Uncovering the Charge Transfer between Carbon Dots and Water by In Situ Soft X-ray Absorption Spectroscopy.

Abstract

ABSTRACT. Carbon dots (CDs) exhibit outstanding physiochemical properties which render them excellent materials for various applications, often occurring in an aqueous environment, such as energy harvesting and fluorescence bioimaging. Here we characterized the electronic structures of carbon dots and water molecules in aqueous dispersions using in situ X-ray absorption spectroscopy. Three types of carbon dots with different core structures (amorphous vs. graphitic) and compositions (undoped vs. nitrogen-doped) were investigated. Depending on the CD core structure, different ionic currents generated upon X-ray irradiation of the CD dispersions at the carbon K-edge were detected, which are interpreted in terms of different charge transfer to the surrounding solvent molecules. The hydrogen bonding networks of water molecules upon interaction with the different CDs were also probed at the oxygen K-edge. Both core graphitization and nitrogen doping were found to endow the CDs with enhanced electron transfer and hydrogen bonding capabilities with the surrounding water molecules.