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

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.