Synthesis method

The synthetic method of CONPs are introduced in our previous study. All chemicals used in the experiment were of analytical grade. The synthetic method of CONPs are as follows: First, 0.35 mL of 0.1 M CuSO4 (aq) and 3 mL of 0.1 M cetyltrimethylammonium bromide (CTAB) (aq) were added into a test tube, the tube was shaken vigorously by a vortex mixer. The mixture turned red-brown rapidly when the 10 mL of fresh, cold 0.04 M NaBH₄ (aq) was added into it. The test tube was in the incubation at 26°C–28°C until the mixture turned into bright yellow for about 18 hours. The solution was centrifuged at 26°C for 15-20 minutes at 12,000 rpm and washed with ethanol and deionized water for several times. After removing the supernatant, the vacuum dry method is applicable for the product. After about 15 hours, the dried product turned into black powder and was stored in a 4°C refrigerator [13, 14].