Photochemical Transformations of Carbon Dots in Aqueous Environments

Benjamin P. Frank, Leslie R. Sigmon, Alyssa R. Deline, Ronald S. Lankone, Miranda J. Gallagher, Bo Zhi, Christy L. Haynes, D. Howard Fairbrother

Research output: Contribution to journalArticlepeer-review


The unique physicochemical and luminescent properties of carbon dots (CDs) have motivated research efforts toward their incorporation into commercial products. Increased use of CDs will inevitably lead to their release into the environment where their fate and persistence will be influenced by photochemical transformations, the nature of which is poorly understood. This knowledge gap motivated the present investigation of the effects of direct and indirect photolysis on citric and malic acid-based CDs. Our results indicate that natural sunlight will rapidly and non-destructively photobleach CDs into optically inactive carbon nanoparticles. We demonstrate that after photobleaching, âOH exposure degrades CDs in a two-step process that will span several decades in natural waters. The first step, occurring over several years of âOH exposure, involves depolymerization of the CD structure, characterized by volatilization of over 60% of nascent carbon atoms and the oxidation of nitrogen atoms into nitro groups. This is followed by a slower oxidation of residual carbon atoms first into carboxylic acids and then volatile carbon species, while nitrogen atoms are oxidized into nitrate ions. Considered alongside related CD studies, our findings suggest that the environmental behavior of CDs will be strongly influenced by the molecular precursors used in their synthesis.

Original languageEnglish (US)
Pages (from-to)4160-4170
Number of pages11
JournalEnvironmental Science and Technology
Issue number7
StatePublished - Apr 7 2020

Bibliographical note

Funding Information:
This work was supported by National Science Foundation under the Center for Sustainable Nanotechnology, CHE-1503408. The CSN is part of the Centers for Chemical Innovation Program. L.R.S. is supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1746891. The authors would like to thank Steven Chow for assistance with ion chromatography measurements, the Materials Characterization Facility at Johns Hopkins University, and the U.S. Department of Energy (DOE)/NREL/ALLIANCE for the solar irradiance data as well as Casey Smith for assistance with figures and Dylan Brach for CD photographs. TEM characterization was carried out in the Characterization Facility, University of Minnesota, which receives partial support from the MRSEC program (DMR-1420013).

Publisher Copyright:
Copyright © 2020 American Chemical Society.

How much support was provided by MRSEC?

  • Shared

Reporting period for MRSEC

  • Period 7

PubMed: MeSH publication types

  • Journal Article
  • Research Support, U.S. Gov't, Non-P.H.S.


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