Abnormal Size Effect of Metal-Catalyzed Contaminant Reduction: Why Bigger Nanoparticles Perform Better

Nanoparticles made of noble metals such as platinum (Pt), palladium (Pd), and gold (Au) have attracted increasing attention as catalysts for degrading organic and inorganic contaminants found in water and wastewater. Compared to conventional treatment techniques, the use of catalysts can shorten treatment time, target recalcitrant compounds, and selectively transform wastes into valuable products. So far, most of efforts in nanoparticle design have been made to reduce nanoparticle size, following the conventional “smaller-is-better” rationale, to improve treatment kinetics and thus efficiency. Here, we show that the kinetics of Pd-catalyzed reduction of N-dimethylamine (NDMA) and p-nitrophenol in water increases with the increase of Pd nanoparticle size, indicating a new “bigger-is-better” principle in nano-catalyst design. We further show that this abnormal size effect can be explained by the size dependence of hydrogen adsorption by palladium. These results provide new insight for the development of nano-enabled catalytic technologies for water and wastewater treatment.