Synthesis of Ag-ZnO core-shell nanoparticles with enhanced photocatalytic activity through atomic layer deposition

Highlights: • The ALD technology is applied to fabricate Ag-ZnO nanoparticles for photocatalyst. • Stable ZnO shell layers with wurtzite structure are deposited on Ag core particles. • Ag-ZnO shows ~2.5 to 4 times enhanced photodegradation compared with pure ZnO. • SPR effect of Ag increases photocatalytic performance of Ag-ZnO photocatalyst. • Ultra-thin ZnO shells on Ag cores increase photocatalytic performance in UV-region. -- Abstract: Herein, Ag-ZnO core-shell nanoparticles (NPs) with enhanced photocatalytic activity were prepared by coating Ag metal cores with ZnO semiconductor shells through atomic layer deposition (ALD). Instrumental analysis revealed that the ultra-thin and conformal nature of the shell allowed the core-shell NPs to simultaneously exploit the photocatalytic properties of ZnO and the plasmonic properties of Ag. In a rhodamine B photodegradation test performed under artificial sunlight, Ag-ZnO core-shell NPs exhibited better photocatalytic performance than other prepared photocatalysts, namely ZnO NPs and ALD-ZnO coated ZnO NPs. The performance enhancement was ascribed to the effect of noble metal-semiconductor heterojunctions, which increased the efficiency of electron-hole separation, i.e., the Ag core effectively captured excited electrons at the ZnO surface, which resulted in the elevated production of hydroxyl radicals from holes remaining at ZnO. A three-dimensional finite-difference time-domain simulation of the Ag-ZnO NPs with variable shell thickness showed that ZnO shells on Ag metal cores increase the intensity of light around NPs, allowing the plasmonic cores to fully utilize incident light.