Synthesis and Characterization of Carbon Nanodots

Carbon nanodots (CNDs) were synthesized and characterized following our published method [44 (link),45 (link)]. Briefly, CNDs were synthesized by mixing 0.96 g of citric acid (CA) and 1 mL of Ethylenediamine (EDA) in 1 mL of deionized water. The solution was heated in a microwave synthesizer (CEM Corp 908005 (Matthews, NC, USA)) at 300 W for 10 min. To purify the CNDs, the solid was dissolved in DI water and dialyzed through a dialysis membrane with MWCO (molecular weight cut out) of 1000 Da for 24 h. The structure of CNDs was characterized using Fourier transform infrared spectroscopy (FTIR, Varian 670 (Palo Alto, CA, USA), and the size and morphology were characterized by atomic force microscopy (AFM, Agilent 5600LS (Santa Clara, CA, USA)). X-ray diffraction (XRD, Agilent Technologies Oxford Gemini, The Woodlands, TX, USA) was used to analyze the crystal structure of the CNDs. To study the chemical content and the structure of the CNDs, Fourier transform infrared spectroscopy (FTIR) was performed. The fluorescence intensity peaks were measured using a Cary fluorescence spectrophotometer to find the emission and excitation wavelengths for the CNDs. The CND concentration in distilled water for analysis was 0.06 mg/mL. The surface chemistry of CNDs was studied using carbon 1s X-ray photoelectron spectroscopy (XPS, ESCALAB 250 Xi, Thermo Fisher, West Sussex, UK).