Theoretical study of water adsorption and reactivity on single-walled boron nitride nanotubes

Carbon nanotubes (CNTs) have been investigated extensively over the past decade for various applications due to their unique electrical and mechanical properties. Soon after the discovery of CNTs, efforts were made to search for a nanotube made of non-carbon material. In 1994, Blase and his co-workers [1] predicted theoretically the boron nitride nanotube (BNNT) by exploring the similarity between hexagonal boron nitride and graphite. The existence of BNNTs was later confirmed by experimental synthesis [2]. BNNTs exhibit appealing properties such as a large electronic band gap, mechanical strength, and chemical inertness. Thus, BNNTs have attracted considerable attention recently.BNNTs possess many of the superior properties of CNTs such as high material stiffness [3, 4] (estimated Young’s modulus is 1.1- 1.3 TPa) and high heat conduction [5] (estimated thermal conductivity is ~300 W/mK at 300 K). BNNTs exhibit semiconducting properties with wide band gap values (~5.5 ev) nearly independent of their chirality and diameter [1]. Recently, it has been reported that the band gap of BNNTs can be tuned through a transverse electric field or covalent functionalizations [5]. This opens up many new applications of BNNTs, for example, as electro-optical devices. Because of their exciting properties, BNNTs can also find interesting applications in biological nanofluidic systems. Won and Aluru [6] recently reported that comparatively strong interactions between N atoms on a BNNT and water molecules induce a favorable filling of an empty finite-length (5,5) BNNT with water molecules. Furthermore, the diffusion coefficient of water molecules in a finite-length (5,5) BNNT is comparable to that in a (6,6) CNT. These superior filling and transport properties of water in a subnanometer BNNT suggest that a BNNT can be an excellent water conductor. However, there have been no reported studies so far on water structural and transport properties in a BNNT.