Purification and Enrichment of Boron Nitride Nanotube Feedstocks

Abstract

A method for purifying a boron nitride nanotube feedstock is disclosed, including an initial step of mixing a boron nitride nanotube (BNNT) feedstock with a solvent to form an initial mixture. This BNNT feedstock is made up of hexagonal boron nitride (h-BN) particles and less than about 50 weight percent BNNTs on a dry basis. This initial mixture is then sonicated within a treatment vessel using an ultrasonic probe. At least a portion of the initial mixture is filtered out of the treatment vessel and across a nanoporous membrane at the same as the sonication. In this manner, the method provides a filtrate which is enriched in h-BN particles relative to the initial mixture and a retentate which is enriched in BNNTs relative to the initial mixture.

What is claimed is: 
     
         1 . A system for purifying a boron nitride nanotube feedstock comprising:
 a treatment vessel having an interior volume for receiving an initial mixture of a boron nitride nanotube (BNNT) feedstock with a solvent, the BNNT feedstock comprising hexagonal boron nitride (h-BN) particles and less than about 50 weight percent BNNTs on a dry basis   a nanoporous membrane in flow communication with the treatment vessel interior volume; and   an ultrasonic mixing probe disposed within the treatment vessel interior volume,   wherein the initial mixture of the boron nitride nanotube (BNNT) feedstock with the solvent is sonicated within the treatment vessel interior volume while, at the same time, at least a portion of the mixture is filtered across the nanoporous membrane and out of the treatment vessel to provide a filtrate.   
     
     
         2 . The system of  claim 1 , wherein the initial mixture further comprises a non-metal containing surfactant. 
     
     
         3 . The system of  claim 1 , wherein the retentate comprises at least 90 weight percent BNNTs on a dry basis. 
     
     
         4 . The system of  claim 1 , wherein the solvent comprises at least one polar aprotic solvent. 
     
     
         5 . The system of  claim 1 , wherein the nanoporous membrane comprises polytetrafluoroethylene. 
     
     
         6 . The system of  claim 1 , wherein the nanoporous membrane comprises a plurality of pores, the pores having an average pore size from about 0.1 μm to about 100 μm. 
     
     
         7 . The system of  claim 1 , further comprising a receiving vessel for collecting filtrate from the nanoporous membrane, wherein the receiving vessel is maintained at a sub-atmospheric pressure in order to draw filtrate across the membrane. 
     
     
         8 . The system of  claim 1 , further comprising a solvent supply reservoir and a solvent supply line for adding makeup solvent to the mixture in the treatment vessel.