Nitrogen-Doped Carbon Dots Derived from Green Biomass Arabic Gum for Detection of Chromium (VI) in Industrial Wastewater

Using green biomass Arabic gum (AG) as carbon source and trimethylaminomethane (Tris) as nitrogen source, the two raw materials were mixed at a mass ratio of 1∶4 to prepare a novel nitrogen-doped carbon dots (NACDs) by hydrothermal method, and a fluorescent sensor based on NACDs was constructed for the detection of Cr(VI) in industrial wastewater. 200 μL of sample solution, 100 μL of NACDs solution, and 200 μL of 0.2 mmol·L⁻¹ disodium hydrogen phosphate-sodium hydrogen phosphate buffer solution (pH 8.0) were added to a 2 mL-EP tube, and the mixture was made its volume up to 1 mL with water. After reaction for 10 min at room temperature, the system was scanned at 365 nm of excitation wavelength, and the fluorescence intensity of the system was measured at 430 nm. As shown by the results, at the excitation wavelength of 365 nm, NACDs had strong fluorescence signal at 430 nm and its fluorescence could be selectively quenched by Cr(VI). Linear relationship between the fluorescence quenching values of NACDs and mass concentrations of Cr(VI) were found in the range of 0.25-3.00 mg·L⁻¹, with detection limit (3s/k) of 0.13 mg·L⁻¹. Test for recovery on the simulated industrial wastewater samples by the standard addition method, giving results in the range of 103%-105%, with RSDs of the determined values (n=6) less than 3.0%. There was no significant difference between the determined results obtained by this method and those obtained by the national standard method GB/T 15555.4—1995.