7316
J. Phys. Chem. C 2009, 113, 7316–7321
Development of Anion Stereoselective, Activated Carbon Molecular Sieve Electrodes Prepared by Chemical Vapor Deposition Malachi Noked, Eran Avraham, Yaniv Bohadana, Abraham Soffer, and Doron Aurbach* Department of Chemistry, Bar-Ilan UniVersity, Ramat-Gan, 52900 Israel ReceiVed: December 21, 2008; ReVised Manuscript ReceiVed: March 12, 2009
The electrochemical properties of nanoporous, activated carbon cloth electrodes in NaCl and NaNO3 solutions were investigated before and after carbon chemical vapor deposition (CVD) on the high surface area of nanoporous carbon samples. Different CVD reagents, temperatures, and pressures were employed. We achieved a sharp ion sieving effect for CDV-treated carbon samples/electrodes by selecting a given CVD reagent (namely, benzene) and a temperature that was too low to affect chemical decomposition of benzene in the gaseous phase, but sufficiently high to enable its decomposition on the outer surface of the carbon substrate, to form surface carbon deposits. The electroadsorption stereo selectivity achieved by optimized CVD treatment was so sharp that clear discrimination could be obtained even between anions of very similar dimensions, such as Cl- and NO3-. Here, the nitrate behaves as the smaller entity since, being a planar ion, it fits better into the carbon micropores known to have slit-shaped pores. The CVD treatment affects mainly the mouths of the pores and not their interior/volume. This was proven by adsorption experiments. From the gas phase, the stereoselectivity obtained by these CVD treatments was also demonstrated by discrimination between the adsorption of CO2 and N2 into the CVD-treated activated carbon. Introduction Partial and well-controlled burnoff of carbons by oxidants develops porosity, which typically falls within the micropore (99%), magnesium chloride, and MTBE were purchased from Frutarom Israel. The surface area of the samples was analyzed using an Autosorb-1 MP (Quantachrome, USA, Boynton Beach, Florida) by measuring N2 and CO2 adsorption isotherms at 77 and 273.2 K, respectively. Total pore and micropore volume and the average diameter were obtained, as well. The specific surface area was calculated using the BET model for the N2 adsorption isotherms. The micropore volume and micropore surface area were determined using the Dubunin-Radushkevich (DR) equation for CO2 adsorption isotherms. The use of different models is needed here because of the different P/P0 relations of the isotherms related to the adsorption processes of the two gases. In both cases, pore-size distribution was determined by the DFT model. Adsorption kinetics measurements from the gas phase into activated carbon samples were carried out using a standard vacuum system consisting of high-vacuum pumps, a main vacuum line with vacuum gauges, and a gas manifold for the supply of different gases and vapors. The adsorption kinetics for CO2 and MTBE was measured at 195 K and for N2 and O2 at 77 K. The equilibrium pressures for CO2, N2, O2, and MTBE were 285, 330, 93, and 150 Torr, respectively. Electrochemical measurements were carried out with simple three-electrode cells using a PGSTAT Autolab electrochemical measuring system from Ecco Chemie, Inc., The Netherlands. Cyclic voltammograms for assessing the EDL capacitance of the carbon cloth electrodes before and after CVD were measured at 1 mV/s within the potential range of -0.5 to 0.5 V vs a reference saturated calomel electrode. Due to the natural wetting problems of the hydrophobic CVD-treated carbon electrodes, the electrodes were dipped in solutions before the experiments. The solution was brought to boiling for a few minutes. This treatment removed all the air trapped in the pores and allowed a very good wetting of the porous activated carbon. The CVD processes were carried out by the decomposition of the organic precursor at high temperature (gas phase) in a tubular cell that contained the carbon sample, which led to the deposition of the carbon layers on the sample. In the case of benzene as the CVD reagent, nitrogen was used as the vapor carrier of the benzene in a standard vacuum system. Liquid benzene vapor pressure was kept low by an ice bath, and nitrogen was bubbled through it at a flow rate of 25 mL/min on the way to the CVD tubular cell that was placed in a tubular furnace that controlled the CVD temperature. Preliminary experiments had shown that CVD at too high temperatures (>900 °C) led to impervious carbon deposits that were too stable to enable back-activation for the fine manipulation of the pores’ size. We found an optimal temperature that allowed the completion of the CVD process which affected properly the pores’ size in less than 2 h.
7318 J. Phys. Chem. C, Vol. 113, No. 17, 2009
Figure 1. Comparison of pressure vs temperature dependence of known doses of methane and propene as CVD precursors in the vacuum system used in this work. Nitrogen served as an ideal gas reference. The measurements were carried out in the presence and absence of activated carbon samples in the system. Deviation of the precursors’ behavior from that of nitrogen occurred when its decomposition and following carbon deposition begin: insertion of a typical pressure vs temperature behavior of benzene vapor as the CVD precursor in the vacuum system used herein, in the presence of an activated carbon sample.
Results and discussion General. A clear discrimination between the adsorption of ions with similar dimensions (in electrochemical measurements) and the selective adsorption of molecular probes in the gas phase was achieved using molecular sieve, activated carbon substrates/ electrodes prepared by a controlled carbon CVD process on the surface of samples of the activated carbon cloth precursor used herein. Ion sieving effects were clearly observed by voltammetric measurements of electrodes comprising this carbon. The molecular sieving effect was also demonstrated by the adsorption kinetics of gas molecules used as molecular probes. On the Optimization of the CVD Process. Fixed doses of the CVD reagent were used for the formation of a carbon layer on the activated carbon samples at different measured temperatures. The onset of the CVD process was detected by an increase in pressure (above the reference value) due to the decomposition of the reagent when the temperature applied was sufficiently high. The reference pressure was obtained by measuring the behavior of nitrogen in the system, which demonstrated an ideal gas behavior. For recording the effect of the pyrolysis of the CVD reagent, the pressure-temperature curve for nitrogen was subtracted from that of the CVD reagent. The pressure-temperature response was measured with and without carbon samples, and as expected, the behavior of the CVD reagent was found to depend on the presence of the carbon cloth sample in the system (Figure 1). The pyrolysis occurred at lower temperatures in the presence of the carbon samples. These phenomena may be due to the catalytic influence of the carbon substrates on the thermal decomposition of the CVD reagent and the subsequent carbon deposition, as already suggested (e.g., related to the large surface area of the activated carbon sample, available for decomposition).25 The temperature at which the pyrolysis occurs only in the presence of carbon samples (but not at all in the empty tube) was chosen as the temperature at which the CVD process was carried out. As demonstrated by the following results, this process deposits carbonaceous species mainly on the mouths of the pores of the activated carbon surface, which gradually blocks the entrance of the pores of the activated carbon, leaving it with a narrow pore-size distribution with molecular sieving properties. It is shown later that the CVD process does not decrease the overall surface area of the activated carbon and the micropore volume,
Noked et al. because it takes place mainly on the outer area of the porous carbon (i.e., on the entrance walls and on the surface around the pores’ mouths). To develop highly selective, molecular sieve-activated carbon electrodes, the size of the mouths of the pores has to be between the size of the ions that need to be separated. The size of the precursor determines the size of the pore’s mouth, and therefore, it needs to be close to the size of the relevant hydrated28 ions. In the present work, we managed to develop carbon molecular sieve electrodes that can discriminate between Cl- and NO3ions, the sizes of which differ from each other on a subAngstrom scale. It is hard to determine by conventional methods which one is bigger. Although it is obvious that the equatorial N-O distance in the planar NO3- is larger than Cl-, water molecules that hydrate NO3- can approach the nitrogen atom closely, so that the overall size of hydrated NO3- ions may be smaller than the size of hydrated Cl- ions.37 According to Eliad et al.,28 the thickness of NO3- ions is indeed smaller than that of Cl- ions (detected through the higher EDL capacitance of activated carbon electrodes in solutions containing nitrates, as compared to chlorides). In any event, the diameter of chloride ions and the thickness of nitrate ions is around 3.2-3.3Å,37and thereby, it is a challenge to discriminate between them by electroadsorption processes. To control the thickness of the carbon CVD layer on top of the outer surface of the carbon fibers used herein, the precursor needs to be a molecule with low reactivity,25,26 such as an aromatic compound or methane. We assume that if too reactive vapor deposition precursors will be used, intermediates that have various dimensions and shapes may be formed, resulting in the formation of deposited layers with irregular structure and morphology. Hence, it will not be possible to achieve the goal of this work (i.e., to reliably control the selectivity of activated carbon electrodes). In the present work, we used benzene (3.7 Å thick26) as the precursor for the carbon CVD process. Benzene was chosen because its decomposition at high temperatures does not produce intermediate species (which may help the formation of uniform layers on the activated carbon substrates). The temperature range that was found to be suitable for the CVD process with benzene on the activated carbon electrode was between 700 and 800 °C. The thickness of the carbonaceous species deposited by the CVD process is smaller than the width of benzene molecules due to the fragmentation of benzene by the process, release of hydrogen, and cracking. The width and thickness of benzene molecules are determined by the length of both its C-C and C-H bonds. Hence, after release of hydrogen, the carbon rings and their fragments are, indeed, smaller than the pores’ width. (For comparison, the thickness of the graphite layer is only 3.3 Å), and hence, the dimensions of the carbonaceous species thus deposited are expected to be close enough to the size of the hydrated ions. Thereby, the relative size of the pores’ mouths, the deposited carbon species, and the entering ions enable carbon samples that demonstrate clear molecular sieving effects to be obtained. The carbon deposits are the thickest around the pores’ mouths, and they become thinner within the pores (as a function of distance from the pore’s mouth). However, even at the surface, the thickness of the carbon layer deposited does not exceed 1 nm in the temperatures used herein. This is also true for prolonged CVD processes (150 min), as demonstrated by the HR-SEM measurements of these carbon samples before and after the CVD processes. 39 It is important to emphasize that there is no homogeneity issue in these CVD processes since the precursor is introduced to the activated
Activated Carbon Molecular Sieve Electrodes
Figure 2. Typical steady-state cyclic voltammograms (current density translated to specific capacity) measured with electrodes comprising the activated carbon before and after CVD processes with benzene during different periods (as indicated) in a 0.1 M MgCl2 probe solution at 1 mV/s.
carbon sample by filling the entire volume of the tubular cell with the precursor (benzene), which flows continuously during the entire CVD process. The Electrochemical Studies. The electrochemical behavior of activated carbon electrodes before and after the CVD processes was compared. A typical steady-state cyclic voltammogram of an electrode comprising the pristine (as received) activated carbon cloth in a 0.1 M MgCl2 solution is presented in Figure 2. This voltammogram shows the typical butterfly shape of the I (translated to specific capacitance)-vs-E response of an activated carbon electrode whose pores are wide enough to allow adsorption of both anions and cations at potentials positive and negative to the point of zero charge (PZC). The latter is the potential value at which the capacitive currents show minima. A series of activated carbon electrodes was prepared by the stepwise treatment of carbon CVD processes. Electrodes after CVD processes during different periods of time with benzene as the active reagent were tested in MgCl2, NaCl, and NaNO3 solutions. Figure 2, which shows the steady-state CV response of the activated carbon electrodes in MgCl2 solutions, demonstrates the development of selectivity toward the adsorption of Mg2+ ions due to the application of the CVD process during longer periods. MgCl2 solutions were used for demonstrating the gradual development of the molecular sieving behavior of these electrodes due to the stepwise application of the CVD treatment to the activated carbon electrodes because of the relatively large difference between the effective size of divalent Mg2+ cations (6-7 Å) and Cl- anions (3.2-3.3 Å). When such differences between the size of the ions in solutions exist, electrodes with molecular sieving properties are readily recognized by their triangular cyclic-voltammetric response (Figure 2). The molecular sieving behavior of these electrodes can be much less expressed with NaCl solutions in which the ions have a similar size (3.2-3.3 and 4 Å for Cl- and Na+, respectively).28,34 The cathodic currents (due to cation adsorption) exhibited by the CV curves in Figure 2 are, indeed, lower (i.e., develop a triangular shape) because the CVD process applied to the carbon was longer. However, as seen in Figure 2, the durations of these CVD processes were sufficiently short so that the adsorption of chloride ions to the electrodes at potentials positive to the PZC is not affected. After the application of the CVD process for 100 min, no adsorption of Mg2+ ions into these electrodes could be obtained. Figure 3 presents typical steady-state CVs of CVD-treated activated carbon electrodes in NaCl and NaNO3 solutions. The selectivity of these electrodes toward preferred nitrate ion adsorption at positive potentials is clearly evident: the EDL capacity of these electrodes related to anion adsorption at positive potentials (to the
J. Phys. Chem. C, Vol. 113, No. 17, 2009 7319
Figure 3. Typical steady-state cyclic voltammograms (current density translated to specific capacity) measured with activated carbon electrodes after a CVD process with benzene during 125 min in NaCl and NaNO3 0.1 M solutions at 1 mV/s, as indicated. The yellow voltammogram in this (very low current) was measured with an activated carbon electrode that underwent more prolonged CVD treatment (for 150 min) in a 0.1 M NaNO3 solution at 1 mV/s. The pores of the activated carbon seem to be completely closed for the adsorption of ions, due to the prolonged CVD process. Hence, there is no sign that any redox reaction can occur in these systems (activated carbon electrodes, aqueous solutions, chloride or nitrate salt solutions) within the potential domains studied herein.
PZC) is remarkably higher in nitrates than in chloride solutions. The stereo selectivity of these electrodes toward the electroadsorption of nitrate vs chloride was, indeed, achieved by treating the activated carbon with a controlled carbon CVD process. The electrochemical properties of the carbon CVD-treated electrodes are highly reliable and reproducible. Repeated experiments with highly reproducible results were performed. It is also evident from Figure 3 that the capacity for the adsorption of Cl- ions (which scarcely occurs) is still higher than that related to Na+ ion adsorption (which is negligible), although they are reported to be very close in size.19,28 It should be noted that this selectivity may be due not only to stereoselective adsorption, but also to the deposition of surface species with positive C-H dipoles by the CVD process. Such surface dipoles attract anions (and thus, may interact differently with nitrate or chloride ions) and repel cations.28 Thereby, the CVD-treated electrodes may not allow the entry of the Na+ ions into the blocked pores, while Cl- ion electroadsorption is hardly possible (as seen in Figure 3). Hence, the electrochemical data in Figure 3 show that sufficiently prolonged CVD treatment (e.g., for 125 min) forms molecular sieve, activated carbon electrodes that are selective to Cl- ions, but absorb NO3- ions. It is clear that the asymmetric CVs thus obtained (Figure 3) do not relate at all to any redox reactions of these electrodes, since the current peaks fall within the EDL potential range, far from the redox potentials of these solutions. The fact that no redox reactions take place in the potential domain that we relate to adsorption processes only is further demonstrated by the voltammogram of the “overtreated” carbon electrode presented also in Figure 3. As indicated, this figure shows the steady-state CV (in yellow) of an electrode covered by a CVD layer formed during 150 min (which is probably thick enough to block the pores). The yellow CV in Figure 3 demonstrates currents that are negligible over the entire potential range, including the potential range that shows a significant current for electrodes that underwent CVD processes for 125 min. Thus, the main factor that affects the electroadsorption activity of these systems is the morphology of the pores in the carbon electrodes in relation to the molecular dimension of the adsorbates. Adsorption Processes from the Gas Phase. The adsorption kinetics of different gaseous molecules onto activated carbon samples before and after CVD treatment for 125 min are presented in Figures 4 and 5 (N2, O2, CO2, and MTBE molecules). As seen in these figures, the initial adsorption rates for all the above
7320 J. Phys. Chem. C, Vol. 113, No. 17, 2009
Noked et al.
Figure 4. Comparison of the adsorption kinetics of MTBE and N2 onto pristine activated carbon samples.
Figure 5. Comparison of the adsorption kinetics of CO2, O2 and N2 into activated carbon samples before and after the CVD process with benzene, during 125 min.
molecular probes into pristine activated carbon samples are very high and, hence, indicate that all of these molecules enter quite easily into the pores of the pristine activated carbon. The specific amount of MTBE adsorbed into the pristine samples (Figure 4), which is smaller compared to that of CO2, O2, and N2, can be attributed to its high specific molar volume and not to any molecular sieving phenomena. Such behavior of voluminous molecules in absorption processes is typical of substrates containing microporous systems (the Gurvitsch rule).38 Figures 4 and 5 show that the treatment of the activated carbon samples by CVD with benzene (125 min) has a minor effect on CO2 and O2 adsorption. The adsorption of N2 is strongly affected (inhibited) by CVD treatment compared to that of O2 and CO2: the degree of N2 adsorption into these activated carbon samples decreased considerably due to CVD treatment. It appears that the results of these adsorption experiments from the gas phase correlate very well with the electrochemical data presented above. The CVD process that allows discrimination between NO3- and Cl- adsorption, despite their very close size, could do that only via a partial closure of the pores’ mouths. The selectivity observed can be explained by the formation of narrow and elongated pore mouths that could allow the entry of the flat-shaped NO3- ions, but block transport of the bulkier Cl- ions, as explained by the illustrations in Figure 6. CO2 and O2 also have an elongated shape, which may allow them to easily enter the narrow pore mouths formed by CVD treatment, whereas the bulky MTBE molecules can not enter through these narrow mouths. N2 molecules are bulkier than O2 and CO2 (see illustration in Figure 6), and thereby, their adsorption is slowed down due to the carbon’s treatment by the CVD process. Specific (BET) surface area and DFT pore distribution assessments of the activated carbon samples were first taken with N2 as the adsorbed gas. Figure 7 shows the adsorption isotherms of N2 at 77 K measured with activated carbon samples before and after CVD treatment (with benzene, 780 °C, 125 min). The isotherms in this figure are in line with the kinetic data for the N2 adsorption
Figure 6. An illustration of the pore morphology after treatment of the activated carbon by a CVD process with benzene and the impact (narrowing) of the pore mouths thus formed on the electroadsorption of various ions and gas molecules into the pores. (a) Pristine carbon; (b) the CVD-treated carbon with an emphasis on the surface morphological effect; (c) the molecular sieving effect on different moieties: (1) adsorbed gas molecules; (2) electroadsorbed ions from the solution phase.
Figure 7. Typical adsorption isotherms of N2 measured with pristine activated carbon at 77 K upon increasing and decreasing the gas pressure. The insert to this figure represents adsorption isotherm of N2 at 77 K into activated carbon samples after the CVD process with benzene for 125 min.
presented in Figure 5 and clearly demonstrate the effect of the CVD process on the pores’ morphology. These results support our suggestion that the pore mouths become narrow due to carbon deposition (surface impact only) that slows down adsorption, but does not prevent it, because the pore volume does not change too much. Due to the effect of the CVD treatment on the adsorption of nitrogen into the activated carbon, as described above, it was impossible to obtain a reasonable model for the pore size distribution of the CVD-treated samples by the N2 adsorption measurements. Thereby, a better probe molecule, namely CO2 (see Figures 5, 6 and related discussion), was used for modeling pore-size distribution, thus, comparing the carbon samples before and after the CVD processes. Figure 8 presents the adsorption isotherms (273 K) of CO2 into a pristine carbon sample and a sample after the CVD treatment. The difference between the adsorption isotherms of CO2 and N2 is very significant in the case of the CVD-treated samples, as demonstrated in Figures 7 and 8. The surface areas calculated for the pristine carbon from the adsorption isotherms of N2 and CO2 were 1250 and 1650 m2/g, respectively. This
Activated Carbon Molecular Sieve Electrodes
J. Phys. Chem. C, Vol. 113, No. 17, 2009 7321 smoothly adsorb CO2, but hardly, and slowly, adsorb nitrogen. The analysis of gas adsorption isotherms (mostly CO2) related to these carbons shows that the CVD processes do not significantly change the pore volume but, rather, change their openings (mouths). Hence, it was possible to conclude that the CVD process with benzene forms narrow, slit-shaped pore mouths that allow the easy adsorption of flat ions or molecules, such as NO3- or CO2. Hence, for even slightly more bulky (ball shape) moieties, such as Cl- ions or N2 molecules, the pore mouths thus formed are barriers that slow down, or even prevent, their penetration into the pores (the volume of which does not change significantly due to the CVD process). References and Notes
Figure 8. Adsorption isotherms of CO2 at 273 K measured with activated carbon samples before (pristine) and after a CVD treatment with benzene for 125 min.
Figure 9. Pore size distribution for the activated carbon samples before and after the CVD process with benzene (125 min) calculated from CO2 adsorption measurements using the DFT model.
difference is not too significant. However, the surface area of the CVD-treated carbons, which demonstrated such pronounced molecular sieving properties, as demonstrated above, was found to be strongly dependent on the adsorbate gas used. The surface area calculated from the N2 adsorption isotherms shown in the insert in Figure 7 was negligible, whereas the surface area calculated by the CO2 adsorption is 1300 m2/g. Highly important is the pore-size distribution calculated for the pristine activated carbon and the molecular sieving, CVD-treated carbon from CO2 adsorption measurements using the DFT model (see Figure 9). The similarity in the pore size distribution calculated for both carbons is striking and presents strong evidence that the CVD treatment indeed affects mostly the pore openings (mouths) and not their inner volume. These measurements and related calculations complete the picture and demonstrate the mechanism through which the molecular sieving properties of these carbons are obtained by carbon CVD treatments. Conclusion The preparation of molecular sieving carbon with highly specific properties was demonstrated by the application of carbon CVD processes to activated carbon, which possesses an opened pore system. By using benzene as the CVD reagent and choosing the appropriate temperatures and process duration, it was possible to obtain carbon electrodes that discriminate between the electroadsorption of NO3- and Cl- anions and, hence, can be used for the selective removal of nitrates from aqueous solutions without expending energy on Cl- ions’ (the main anions in salty water) electroadsorption. These carbons also demonstrated impressive selectivity regarding the adsorption of atmospheric gases. They
(1) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Pure Appl. Chem. 1985, 57, 603. (2) Kyotani, T. Carbon 2000, 38, 269. (3) Bird, A. J.; Trimm, D. L. Carbon 1983, 21, 177. (4) Kaneko, K.; Murata, K.; Shimizu, K.; Camara, S.; Suzuki, T. Langmuir 1993, 9, 1165. ´ lvarez, P.; Masa, F. J. (5) Garcı´a-Araya, J. F.; Beltran´a, F. J.; A Adsorption 2003, 9, 107. (6) Fritz, W.; Schl, E. U. Chem. Eng. Sci. 1981, 36, 721. (7) Park, S. J.; Jang, Y. S. J. Colloid Interface Sci. 2003, 261, 238. (8) Suzuki, M. Carbon 1994, 32, 4–577. (9) Conway, B. E. Electrochemical Supercapacitors; Kluwer Academic/ Plenum Publishers: New York, 1999. (10) Mayer, S. T.; Pekala, R. W.; Kaschmitter, J. L. J. Electrochem. Soc. 1993, 140, 446. (11) Farmer, J. C.; Fix, D. V.; Mack, G. V.; Pekala, R. W.; Poco, J. F. J. Electrochem. Soc. 1996, 143, 159. (12) Oren, Y.; Soffer, A. J. Appl. Electrochem. 1983, 13, 489. (13) Breck, D. W. Zeolite Molecular SieVes: Wiley: New York, 1974. (14) Barrer, R. M. Zeolites and clay minerals as sorbents and molecular sieVes; Academic Press: New York, 1978. (15) Ismail, A. F.; David, L. I. B. J. Membr. Sci. 2001, 193, 1. (16) Hsieh, H. P. Membr. Mater. Processes 1990, 84, 1. (17) Koresh, J.; Soffer, A. J. Chem. Soc., Faraday Trans.I 1980, 76, 2472. (18) Koresh, J.; Soffer, A. J. Chem. Soc., Faraday Trans I 1980, 76, 2507. (19) Koresh, J.; Soffer, A. J. Chem. Soc., Faraday Trans I 1981, 77, 3005. (20) Koresh, J.; Soffer, A. Sep. Sci. Technol. 1983, 18, 723. (21) Koresh, J.; Soffer, A. J. Chem. Soc., Faraday Trans. I 1986, 82, 2057. (22) Koresh, J.; Soffer, A. Sep. Sci. Technol. 1987, 22, 973. (23) Jones, C. W.; Koros, W. J. Carbon 1994, 32, 1419. (24) Centeno, T. A.; Fuertes, A. B. J. Membr. Sci. 1999, 160, 201. (25) Kawabuchi, Y.; Kishino, M.; Kawano, S.; Whitehurst, D. D.; Mochida, I. Langmuir 1996, 12, 4281. (26) Mochida, I.; Yatsunami, S.; Kawabuchi, Y.; Nakayama, Y. Carbon 1995, 33, 1611. (27) Verma, S. K.; Walker, P. L., Jr. Carbon 1990, 28, 175. (28) Eliad, L.; Salitra, G.; Soffer, A.; Aurbach, D. J. Phys. Chem. B 2001, 105, 6880–6887. (29) Kunwar Singh, P.; Malik, A.; Sinha, S.; Ojha, P. J. Hazard. Mater. 2008, 150, 626. (30) Mohan, D.; Kunwar Singh, P.; Sinha, S.; Gosh, D. Carbon 2005, 43, 1680. (31) Gileadi, E. Electrosorption. Gileadi, E., Ed.; Plenum Press: New York, 1967; Chapter 1. (32) Salitra, G.; Soffer, A.; Eliad, L.; Cohen, Y.; Aurbach, D. J. Electrochem. Soc. 2000, 147 (7), 2486. (33) Farmer, J. C.; Fix, D. V.; Mack, G. V.; Pekala, R. W.; Poco, J. F. J. Appl. Electrochem. 1996, 26, 1007–1028. (34) Avraham, E.; Bouhadana, Y.; Soffer, A.; Aurbach, D. J. Phys. Chem. C 2008, 112, 7385. (35) Knobeloch, L.; Salna, B.; Hogan, A.; Postle, J.; Anderson, H. EnViron. Health Perspect. 2000, 108, 7. (36) Nosengo, N. Nature (London) 2003, 425, 894. (37) Marcus, Y. Chem. ReV. 1988, 88, 1475. (38) Gurvitsch, L. J. Phys. Chem. Soc. Russ. 1915, 47, 805. (39) Noked, M.; Soffer, A.; Aurbach, D. Surface morphology of activated carbons that show molecular sieving effects, 2009. In preparation.
JP811283B
