Ellagic acid

Gallic acid (GA, 98%), tannic acid (TA, 95%), 1,3,5-trihydroxybenzene (phloroglucinol, HB, 99%) were supplied by J & K Scientific Ltd. Ellagic acid (EA, 98%) and arbutin (AR, 98%) were obtained from Macklin Biochemical Co., Ltd. Benzidine (BE, 98%) was obtained from Aladdin. Cesium chloride, sodium nitrite, sodium carbonate and other regents were provided by Tianjin Guangfu Reagent. Ground water sampled from Tibet, China was used for adsorption performance evaluation of the adsorbents.

Acetic acid, citric acid, ellagic acid, tartaric acid, and propionic acid were purchased from MACKLIN^® (Shanghai, China), with a purity of 99.7%, 99.5%, 99.5%, 95%, and 99.5%, respectively. Oxalic acid and succinic acid were purchased from Aladdin^® (Shanghai, China), with a purity of 99% and 96%, respectively. Fumaric acid was purchased from OKA^® (Beijing, China), with a purity of 95%. The above compounds at 0.01 g were accurately weighed, and the standard solutions at 0.01 mg ml⁻¹ were prepared using H₃PO₄ (0.02 mol L⁻¹; mobile phase) and were then filtered by 0.22-µm microporous membrane. All the decomposition leachates of milk vetch were filtered through filter paper and further filtered through the 0.22-µm microporous membrane and then analyzed by LC-SPD-20A with an HP-C18 (250 mm, 4.6 mm, and 5 µm) chromatographic column, with chromatographic conditions as follows: mobile phase was 100% H₃PO₄ (0.02 mol L⁻¹); elution method: equal gradient elution; detection wavelength was 220 nm; column temperature was 37°C; injection volume was 10 µl; flow rate was 1.4 ml min⁻¹. Data were processed on Origin 2018 (Originlab^®). Acid fraction quantification was achieved by the absorbance recorded in the chromatograms relative to external standards using the following equation:

A total of 2 g melamine (Macklin, Shanghai, China), 0.5 g ammonium iodide (Macklin, Shanghai, China), and 2 g ellagic acid (Macklin, Shanghai, China) were put in 60 mL distilled water for stirring for 1 h. The mixtures were transferred into a Teflon-lined stainless-steel autoclave and kept at 180 °C for 16 h. The solid product was collected by filtration after it had cooled down to room temperature. After this, the collected hybrids were directly carbonized at 900 °C for 1 h under N₂ atmosphere at a heating rate of 5 °C/min. The obtained carbon product was also further activated with potassium hydroxide (mass ratio: 1:1) at 900 °C for 1 h. The activated sample was washed with 0.5 M hydrochloric acid and dried at 70 °C, termed as I, N-CNCs. For comparison, 2 g melamine and 2 g ellagic acid were hydrothermally treated and activated as N-CNCs. CMs were prepared with 2 g ellagic acid under the same conditions as I, N-CNCs.
Morphological and structural characterization, electrochemical measurements, theoretical calculations, and computational formula were specified in supporting information.