Strategic Aliovalent Dopant Engineering in ZnO Nanoparticles for Enhanced Visible-Light-Driven Photocatalysis

The most common method for improving the catalytic properties of semiconducting metal oxide nanoparticles (MO NPs) is to enhance the surface defect engineering, typically by doping or structural transformation. Specifically, doping with transition metals can significantly promote the formation of oxygen vacancy that can enhance both of electron–hole localization and photocatalytic activity. Here, we report an integrated experimental and theoretical investigation on incorporation of Cr and Fe ions into ZnO NPs to induce aliovalency that produces highly efficient visible-light-driven photocatalysis. Comprehensive structural and chemical characterizations revealed that the amount of oxygen vacancies was increased by doping with Cr or Fe ions during visible light photoactivation. Density functional theory (DFT) simulation demonstrated that dopant-oxygen bonds distorted surface Zn-O bonds for facile vacancy generation, thereby creating trap states for efficient electron–hole separation. To directly link the formation of surface oxygen vacancies introduced with improved photocatalytic activity by different-valence metal doping, the selective photocatalytic oxidation of 2,5-hydroxymethylfurfural was investigated under visible light irradiation. ZnO NPs doped with Cr or Fe ions exhibited high efficiency and selectivity in oxidizing 2,5-hydroxymethylfurfural to the valuable platform chemical, 2,5-furanedicarboxylic acid. The distinct photocatalytic activity of three different MO NPs was rationalized by the localized defect states created by oxygen vacancy in DFT simulation. This work highlights, through a tight integration of experiment and theory, how judicious surface engineering—through strategic dopant incorporation and controlled oxygen vacancy formation—could fundamentally transform wide-bandgap oxides into efficient, visible-light-driven photocatalysts for sustainable chemical synthesis.