Effect of polyvinylpyrrolidone on morphology and structure of In2O3 nanorods by hydrothermal synthesis

Indium oxide (In2O3) nanorods were hydrothermally synthesized from aqueous InCl3 solution in urea with addition of polyvinylpyrrolidone (PVP) as a steric stabilizer. Indium hydroxide, In(OH)3, was precipitated at 60 °C and was changed into a transient InOOH phase upon calcination at ∼250 °C in air. X-ray diffractometry revealed that the existence of PVP delays the phase transformation of InOOH. Cubic-structured In2O3 phase was then formed when temperature was raised to 350 °C, regardless of the PVP concentration. The In(OH)3 phase without the PVP showed a rod-based, flower-like morphology of polycrystalline character. Minor addition of the PVP, i.e., 0.1–2 wt.%, resulted in a pronounced evolution in morphology from the three-dimensional, flower-like form to discrete, one-dimensional nanorods aligned in planar form. Both the flower-like and discrete nanorod morphologies were preserved after heat treatments at 250 and 350 °C. This reveals that the morphological change is attributable to preferential adsorption of the PVP molecules on the In(OH)3 crystallite surface, so that the aggregate attachment responsible for the multipod growth is inhibited.