General approach for automated purification of quantum dots using size-exclusion chromatography

Abstract

Colloidal semiconductor nanocrystals or quantum dots (QDs) are a class of materials with size and shape-dependent optoelectronic properties that show potential for a range of applications. Discovery of new QDs with interesting properties and optimization of their synthesis require a rapid, generalizable, and scalable purification method to separate QDs from reaction mixtures. This paper describes a size-exclusion chromatography (SEC)-based approach that enables rapid, efficient separation of QDs from crude QD reaction mixtures. Using commercially available C-18 capped silica columns and off-the-shelf components, we report an automated liquid-chromatography platform with integrated optical characterization (UV-vis) for in-line optical characterization. This platform was used to investigate the effects of column operating parameters on QD separation performance and was further validated using six crude QD samples of different sizes, shapes, and compositions. Ligand coverage of the purified QD fractions can be tuned by controlling column parameters, with higher temperatures and residence times leading to ligand shedding of QDs. NMR analysis of purified QDs showed reduced solvent and ligand impurities when compared to samples purified using a precipitation–redissolution method. This SEC method provides a rapid (<2 min) approach for one-step purification of crude QDs on analytical or preparative scales and can be seamlessly integrated into existing QD or other nanocrystal research workflows.