Controllable generation of multi-row bubbly flow in coupled microstructures and its boosting of photocatalytic decarboxylative carbonylation

Continuous-flow microreactor technology has emerged as a powerful driver of process innovation in photocatalysis. However, microfluidic schemes that are ideal for gas–liquid photoreactions are still limited by the low specific interfacial area. Herein, we invent for the first time a coupled microstructure comprising sudden contraction, shearing, and sudden expansion parts, which can generate microbubbles with smaller sizes under lower flow rates compared with the conventional T-junction. Based on bubble dynamics studies, a predictive model for the bubble size, with prediction errors of less than 10%, is established. Interestingly, the generated microbubbles can be induced by the expansion flow to form a multi-row bubbly flow. Additionally, predictive models for the row number are proposed to guide its controlled production. Computational fluid dynamics simulations show a 22.8-fold increase in specific interfacial area for the five-row bubbly flow compared to the segmented flow. Moreover, the average dissolved oxygen concentration at a given time increases by 34.0 times. Further, photocatalytic decarboxylative carbonylation limited by oxygen mass transfer is employed as the model reaction, demonstrating the excellent performance of multi-row bubbly flow in enhancing the gas–liquid photocatalysis, and the stronger enhancement at higher row number. Subsequently, the phototransformation achieves 96.3% yield within 19 min at a six-row bubbly flow, and the space–time yield reaches 6.82 gL–1 h−1, thus indicating the high efficiency of the developed microdevice. The multi-row bubbly flow enabled by this coupled microstructure provides a new process window for continuous, efficient, and controllable gas–liquid photocatalysis.