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Abstract
The oxidation of renewable resources is a promising process that has great potential in addressing the climate change and building the circular economic, sustainable society and green chemical supply chain. This study explores the application of ultrasound in oxidation processes using the wastewater treatment as a case study. Advanced oxidation processes (AOPs) are highly effective for degrading the pollutants in wastewater through the generation of oxidative radicals, with ultrasound emerging as a promising AOP method due to its mild conditions and synergistic potential with other methods. However, ultrasound alone faces challenges in efficiently degrading complex compounds like azo dyes, partly due to issues with cavitation bubble stability and non-uniform ultrasonic fields. Microfluidic reactor combined with microbubble technology offers a solution to enhance ultrasound efficiency by improving bubble stability and energy distribution. In this study, we investigate microbubble formation in a microfluidic reactor with T-junction and flow-focusing inlets, aiming to enhance ultrasound-driven AOPs. The flow-focusing design successfully generates relatively small and monodisperse bubbles allowing for effective ultrasound application at 108.5 kHz using a piezoelectric transducer. Our results demonstrate a relatively high H2O2 generation rate of 0.54 μM/s, among the highest reported in the literature, and a methyl orange (MO) degradation efficiency of 35% in just 2.9 seconds - significantly surpassing conventional systems and prior microfluidic studies. This work demonstrates the novelty of integrating microbubble technology with microfluidic reactors to enhance the energy efficiency of ultrasound - assisted oxidation processes, providing an efficient approach to the chemo-selective conversion of renewable resources to high-value specialty chemicals that are inaccessible via conventional routes.
