In-situ growth of CNTs in silica powder by polymer pyrolysis chemical vapor deposition and their separation resistances

This study investigated the in-situ growth of carbon nanotubes (CNTs) in silica (SiO2) powder by polymer pyrolysis chemical vapor deposition with a polyethylene glycol (PEG) carbon source and cobalt nitrate catalyst. The mass ratio of PEG:citric acid:cobalt nitrate was determined to control the microstructures of the in-situ CNTs. Results indicated that with an increase in the mass ratio of PEG:citric acid:cobalt nitrate, the in-situ generated CNTs content in the SiO2 powder increased, the CNTs diameters (approximately 40 nm) did not significantly change, and the CNTs lengths decreased from 400–800 nm to 200–400 nm. Additionally, the in-situ CNTs that were anchored on the surfaces of SiO2 particles presented fewer defects and a high degree of graphitization. However, when the mass ratio of PEG:citric acid:cobalt nitrate exceeded the critical value, excessive amounts of amorphous carbon grown in situ on SiO2 particles were obtained. The suspension experiments showed that unlike the CNTs/SiO2 powders prepared by a combination of surfactant and ultrasonic methods with commercial CNTs, in-situ CNTs grown in SiO2 powders exhibited improved separation resistance in water. This would favor the uniform dispersion of CNTs within the matrix, improving the performance of nanocarbon-modified cement-based composites.