Influence of Defects in Boron Nitride Nanotubes in the Adsorption of Molecules. Insights from B3LYP-D2* Periodic Simulations

Oriol Matarín,Albert Rimola

doi:10.3390/cryst6050063

Abstract

The adsorption of H2O, NH3 and HCOOH as polar molecules and C6H6 and CH4 as non-polar ones on a series of zig-zag (6,0) single-walled boron nitride nanotubes (BNNTs) both being defect-free (P_BNNT) and containing defects at the nanotube walls has been studied by means of B3LYP-D2* periodic calculations. We focused on defects derived from monovacancies of B (N-rich_BNNT) and N (B-rich_BNNT) atoms and also on Stone-Wales defects (SW_BNNT). The adsorption of polar molecules with defective BNNTs is generally based on dative interactions and H-bonding, and their adsorption energies strongly depend on the type of BNNT. N-rich_BNNT is the most reactive nanotube towards adsorption of polar molecules, as in all cases deprotonation of the polar molecules is spontaneously given upon adsorption. The strength in the adsorption energies is followed by B-rich_BNNT, SW_BNNT and P_BNNT. Adsorption of non-polar molecules is mainly dictated by dispersion interactions, and, accordingly, the adsorption energies are almost constant for a given molecule irrespective of the type of nanotube.

Highlights

Boron nitride nanotubes (BNNTs) are isosteres and structurally similar to carbon nanotubes (CNTs), in which alternating B and N substitute for C atoms
Periodic quantum mechanical calculations have been used to simulate the adsorption of H2 O, NH3 and HCOOH and C6 H6 and CH4 on different zig-zag (6,0) single-walled boron nitride nanotubes (BNNTs) that are defect-free (P_BNNT) or defective BNNTs based on B (N-rich_BNNT) and N (B-rich_BNNT) monovacancies and on Stone-Wales defects (SW_BNNT), with the aim of determining the influence of nanotube defects in the adsorption energies
Adsorption of polar molecules on the defective BNNTs is in general dictated by dative interactions established between the electron donor atoms of the molecules and the B atoms of the BNNTs, which produce large charge transfers from the molecules to the BNNT

Summary

Introduction

Boron nitride nanotubes (BNNTs) are isosteres and structurally similar to carbon nanotubes (CNTs), in which alternating B and N substitute for C atoms. 5.5 eV, which is practically independent of their morphology, diameter, helicity and concentric layers. BNNTs are electrical insulators with an almost constant band gap of ca. This is at variance with CNTs, which exhibit metallic or semiconducting characters, which in turn strongly depend on the tubular geometry features. Excellent recent reviews focused on the structure, synthesis and applications of BNNTs are available [8,9,10]. The stable band gap and the low reactivity towards molecule adsorption (which essentially takes place via physisorption) may impose some limitations for extensive applications of BNNTs, for instance, as nanoelectro-optical devices. The conditions under which BNNTs are Crystals 2016, 6, 63; doi:10.3390/cryst6050063 www.mdpi.com/journal/crystals

Objectives

Results

Conclusion