Molar ratio of In to urea directed formation of In2O3 hierarchical structures: cubes and nanorod-flowers

Abstract

In this work, different morphologies of In₂O₃ products were fabricated by the calcination of In(OH)₃, which was synthesized through a hydrothermal route, with tuning of the molar ratio of indium to urea. The In₂O₃ inherited the morphology of its precursor and the proposed formation mechanisms for the In(OH)₃ structures, assisted by the molar ratio of indium to urea, were put forward. The formation mechanism of In(OH)₃ cubes at a higher molar ratio of In to urea was ascribed to Ostwald ripening mechanism, while the growth of In(OH)₃ nanorod-based flowers at a lower molar ratio of In to urea was attributed to the oriented attachment of In(OH)₃ nanoparticles coordinated with the complexation of In³⁺ to urea, in which the urea may play ternary roles including being the alkaline media, the coordinating agent and the surface anchored organic molecules.