*3.6. Adsorption of Dencichine on the RCMs and RPMs at Different PH Levels*

To understand the effect of PH on the adsorption amount of dencichine on the RCMs and RPMs, the results were discussed for the different PH levels, and the results are shown in Figure 9. The adsorption of dencichine on the RCMs and RPMs at the different PH levels of 1, 3, 5, 6, 7, 8, 9 and 11 are shown in Figure 9a.

**Figure 9.** (**a**) Adsorption of dencichine on RCMs and RPMs in different pH conditions; (**b**) The zeta potential of RCM and RPM adsorption amounts.

As shown in this Figure 9a, the maximum dencichine adsorption amount of the RPMs is reached when the pH is 6, and the RCMs are reached when the pH is 7. The results are due to the fact that dencichine is acidic and 4-ethylpyridine is basic, and proves that a weakly acidic or neutral condition could favor the adsorption process. The zeta potentials of the RCMs and RPMs at various pH levels were measured, and the results are presented in Figure 9b. The points of zero charges are at the pH values: 1.7 for RCMs and 8.0 for RPMs, the zeta potential of the RCMs and RPMs decreased as PH increased, and RCMs have more surface negative charge than RPMs. The results indicate that the amino group in PAN reduces the surface charge. Therefore, the adsorption of dencichine by RCMs may be affected by electrostatic interactions. These results further prove that RCMs have exceptional promise for the separation and enrichment of dencichine.
