Theoretical Studies of the Interaction of an Open-Ended Boron Nitride Nanotube (BNNT)with Gas Molecules

Jing-xiang Zhao†,‡ and Yi-hong Ding*,†

State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry,Jilin UniVersity, Changchun 130023, People’s Republic of China, and Department of Chemistry,Harbin Normal UniVersity, Harbin 150080, People’s Republic of China

ReceiVed: July 1, 2008; ReVised Manuscript ReceiVed: NoVember 4, 2008

We have systematically studied the effects of several gaseous adsorbates (H2, N2, O2, and H2O) on the electronicproperties of open edges of boron nitride nanotubes (BNNTs) by using density functional theory calculations.The results indicate that all of the molecules, except N2, dissociate and chemisorb on open BNNT edges withlarge adsorption energies because the tube edge has either an open or capped structure and thus has danglingbonds or pentagonal defects. The high reactivity of an open-ended BNNT even can be comparable with thatof its carbon counterpart, although the wall of the BNNT is chemically more stable than a single-walledcarbon nanotube’s wall. Moreover, we note that adsorption of gases at the tips of open BNNTs can modifytheir electronic properties in various ways. A considerable amount of charge transferred for the adsorption ofgases on the open BNNTs may account for the changes of the electronic properties. Interestingly, the open(5,5) BNNT exhibits the properties of wide-band-gap materials when gases are adsorbed at top sites, whilea smaller band gap is observed when these gases are adsorbed on seat sites. Additionally, the magnetic momentsof gas-adsorbed N atoms in the open N-rich-ended (8,0) are significantly decreased because the danglingbonds are “saturated”. The present results might be helpful in the design of BNNT-based nanomaterials suchas field emitters or nanojunctions.

1. Introduction

Since their discovery in 1991,1 single-walled carbon nano-tubes (SWCNTs) have opened up new fields in science andtechnology and have been shown to be able to fabricate versatilenovel nanoscale materials because of their unique electronic,2,3

optical,4,5 and mechanical6,7 properties. Recently, studies ofSWCNT tips, which have been obtained with an electron beam,8

and their functionalization with different groups have attractedconsiderable attention because of their wide application suchas in the understanding of the growth process,9,10 the selectivemanipulation of armchair/zigzag CNTs,11,12 and the fabricationof novel nanomaterials such as molecular magnets13 and fieldemission display.14

Similar to the SWCNTs, boron nitride nanotubes (BNNTs)15

also possess unique properties. For example, BNNTs aresemiconductors with a wide band gap of ∼5.5 eV that is weaklydependent on the tube diameter, helicity, and wall numbers.16

Importantly, BNNTs are chemically and thermally more stable17-20

than SWCNTs, which makes BNNTs most valuable in nanode-vices working in hazardous and high-temperature environments.Considering the potential applications of BNNTs, many theo-retical studies21-26 have reported the BNNTs and their chemicalfunctionalizations. For example, Zeng et al. investigated thetransition-metal and NH3-functionalized BNNTs using densityfunctional theory (DFT) calculations.21a,c Zhou et al. exploredthe applications of BNNTs in sensing gas or the storage oflithium and hydrogen.26c,d

Recently in his laboratory, Zuo et al. reported that high-energyelectron irradiation of BNNTs can be used to form sharp,

crystalline, conical tips or to cut BNNTs by controlling theelectron beam size.27 Theoretically, Duan et al. have elucidatedthe geometrical, magnetic, and electronic structures of a seriesof open BNNTs with different chiralities,28 indicating thatintrinsic magnetism can be induced in the open-ended BNNT.We note that the above studies focused on the functionalizationof the BNNT’s wall or the properties of open-ended BNNTs.To our knowledge, there is no report on the interaction of open-ended BNNTs with adsorbates, which is very necessary not onlyto deeply understand the properties of the open-ended BNNTsbut also to further design covalent linkages for interconnectingBNNTs.

Thus, in the present work, we computationally report anattempt on the interaction of various adsorbates, including H2,N2, O2, and H2O molecules, with zigzag (8,0), including openB- and N-rich-ended BNNTs, and armchair (5,5) BNNTs withopen edges by using DFT calculations.

2. Theoretical and Computational Details

Two models of finite-sized BNNTs with open edges, zigzag(8,0) B48N48H8 and armchair (5,5) B40N40H10, were adopted inour work, where one mouth is opened and the other is saturatedby H atoms to mimic the presence of a long BNNT below thetip in actual experiments. This model has been used in a previousreport and has been proven to be accurate enough for describingthe BNNT with open tips.28a In contrast to the open-endedSWCNTs, there are two distinctly different atom terminationsat the open BNNTs because they consist of two kinds of atoms(B and N), so open B- and N-rich-ended (8,0) BNNTs are usedto model the adsorption of various adsorbates at the BNNTedges. We define the adsorption energy (Ead) of adsorbates asEad ) Etot(molecule + open-ended BNNT) -Etot(open-ended

* To whom correspondence should be addressed.† Jilin University.‡ Harbin Normal University.

J. Phys. Chem. C 2008, 112, 20206–2021120206

10.1021/jp805790s CCC: $40.75 2008 American Chemical SocietyPublished on Web 12/02/2008

BNNT) - Etot(molecule), where Etot is the total energy of agiven system. A positive or negative value in Ead refers to anendothermic or exothermic adsorption, respectively.

The structural optimizations and corresponding total energycalculations are performed by using the spin-polarized DFTformalism within the generalized gradient approximation(GGA), as implemented in the DMol3 code.29 The Perdew-Wangcorrelation functional30 with the Becke exchange functional31

in GGA is adopted. All-electron calculations are employed withthe double-numerical basis sets plus polarization functional. Theforces on each atom converged during structural optimizationsare less than 10-3 au.

3. Results and Discussion

3.1. Structures of the Open-Ended (8,0) and (5,5) BNNTs.Duan et al. have reported the stable geometries of various open-ended BNNTs.28a Here we interpret in detail why the open B-and N-rich-ended tubes structurally behave so different fromeach other. In principle, both of the open tubes are generatedfrom a H-saturated tube through the respective breaking of theB-H and N-H bonds. So, the initial structures should haveunpaired electrons at the end B and N atoms (the nearest B · · ·Band N · · ·N distances are 2.43 and 2.44 Å, respectively). Theeventual optimization of the open B-rich-ended (8,0) tubenaturally leads to a closing mouth (Figure 1a) with a B-B bondlength of 1.63 Å due to the effective coupling between thenearest two B atoms. However, the optimized open N-rich-ended(8,0) tube has a broader mouth in which the distance betweenthe nearest two N atoms is increased to as large as 2.58 Å(Figure 1b). This is probably due to the fact that (1) thethermodynamic driving force to form a N-N bond is very low(the N-N single bond energy is 159 kJ/mol, much lower than297 kJ/mol of the B-B single bond)32 and (2) the nearest Nlone pairs induce strong repulsion to hinder the N-N coupling.It is thus clear that the open B-rich-ended (8,0) tube is subjectto a severe structural distortion from the parent BNNT, whereasthe open N-rich-ended (8,0) tube shows only a slight distortion.This is further supported by the calculated distortion energy(Edis) of the two tubes, which is defined as the energy differencebetween the distorted and undistorted tubes. The open B-rich-ended (8,0) tube has a much larger Edis (13.10 eV) than theopen N-rich-ended (8,0) tube (5.43 eV).

Cutting the end B-H and N-H bonds of (5,5) BNNT resultsin a different yet interesting situation; i.e., there are two kindsof (B,N) pairs at the tips of the open (5,5) tube, namely, (N1,B2)(top site) and (N1,B2′) pairs (seat site) (see Figure 1c). The topsite has considerable structural distortion because the unpaired

electrons of the (N1,B2) pair strongly couple each other,resulting in a much shortened B-N bond (1.31 Å; the B-Nbond in the parent BNNT is 1.45 Å). For the seat site, the B · · ·Ndistance is as long as 3.04 Å. In both sites, there is no electronlone-pair repulsion within the (B,N) pairs. The calculateddistortion energy (Edis) of open (5,5) is 10.43 eV, intermediatebetween the N-rich-ended (5.43 eV) and B-rich-ended (13.10eV) open (8,0) BNNTs.

It might be of interest to compare the above three open-endedBNNT tubes with borazynes (B3N3H4). Intuitively, open BNNTis distinctly different from borazyne because the former is anextended system with a large curvature, whereas the latter simplycontains a B3N3 six-membered planar ring. Fazen and Burkehave recently studied in detail the structures and energetics ofborazyne isomers by using various theoretical methods.33 Theyfound that all borazynes have a singlet ground state. Similarly,the open B-rich-ended (8,0) and the open B,N-ended (5,5) tubesboth have singlet ground states, yet the open N-rich-ended (8,0)tube has a high-spin ground state, resulting in magnetism.Structurally, the open (5,5) BNNT has B-N distances (1.31 Åfor the top site and 3.04 Å for the seat site) similar to those ofthe corresponding borazynes [1.290 Å in the 1,2-(N,B)-pairedborazyne and 2.57 Å in the 1,4-(N,B)-paired borazyne].However, both the open B-rich-ended (the B-B distance is 1.63Å) and the open N-rich-ended (8,0) tubes (the N · · ·N distanceis 2.58 Å) show marked structural differences from those ofthe corresponding borazynes [2.32 Å in the 1,3-(B,B)-pairedborazyne and 1.70 Å in the 1,3-(N,N)-paired borazyne]. Notethat, although not pointed out by Fazen and Burke, the ratherlong B · · ·B distance shows that the 1,3-(B,B)-paired borazyneshould have diradical character. A possible explanation for theabove structural and energetic difference is that the former isan extended conjugated π system.

3.2. Geometries of Adsorbates at the Ends of BNNTs. Inthis section, we explore the stable configurations of several gasmolecules (H2, N2, O2, and H2O) adsorbed at the edges of open-ended BNNTs. After optimization, the most stable structuresof these gas molecules attached to the open B- and N-rich-ended(8,0) BNNTs are shown in Figures 2 and 3. Upon adsorptionof a H2 molecule on the B-B bond or the N-N bond of theedge, the molecule dissociates and the H-H bond lengths are2.45 and 2.52 Å, respectively, and the distances between H2

and the open-ended BNNTs are shown in Figures 2a and 3a.On the other hand, the changes of the structures of B- andN-rich-ended tubes are different: for the B-rich-ended tube, afteradsorption of H2 molecules, the two B atoms are saturated bytwo H atoms, the B-B bond is broken with a bond length of2.41 Å, and the other three pairs of B-B dimerization stillremain (Figure 2a). Upon H2 adsorption on the edge of N-rich-ended (8,0), the N-N bond length decreases from 2.58 to 2.54Å because of the adsorption of H2 molecules on a N-rich-endedtube edge (Figure 3a). Moreover, the adsorption energies of H2

adsorption on the B- or N-rich-ended (8,0) BNNTs are -3.41and -5.71 eV, respectively (Table 1).

Similar to H2 molecule adsorption, a single H2O moleculedissociates into a H atom and an OH group upon being adsorbedon the B- or N-rich-ended (8,0) BNNTs (Figures 2b and 3b)with larger adsorption energies of -4.45 and -3.37 eV,respectively, suggesting that the open B-rich-ended BNNTshows higher reactivity toward the H2O molecule than the openN-rich-ended BNNT because of the formation of the muchstronger B-O bond. Different from the case of H2 or H2Oadsorption, the N2 molecule does not dissociate when it isbonded to the edge of the B- or N-rich-ended (8,0) BNNTs, so

Figure 1. Optimized geometrical structures of open BNNTs: (a) B-rich-ended, (b) N-rich-ended (8,0) BNNT, and (c) (5,5) BNNT with openedges. The bond lengths are in units of angstroms.

Interaction of a BNNT with Gas Molecules J. Phys. Chem. C, Vol. 112, No. 51, 2008 20207

a pentagon can be obtained at the tube edge (Figures 2c and3c). After being adsorbed on the B- or N-rich-ended (8,0)BNNTs, the bond lengths of N-N are elongated to 1.28 and1.26 Å from the isolated bond length of 1.10 Å with adsorptionenergies of -1.49 and -1.73 eV, respectively.

The adsorption of O2 on the B- and N-rich-ended (8,0)BNNTs behaves in a strikingly different way. When adsorbedon the open B-rich-ended (8,0) BNNT edge, a metastable(intermediate) state is obtained, as shown in Figure 2d. Afterfull relaxation, the O-O bond (2.46 Å) is completely separated.The B-O bond strengths are stronger with a bond length of1.33 Å, and the B2 dimer that is attached by the O-O bonddissociates. This leads to a stronger adsorption energy of -6.27

eV. A more stable configuration is obtained by elongating theO-O bond a little, as shown in Figure 2e. Two tetragons areformed with B-O bonds of 1.43 Å. The O-O distance is farapart by 3.19 Å. This configuration is the most stable, with anadsorption energy of -10.67 eV. The energy barrier from partsd and e of Figure 2 is about 1.60 eV, and the Cartesiancoordinates of the transition state can be found in the SupportingInformation.

Unlike the open B-rich-ended BNNT edge, where oneintermediate state exists, the adsorption of an O2 molecule atthe open N-rich-ended BNNT edge shows only one stableconfiguration. The O2 molecule dissociates (2.65 Å) and thenchemisorbs on two adjacent N atoms, resulting in the formationof N-O bonds with bond lengths of 1.26 Å. The calculatedadsorption energy is -3.60 eV, which is much smaller thanthat at the edge of the open B-rich-ended BNNT.

Molecules can adsorb at the seat and top sites at an armchairedge, as presented in Figures 4 and 5. We note that theadsorption energies at the armchair tip are smaller than that atthe zigzag tip, as shown in Table 1. Similar to adsorption atzigzag tube tips, the H2 molecule also dissociates at the armchair

Figure 2. Fully optimized configurations of various molecules on theedge of the B-rich-ended (8,0) BNNT: (a) H2, (b) H2O, (c) N2, and (d)O2. The bond lengths are in units of angstroms.

Figure 3. Fully optimized configurations of various molecules on theedge of the N-rich-ended (8,0) BNNT: (a) H2, (b) H2O, (c) N2, and (d)O2. The bond lengths are in units of angstroms.

TABLE 1: Structural Parameters and Adsorption Energiesof Various Gas Molecules Adsorbed on the (8,0) and (5,5)BNNTs with Open Edges (Distance in Å; Ead in eV)

H2 N2 O2 H2O

Ead dH-H Ead dN-N Ead dO-O Ead dO-H1 dO-H2

B-rich -3.41 2.45 -1.49 1.28 -10.67 3.19 -4.45 2.62 0.97N-rich -5.71 2.53 -1.73 1.26 -3.60 2.64 -3.37 2.47 1.00(5,5) seat -0.94 1.99 -0.31 1.11 -4.24 2.90 -2.26 1.74 0.97(5,5) top -3.34 2.51 -0.85 1.56 -3.93a

(-0.38)b2.55

(2.74)0.99

(0.98)

a The configuration is presented in Figure 5b. b The configurationis presented in Figure 5c.

20208 J. Phys. Chem. C, Vol. 112, No. 51, 2008 Zhao and Ding

tube tip. The distance in the top site is farther than that in theseat site of the armchair edge (see Table 1), resulting in thereduction of the H-H repulsion. As shown in Figure 5a, wefind that the B-N bond that is adsorbed by the H2 molecule isincreased from 1.31 to 1.44 Å, while the change of the adsorbedB-N bond is small in the seat site of an armchair edge, as shownin Figure 4a. This results in a larger adsorption energy for theH2 molecule at the top site than at the seat site. Only a stablestructure is obtained when the N2 molecule is adsorbed at thearmchair edge (Figure 4c) and the adsorption energy is only-0.31 eV.

A H2O molecule dissociates into a H atom and an OH groupat a top site or a seat site of the armchair edge, and three stableconfigurations are obtained with adsorption energies of -2.26,-3.93, and -0.38 eV, as shown in Figure 4b and parts b andc of Figure 5, respectively. The O2 molecule behaves in adifferent way when adsorbed at the top and seat sites: uponadsorption at a top site, the O2 molecule dissociates with a O-Obond of 2.90 Å (Figure 4d), whereas the O-O distance isincreased to 1.56 Å at a seat site (Figure 5d); thereby a smalladsorption energy (-0.85 eV) is found, as shown Table 1.

Additionally, taking the H2O molecule as an example, wecalculate its adsorption at open-ended (9,0) and (10,0) BNNTs.It is shown that the adsorption configurations and the adsorptionenergies are similar to those of a (8,0) tube. In other words, theadsorption at the edges of open BNNTs does not depend on itsdiameter. This is expected because the tube edge with danglingbonds or pentagonal defects has a high reactivity toward guestadsorbates. Compared with this, the influence of the tubediameter on the adsorption of these gaseous molecules can beneglected.

Overall, we summarize the adsorption energies and structuralparameters as shown in Table 1 and find that O2 adsorption onB-rich-ended open tubes provides the largest adsorption energybecause the most significant charge is transferred from the Batoms to the O atoms and a strong B-O bond is formed,whereas the adsorption energy of N2 at the armchair tube edgeis the smallest because of the relatively weak bonds betweenN2 and the tube tip. Understandably, the adsorption energy ofvarious adsorbates on the BNNTs with open tips is dependenton two factors: (a) the bond dissociation energy of variousadsorbates and (b) the binding energy between various adsor-bates and the open-ended BNNTs. For example, the O2 moleculehas a moderate dissociation energy (493.59 kJ/mol), and theB-O binding energy is very large (806 kJ/mol).32 So, theinteraction between the O2 molecule and B-rich-ended (8,0)tubes is the strongest. However, because the N2 moleculepossesses the largest dissociation energy among these gaseousmolecules, its adsorption energy on BNNTs with open ends issmall.

3.3. Effects of Adsorption on the Open-Ended BNNT. Thechemical functionalization of various gas molecules on the open-ended BNNT might lead to an amount of charge transfer. InTable 2, we give the charge transfer of these gas moleculesadsorbed on the open-ended (8,0) BNNT using the Hirshfeldmethod, which is based on the deformation electron density andseems less sensitive to the selected basis sets than the Mullikencharge analysis.21a The calculated results indicate that the chargetransfer strongly depends on the atomic configuration of themouth of the open-ended BNNT and the adsorbate. For example,

Figure 4. Optimized structures of various adsorbed molecules at theseat site of the (5,5) BNNT edge: (a) H2, (b) H2O, (c) N2, and (d) O2.The bond lengths are in units of angstroms.

Figure 5. Optimized structures of various adsorbed molecules at thetop site of the (5,5) BNNT edge: (a) H2, (b) H2O (an H atom of theH2O molecule is attached to the N atom of the tube), (c) H2O (an Hatom of the H2O molecule is attached to the B atom of the tube), and(d) O2. The bond lengths are in units of angstroms.

Interaction of a BNNT with Gas Molecules J. Phys. Chem. C, Vol. 112, No. 51, 2008 20209

charges are transferred from the open B-rich-ended BNNT toall studied adsorbates in the present work. This may originatefrom the characteristics of the lacked electron for the B atomsat the tube edge. On the other hand, the H2 and H2O moleculesadsorbed onto the N-rich-ended (8,0) BNNT lose an amount ofelectrons, whereas the opposite is the case for N2 and O2

adsorptions, as shown in Table 2. Upon adsorption at thearmchair edge, the direction of charge transfer of thesemolecules is the same except for the H2O molecule, for whichthe manner of charge transfer can vary with the location of theadsorption site (Table 2). This correlates with the attached atomby an OH group: when an OH group is attached to a B atom,the charge is transferred from the H2O molecule to the armchairtube, whereas on the contrary the opposite direction of chargetransfer is observed. The charge transfer may induce changesof the field emission properties of BNNTs, which is necessaryfor the design of efficient field emitters of molecular electronicdevices.

A number of investigations have indicated that chemicalfunctionalization would have significant effects on the electronicproperties of the BNNT.20-26 How does the gas adsorption atthe open-ended BNNT’s edge affect its property? To explainthe problem, we elucidate the modifications of band gaps beforeand after various gas molecule adsorptions, as shown in Table2. We note that the adsorption of molecules decreases the bandgap of the open-ended BNNT in various ways, except the N2

molecule adsorbed on the open N-rich-ended tube. For example,upon adsorption of H2 and H2O molecules, the band gap of theopen B-rich-ended (8,0) BNNT is somewhat reduced from 3.50eV to 3.47 and 3.39 eV, while a smaller band gap of 1.07 and1.95 eV is observed when N2 or O2 is adsorbed onto the B-rich-ended (8,0) BNNT. A similar case is also observed for thesegases adsorbed on the N-rich-ended (8,0) tubes. Interestingly,as shown in Table 2, the band gaps of the open (5,5) BNNTshow different electrical property changes upon adsorption ofgases at different sites. For example, when the H2 molecule isadsorbed at the top sites, the band gap of the bare tube is reducedfrom 4.08 to 3.79 eV, suggesting that the tube is still a wide-gap material and has poor electroconductivity. However, uponH2 adsorption at seat sites, the band gap of the bare tube issignificantly lowered to 0.92 eV. The existence of this smallband gap suggests that the system can be converted into anarrow-gap semiconductor material. Such a big decrease of theband gap of the (5,5) tube upon H2 adsorption on seat sitesoriginates from the changes of the highest occupied molecularorbital (HOMO) and the lowest unoccupied molecular orbital(LUMO) of these systems. As shown in Figure 6, the HOMOand LUMO densities of pure (5,5) BNNT are mainly positioned

at the tube wall (Figure 6a), while those of the open-endedBNNT with H2 adsorbed at the seat sites are mainly localizedwithin the B-H or N-H bonds (Figure 6b). All of these suggestthat different electronic properties of an open (5,5) BNNT canbe achieved through adsorption of the tube by the sameadsorbates on different sites.

Another interesting issue is to explore the effects of adsorptionon the magnetic properties of the open N-rich-ended tubes. TheN-rich-ended (8,0) has a 8 µB net magnetic moment, whichcannot be broken by external perturbations such as an electricfield and doping.28a We find that the magnetic moments of theattached N atoms by gas molecules are significantly decreased,while little changes are observed for other N atoms. In detail,the magnetic moments of the adsorbed N atoms by H2, O2, andN2 are 0.05, 0.03, and 0.03 µB, respectively, which are muchsmaller than that of the N atoms before gas molecule adsorptionwith a magnetic moment of 1 µB. Thus, the magnetic momentsof the terminated N atoms can possibly completely disappearwhen more molecules are attached to the open N-rich-endedBNNT edge. The results can be rationalized by the fact that,by the attachment of more gas molecules to N atoms of theopen N-rich-ended (8,0) BNNT’s edge, the dangling bonds aredrastically “saturated”, so the spin configuration will be brokenby adsorbates, and even disappear.

In short, our DFT calculations demonstrate that the BNNTedge is an interesting site for adsorption because it is more viableto react with gas adsorbates than the tube wall because of theexistence of dangling bonds or pentagonal defects. Adsorptionof gases at BNNT edges also modifies their physical propertiesin various ways. Most importantly, introducing gas adsorbatesat open BNNT edges might change their field emissionproperties such as effectively lowering their ionization potentialand facilitating the loss of electrons, which is expected toprovide helpful guidance to the development of more excellentBNNT-based field emitters because BNNTs are chemically andthermally more stable than CNTs, which is also our investigativegoal. Additionally, similar to the case of CNTs, the function-alization of BNNT tips with various gases can provide nanotipsfor chemical force microscopy, which is an application tochemically sensitive imaging of nanomaterials or biomolecules.

4. Conclusion

We have performed DFT calculations to study the adsorptionof several gas molecules (H2, N2, O2, and H2O) on open-endedBNNTs. The molecules H2, O2, and H2O dissociate andchemisorb on BNNT edges with large adsorption energies,whereas N2 does not dissociate upon adsorption. The adsorptionenergies significantly depend on the structure and adsorption

TABLE 2: Charge Transfer and HOMO-LUMO Gap(Band Gap) of Various Gas Molecules Adsorbed onto OpenBNNTs (Charge Transfer in e; HOMO-LUMO Gaps in eV)

charge transfera HOMO-LUMO gapsb

(8,0) tube (5,5) tube (8,0) tube (5,5) tube

B-rich N-rich seat top B-rich N-rich seat top

H2 -0.10 0.25 0.07 0.06 3.47 0.87 0.92 3.79O2 -0.50 -0.20 -0.14 -0.29 1.89 0.25 1.61 2.69N2 -0.25 -0.08 -0.04 1.07 0.96 2.16H2O -0.10 0.16 0.06 -0.01c (0.17)d 3.39 0.37 1.35 3.94c (3.52)d

a The positive values suggest that charges are transferred from theadsorbates to the open BNNTs. b The band gaps of B- andN-rich-ended (8,0) BNNTs are 3.48 and 0.93, respectively. c Theconfiguration is presented in Figure 5b. d The configuration ispresented in Figure 5c.

Figure 6. Side views of HOMO and LUMO of (a) open (5,5) BNNT,(b) H2 adsorption of top sites of open (5,5) BNNT, and (c) H2 adsorptionof seat sites of open (5,5) BNNT.

20210 J. Phys. Chem. C, Vol. 112, No. 51, 2008 Zhao and Ding

sites of BNNT edges. Adsorption of these molecules induces acharge transfer and thus results in changes of the electronicproperties to different degrees. The magnetic moments of theadsorbed N atoms by these molecules in the open N-rich-ended(8,0) dramatically decrease. The present results might be usefulnot only to deeply understand the properties of open-endedBNNTs but also to develop efficient field emitters of molecularelectronic devices.

Acknowledgment. This work is supported by the NationalNatural Science Foundation of China (Grants 20103003,20573046, and 20773054), Doctor Foundation by the Ministryof Education (Grant 20070183028), Excellent Young TeacherFoundation of Ministry of Education of China, Excellent YoungPeople Foundation of Jilin Province (Grant 20050103), andProgram for New Century Excellent Talents in University(NCET). The authors express their gratitude for the reviewers’invaluable comments and suggestions.

Supporting Information Available: Cartesian coordinatesof the transition state of an oxygen molecule adsorbed on theedge of an B-rich open-ended (8,0) BNNT. This material isavailable free of charge via the Internet at http://pubs.acs.org.

References and Notes

(1) Iijima, S. Nature 1991, 354, 56.(2) Mintmire, J. W.; Dunlap, B. I.; White, C. T. Phys. ReV. Lett. 1992,

68, 631.(3) Hamada, N.; Sawada, S.-I.; Oshiyama, A. Phys. ReV. Lett. 1992,

68, 1579.(4) Charlier, J.-C.; Limbin, Ph. Phys. ReV. B 1998, 57, 15037.(5) Corio, P.; Shapro, M. Phys. ReV. Lett. 2001, 86, 131.(6) Demczyk, B. G.; Wang, Y. M.; Cumings, J.; Hetman, M.; Han,

M.; Zettl, A.; Ritchie, R. O. Mater. Sci. Eng. A 2002, 334, 173.(7) Yakobson, B. I.; Avouris, Ph. In Carbon Nanotubes: Synthesis,

Structure, Properties, and Applications; Dresselhaus, M. S., Dresselhaus,G., Avouris, Ph., Eds.; Springer-Verlag: Berlin, 2000; p391.

(8) Banhart, F.; Li, J. X.; Terrones, M. Small 2005, 1, 953.(9) Seo, K.; Kim, C.; Kim, B.; Lee, Y. H.; Song, K. J. Phys. Chem. B

2004, 108, 4308.(10) (a) Ding, F.; Larsson, P.; Larsson, J. A.; Ahuja, R.; Duan, H.; Rosen,

A.; Bolton, K. Nano Lett. 2008, 8, 463. (b) Ohta, Y.; Okamoto, Y.; Irle, S.;Morokuma, K. ACS Nano 2008, 2, 1473.

(11) Basiuk, V. A.; Basiuk, E. V.; Saniger-Blesa, J.-M. Nano Lett. 2001,1, 657.

(12) Gustavsson, S.; Rosen, A.; Grennberg, H.; Bolton, K. Chem.sEur.J. 2004, 10, 2223.

(13) Kim, Y. H.; Choi, J.; Chang, K. J.; Tomanek, D. Phys. ReV. B2003, 68, 125420.

(14) (a) Zhou, G.; Duan, W. H.; Gu, B. L. Phys. ReV. Lett. 2001, 87,095504. (b) Kim, C.; Choi, Y. S.; Lee, S. M.; Park, J. T.; Kim, B.; Lee,Y. H. J. Am. Chem. Soc. 2002, 124, 9906. (c) Akdim, B.; Duan, X.; Pachter,R. Nano Lett. 2003, 3, 1209.

(15) Rubio, A.; Corkill, J. L.; Cohen, M. L. Phys. ReV. B 1994, 49,5081.

(16) Blase, X.; Rubio, A.; Louie, S. G.; Cohen, M. L. Eur. Phys. Lett.1994, 28, 335.

(17) Hernandez, E.; Goze, C. P.; Bernier, A.; Rubio, A. Phys. ReV. Lett.1998, 80, 4502.

(18) Suryavanshi, A. P.; Yu, M.; Wen, J.; Tang, C. C.; Bando, Y. Appl.Phys. Lett. 2004, 84, 2527.

(19) Han, W. Q.; Bando, Y.; Kurashima, K.; Sato, T. Appl. Phys. Lett.1998, 73, 3085.

(20) (a) Golberg, D.; Bando, Y.; Tang, C. C.; Zhi, C. Y. AdV. Mater.2007, 19, 2413. (b) Terrones, M.; Romo-Herrera, J. M.; Cruz-Silva, E.;Lopez-Urias, F.; Munoz-Sandoval, E.; Velazquez-Salazar, J. J.; Terrones,H.; Bando, Y.; Golberg, D. Mater. Today 2007, 10, 30.

(21) (a) Wu, X. J.; Zeng, X. C. J. Chem. Phys. 2006, 125, 044711. (b)Wu, X. J.; Yang, J. L.; Zeng, X. C. J. Chem. Phys. 2006, 125, 044704. (c)Wu, X. J.; An, W.; Zeng, X. C. J. Am. Chem. Soc. 2006, 128, 12001. (d)An, W.; Wu, X. J.; Yang, J. L.; Zeng, X. C. J. Phys. Chem. C 2007, 111,14105. (e) Wu, X. J.; Yang, J. L; Hou, J. G.; Zhu, Q. S. J. Chem. Phys.2004, 121, 8481.

(22) Zhi, C. Y.; Bando, Y.; Tang, C. C.; Golberg, D. Phys. ReV. B 2006,74, 153413.

(23) Lai, L.; Song, W.; Lu, J.; Gao, Z. X.; Nagase, S.; Ni, M.; Mei,W. N.; Liu, J. J.; Yu, D. P.; Ye, H. Q. J. Phys. Chem. B 2006, 110, 14092.

(24) Li, J.; Zhou, G.; Liu, H. T.; Duan, W. H. Chem. Phys. Lett. 2006,426, 148.

(25) Zhang, J.; Loh, K. P.; Yang, W. S.; Wu, P. Appl. Phys. Lett. 2005,87, 243105.

(26) (a) Zhou, Z.; Zhao, J. J.; Chen, Z. F.; Schleyer, P. v. R. J. Phys.Chem. B 2006, 110, 25678. (b) Li, Y. F.; Zhou, Z.; Zhao, J. J. J. Chem.Phys. 2007, 127, 184705. (c) Zhou, Z.; Zhao, J. J.; Chen, Z. F.; Gao, X. P.;Yan, T. Y.; Wen, B.; Schleyer, P. v. R. J. Phys. Chem. B 2006, 110, 13363.(d) Zhou, Z.; Zhao, J. J.; Gao, X. P.; Chen, Z. F.; Yan, T. Y.; Wen, B.;Schleyer, P. v. R.; Morinaga, M. Chem. Mater. 2005, 17, 992. (e) Li, Y. F.;Zhou, Z.; Zhao, J. J. Nanotechnology 2008, 19, 015202. (f) Li, Y. F.; Zhou,Z.; Golberg, D.; Bando, Y.; Schleyer, P. v. R.; Chen, Z. F. J. Phys. Chem.C 2008, 112, 1365. (g) Zhou, Z.; Nagase, S. J. Phys. Chem. C 2008, 111,18533. (h) Zhou, Z.; Zhao, J.; Chen, Z.; Gao, X.; Lu, J. P.; Schleyer, P. v.R.; Yang, C.-K. J. Phys. Chem. B 2006, 110, 2529.

(27) Celik-Aktas, A.; Stubbins, J. F.; Zuo, J.-M. J. Appl. Phys. 2007,102, 024310.

(28) (a) Hao, S. G.; Zhou, G.; Duan, W. H.; Wu, J.; Gu, B.-L. J. Am.Chem. Soc. 2006, 128, 8453. (b) Blase, X.; De Vita, A.; Charlier, J.-C.;Car, R. Phys. ReV. Lett. 1998, 80, 1666.

(29) (a) Delley, B. J. Chem. Phys. 1990, 92, 508. (b) Delley, B. J. Chem.Phys. 2000, 113, 7756.

(30) Perdew, J. P.; Wang, Y. Phys. ReV. B 1992, 45, 13244.(31) Becke, A. D. Phys. ReV. A 1988, 38, 3098.(32) Dean, J. A. Lange’s Chemistry Handbook, 15th ed.; McGraw-Hill:

New York, 1992.(33) Fazen, P. J.; Burke, L. A. Inorg. Chem. 2006, 45, 2494.

JP805790S

Interaction of a BNNT with Gas Molecules J. Phys. Chem. C, Vol. 112, No. 51, 2008 20211