Morphological dependency of antioxidant enzyme-like activities of nanoceria in energy-band structure aspect

Controlling the morphology of ceria nanoparticles (CeNPs) has been proven an effective approach to mimic the activities of antioxidant enzymes including catalase (CAT) and superoxide dismutase (SOD). However, the mechanism of the morphology-dependent enzyme-like activities was elusive. Energy-band structure tailoring of NPs through morphologies closely correlates with their catalytic activities. Herein, three kinds of CeNPs with octahedron, cube and rod morphologies were synthesized. Octahedron-CeO2 with exposed {111} facets, cube-shaped CeO2 with {100} facets and rod-shaped CeO2 with {110} and {111} facets were observed. Due to the lower formation energy of oxygen vacancy (VO) for {110} facets, higher VO content was detected for rod-CeO2, which directly correlated with the energy level of surface defect states (ESDS). The ESDS for rod-CeO2 (0.86 V) roughly lied in the middle point of E0 (H2O2, H+/H2O) and E0(O2, H+/H2O2) (0.83 V), which resulted in higher CAT-like activity. Likewise, the ESDS of octahedron-CeO2 (0.48 V) approximately located at the midpoint of two half-reaction potentials in SOD catalytic cycle (0.39 V) which was agreement with its enhanced SOD-like activity. Overall, regulating ESDS towards the midpoint of the half-reaction potentials becomes a feasible approach to achieve enhanced catalytic efficiency.