The Buffering Activity of Ceria toward Reactive Oxygen Species: A Density Functional Theory Perspective

Nanocrystalline ceria exhibits nanozymatic activities, which are strongly affected by surface composition and surface Ce³⁺ concentration. Here, we use density functional theory to perform a scan of the compositional landscape of the most important {111}, {110}, and {100} ceria nanoparticle surfaces and their buffering activity toward reactive oxygen species (ROS) involved in the superoxide dismutase (SOD) and catalase (CAT) enzymatic mimetic activity of ceria. This study displays that pristine and surface sublayer oxygen-deficient surfaces can perform catalytic activities, whereas surface layer oxygen-deficient surfaces can only perform noncatalytic reactions as the oxygen vacancy is healed by ROS changing surface stoichiometry. Our findings corroborate conventional literature that higher concentrations of Ce³⁺ favor SOD, whereas Ce⁴⁺ favors CAT while also highlighting contributions of specific subprocess reactions. {111} surfaces perform best as fully oxidized (CAT) and fully reduced (SOD), while this is not the case for the {110} and {100} surfaces. As we follow plausible reaction mechanisms of SOD and CAT, we depict a complex situation highly dependent on the surface composition, which clearly implies that it is vital to control subprocess reactions for optimal buffering, and the desorption of products is a critical step in all reactions.