Modeling of Mass Transfer and Reaction Kinetics in ZnO Nanoparticle Micro-Reactor Systems for AMX and DOX Degradation

Abstract

This study aims to model the coupled phenomena of photocatalytic reaction and mass transfer in the degradation of Amoxicillin (AMX) and Doxycycline (DOX) using Zinc oxide (ZnO) nanoparticles within microreactor systems. The objective is to gain a comprehensive understanding of the dynamic interaction between the photocatalytic degradation kinetics and the mass transfer processes to optimize the conditions for efficient antibiotic removal from contaminated water. This involves characterizing the reaction kinetics via the Langmuir-Hinshelwood model, estimating the mass transfer coefficients, and analyzing the effects of axial dispersion to ensure the accurate determination of intrinsic kinetic constants and minimize mass transfer limitations. This study used a syringe pump to ensure a consistent flow of antibiotic solution into the microreactor. The results indicate that AMX reaches adsorption equilibrium more rapidly than DOX, corresponding to its faster photocatalytic degradation kinetics and higher final conversion rate (89% for AMX, 86% for DOX). The mass transfer coefficient (kd) was estimated using the Sherwood number, derived from three different models, with the constant Sherwood model best fitting the R1 microreactor data. An analysis of the Damköhler number (DaII) indicates that high flow rates minimize mass transfer limitations in the R1 microreactor, allowing the determination of near-intrinsic kinetic constants. On the contrary, at low flow rates, kinetic constants are apparent as a result of mass-transfer limitations. The study concludes that higher flow rates (≥ 10 mL/h) in the R1 microreactor are preferable to approach intrinsic kinetics and reduce mass transfer limitations during photocatalytic degradation of antibiotics. These findings underscore the potential of ZnO-based oxidation processes in treating antibiotic-contaminated water with optimized conditions, providing a pathway for efficient and sustainable wastewater treatment.