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.