Ultrasound enhancing the mass transfer of droplet microreactor for the synthesis of AgInS2 nanocrystals

Droplet microreactors are powerful tools for synthesizing chemicals, nano materials and biomolecules, but traditional methods, such as mechanical stirring, are hard to enhance the internal mass transfer of droplet microreactor due to its small reaction space. In this study, we propose a novel ultrasonic-enhancing method for droplet microreactor, and report the effect of bubbles inside micro-droplets for the first time. On this basis, the synthesis of AgInS2 nanocrystals is selected as model reaction to study the enhancement mechanism. It is discovered that the flow field in micro-droplet is significantly improved owing to acoustic streaming and cavitation microstreaming. Benefiting from them, the mass transfer coefficient is enhanced by 72.5 %, and AgInS2 nanocrystals are successfully synthesized with smaller, more uniform particle size, as well as more adjustable performance compared with no ultrasonic radiation condition. This work provides a new method and a deep insight of ultrasound enhancing droplet microreactor, enabling the continuous production of fine chemical synthesis.