Miniaturized droplets flow reactor for one-step highly controlled synthesis of SnO₂ quantum dots at room temperature

Abstract

In recent years, the conventional methods of synthesizing nanomaterials have been surpassed by the emergence of the microfluidics route, which has brought forth numerous advantages and transformed the domain of nanomaterial synthesis. However, the synthesis of semiconducting oxide nanomaterials, specifically Tin oxide (SnO2), remains a crucial area of research due to its remarkable advantages as a viable alternative to toxic and costly materials. Additionally, SnO2 quantum dots (QDs) exhibit immense potential across a diverse range of applications due to their exceptional optical and electrical properties. The existing synthesis methods for SnO2 QDs are either time-consuming or involve high-temperature conditions. To address these challenges, droplet-based microfluidic technique has emerged as a promising approach for the controlled synthesis of various semiconducting nanomaterials. This article highlights the synthesis of SnO2 QDs with tunable size through the utilization of a droplet-based microfluidic technique, providing precise control over droplet volumes. X-ray diffraction analysis verified the presence of rutile-type tetragonal structure in SnO2 QDs. From the transmission electron microscopy analysis, the average particle size was calculated to be 1.90 nm, 2.09 nm and 2.63 nm for the volume of droplet corresponding to 33.25 µl, 27.84 µl and 18.25 µl respectively. Furthermore, with a decrease in particle size a tunabilty in optical bandgap, from 4.60 eV to 4.00 eV was observed. This work provides insights into the influence of droplet volume on the particle size which in turn affects the associated properties of SnO2 QDs in a droplet-based microfluidic synthesis system.