Influence of the Mixing Ways of Reactants on ZnO Morphology

Abstract

ZnO particles with various morphologies were synthesized by mixing ZnSO4and NaOH solutions at 25°C followed by aging of the suspensions at 40–80°C for 2.0 h, keeping the initial molar ratio of Zn2+to OH−at 1 : 4. ZnO irregular plates were prepared by adding NaOH to ZnSO4whileε-Zn(OH)2rhombic particles were produced using the opposite mixing way. After aging of the slurries at 80°C for 2.0 h, the ZnO plates were kept stable while theε-Zn(OH)2rhombic particles were converted to ZnO whiskers with a length of 1.0–4.0 μm and a diameter of 0.03–0.3 μm. Thermodynamic analysis indicated that the formation of the Zn-bearing precipitates (ZnO orε-Zn(OH)2) at room temperature was connected closely with the solution composition.

Synthesis of Al doped ZnO nanoparticles by aqueous coprecipitation

“…These experimental conditions lead to a formation of particles in a basic solution (final pH>12) whereas in the conventional method crystallization occurs from pH = 3 to 12. Yang et al [29] have also obtained -Zn(OH) 2 when they added the cationic solution to the soda solution. In order to investigate the relationships between ZnO and -Zn(OH) 2 , a part of the slurry was aged 24 hours under vigorous stirring.…”

“…Oliveira et al [28] have proposed a precipitation under double-jet conditions to produce micrometric ZnO particles at room temperature. Moreover, recently, Yang et al [29] have reported the obtention of ZnO at 25°C by adding soda to a Zn sulfate solution. However, in many applications ZnO doping is necessary in order to reach the best properties, especially Al doping.…”

Controlled dispersion of ZnO nanoparticles produced by basic precipitation in solvothermal processes

“…In synthesis I, the precipitation process started immediately when NaOH was added to the Zn 2þ solution. According to the literature, the precipitated white powder corresponds in a first stage to Zn(OH) 2 intermediate, but as soon the pH increases, it becomes ZnO [53,54,55,56]. The general reaction of this synthetic procedure can be described by the following equation:…”