Synthesis of tin (II or IV) oxide coated multiwall carbon nanotubes with controlled morphology

How to obtain tin oxide (SnO or SnO2) coated multiwall carbon nanombes (MWNTs) by a simple SnCl2 solution method and finely control the coverage rate and particle size of SnO2 deposits is reported. We find that the amount of HCl added plays a key role in the synthesis. Without adding HCl, SnO but not SnO2 coated MWNTs is obtained due to the hydrolysis of the SnCl2 in water. In the case of adding the minimum amount of HCl, which can completely suppress the hydrolysis, a continuous SnO2 coating is formed on MWNTs with abundant surface graphitic edges. Due to the inhibition effect of HCl on SnO2 growth, increasing the amount of HCl added leads to the formation of uniformly dispersed and discontinuous SnO2 nanoparticles with smaller sizes of 2-4 nm and higher crystallinities on the MWNTs. Surface graphitic edges on MWNT side walls causing high surface energy facilitate the deposition of SnO2 nanoparticles. For MWNTs with perfect surface structure, few SnO2 nanoparticles are deposited on the nanotubes and the agglomeration of SnO2 nanoparticles is prone to happen.