Preparation of large In(OH)₃ and In₂O₃ particles through a seed-mediated growth method in a microreactor

Indium hydroxide (In(OH)₃) and indium oxide (In₂O₃) particles are typically synthesized through chemical precipitation methods. In this study, we used a seed-mediated growth method and microreactor-based synthesis process. We synthesized cubic In(OH)₃ particles with a crystal size of 172 nm from an 5% (w/v) indium chloride solution. The In₂O₃ particles synthesized through the thermal decomposition of In(OH)₃ particles featured crystals up to 90 nm in size with an average size of 73 nm, which were much larger than the 20–30 nm In₂O₃ particles synthesized by a traditional precipitation method. The concentrations of the seed and growth solutions were varied from 1% to 7% (w/v). The crystal size of the particles increased with the concentration of the seed and growth solutions; this tendency was the opposite to that observed for the precipitation method. Through the use of a 5% (w/v) seed solution, the flow rate of the growth solution was varied from 1 to 10 mL/min, and the resulting crystal size decreased as the flow rate was increased. To understand the reasons for this trend, the growth rate of the crystals was determined at different flow rates (i.e., 1, 5, and 10 mL/min). A growth model consistent with the experimental results was established, which demonstrated that slow addition of the growth solution was beneficial for preparing large indium hydroxide particles.