Multifunctional nitrogen-doped carbon dots from maleic anhydride and tetraethylenepentamine via pyrolysis for sensing, adsorbance, and imaging applications

Carbon dots are materials with fascinating optical and electronic properties that can replace organic dyes and fluorescent semiconductor nanocrystals. In this work, we developed a one-step pyrolysis for producing fluorescent, water-soluble, and highly nitrogen-doped carbon dots (NCDs) from the readily available chemical precursors: tetraethylenepentamine and maleic anhydride. NCDs exhibited blue fluorescent emission with a relatively high quantum yield of 21% and average diameter of approximately 8 nm. These NCDs were found to be selective sensors for Cu²⁺, with a limit of detection of 0.62 μM. A simple NCD-coated, paper-based sensor demonstrated that the NCDs were highly responsive to and selective of Cu²⁺. Furthermore, X-ray absorption fine structure measurements showed the unique coordinating properties of the NCDs. The copper complex changed from a distorted octahedral to a square planar structure upon the addition of NCDs. The NCDs were also found to be an excellent adsorbent for Cu²⁺, with a surface coverage of 1.5 ions nm⁻², equivalent to 214 mg g⁻¹ adsorption capacity. In addition, NCDs were used to image a human fingerprint and for the preparation of fluorescent plastics. These results demonstrated that the multifunctional NCDs with excellent optical properties and water solubility produced in this work can be used in a range of applications, including sensors, adsorbents, imaging, and forensic science.