Adsorption properties of boron nitride nanotubes

Khan, Saeed Ahmad
The developments in nanotechnology in last decades have provided use of nanoparticles for many applications in various areas such as electronics, fuel cells, composites, cosmetics, and biomedical. They have excellent mechanical, thermal, and electrical properties. Nanotechnology is one of the fastest growing areas in materials and engineering science and biotechnology. Nanotubes have been one of the most regarded and studied type of nanoparticles up to now. Boron nitride nanotubes (BNNTs) are an important member of nanotube family. BNNTs are structural analogues of carbon nanotubes (CNTs). They are formed by rolling and folding of boron nitride atom sheets into cylindrical forms. In this study, the nanotubes were synthesized in a tubular reactor at 1300oC, with an ammonia flow rate of 125 sccm and boron to iron oxide or iron ratio of 15/1. Two types of precursor materials (iron oxide and iron) were used in this study for BNNTs synthesis. The material was purified by acid treatment using HNO3 and HCl and characterized. Adsorption properties of BNNTs were investigated in order to analyze its potential applications as an adsorbent, catalyst support etc. XRD results revealed the presence of mostly hexagonal and little rhombohedral boron nitride solid phases. Some impurities like cubic iron and compound of boron and iron (FeB49) were also observed in the synthesized material. Hollow cylindrical, bamboo-like and agglomerated nanotubes were obtained with the diameters range of 10-300 nm and length of several micrometers. Most of the nanotubes were in the diameter range of 15-100 nm. Nitrogen adsorption isotherms were obtained for BNNTs and the type-II isotherms were observed with hysteresis loops resembling to both type A and type B which indicate the presence of cylindrical and slit like pores in the material. The highest BET surface area for material synthesized using iron oxide and iron were found to be 145.2 m2/g and 141.4 m2/g, respectively. The average surface area for all the samples synthesized in this study was 133.66 m2/g. The total pore volume for iron oxide and iron samples were 0.46 cm3/g and 0.45 cm3/g while the average BJH pore diameters were 41.7 Å and 37.5 Å, respectively. The micropore volume obtained for both synthesized materials from t-plot was 0.05 cm3/g. The micropore volumes (D-R method) obtained from carbon dioxide adsorption for materials synthesized using iron oxide and iron were 0.053 cm3/g and 0.040 cm3/g, respectively. Chemisorption results showed the presence of acid sites on the material. The total acidity was found to be 0.136 and 0.155 mmol/g for BNNTs synthesized using iron oxide and iron, respectively. The properties of samples, synthesized from both precursors, were compared and it was observed that properties of the synthesized material were almost the same.
Citation Formats
S. A. Khan, “Adsorption properties of boron nitride nanotubes,” M.S. - Master of Science, Middle East Technical University, 2016.