A novel aqueous co-precipitation process to prepare indium tin oxide nanopowders

In this paper, a novel aqueous co-precipitation process for preparing ITO (indium tin oxide) nanopowders was investigated. In this process, the solutions of In3+–Sn4+ ions and 25% NH3·H2O were simultaneously added into the solution of (NH4)2SO4–NH3·H2O, NH4Cl–NH3·H2O and NH3·H2O to make different reaction solutions. When (NH4)2SO4–NH3·H2O solution was used as the primary reaction liquid with pH value in the range of 6.5–7.0, spherical ITO particles with uniform particle size (10–20 nm), low agglomeration and large specific surface were obtained. The ITO particles were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and energy-dispersive spectrometer (EDS). The EDS analysis indicated that the distribution of In and Sn elements in the ITO powders was uniform and their mass ratio was close to 9:1, which would result from the co-precipitation process that provided a stable chemical circumstance for In3+ and Sn4+ to be co-precipitated.

Research highlights
► In this work, in order to reduce the pH value fluctuation in the conventional chemical precipitation process, a novel aqueous co-precipitation process for preparing ITO nanoparticles is studied. The inorganic solution containing (NH4)2SO4–NH3·H2O, NH4Cl–NH3·H2O and NH3·H2O was employed as primary reaction liquid. The mixed solution of In3+–Sn4+ ions and the precipitator solution of 25% NH3·H2O were simultaneously injected into the primary reaction liquid. The injection rates were controlled to maintain the pH of the reaction system stable. The influences of different primary reaction liquids and different pH values of the reaction system on ITO nanoparticles were investigated.