Abstract: An efficient method for separating thin-long carbon nanotubes (CNTs)from carbon fibers is presented. The process involves grinding, dispersion, flocculating deposition and filtration treatments. SEM, TEM and TGA were used to evaluate the purification effect. The as-prepared CNTs specimen consists of large amounts of thin-long entangled CNTs that are 10～20 nm in outer diameter and some larger carbon fibers with diameters of more than 100 nm. After grinded, carbon fibers can be broken, while thin-long CNTs are undamaged. Dispersed in a water/surfactant solution under ultra-sonic treatment, most pieces of fibers and carbonaceous impurity were left suspended in a kinetically stable colloidal solution, while many thin-long CNTs flocculated into agglomerates and settled down. Most CNTs were extracted from the suspension as flocculated agglomerates leaving pieces of carbon fibers and other carbonaceous impurity in the filtrate. The purification mechanism is based on the difference of tensile strength and dispersibility of thin-long CNTs with that of carbon fibers.

Key words: Carbon nanotubes, Carbon fibers, Purification, Dispersion, Flocculation