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Benzonitrile Adsorption on Fe-Doped Carbon Nanostructures A. L. Aguiar,† S. B. Fagan,*,‡ L. B. da Silva,‡ J. Mendes Filho,† and A. G. Souza Filho† Departamento de Fı´sica, UniVersidade Federal do Ceara´, CP 6030, CEP 60455-900, Fortaleza, CE, Brazil, A´rea de Cieˆncias Tecnolo´gicas, Centro UniVersita´rio Franciscano, CEP 97010-032, Santa Maria, RS, Brazil ReceiVed: April 11, 2010
In this work we report a first principles study of benzonitrile (BZN) interaction with pristine and Fe-doped single-walled carbon nanotubes (SWNTs), graphene, and C60. The results show that the BZN molecule weakly adsorbs on SWNTs, graphene, and C60 through π-π aromatic ring stacking. This interaction can be considerably strengthened by the inclusion of Fe atoms, which leads to a strong π-3d-π covalent bond linking the BZN to the carbon nanostructure. The calculated binding energy values suggest that the BZN molecule adsorption with Fe atoms is much stronger than those for Fe-SWNT, Fe-C60, or Fe-graphene interaction. Indeed, the BZN-Fe stability on each carbon nanostructure surface was studied and the SWNTs complexes are more stable than those of C60 and graphene. Introduction
Computational Details
Carbon nanostructures have been extensively studied in the last two decades. The physical-chemical properties of fullerenes (specially C60), single-walled carbon nanotubes (SWNTs), and graphene have opened up a new and rich research area in materials science with great potential for technological applications.1–3 In particular, carbon nanotubes and graphene have been considered candidate materials to be used as building blocks for future nanoelectronic devices at the molecular level.4,5 One of the more promising routes for obtaining new materials with tailored properties is through the association of carbon nanostructures with donor-acceptor molecules and/or by doping with individual atoms.6–11 In this perspective, the benzonitrile (BZN) is a bifunctional molecule that has an aromatic and a ciano (nitrile) group. It is a molecule with high dipole moment due to the high charge density around the nitrile group and it is a typical Lewis basis with one free electronic pair. Furthermore, this molecule is toxic and one of our purposes is to theoretically test the carbon nanomaterial interaction aiming to predict whether or not these materials could be used efficiently for BZN adsorption. Furthermore, it is not clear, from the experimental evidence, if the interaction between the aromatic compounds and SWNTs or C60 samples is entirely due to the direct adsorption of the molecule on the carbon surface or from some other kinds of interaction mechanisms that are involved.12 In this way, the purpose of this paper is to investigate how a transition metal (TM) atom can intermediate the BZN adsorption on SWNT, graphene, or C60 surface. The π orbitals play a fundamental role in the BZN adsorption on SWNTs, graphene, and C60 surface. It is well-known that the π-metal-π interaction is generally stronger than direct π-π interaction.13 In addition, a TM atom covering C60 and SWNT surfaces has been suggested as a catalyst or substrate for gas storage, chemical sensors, and filters14,15 and has been proposed as an alternative and efficient way for functionalizing carbon nanomaterials with many molecules.13
The BZN interaction with carbon nanostructures is evaluated through total energy calculations based on the solution of the Kohn-Sham (KS) equations within the framework of density functional theory.16 All calculations were done with use of SIESTA code, which performs fully self-consistent calculations expanding the KS orbitals with a linear combination of pseudoatomic orbitals for valence electrons.17 Additionally, we use the generalized gradient approximation (GGA) for all the studied systems when we describe the exchange-correlation term.18–20 In Fe-doped systems we have used spin polarized calculations due to the unpaired valence electron of the iron atom and the resulting complex. The norm-conserving pseudopotential is fitted by the Troullier-Martins method.21 For a better description of physical quantities, a high dense Brillouin zone sampling is necessary and the Monkhorst-Pack block was set to 1 × 1 × 10 and 5 × 5 × 1 for SWNTs and graphene systems, respectively, and 1 × 1 × 1 (only Γ point) for C60 nanostructures.22 A cutoff energy of 150 Ry was used to represent the charge density. The relaxed atomic configuration of the systems were obtained by using conjugated gradient techniques when the force was smaller than 0.05 eV/Å on each atom. For (5,5) [(8,0)] SWNT, we used five [three] unit cells with a total of 100 [96] atoms in the supercell with dimensions 25 × 25 × 12.37 [25 × 25 × 12.87] Å3. The lateral separation of 25 Å was used in x and y directions in order to ensure that tube images have no interaction in the xy plane. For graphene we use a twodimensional 7 × 7 array with a total of 98 atoms, and for the C60, a single molecule in a unit cell is set. The valence electrons of all systems were described by using a double-ζ pseudoatomic basis set including polarization functions (DZP). The range of those basis functions was controlled by the energy shift parameter, which was set to 0.05 eV.33 The binding energies were calculated as
* To whom correspondence should be addressed. † Universidade Federal do Ceara´. ‡ Centro Universita´rio Franciscano.
Eb ) - {E[A + B] - E[Aghost + B] - E[A + Bghost]} (1) where E[A+B] is the total energy of the A + B systems, where A and B can be SWNTs, graphene, C60, or BZN molecule. The
10.1021/jp103402s 2010 American Chemical Society Published on Web 05/26/2010
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J. Phys. Chem. C, Vol. 114, No. 24, 2010 10791 TABLE 1: Calculated ∆d, Binding Energy (Eb), and the Charge Transfer (∆Q) Values for BZN Molecule Adsorbed on Pristine SWNTs, Graphene, and C60a scheme
carbon nanostructure
∆d (Å)
Eb (eV)
∆Q (10-3 e-/C)
π-π (3) π-CN (2) π-π (3) π-CN (2) π-π (3) π-CN (1) π-π (4) π-CN (2)
(5,5) SWNT (5,5) SWNT (8,0) SWNT (8,0) SWNT C60 C60 graphene graphene
3.55 to 3.63 3.62 to 3.75 3.43 to 3.57 3.60 to 3.71 3.45 to 3.55 2.82 3.15 to 3.26 3.59 to 3.64
0.08 to 0.09 0.01 to 0.05 0.03 to 0.05 0.01 to 0.03 0.07 to 0.09 0.10 0.14 to 0.11 0.06
-0.1 +0.2 -0.1 +0.1 to +0.2 -0.1 +0.6 -0.1 +0.2
a
Figure 1. (a) BZN molecule interacting with pristine SWNTs and C60 in the “π-π” and “π-CN” configurations. The ∆d parameter is defined for each configuration. (b) Relaxed structures for the “π-π” configurations. Red and gray colors represent the carbon atoms for the BZN molecule and SWNTs or C60, respectively.
term E[Aghost+B](E[A+Bghost]) is the total energy of B (A) system plus A (B) basis wave functions. The label ghost indicates that corresponding system have no interaction potential with the other system. This method guarantees the elimination of basis set superposition error (BSSE). Results and Discussions I. BZN Adsorption on Pristine Carbon Nanostructures: SWNTs, Graphene, and C60. The interaction of BZN with SWNTs, graphene, and C60 was investigated in two geometries based on the approximation of its functional groups to the carbon ring. The configuration for which BZN axis is perpendicular to SWNT or C60 surface was called “π-CN” where the CN group is placed close to π orbitals of the carbon atoms. The other configuration is defined when the BZN axis is parallel to nanotubes, C60, and graphene surface and it was called “π-π” due to the approximation of aromatic rings of interacting systems (see Figure 1a). The total energy calculations were performed for three different configurations of BZN molecule for each studied SWNT in the “π-π” scheme by varying the angle between molecule axis and the tube axis and by displacement of the aromatic ring of the molecule along the tube surface. We defined the parameter ∆d as the distance between the cylindrical tube surface and the plane created by the rotational displacement of the molecule axis. In the “π-CN” scheme, we simulated two configurations for each SWNT. These configurations were based on placing the molecule axis toward the center of a hexagon, to a C-C bond, and to a carbon atom of the SWNT. The molecule axis stands parallel to the normal vector of the (5,5) or (8,0) nanotube surface. The ∆d parameter, for this case, stands for the distance between the N atom of the CN group and the tube surface (see Figure 1). The obtained results for the studied systems are summarized in Table 1. The ∆d values (as Table 1) vary from 3.43 (3.55) Å to 3.57 (3.63) Å for (8,0) ((5,5)) SWNT and 3.15 Å to 3.26 Å for graphene. The ∆d values for SWNTs (graphene) are slightly larger (smaller) than the distance 3.3 Å between the graphene layers in graphite also interacting through dispersive forces23 but they are in accordance with the benzene-SWNT distance reported in the literature.24,25 Indeed, the GGA exchange term has the tendency to overestimate the binding distances for almost
The values in parentheses in the first column stand for the number of configurations studied for each case and the represented value is the most stable one. The minus sign for charge transfer (electrons per carbon atom) means that the carbon system ((8,0) and (5,5) SWNTs, graphene, and C60) for all studied “π-π” (π-CN) schemes acts as a donor (acceptor) species.
all molecular systems. We observed that ∆d values obtained for the “π-CN” scheme are slightly higher than those for the “π-π” scheme for SWNTs and graphene. That behavior could be attributed by the fact the π-π stacking coupling would be more favorable. To support that assumption we calculated the binding energy of the BZN molecule on the tube surface (eq 1). The calculated binding energy fluctuates from 0.01 to 0.09 eV for both tubes (see Table 1). The BZN interacts weakly with SWNT and graphene for the “π-CN” scheme when compared with the “π-π” one. The calculated Eb values also show a slight preference for molecule adsorption on the metallic (5,5) over the semiconductor (8,0) SWNT. However, the values are very small when we compare them with those for the 25 meV room temperature thermal energy. So, those results can be negligible within a finite temperature environment. We have done extra calculations with these pristine systems using the Local Density Approximation (LDA)18 for the exchange functional and the binding energies were slightly increased up to 0.25 (0.40) and 0.12 (0.20) eV for the “π-π” and “π-CN” schemes, respectively, in SWNTs (graphene) indicating a weak interaction. The LDA approach is often used for weakly interacting systems such as these.26 Indeed, that binding energy overestimate is a wellknown signature for the LDA description. The GGA description was used aiming to compare the results discussed above with those in Fe-doped systems. An analysis of the electronic band structure shows that the electronic properties of (8,0) and (5,5) SWNTs are unperturbed by the presence of the BZN molecule close to their surface. No significant changes in the density of states (DOS) are observed near the Fermi level of the SWNTs, showing a superposition of the electronic states of SWNTs with those from the molecule which are located at about 2.0 eV from the Fermi energy (see Figure 2). For graphene, the results are very similar to those for SWNTs and they are not shown here. The results suggest that the interaction of BZN and pristine SWNTs is very weak and can be identified as a physisorption process. The interaction of BZN with pristine C60 molecules was also analyzed. The binding energy values reveal that the interaction of BZN with pristine C60 is also very weak, having values changing from 0.07 to 0.09 eV for the “π-π” scheme. We have not observed any preference of “π-π” interaction against “π-CN” one. The value found for this system in the “π-CN” scheme was 0.10 eV (which is higher than that for nanotubes in the same scheme) but differs from the “π-π” interaction at most by 0.01 eV, which is not reliable for comparing and
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Aguiar et al. TABLE 2: Relaxed Distances (∆d1 and ∆d2) and Charge Transfer between Studied Systems for BZN (∆QC) Adsorption on Fe-Doped (∆QFe) Carbon Nanostructuresa studied system BZN/Fe-(8,0) BZN/Fe-(5,5) BZN/Fe-C60 (6) BZN/Fe-C60 (5) BZN/Fe-graphene
∆d1 ∆d2 ∆QC ∆QBZN ∆QFe (Å) (Å) (10-3e-/C) (10-3e-/C) (10-3e-/C) 1.65 1.74 1.89 1.88 1.84
1.64 1.64 1.60 1.53 1.60
-3.4 -3.1 -3.0 -4.0 -2.2
-2.3 -2.2 -3.6 -4.8 -1.5
+5.7 +5.3 +6.6 +8.8 +3.7
a The plus sign for charge transfer (electron per carbon atom) means that the Fe atom plays the role of acceptor compound. The indices (5) and (6) refer to the system with iron atom in the center of the pentagonal or hexagonal site of C60, respectively. The values in parentheses in the second column hold for isolated Fe-doped systems.
Figure 2. The DOS for the studied systems sketched in Figure 1b are shown on the left. The plot of an isosurface of the total electronic charge density is shown in the right panels for these systems. The contour value used for these isosurfaces was 0.04 e/Å3.
Figure 3. The BZN molecule interacting with SWNTs, graphene, and C60 through Fe atomic intermediation. The definition of ∆d1 and ∆d2 parameters is also shown.
predicting favorable interacting configurations. The electronic molecular levels of C60 near the Fermi level (HOMO and LUMO) are unperturbed by the presence of the BZN molecule (see Figure 2) with hybridization of HOMO-1 and LUMO+1 levels of C60 and the HOMO and LUMO levels of the molecule. The last column of Table 1 also shows the charge transfer between those systems. Since the values are on the order of 10-3 per carbon atom, we can confirm that there is not enough charge transfer to modify significantly their electronic structures. In Figure 2 is also shown a 3D view of the charge density plot for most favorable arrangements of BZN interacting with carbon nanostructures, thus showing no charge density around the interstitial region between the adsorbed systems. II. BZN Adsorption on Fe-Doped Carbon Nanostructures: SWNT, C60, and Graphene. The results obtained in the previous section suggest that the interaction of the BZN molecule with pristine carbon nanostructures (SWNTs, C60, and graphene) is very weak. Hexahedral Fe doping on the SWNTs,
Figure 4. Charge density and spin density of electronic states (DOS) of Fe-doped (a) (8,0) SWNT, (b) (5,5) SWNT, and (c) C60(6) interacting with the BZN molecule. The bottom panels (red and blue lines) present the calculated DOS (majority and minority spins) for Fe adsorption on SWNTs/C60 and the black lines are the DOS for pristine carbon species for comparison. The middle panels are the DOS for BZN adsorption on Fe-doped SWNTs/C60 systems. For the contour plot the value used for the isosurfaces was 0.04 e/Å3.
graphene, and C60 surfaces has been intensively studied because this process leads to a more reactive shell through the formation of a hybrid system with characteristics of both entities.27–30 The presence of a transition metal atom (Fe, Ti, Mn, etc.) on the nanotube/graphene/C60 surface modifies significantly their electronic properties because of the hybridization of d orbitals from TM with p orbitals from the carbon systems and differs noticeably depending on the species involved. Then, in this work, we used those previous literature results for Fe-doped carbon systems. It was suggested that the most stable position of an Fe atom adsorbed on SWNTs and graphene surface is at the hexagonal center site.28,31 We extend this result for fullerene and we found similar relaxed structures of the Fe atom on the hexagonal and pentagonal center of C60. Our structural, electronic, and energetic results for Fe-doped carbon systems are in agreement with previous studies. Large binding energy values for the Fe-doped (8,0) SWNT (Eb ) 1.28
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TABLE 3: Binding Energy (Eb) Values for Relaxed Structures of BZN-Fe-SWNTs, BZN-Fe-C60, and BZN-Fe-graphenea binding scheme (1) (2) (3) (4)
f f f f
X ) (8,0) X ) (5,5) X ) C60(6)/ SWNT SWNT X ) graph C60(5)
X + (Fe/BZN) (X/Fe) + BZN (X/BZN) + Fe X + Fe + BZN
1.28 1.91 3.17 3.07
1.40 1.95 3.41 3.43
1.09/1.54 1.96/2.64 2.83/3.50 2.84/3.42
0.88 2.25 2.89 2.80
a The first column shows the binding schemes suggested for these complexes. All the binding energy values are represented in eV. The indices (5) and (6) correspond to the system with iron atom in the center of the pentagon or hexagon site of fullerene, respectively.
TABLE 4: Binding Energy (Eb) Values for BZN-Fe and X-Fe, Where X Holds for Carbon Structures (from ref 32)a binding scheme Eb(X-Fe) Eb(BZN-Fe)
X ) (8,0) X ) (5,5) X ) C60(6)/ C60(5) SWNT SWNT X ) graphene 1.16 1.79
1.48 2.02
0.88/0.78 1.75/1.88
0.55 1.91
a All the binding energy values are represented in eV. The indices (5) and (6) refer the system with iron atom in the center of the pentagon or hexagon site of C60, respectively.
eV) and (5,5) SWNT (Eb ) 1.37 eV), Fe-doped graphene (Eb ) 1.04 eV), and Fe-doped C60 (Eb ) 1.38 eV) confirm the covalent adsorption process.30,31 The adsorption of the BZN molecule on Fe-doped SWNTs, C60, graphene, and the complexes BZN-Fe-SWNT, BZNFe-C60, and BZN-Fe-graphene were evaluated. Previous results in the literature present SWNTs complexes with metals studied by intermediation of Ca, Li, Mn, Ti, and Fe for adsorption of other pollutant molecules such as SO229 and dioxin molecules (aromatic compounds).13 Theoretical studies predicted that these complexes are extremely stable with binding energies on the order of 3 eV. In this work, an Fe atom in a single configuration for each SWNT, graphene, and C60 was analyzed with the BZN placed on aromatic rings parallel to the Fe-SWNT/ graphene/C60 surface (as in Figure 3).
The final relaxed structures are shown in Figure 3 and a summary of the general results is showed in Table 2. When we compare the BZN adsorption in Fe-doped systems we observe that the distance between the Fe atom and carbon nanostructure surface (∆d1 parameter) is increased by the presence of BZN more noticeably in C60 and graphene (see the second column in Table 2). A significant charge transfer between the species is predicted (see the last columns in Table 2, cf. Table 1). In fact, there is a charge redistribution that makes the BZN molecule and carbon species behave as donor and the Fe atom as acceptor compounds. The electronic charge amount per carbon atom transferred in the graphene complex is slightly smaller than that for SWNTs and C60, and this can be attributed to the C60 and SWNT surface curvature. An energy analysis can be used to predict the interaction behavior and the binding strength between BZN and Fe-doped nanostructures (Figure 4). In Table 3 are listed the binding energies for different schemes of BZN-Fe-SWNT/graphene/ C60 complexe formation. We use four schemes for binding energy calculations: the scheme labeled “1” present the binding energy of an interaction of the BZN-Fe system with isolated carbon nanostructure; scheme “2” demonstrates the binding energy of BZN interacting with a Fe-nanostructure system; scheme “3” represents the binding energies of Fe interaction intercalated on the BZN-SWNT/graphene/C60 systems, and finally, scheme “4” presents the energies involved in formation of complex by an individual union of elements. If we compare the values on the second line of Table 3 we conclude that BZN-Fe is less bound (around 0.2-0.3 eV) on the graphene surface than other carbon nanostructures. Scheme “2” presents binding energy values higher than those for scheme “1”. These results suggests that after the complex formation process, the dissociation of the system through scheme “1” is energetically more favorable than through scheme “2”. Indeed, those results point to a strong interaction of BZN and Fe for graphene and C60(5). In other words, the presence of the BZN molecule decreases considerably the Fe atom binding on the SWNT/C60 surface at the same time that the BZN-Fe interaction becomes strong
Figure 5. PDOS of BZN adsorption on Fe-doped systems. The electronic states are projected on 4s and 3d orbitals of the Fe atom and on the BZN molecule for the adsorption on (8,0) and (5,5) SWNTs and C60 Fe-doped surface. The red and blues lines represent the spin majority and minority carries for the PDOS for the complex BZN-Fe-SWNT/C60. The black lines are the Fe-PDOS when the BZN is not interacting with Fe-doped SWNTs/C60 systems. The indices (5) and (6) correspond to the system with iron atom in the center of the pentagon or hexagon site of fullerene, respectively.
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enough to not allow the recovering of previous Fe-doped systems without BZN, which becomes energetically unfavorable. Scheme “3” represents the energetic stability of the Fe atom between BZN and SWNT/graphene/C60 systems, and we observe higher values than for schemes “1” and “2”. From this point of view, removing individually the Fe atom from BZN-SWNT/graphene/C60 system is less favorable than the other discussed schemes. Finally, scheme “4” shows that the union of individual elements also involves very large energies being of the order of 3.0 eV for studied systems as expected for TM systems.13 This last result shows that formation of BZN-Fe-SNWT/graphene/C60 complexes is highly favorable and they also represent extremely stable systems. As we have concluded, the Fe atom binding with the benzonitrile molecule is stronger than that binding to C60/SWNT/ graphene. This can be better visualized when we use again eq 1, only slightly modified.32 Table 4 shows those new binding energies and it is clear that for all carbon systems the Fe atom is strongly bound in the BZN molecule. Indeed, in C60 and especially graphene the difference is around 1.0 eV. Our results show that SWNTs complexes are energetically more stable than C60 and graphene ones. Furthermore, the disassociation process is favorable through separation of Fe-BZN from carbon systems, acting as a purification process. At the electronic level, the plot of PDOS for the studied systems can be used to clarify the nature of the interaction. In Figure 5, the PDOS on the Fe atom and the BZN molecule reveals that there are two localized majority levels near the Fermi energy in the valence band with a mix character of 3d orbitals from Fe atom and some BZN levels. A localized level can be seen with the 3d minority character. These results are observed for both (8,0) and (5,5) tubes, meaning that the behavior of the BZN interacting with both tubes is very similar. It can be seen that there is a density of levels amount from BZN near the Fermi level in the valence band in the same energy values as that for 3d-Fe levels. This indicates a strong hybridization of BZN and Fe levels, and, as a consequence, a strong interaction between these systems. For fullerene complex we obtained similar results, except that in 3d-Fe orbitals two minorities and one majority spins levels near the Fermi energy are observed and for BZN-Fe-SWNTs complexes there are two majority and one minority levels near the Fermi energy observed. This suggests a different electronic configuration behavior of the Fe atom interacting with these two carbon species in the presence of BZN. A common effect in SWNT and fullerene is that there is no contribution for DOS of the 4s-Fe level near the Fermi energy. The PDOS results obtained for graphene are similar to those for (5,5) SWNT and they would be redundant to show. These results reveal the strong covalent character of the interaction between the BZN molecule and the TM (Fe)doped carbon nanostructures graphene, C60, and SWNTs, mediated by π-3d-π orbitals. Conclusions We report a systematic study of the structural and electronic properties of the BZN molecule interacting with pristine and Fe-doped SWNTs/graphene/C60. We observed that BZN interacts weakly with undoped SWNTs and C60 with binding energies varying from 0.01 to 0.10 eV. For the SWNTs the BZN adsorption is slightly more favorable through π-π stacking than π-CN interaction. Insignificant changes in the DOS for SWNTs, graphene, and C60 confirm the weak interaction regime with no chemical bound observed
Aguiar et al. between the aromatic molecule and the pristine carbon nanostructures. However, Fe covering carbon nanostructures was used to create reactive sites in carbon species for an efficient BZN adsorption. This doping introduces a strong cooperative binding of carbon systems with BZN whose binding energy values were in the 1.0 to 3.0 eV range between these systems that confirms the formation of a strongly bound complex BZN-Fe-SWNT/graphene/C60. We also have shown that 3d orbitals of the Fe atom contribute effectively to the interaction while carbon systems and BZN contribute with π orbitals, creating a strong π-3d-π bonding orbital between those systems. With the binding energy analysis we predicted a favorable separation of the complex systems through a BZN-Fe disconnecting from the SWNTs, graphene, or C60 surface. This result suggests that aromatic compounds (such as BZN) can be used to remove Fe atoms from the nanotube/graphene/C60 surface and it leads to an alternative system for purifying carbon nanotubes samples. Acknowledgment. The authors acknowledge CENAPADSP for computer time and financial support from Brazilian agencies CNPq, FAPERGS, CAPES, and FUNCAP. This is a contribution of Rede Nacional de Pesquisa em Nanotubos de Carbono and INCT-Nanomateriais de Carbono (MCT/CNPq Brazil). References and Notes (1) Baughman, R. H.; Zakhidov, A. A.; de Heer, W. A. Science 2002, 297, 787–792. (2) Tans, S. J.; Verschueren, A. R. M.; Dekker, C. Nature 1998, 393, 49–52. (3) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Science 2004, 306, 666–669. (4) Stankovich, S.; Dikin, D. A.; Dommett, G. H. B.; Kohlhaas, K. M.; Zimney, E. J.; Stach, E. A.; Piner, R. D.; Nguyen, S. T.; Ruoff, R. S. Nature 2006, 442, 282–286. (5) Gallo, M.; Favilaa, A.; Glossman-Mitnik, D. Chem 2007, 447, 105– 109. (6) Fagan, S. B.; da Silva, A. J. R.; Mota, R.; Baierle, R. J.; Fazzio, A. Phys. ReV. B 2003, 67, 03340. (7) Barros, E. B.; Souza Filho, A. G.; Lemos, V.; Mendes Filho, J.; Fagan, S. B.; Herbst, M. H.; Rosolen, J. M.; Luengo, C. A.; Huber, J. G. Carbon 2005, 43, 2495–2500. (8) Guldi, D. M.; Rahman, G. M. A.; Zerbetto, F.; Prato, M. Acc. Chem. Res. 2005, 38, 871–878. (9) Konarev, D. V.; Semkin, V. N.; Graja, A.; Lyubovskaya, R. N. J. Mol. Struct. 1998, 450, 11–22. (10) Fagan, S. B.; Azevedo, D. L.; Mendes Filho, J.; Souza Filho, A. G. AIP Conf. Proc. 2007, 893, 1027–1028. (11) Baierle, R. J.; Fagan, S. B.; Mota, R.; da Silva, A. J. R.; Fazzio, A. Phys. ReV. B 2001, 64, 085413. (12) Ferreira, O. P.; Otubo, L.; Alves, O. L.; Aguiar, A. L.; Silva, J. J. A.; Mendes Filho, J.; Souza Filho, A. G.; Fagan, S. B. J. Nanopart. Res. 2009, 11, 2163–2170. (13) Kang, H. S. J. Am. Chem. Soc. 2005, 127, 9839–9843. (14) Goldoni, A.; Petaccia, L.; Gregoratti, L.; Kaulich, B.; Barinov, A.; Lizzit, S.; Laurita, A.; Sangaletti, L.; Larciprete, R. Carbon 2004, 42, 2099– 2112. (15) da Silva, L. B.; Fagan, S. B.; Mota, R. Nano Lett. 2004, 4, 65–67. (16) Kohn, W.; Sham, L. J. Phys. ReV. 1965, 140, A1133–A1138. (17) Soler, J. M.; Artacho, E.; Gale, J. D.; Garcıa, A.; Junquera, J.; Ordejon, P.; Sanchez-Portal, D. J. Phys.: Condens. Matter 2002, 14, 2745– 2779. (18) Ceperley, D. M.; Alder, B. J. Phys. ReV. Lett. 1980, 45, 566–569. (19) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. ReV. Lett. 1996, 77, 3865–3868. (20) Perdew, J. P.; Zunger, A. Phys. ReV. B 1981, 23, 5048–5079. (21) Troullier, N.; Martins, J. L. Phys. ReV. B 1991, 43, 1993–2006. (22) Monkhorst, H. J.; Pack, J. D. Phys. ReV. B 1976, 13, 5188–5192. (23) Hasegawa, M.; Nishidate, K. Phys. ReV. B 2004, 70, 205431. (24) Chakarova Kack, S. D.; Schroder, E.; Lundqvist, B. I.; Langreth, D. C. Phys. ReV. Lett. 2006, 96, 146107. (25) Tournus, F.; Charlier, J. C. Phys. ReV. B 2005, 71, 165421.
Benzonitrile Adsorption on Carbon Nanostructures (26) Giannozzi, P.; Car, R.; Scoles, G. J. Chem. Phys. 2003, 118 (3), 1003. (27) Mao, Y. L.; Yan, X. H.; Xiao, Y. Nanotechnology 2005, 16, 3092– 3096. (28) Fagan, S. B.; Mota, R.; da Silva, A. J. R.; Fazzio, A. Phys. ReV. B 2003, 67, 205414. (29) da Silva, L. B.; Fagan, S. B.; Mota, R.; Fazzio, A. J. Phys. Chem. C 2008, 112, 6677–6680. (30) Zanella, I.; Fagan, S. B.; Mota, R.; Fazzio, A. J. Phys. Chem. C 2008, 112 (25), 9163–9167. (31) Sevinc¸li, H.; Topsakal, M.; Durgun, E.; Ciraci, S. Phys. ReV. B 2008, 77, 195434.
J. Phys. Chem. C, Vol. 114, No. 24, 2010 10795 (32) Additional calculations were done modifying the equation (1) with “X” holding for SWNTs, graphene, and C60: Eb(X-Fe) )-{E[X + Fe + BZNghost]- E[X + Feghost + BZNghost]- E[Xghost + Fe + BZNghost]} and Eb(BZN-Fe) )-{E[Xghost + Fe + BZN]- E[Xghost + Feghost + BZN]E[Xghost + Fe + BZNghost]}. Those different approaches allow us to calculate the binding of iron atom in BZN (Eb(BZN-Fe)) and carbon structures (Eb(X-Fe)) separately. (33) Junquera, J.; Paz, O.; Sanchez-Portal, D.; Artacho, E. Phys. ReV. B 2001, 64, 235111.
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