Synthesis of EDTA-CDs
EDTA-CDs was prepared by hydrothermal method with ethylenediamine tetraacetic acid (EDTA) and o-phenylenediamine (o -PD) in deionized water. Simply, a mixture of EDTA (0.88 g), o -PD (0.40 g) and deionized water (30 mL) is transferred to a 50 mL poly (tetrafluoroethylene) liner, which is placed in the stainless steel reaction. After heating at 180 oC for 6 h, the solution was cooled to room temperature naturally. After dark blue solution filtration (0.22 μm), the unreacted EDTA-CDs and o-PD were removed by dialysis with MWCO 500-1000 Da in a cellulose dialysis tube for 48 h. Finally, the dialysate was freeze-dried and the powder was obtained.