From coordination spheres to catalytic sites: Defect engineering in metal oxide photocatalysts

Abstract

Lattice defects in metal oxide semiconductors, once regarded as performance-limiting flaws, are recognized as powerful tools for enhancing photocatalytic activity. These structural imperfections, including oxygen vacancies (Vo), cation deficiencies, interstitials, and dopant-induced distortions, are not mere flaws but products of deliberate defect engineering rooted in coordination chemistry principles. The deliberate distortion of the local coordination environment around metal centers introduces specific defects that, in turn, directly modulate the electronic band structure, redefine surface properties, and alter charge carrier transport. In the photocatalytic oxidation of volatile organic compounds (VOCs), defect engineering enables improved light absorption, more efficient charge separation, and increased generation of reactive oxygen species. This review deciphers how engineered defects in metal oxides boost photocatalytic removal performance of VOCs. The connection between synthesis, characterization, and mechanism is thus established to offer mechanistic insights into how coordination sphere distortion at metal sites governs the photomineralization of VOCs. Selected case studies, including TiO₂, ZnO, WO₃, and CeO₂, are used to highlight key structure–function relationships and real-world performance. The review concludes by addressing critical challenges in quantifying and stabilizing defects, scaling up defect-engineered materials, and designing catalysts with enhanced selectivity, sustainability, and long-term usability.