Effect of nitrogen atom positioning on the trade-off between emissive and photocatalytic properties of carbon dots

Abstract

Carbon dots (CDs) are a versatile nanomaterial with attractive photoluminescent and photocatalytic properties. Here we show that these two functionalities can be easily tuned through a simple synthetic means, using a microwave irradiation, with citric acid and varying concentrations of nitrogen-containing branched polyethyleneimine (BPEI) as precursors. The amount of BPEI determines the degree of nitrogen incorporation and the different inclusion modes within the CDs. At intermediate levels of BPEI, domains grow containing mainly graphitic nitrogen, producing a high photoluminescence yield. For very high (and very low) BPEI content, the nitrogen atoms are located primarily at the edge sites of the aromatic domains. Accordingly, they attract photogenerated electrons, enabling efficient charge separation and enhanced photocatalytic hydrogen generation from water. The ensuing ability to switch between emissive and photocatalytic behavior of CDs is expected to bring substantial improvements on their efficiency for on-demand light emission or energy conversion applications.

Solvent‐Controlled Synthesis of Highly Luminescent Carbon Dots with a Wide Color Gamut and Narrowed Emission Peak Widths

“…Interestingly, the PL QYs of our CDs do not decrease distinctly as their particle size increase, which is inconsistent with the typical surface‐state controlled emission, suggesting that the improved contents of graphitic nitrogen atoms within carbon cores make a significant contribution to the PL QYs. The graphitic nitrogen content is able to enhance the rigidity of the domains, so as to reduce the non‐radiative relaxation through molecular vibrations on CD surfaces . Therefore, we believe both the particle size and the graphitic nitrogen content control the PL emission of our CDs synergistically.…”

Carbon Dots: Bottom‐Up Syntheses, Properties, and Light‐Harvesting Applications

“…developed N‐doped CDs to confirm the N effect in photocatalytic efficiency. They prepared the different N contents and configuration of CDs (from citric acid) by controlling the amounts of polyethyleneimine (PEI) . At a high PEI content, N atoms were distributed at the edge sites of the aromatic domains, thus enabling efficient charge separation and production of H 2 at a rate of 18.7 μmol g −1 h −1 .…”

Customizing the Electrochemical Properties of Carbon Nanodots by Using Quinones in Bottom‐Up Synthesis

“…Unfortunately, for CNDs, it is still necessary to tediously purify the as‐prepared mixtures of carbon dots, which contain various sizes, doping ratios, and surfaces . Since CNDs could play an important role in applications such as energy conversion and photocatalysis, for example, hydrogen evolution, several improvements have been proposed, among which are graphitization and N‐doping . Remarkably, carbon‐based dots were also coupled, as light harvesters, with natural redox enzymes displaying long‐term solar hydrogen production …”