Controlled precipitation of zinc oxide particles

Abstract

The scope of this work consisted of precipitating directly zinc oxide particles from zinc nitrate and zinc sulphate solutions using sodium hydroxide at pH 10,5, 2 h and 25 or 60 °C. For the zinc nitrate system, the effect of additives at 25 °C, such as sodium sulphate and sodium dodecyl sulphate, was also investigated. Precipitated powders were characterized in terms of their crystalline structure (X-ray diffraction), morphology and size (scanning electron microscopy, transmission electron microscopy). Precipitation in distilled water with zinc nitrate produced homogeneous star-type particles (1 μm) composed of assembled 30-nm crystallites at 25 °C and ellipsoidal and spherical particles (100 nm to 1 μm) at 60 °C. On the other hand, for the zinc sulphate system at 25 °C, several different morphologies were obtained as ellipsoids (250 × 800 nm), half ellipsoids (250 × 350 nm), fibres (40 × 700 nm) and unshaped particles (700 nm), whilst half ellipsoids (100 nm) were precipitated as well as smaller particles (25–60 nm) at 60 °C. The investigation of the additive effect showed that precipitation from zinc nitrate solution in the presence of sodium sulphate led to half ellipsoids with a size range from 100 to 300 nm. In contrast, the addition of sodium dodecyl sulphate resulted in a mixture of morphologies that included half ellipsoids (150–200 nm), asymmetrical and symmetrical ellipsoids, as well as small particles of 30 nm. This study evidenced the effect of additives on morphology and size control of submicrometric particles constituted of assembled nanocrystallites.