Organometallic one-pot synthesis of ZnO quantum dots coated by sulfoxides as L-type ligands

Abstract

Although an extraordinary amount of research into the chemistry of nanoscale zinc oxide (ZnO) has been conducted over the past three decades, application-driven design and reproducible fabrication of colloidal ZnO quantum dots (QDs) remain a great challenge. The application of low-molecular-weight, non-interfering protecting ligands may be potentially beneficial for the design of quantum-sized ZnO crystals, simultaneously providing colloidal stabilization and long-term functionality. Herein, we pursue the idea of ‘less is more’ and continue our systematic investigations on a non-external-surfactant-assisted organometallic approach for the preparation of colloidal ZnO QDs via direct injection of Et₂Zn to ligand-like solvent followed by exposition towards atmospheric air as well as we introduce a novel approach toward ZnO QDs through the transformation of sulfoxide-modulated Et₂Zn-based precursors in a THF solution. The application of sulfoxides as L-type protectors contributes to the formation of uniform ZnO QDs with average diameters of 5.4 to 8.2 nm, depending of the character of applied sulfoxide, and the low surface grafting density of the coating ligand without impeding their colloidal as well as solid-state stability. The reported QDs exhibit almost identical absorption parameters and show particularly long, multiexponential PL decays reaching recombination times up to 2.3–2.8 μs. In turn, preliminary control experiments involving photodegradation of methylene blue demonstrate dramatically different photocatalytic performance of QDs derived from the neat ligand-like solvent synthesis and the new approach based on the finetuning of precursors’ reactivity by Lewis-base chemical additives.