We have made some progress in our research toward reacting boron-containing compounds with single-walled carbon nanotubes (SWCNTs).� I took very seriously the warning of one reviewer who said, ��my recommendation would be to drop [the reaction of diborane with SWCNTs] in favor of an expanded effort on the liquid phase studies that use BH₃ complexes.�� Our work thus far indicates that the BH₃ complexes we have tried, BH₃-THF and BH₃-triethylamine, do not react with SWCNTs.� For BH₃-THF and SWCNTs at 0�C or 25�C, infrared and Raman spectroscopies indicate that no reaction takes place.� For BH₃-triethylamine and SWCNTs at 0�C, 25�C, or 65�C, spectroscopic analysis also indicates no reaction.� Presumably, under these conditions, the borane complexes are not reactive enough to attack the conjugated pi system of the SWCNTs.

Consequently, we determined to try a more reactive boron-containing compound, diborane.� One way to generate small quantities of diborane gas is the reaction of phosphoric acid with sodium borohydride:

2H₃PO₄(l) + 6NaBH₄(s) � 3B₂H₆(g) + 3H₂(g) + 2Na₃PO₄(s)

Because phosphoric acid is a non-oxidative acid, we expect that it will not react with SWCNTs, but we will of course run control experiments.� Figure 1 shows a preliminary FTIR spectrum of SWCNTs reacted with diborane gas produced using the above reaction.

Figure 1.� FTIR spectrum of SWCNTs reacted with diborane gas.

In this spectrum, peaks at 2200�2400 cm^�1 are present.� These peaks are consistent with the B�H stretching vibrations of a �BH₂ group.� Thus, this spectrum suggests that the SWCNTs have been functionalized with �BH₂ groups.� Therefore, we will continue to study this reaction.

We also have preliminary results suggesting that a photochemical reaction between BH₃-THF and SWCNTs is possible.� SWCNTs were immersed in BH₃-THF under a nitrogen atmosphere and subjected to radiation from a mercury lamp for 2 h.� Figure 2 shows the FTIR spectrum of the product of this process.

Figure 2.� FTIR spectrum of SWCNTs photochemically reacted with BH₃-THF.

Figure 2 shows peaks from 2200�2400 cm^�1, again consistent with B�H stretches.� In this spectrum, peaks at 1490 cm^�1 and 1275 cm^�1 are apparent.� Previous researchers have associated these peaks with boron-substituted SWCNTs.¹� Consequently, these data indicate that the SWCNTs might be functionalized with �BH₂ groups.� Therefore, we will pursue the photochemical reaction of BH₃-THF with SWCNTs.

We have had some other successes in the research.� Previously developed methods of functionalizing SWCNTs include attaching a benzene ring with an �NO₂ group para to the bond to the SWCNT.� Later reserachers used this diazonium reaction, followed by an electrochemical reduction of the �NO₂ group to an �NH₂ group.� Our work demonstrates that this reduction can be achieved using the BH₃-THF or BH₃-triethylamine complex, which is simpler and avoids most of the complications of the electrochemical reduction.

Another side project that is ongoing is the use of borane complexes to reduce oxygen-containing functional groups on SWCNTs.� Purified SWCNTs contain functional groups such as carboxylic acids, ketones, and aldehydes.^2,3� Borane complexes can reduce these functional groups, so we are purifying SWCNTs with strongly oxidizing acids, such as nitric acid, to produce SWCNTs with significant numbers of oxygen-containing functional groups.� We will then attempt to reduce these functional groups with BH₃-THF or BH₃-triethylamine.

This grant has been acknowledged in one submitted article, reference 4.� A research student designed and carried out a project to attach DNA to SWCNTs.� His work was not directly supported by this ACS PRF grant.� However, he did use SWCNTs purchased with funds from this grant.� Therefore, I thought it appropriate to acknowledge this ACS PRF grant in the manuscript.

A total of 7 students have worked or are working on the experiments described above.� Five of these students presented posters on their research at the Mid-Atlantic Regional Meeting of the ACS on May 16, 2007.

References

(1)� Borowiak-Palen, E., Pichler, T.; Fuentes, G. G.; Graff, A.; Kalenczuk, R. J.; Knupfer, M.; Fink, J. Chem. Phys. Lett. 2003, 378, 516.

(2)� Feng, X.; Matranga, C.; Vidic, R.; Borguet, E. J. Phys. Chem. B 2004, 108, 19949.

(3)� Kuznetsova, A.; Popova, I.; Yates, J. T., Jr.; Bronikowski, M. J.; Huffman, C. B.; Liu, J.; Smalley, R. E.; Hwu, H. H.; Chen, J. G. J. Am. Chem. Soc. 2001, 123, 10699.

(4)� Ellison, M. D.; Gasda, P. J. submitted to Journal of Physical Chemistry C 2007.