Dotted crystallisation: nucleation accelerated, regulated, and guided by carbon dots.

Crystallisation from solution is an important process in pharmaceutical industries and is commonly used to purify active pharmaceutical ingredients. Crystallisation involves phase change and the mechanisms involved are random which makes the process stochastic. This creates a variation in the time required to reach a fixed percentage of yield from batch to batch. It is essential to regulate the batch crystallisation process and make it more predictable for industrial applications for the ease of process chain scheduling of upstream and downstream unit operations. In this work, we propose a new technique called dotted crystallisation, where carbon dots are used to dictate and regulate events associated with nucleation and crystallisation processes. Following the rules of two-step nucleation theory, the carbon dots intentionally added to a supersaturated solution of curcumin anchors the crystallising compound to form prenucleation clusters that evolve into stable nuclei. Using curcumin as a model compound, we showed that the nucleation of this compound in isopropanol can be regulated, and the nucleation rate can be improved via addition of small quantities of carbon dots to the supersaturated solution. Our results confirmed that the nucleation rate of curcumin by dotted crystallisation was roughly four times higher than the nucleation rate by conventional cooling crystallisation and produced smaller sized crystals with a narrow size distribution. [ABSTRACT FROM AUTHOR]