The enzyme-like catalytic activity of cerium oxide nanoparticles and its dependency on Ce3+ surface area concentration

TL;DR

This study investigates how cerium oxide nanoparticles mimic enzyme activities, revealing that smaller particles with higher Ce3+ surface area enhance catalytic effects, which can be predicted from physical and chemical properties.

Contribution

It introduces a particle-independent redox mechanism model and a new scaling approach to predict catalytic activity based on Ce3+ surface area concentration.

Findings

Smaller nanoparticles show higher catalytic activity.

Ce3+ surface area concentration correlates with enzyme-like activity.

H2O2 adsorption varies with particle type and affects catalysis.

Abstract

Cerium oxide nanoparticles are known to catalyze the decomposition of reactive oxygen species such as superoxide radical and hydrogen peroxide. Herein, we examine the superoxide dismutase (SOD) and catalase (CAT) mimetic catalytic activities of nanoceria and demonstrate the existence of generic behaviors. For particles of size 4.5, 7.8, 23 and 28 nm, the SOD and CAT catalytic activities exhibit the characteristic shape of a Langmuir isotherm as a function of cerium concentration. Results show that the catalytic effects are enhanced for smaller particles and for the particles with the largest Ce3+ fraction. The SOD-like activity obtained from the different samples is found to superimpose on a single master curve using the Ce3+ surface area concentration as a new variable, indicating the existence of particle independent redox mechanisms. For the CAT assays the adsorption of H2O2 molecules at the particle surface modulates the efficacy of the decomposition process and must be taken into account. We design an amperometry-based experiment to evaluate the H2O2 adsorption at nanoceria surfaces, leading to the renormalization of the particle specific area. Depending on the particle type the amount of adsorbed H2O2 molecules varies from 2 to 20 nm-2. The proposed scalings are predictive and allow determining SOD and CAT catalytic properties of cerium oxide solely from physico-chemical features.