Modeling of turbulence induced shear assisted controllable synthesis of zinc oxide nanoparticles

Abstract

This thesis investigates the synthesis of zinc oxide (ZnO) nanoparticles using a Taylor-Couette flow reactor (TCFR) under controlled turbulent shear conditions. ZnO nanoparticles are widely used in photocatalysis, gas sensing, optoelectronics, and antimicrobial applications, but conventional synthesis methods often suffer from poor control over particle size distribution and morphology due to inadequate mixing. The TCFR provides well-defined hydrodynamic environments with uniform shear rates and enhanced mixing efficiency, offering a promising platform for controllable nanoparticle synthesis.
ZnO nanoparticles were synthesized by precipitating zinc chloride with sodium hydroxide at 60°C across five rotational speeds (2000-10000 rpm), corresponding to Reynolds numbers ranging from 1.98×10⁵ to 9.92×10⁵. Comprehensive characterization was performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Computational fluid dynamics (CFD) simulations were conducted to elucidate the hydrodynamic conditions and validate experimental observations.
XRD analysis confirmed phase-pure hexagonal wurtzite ZnO with crystallite sizes ranging from 23.7 nm (2000 rpm) to 29.9 nm (8000 rpm), exhibiting a non-monotonic relationship with rotational speed. SEM characterization revealed significant morphological evolution: particles at 2000 rpm showed extensive agglomeration with broad size distribution (mean = 0.951 μm, CV = 13.0%), while optimal conditions at 8000 rpm produced well-dispersed particles with narrow distribution (mean = 1.081 μm, CV = 11.9%). The 10000 rpm condition showed slight size increase, suggesting excessive shear may promote collision-induced aggregation.
Systematic correlations between hydrodynamic parameters and particle properties were established. Energy dissipation rates increased from 4.56 to 113.76 W/kg, with Kolmogorov microscales decreasing from 24.3 to 8.5 μm. Mixing efficiency improved from 72% to 96% with increasing rotational speed. Compared to conventional batch synthesis, TCFR achieved 36-48% smaller particles, 2.6-fold narrower size distributions, superior crystal quality (15-31% higher XRD peak intensities), 3.6× higher space-time yield, and 4.5× better reproducibility (±4% vs. ±18% variation).
CFD simulations showed excellent agreement with experimental results, validating mixing times (5.4-10.1% deviation), energy dissipation rates (3.7-10.9% deviation), and particle size trends. The validated model provides a reliable foundation for reactor optimization and scale-up design.
This work demonstrates that Taylor-Couette flow reactors enable superior control over ZnO nanoparticle synthesis compared to conventional methods. The optimal operating window (6000-8000 rpm) balances small particle size, narrow distribution, high crystallinity, and good dispersion. These findings advance fundamental understanding of nanoparticle formation in controlled hydrodynamic environments and demonstrate the viability of continuous flow processing for industrial-scale production of high-quality nanomaterials.

Date of Award	18 Jul 2026
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Xiaogang Yang (Supervisor) & Shanshan Long (Supervisor)