Figure 3 The bonding energy for each coordination process. (a)-(f) correspond to the coordination states in Figure 2.
When Zn2+ is involved in the reaction (1), the coordination effect needs to be considered. As previous research has shown, the Zn2+ ions could coordinate with oxygen species to form different complexes.[37, 38] So, Zn2+ with different hydration number (0, 2, 4, 6) was designed in the calculation. While a Zn2+ in the solution, there are 4 models (including [Zn(H2O)x]2+, for x = 0, 2, 4, 6). Optimized models showed that no matter what hydration number is, both Zn2+ ion can coordinate with ROS activated by CNTs, as shown in Figure 4. The bond length of Zn2+-O (oxygen species) is calculated and shown in Figure S1. When the hydration number was 0, 2, 4, 6, the bond length of Zn2+-ROS is 1.84 Å, 1.80 Å, 1.87 Å and 1.95 Å respectively. All of zinc compounds could form bonds with ROS diffused into solution. As the hydration number goes up, the bond length between Zn2+ and ROS increases. It is indicated that a Zn2+ coordinated sufficient oxygen-containing groups would weakly adsorb ROS. Similarly, it also would weakly adsorb RO· and ROO· (Table S2). In other words, if each Zn2+coordinates sufficient oxygen-containing groups, the inhibition is weakened or even eliminated.