(653f) Synthesis Of Boron Single-Wall Nanotube Using Optimized Mg-Mcm-41
Synthesis of pure Boron single-wall nanotube by reaction of BCl3 with H2 over 1%Mg-MCM-41 was previously reported by our group. Preliminary results suggest Mg-doped Boron nanotube show high temperature superconductivity, so efforts to produce large samples for characterization are important. Parameters including catalyst nature, reaction time and temperature, reactant ratio, BCl3 flow rate, are observed to significantly affect both the yield and quality of the Boron nanostructures. The structure of the catalyst and loading condition of Mg are crucial in optimizing the selectivity to boron nanotube over other nanostructures produced. Optimization of the synthesis conditions for 1%Mg-MCM-41 shows a silicate solution pH=12.0 giving the best result, leading to the highest yield of Boron nanotube and retaining the template structure during synthesis. Based on the tube diameter and template structure sensitivity, a mechanism involving the physical templating of Boron nanotube is proposed. Tubular nanostructures growing out of the silica template are captured in TEM, and confirmed by EELS for Boron. Raman is employed to confirm the tubular geometry and to show the absence of Carbon nanotube contamination. After two rounds of NaOH washes removing the silica template, bundles of nanotubes are found. EXAFS of Boron K-edge further evaluate the structure and exclude the existence of Boron Nitride. Since Mg ions are relatively large, high loading incorporation can collapse the pores in the mesoporous silica template. Ni is introduced by co-incorporation with Mg to increase activity while maintaining in template stability. This catalyst both shifts the optimal reaction temperature down, and improves the Boron nanotube yield.