Phase transition of single crystal VO2(R) nanorods in solution revealed by reversible change in surface charge state and structure

The VO2 single crystal nanorods were synthesized by hydrothermal method and investigated by XRD, SEM, SPM and TEM. Phase transition revealed by a reversible surface charge transfer for VO2 nanorods during heating–cooling circle in solution was observed by zeta potential measurement. The monoclinic VO2 nanorods were negatively charged because the exposed crystal surface planes are mostly composed of oxygen atoms as obtained by structure simulation, while the corresponding crystal planes change to a mostly positively charged state in VO2(R) during phase transition since the exposed planes change into V-atom dominated ones. The study provided a novel method to characterize the phase transition in solution for VO2 nanocrystals, and the phenomenon may have important potential applications.