Site-selective doping mechanisms for the enhanced photocatalytic activity of tin oxide nanoparticles

The addition of transition metal dopants into metal oxide nanoparticles (MO NPs) is an universal strategy to engineer the electronic and chemical properties of NPs. Although doping phenomena strongly rely on interactions with compositional and electronic degrees of freedom, fully understanding the site-specific doping behavior in the lattice framework of MO NP on atomic scale remains challenging. Here, we directly resolve the atomic site-selective (substitutional or interstitial) doping behaviors of Cr and Fe in SnO₂, revealing their different roles in photocatalytic activities. Atomic-resolution microscopy combined with spectroscopy reveals two contrasting doping behaviors: Cr³⁺ substitutes for Sn⁴⁺ associated with the formation of oxygen vacancies, whereas Fe³⁺ occupies interstitial sites accompanied by lattice strain. Theoretical calculations indicate that substitutional dopant-vacancy cooperation and interstitial dopant-strain coupling can be energetically favorable routes for enhancing catalytic properties. Our results provide fundamental insights into atomic-scale doping mechanisms and engineering strategies for high-performance doped MO NPs.