Red-Emissive Carbon Dots as Markers for Onsite Quality Assurance of Fuel

Conventional organic molecules are used as markers to protect the brand and monitor adulteration in fuel. Recently, red-emissive nanomaterial-based sensors have received considerable attention due to less interference by autofluorescence of the matrix, their simplicity, and easy analysis of experiment. However, achieving efficient red-emissive carbon-based nanomaterials under longer-wavelength excitation still remains a bottleneck in terms of synthesis, product purification, compatibility issues, and stability. Herein, we report a simple strategy to produce red-emissive carbon dots (RCDs) and demonstrate their application as an alternative fuel marker to identify the fuel product and monitor adulteration. The RCDs were facilely synthesized via a simple solvothermal method from ortho-phenylenediamine (OPD) and sulfanilic acid (SFA) in ethanol medium. The produced RCDs exhibit emission at longer wavelengths of 605 and 650 nm once excited at wavelengths of more than 500 nm, which could enable the elimination of the background interference of fuel. Dispersion of RCDs in gasoline and diesel fuel showed excellent stability as no aggregation was visually observed, and the fluorescence intensity of the dispersion remained unchanged over the month. Furthermore, RCD-additized fuel displayed distinct red color emission even in the presence of other common dye molecules remaining in the commercial fuel. Importantly, it was found that red emission properties of present RCDs enable the detection of adulteration up to 2–6% (v/v) range in commercial fuel using a simple hand-held fluorometer, which make them capable of onsite detection. All these results firmly indicate potential commercialization of carbon dots (CDs) as fuel markers and be beneficial to the world environment and economy.