Phase Evolution of VO2 Polymorphs during Hydrothermal Treatment in the Presence of AOT

VO2 polymorphic nanoparticles (NPs) were synthesized by hydrothermal reaction in the presence of surfactant bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT). The AOT acts as both growth inhibitor and soft template in the formation of VO2 polymorphs, and there is a definite phase evolution process with prolonging reaction time: (NH4)(2)V6O16 center dot 1.5H2O -> NH4V4O10 -> VO2(B) -> VO2(B+D) -> VO2(D) -> VO2(D+P) -> VO2(P). The formation mechanisms of the VO2(D) and VO2(P) phases were found to be, respectively, a dissolution-recrystallization and recrystallization process. The as -prepared VO2(P) can be easily transformed to VO2(M) NPs after a mild annealing treatment, and the VO2(M) composite films show an excellent infrared performances. The clarification of phase evolution of VO2 polymorphs during hydrothermal treatment can help in understanding the formation mechanism and selective synthesis of different VO2 metastable phases.