Microfluidic steam-based synthesis of luminescent carbon quantum dots as sensing probes for nitrite detection

Abstract In this work, an efficient and green approach has been presented to prepare carbon quantum dots (CQDs) from watermelon juice through a microfluidic steam-based method, with a view to enabling continuous production at scale, i.e., to save time, costs, or energy as compared to conventional production using an autoclave. The evolution of the product formation through multifarious intermediates generated in different stages of the reaction process was characterized. Computational fluid dynamics simulations reveal the pressure and velocity profiles in the microchannel to exert process control. These determine the quality of the obtained CQDs by influencing the particle size transformations and manifold chemicals along the microchannel axis. The optimal reaction conditions and reaction mechanism for the synthesis of CQDs were investigated. Additionally, the synthesized CQDs demonstrated good fluorescence properties as well as a specific response to NO 2 − {\text{NO}}_{2}^{-} in both fluorescence and spectrophotometric modes, providing great potential for their application in environmental monitoring.