Intensified tailoring of ZnO particles in a continuous flow reactor via hydrothermal synthesis

Abstract

ZnO micro-particles of narrow size distribution were successfully produced by the continuous hydrothermal synthesis of zinc nitrate in a coiled flow inverter reactor at different [OH−/Zn2+] molar ratios and flow rates. Results revealed that an increase in mixing intensity and [OH−/Zn2+] molar ratio yields an increase in particle size due to an enhancement in mass transfer between the reacting phases, while the particle size distribution analysis showed that the particles synthesized are monodisperse with polydispersity index below 0.21 and polydispersity P-parameter below 12.3% for all the flow rates tested. The obtained results are a consequence of a dampening effect in axial dispersion due to the formation of a secondary flow and inversion of the velocity profile. Moreover, no significant variation in particle size was obtained by increasing the [OH−/Zn2+] molar ratio at Dean numbers of 20. The experimental results suggest that the coiled flow inverter is an attractive alternative for carrying out the hydrothermal synthesis of metal oxides offering production flexibility with a high quality product if mixing throughout the system meets the hydrodynamic criteria discussed in this work.