Controlling speciation of nitrogen in nitrogen-doped carbon dots by ferric ion catalysis for enhancing fluorescence

The speciation of doped-nitrogen (pyridinic N, pyrrolic N, graphitic N and amino N) was controlled by ferric ion catalysis for improving fluorescence of nitrogen-doped carbon dots (NCDs). Comparing to the synthesis of NCDs without ferric ion catalysis, the present strategy induces two following effects: (1) an increase of pyrrolic N and a decrease of pyridinic N; (2) a more well-organized arrangement of graphitic core and more N moieties exposed on the surface of NCDs. Consequently, absolute fluorescence quantum yield is increased from 6.2% to 27.0% and fluorescence can be further enhanced in acidity-media. Such phenomena provide solid evidence that pyrrolic N enhances the fluorescence of NCDs while pyridinic N inhibits it. Besides, NCDs achieve selective response to ferric ions. The present work provides a deeper insight into the understanding of luminescence mechanism and causes broader interest in manipulating CDs chemical structure. (C) 2016 Elsevier Ltd. All rights reserved.