Advanced synthesis of transition metal oxide quantum dots: A novel approach to tailoring their physical properties

The synthesis of Quantum Dots (QDs) is broadly classified into two approaches: top-down and bottom-up. The top-down approach mainly depends on weakening the van der Waals interactions between adjacent layers and breaking the strong covalent bonds of the material. Top-down approaches can be used to reduce the particle size. Unfortunately, such methods are weakly feasible for high yield QDs synthesis. On the other hand, bottom-up approaches need an insulating ligand coating, which affects the electrical transport properties of the material. Several difficulties persisted in the existing synthesis procedure of Transition Metal Oxide (TMO) QDs, as per the present literature. It depicts that there is a need for an alternative approach to synthesize QDs without any incongruities. Therefore, a simple and rapid hybrid method is proposed and demonstrated to synthesize MoO3 (TMO) QDs. One of the two top-down approaches used to synthesize QD is a combination of thermal evaporation and sonication-induced chemical etching process.
In this work, highly stable and water-soluble MoO3 QDs without any surfactants are successfully synthesized via this hybrid method. The growth mechanism of QDs in different crystalline phases as a function of acid concentration is exemplified in this work. The excitation-dependent Photoluminescence (PL) emission of MoO3 QDs as a function of acid concentration is also investigated. The impact of sonication bath temperature on the morphological, microstructural, size, crystal-structural, and optical properties of MoO3 QDs has been systematically investigated. The controlled sonication bath temperature during synthesis process results in the tunability of the QDs size. The mechanism behind the controlled size of the QDs is deeply rooted in the acoustic cavitation phenomenon. The sensing ability of these QDs is also investigated.