Selected-control hydrothermal synthesis and formation mechanism of 1D ammonium vanadate

Selective-controlled structure and shape of ammonium vanadate nanocrystals were successfully synthesized by a simple hydrothermal method without the presence of catalysts or templates. It was found that tuning the pH of the growth solution was a crucial step for the control of the phase-compositional, structure and morphology transformation. The final products were NH4V4O10 nanobelts, (NH4)2V6O16·1.5H2O nanowires, and (NH4)6V10O28·6H2O nanobundles, respectively, when the pH of the growth solution varied from 2.5 to 1.5, then to 0.5. The hydrogen bonding interaction and the surface free energies were responsible for the formation of the ammonium vanadates with the different structure and morphology. The conductivity measurements showed the one-dimensional (1D) ammonium vanadates were semiconductors at room temperature. The conductivity of 1D ammonium vanadates varied from 1.95×10−4 to 2.45×10−3 S cm−1 due to the different structures.