetic adsorption can be well described by a pseudo-second-order rate equation.

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Figure 2. Effect of MWCNT concentration on Ni(II) adsorption (Co(Ni(II)) ) 6 mgL-1, I ) 0.01 M KNO3, pH 6.55 ( 0.02, T ) 291 ( 1 K).

Effect of MWCNT Concentration and Acid Oxidization. Figure 2 shows an increase of the adsorption percentage of Ni(II) and a decrease of qe with the increase of MWCNT concentration. This phenomenon implied that the adsorption depended on the availability of binding sites. The oxidization treatment had evident impact on the MWCNT adsorption capacity for Ni(II). Figure 2 also shows that the adsorption capacity of oxidized MWCNTs was higher than that of as-grown MWCNTs. Oxidized MWCNTs had larger specific surface area than the untreated MWCNTs.12,13 The amorphous carbon, carbon nanoparticles, and catalyst particles introduced by the CVD preparation process were removed during the course of treatment using HNO3. It is known that oxidation of carbon surface can offer not only a higher specific surface area, but also a larger number of oxygen-containing functional groups, which increases the ion exchange capacity of carbon materials.18 The oxidization of MWCNTs with HNO3 can offer more hydrophilic surface structure and introduces adsorption oxygen-containing functional groups to the surface of nanotubes.15,19 In our earlier report,20 the Fourier transform infrared (FT-IR) studies of acid-treated MWCNTs indicated that this acid treatment generated functional groups on the MWCNTs: hydroxyl groups (3432 cm-1), carboxyl groups (1729 cm-1), carbonyl groups (1588 cm-1), etc. These functional groups are hydrophilic and MWCNTs are dispersed more easily in water. Effect of pH. The solution pH is one of the dominant parameters controlling adsorption. Ni(II) adsorption onto oxidized MWCNTs as a function of pH ranging from 3.5 to 8 is given in Figure 3. The removal of Ni(II) by oxidized MWCNTs was highly dependent on pH. The adsorption of Ni(II) increased from 10% (pH 3.5) to 80% (pH 8). Ni(II) is cationic below pH 8. The reaction scheme for hydroxide formation could be set out as below when the metal ion is supposed to be bivalent, M2+:21

Figure 3. Effect of pH on Ni(II) adsorption onto oxidized MWCNTs (Co(Ni(II)) ) 6 mgL-1, I ) 0.01 M KNO3, m/V ) 0.75 gL-1, T ) 291 ( 1 K).

the adsorption of Ni(II) ions on oxidized MWCNTs could be expressed by the following reactions:

2A-(s) + Ni2+(aq) T [(A-)2Ni2+](s)

(5)

mBH+(s) + Ni(OH)m2-m(aq) T [(BH+)mNi(OH)m2-m](s) (6)
The solution pH affected the surface charge of oxidized MWCNTs, the degree of ionization, and the speciation of the surface functional groups.22 The pHpzc of oxidized MWCNTs was <5. In the pH range lower than the pHpzc, the surface of oxidized MWCNTs became positively charged and Ni(II) ions could be hardly adsorbed on the surface of oxidized MWCNTs because the Ni(II) ions are hydrated cations. Therefore, the amounts of adsorbed Ni(II) ions were very small in the range of pH <5. It was obvious that hydrogen ions competed with Ni(II) ions on the adsorption sites. At lower pH, adsorption of hydrogen ions had apparent preponderance over that of Ni(II) ions, but at higher pH, more Ni(II) ions would be taken up. In conclusion, the increase in Ni(II) adsorption as the pH increases could be explained on the basis of a decrease in competition between protons and Ni(II) ions for the same adsorption sites and by the decrease in positive surface charge, which resulted in a lower electrostatic repulsion between the surface and Ni(II) ions. Effect of Ionic Strength. The ionic strengths of 0.01 and 0.1 M KNO3 and nonfixed ionic strength were chosen to investigate their effect on Ni(II) adsorption by oxidized MWCNTs. Figure 4 shows that Ni(II) adsorption by oxidized MWCNTs decreased with increasing ionic strength. This phenomenon could be attributed to two reasons: (1) Ni(II) ions form electrical double layer complexes with oxidized MWCNTs, which favored the adsorption when the concentration of the competing salt was decreased. This may indicate that the adsorption interaction between the functional groups of oxidized MWCNTs and Ni(II) ions was mainly of ionic interaction nature, which is in agreement with an ion exchange mechanism. (2) Ionic strength of solution influenced the activity coefficient of Ni(II) ions, which limited their transfer to oxidized MWCNT surfaces.22 Adsorption Thermodynamics. Figure 5 shows that the distribution coefficient, Kd (mLg-1), increased with a rise in temperature. Bikerman23 attributed this phenomenon to a negative temperature coefficient of solubility of solutes or a

M2+ T -M(OH)+ T -M(OH)20 T -M(OH)3- T ...

(2)

If the ionization of oxidized MWCNTs having acidic (A) and basic (B) surface sites follows the reaction schemes18

HA(s) T H+(aq) + A-(s) B(s) + H+(aq) T BH+(s)

(3) (4)

Ni(II) ions could be exchanged with ionized surface sites, and

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Figure 4. Effect of ionic strength on Ni(II) adsorption onto oxidized MWCNTs (m/V ) 0.75 gL-1, pH 6.55 ( 0.02, T ) 291 ( 1 K).

negative as expected for a spontaneous process under the conditions applied. The decrease in G° with the increase of temperature indicated more efficient adsorption at higher temperature. At higher temperature, ions are readily desolvated, and therefore their adsorption becomes more favorable. The positive values of entropy change (S°) reflect the affinity of oxidized MWCNTs toward Ni(II) ions in aqueous solutions and may suggest some structure changes in the adsorbents.24,25 Adsorption Isotherm Model Analysis. The final values of pH at adsorption equilibrium were measured, for initial pH 6.55 ( 0.02, for each isotherm. Results of measurements show that, for all initial Ni(II) concentrations, final pH was lower than initial pH with a value which decreases when the initial Ni(II) concentration and temperature increased (given in the Supporting Information, Figure S5). The decrease of pH may be due to a release of H+ ions and may indicate adsorption mechanism by ion exchange.20,26 The experimental data were regressively analyzed with the Langmuir and Freundlich models.27 The Freundlich model assumes that different sites with several adsorption energies are involved, and the Langmuir model assumes that there is no interaction between the adsorbate molecules and the adsorption is localized in a monolayer. The equations of the Langmuir and Freundlich adsorption models are expressed respectively by

qe ) Q0bCe/(1 + bCe) qe ) KCe1/n
Equations 9 and 10 can be rearranged as

(9) (10) (11) (12)

Ce/qe ) Ce/Q0 + 1/(Q0b) ln qe ) ln K + (1/n) ln Ce

Figure 5. Plot of distribution coefficient Kd vs temperature for Ni(II) adsorption onto oxidized MWCNTs (pH 6.55 ( 0.02, I ) 0.01 M KNO3, m/V ) 0.75 gL-1).

steep simultaneous decrease of real adsorption of solvent. The values of enthalpy, H°, and entropy, S°, were calculated from the slopes and intercepts of the plot of ln Kd vs 1/T (given in the Supporting Information, Figure S4) by using the equation

ln Kd ) S°/R - H°/RT

(7)

The Gibbs free energy, G°, of specific adsorption was calculated from the equation

G° )H° - TS°

(8)

where R (8.3145 Jmol-1K-1) is the ideal gas constant and T (K) is the temperature. Relevant data calculated from eqs 7 and 8 are tabulated in Table 2. It is evident that the values of H° were positive, i.e., endothermic. One possible interpretation of endothermicity of the enthalpy of adsorption was that ions such as Ni(II) were well solvated in water. In order for these ions to adsorb, they were to some extent denuded of their hydration sheath, and this dehydration process of ions needed energy. It was assumed that this energy of dehydration exceeded the exothermicity of the ions attaching to the surface. The removal of water molecules from ions was essentially an endothermic process, and it appeared that the endothermicity of the desolvation process exceeded that of the enthalpy of adsorption to a considerable extent. The Gibbs free energy change (G°) was

where Q0 (mgg-1) is the adsorption maximum; b, K, and 1/n are isotherm constants. The linearized Freundlich and Langmuir plots for Ni(II) are given in the Supporting Information (Figures S6 and S7, respectively). The slopes of the linearized Langmuir and Freundlich plots were used to calculate the adsorption constants (Table 3). From Table 3, higher correlation coefficients indicate that the Langmuir model fit the adsorption data better than the Freundlich model. Moreover, oxidized MWCNTs had a limited adsorption capacity; thus, the adsorption could be described better by the Langmuir model (Figure 6) than by the Freundlich model, as an exponentially increasing adsorption was assumed in the Freundlich model. Desorption of Ni(II) from Oxidized MWCNTs. Repeated availability is an important factor for an advanced adsorbent. Such an adsorbent not only possesses higher adsorption capability, but also shows better desorption property, which will significantly reduce the overall cost for the adsorbent. Figure 7 shows the Ni(II) desorption percentages with regard to solutions at various pH values. It was apparent that Ni(II) desorption increased with decreasing pH. About 9% of Ni(II) was desorbed from oxidized MWCNTs at pH >5.5, then increased sharply at pH < 5.0, and eventually reached about 93% at pH <2.0. These results show that the Ni(II) adsorbed by oxidized MWCNTs could be easily desorbed, and thereby oxidized MWCNTs can be employed repeatedly in heavy metal wastewater management. Furthermore, this recovery also indicates that ion exchange was involved in the adsorption mechanism. 4. Conclusion This preliminary study concerning the adsorption capacities of oxidized MWCNTs indicated great potential for the removal

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Table 2. Thermodynamic Parameters for Ni(II) Adsorption onto Oxidized MWCNTs -G° (kJmol-1) Co(Ni(II)) (mgL-1) H° (Jmol-1) S° (Jmol-1K-1) 120.75 104.99 81.47 72.09 67.09 T ) 292 K 35.12 30.54 23.70 20.97 19.52 T ) 303 K 36.57 31.80 24.68 21.84 20.32 T ) 313 K 37.78 32.85 25.50 22.56 20.99 T ) 333 K 40.19 34.95 27.12 24.00 22.34 4 8 12 16 20 14.93 13.04 6.45 4.62 4.07

Table 3. Parameters of the Langmuir and Freundlich Models at Various Temperatures Langmuir constants T (K) 291 303 313 333 Q0 (mgg-1) 8.77 9.43 9.52 9.80 b (Lmg-1) 0.84 0.99 1.27 1.75 R2 0.995 0.994 0.996 0.998 4.45 4.97 5.37 6.00 Freundlich constants K (mg1-1/nL1/ng-1) 1/n 0.26 0.25 0.23 0.21 R2 0.924 0.959 0.964 0.903

of heavy metal ions from aqueous solutions. The predominant ion exchange mechanism involving surface functional groups of oxidized MWCNTs was presumed. These preliminary results warrant further investigations using continuous flow processes. The most important factor currently limiting the use of CNTs in practical environmental protection applications is their high cost. Like most new materials, CNTs are expensive. Many methods of preparing CNTs have been used, including arc

discharge, laser ablation, and chemical vapor deposition (CVD), and each method has its advantages and defects. The two former methods can prepare CNTs of high quality, but their production quantities are relatively low. The third method (CVD) can produce CNTs in larger batches (despite containing a large number of defects), and is deemed to be a promising route to reduce the cost of CNTs in the future, which would increase the use of CNTs in environmental protection applications. Acknowledgment National Natural Science Foundation of China (Nos. 20677058, 20501019) and Centurial Project of Chinese Academy of Sciences, and the analysis of TEM from the Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, are gratefully acknowledged. Supporting Information Available: Figure S1 shows typical TEM images of oxidized MWCNTs. Figure S2 presents speciation diagrams of Ni. Figure S3 displays a test of the pseudo-second-order rate equation for adsorption of various initial Ni(II) concentrations on oxidized MWCNTs. Figure S4 presents a semilogarithmic plot of the distribution coefficient Kd vs reciprocal temperature for various concentrations of Ni(II) adsorption on oxidized MWCNTs. Figure S5 shows the change of final pH as a function of initial Ni(II) concentration and temperature. Figures S6 and S7 display the fitting lines of the Langmuir and Freundlich models to the adsorption data. Table S1 shows the main physicochemical characteristics of MWCNTs. This material is available free of charge via the Internet at http://pubs.acs.org. Literature Cited
(1) Ajmal, M.; Rao, R. A. K.; Ahmad, R.; Ahmad, J. Adsorption studies on citrus reticulate: removal and recovery of Ni(II) from electroplating wastewater. J. Hazard. Mater. B 2000, 79, 117. (2) Kadirvelu, K.; Senthilkumar, P.; Thamaraiselvi, K.; Subburam, V. Activated carbon prepared from biomass as adsorbent: Elimination of Ni(II) from aqueous solution. Bioresour. Technol. 2002, 81, 87. (3) Dabrowski, A. Adsorptionsfrom theory to practice. AdV. Colloid Interface Sci. 2001, 93, 135. (4) Iijima, S. Helical microtubules of graphic carbon. Nature (London) 1991, 354, 56. (5) Kong, J.; Franklin, N. R.; Zhou, C.; Chapline, M. G.; Peng, S., Cho, K.; Dai, H. Nanotube molecular wires as chemical sensors. Science 2000, 287, 622. (6) Ma, R.; Bando, Y.; Zhu, H.; Sato, T.; Xu, C.; Wu, D. Hydrogen uptake in boron nitride nanotubes at room temperature. J. Am. Chem. Soc. 2002, 124, 7672. (7) Kim, C.; Choi, Y. S.; Lee, S. M.; Park, J. T.; Kim, B.; Lee, Y. H. The effect of gas adsorption on the field emission mechanism of carbon nanotubes. J. Am. Chem. Soc. 2002, 124, 9906.

Figure 6. Ni(II) adsorption isotherms onto oxidized MWCNTs at various temperatures: experimental data and Langmuir model fit (pH 6.55 ( 0.02, I ) 0.01 M KNO3, m/V ) 0.75 gL-1).

Figure 7. Desorption of Ni(II) from oxidized MWCNTs adjusting pH of the solution using HNO3 solution (m/V ) 0.75 gL-1, T ) 291 ( 1 K).

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(8) Schlapbach, L.; Zuttel, A. Hydrogen-storage materials for mobile ¨ applications. Nature (London) 2001, 414, 353. (9) Hilding, J.; Grulke, E. A.; Sinnott, S. B.; Qian, D.; Andrews, R.; Jagtoyen, M. Sorption of butane on carbon multiwall nanotubes at room temperature. Langmuir 2001, 17, 7540. (10) Long, R. Q.; Yang, R. T. Carbon nanotubes as superior sorbent for dioxin removal. J. Am. Chem. Soc. 2001, 123, 2058. (11) Liu, Z. W.; Gao, Y.; Bando, Y. Highly effective metal vapor absorbents based on carbon nanotubes. Appl. Phys. Lett. 2002, 81, 4844. (12) Li, Y. H.; Wang, S. G.; Luan, Z. K.; Ding, J.; Xu, C. L.; Wu, D. H. Adsorption of cadmium(II) from aqueous solution by surface oxidized carbon nanotubes. Carbon 2003, 41, 1057. (13) Li, Y. H.; Wang, S. G.; Wei, J. Q.; Zhang, X. F.; Xu, C. L.; Luan, Z. K.; Wu, D. H.; Wei, B. Q. Lead adsorption on carbon nanotubes. Chem. Phys. Lett. 2002, 357, 263. (14) Colomer, J. F.; Piedigrosso, P.; Willems, I.; Journet, C.; Bernier, P.; van Tendeloo, G.; Fonseca, A.; Nagy, J. B. Pruification of catalytically produced multi-wall nanotubes. J. Chem. Soc., Faraday Trans. 1998, 94, 3753. (15) Rinzler, A. G.; Liu, J.; Dai, H.; Nikolaev, P.; Huffman, C. B.; Rodriguez-Macias, F. J.; Boul, P. J.; Lu, A. H.; Heymann, D.; Colbert, D. T.; Lee, R. S.; Fischer, J. E.; Rao, A. M.; Eklund, P. C.; Smalley, R. E. Large-scale purification of single-wall carbon nanotubes: process, product, and characterization. Appl. Phys. A: Mater. Sci. Process. 1998, 67, 29. (16) Boehm, H. P. Surface oxides on carbon. High Temp. High Press. 1990, 22, 275. (17) Benguella, B.; Benaissa, H. Cadmium removal from aqueous solutions by chitin: kinetic and equilibrium studies. Water Res. 2002, 36, 2463. (18) Shim, J. W.; Park, S. J.; Ryr, S. K. Effect of modification with HNO3 and NaOH on metal adsorption by pitch-based activated carbon fibers. Carbon 2001, 39, 1635. (19) Coleman, K. S.; Bailey, S. R.; Fogden, S.; Green, M. L. H. Functionalization of single-walled carbon nanotubes via the Bingel reaction. J. Am. Chem. Soc. 2003, 125, 8722. (20) Wang, X. K.; Chen, C. L.; Hu, W. P.; Ding, A. P.; Xu, D.; Zhou, X. Sorption of 243Am(III) to multiwall carbon nanotubes. EnViron. Sci. Technol. 2005, 39, 2856. (21) Kragten, J. Atlas of metal-ligand equilibria in aqueous solution; Ellis Horwood: Chichester, 1978. (22) Reddad, Z.; Gerente, C.; Andres, Y.; Cloirec, L. P. Adsorption of several metal ions onto a low-cost biosorbent: kinetic and equilibrium studies. EnViron. Sci. Technol. 2002, 36, 2067. (23) Bikerman, J. J. Surface Chemistry: Theory and Applications, 2nd ed.; Academic Press: New York, 1958. (24) Genc-Fuhrman, H.; Tjell, J. C.; Mcconchie, D. Adsorption of arsenic from water using activated neutralized red mud. EnViron. Sci. Technol. 2004, 38, 2428. (25) Altundogan, H. S.; Altundogan, S.; Tumen, F.; Bildik, M. Arsenic ˇ ˇ ¨ removal from aqueous solutions by adsorption on red mud. Waste Manage. 2000, 20, 761. (26) Kadirvelu, K.; Faur-Brasquet, C.; Le Cloirec, P. Removal of Cu(II), Pb(II), and Ni(II) by adsorption onto activated carbon cloths. Langmuir 2002, 16, 8404. (27) Atkins, P. W. Physical Chemistry; Oxford University Press: Oxford, 1978.

ReceiVed for reView June 21, 2006 ReVised manuscript receiVed October 3, 2006 Accepted October 5, 2006 IE060791Z

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