Phenolic compounds degradation: Insight into the role and evidence of oxygen vacancy defects engineering on nanomaterials

Highlights: • Oxygen vacancies could enhance the photocatalysis towards phenolic compounds abatement. • The role of surface and bulk oxygen vacancies defects is critically examined. • Strategic manipulating for designing and constructing of oxygen vacancy is proposed. • The impact of oxygen vacancies on active molecular (O₂, H₂O, and sulphate) is evaluated. • Recent trends, challenges and prospects of vacancy defect engineering are highlighted. Oxygen vacancy as a typical point defect has incited substantial interest in photocatalysis due to its profound impact on optical absorption response and facile isolation of photocarriers. The presence of oxygen vacancy can introduce the midgap defect states, which promote extended absorption in the visible region. The redistribution of electron density at the surface can stimulate the adsorption and activation kinetics of adsorbates, manifesting optimal photocatalytic performance. Despite such alluring outcomes, the ambiguity in understanding the precise location, appropriate concentration, and oxygen vacancy role is still a long-standing task. The present review article comprehensively outlines the identification of oxygen vacancy defects at bulk or on the surface and its ultimate effect on the photocatalytic degradation of phenolic compounds. Particular emphasis has been drawn to summarize the critical influence of oxygen vacancy on different factors such as crystal structure, bandgap energy, electronic structure, and charge carrier mobility by integrating experimental results and theoretical calculations. We have also explored the reaction pathways and the intermediate chemistry of phenol photodegradation by analyzing the molecular activation (O₂, H₂O, and sulphate activation) through oxygen vacancy defects. Finally, the review concludes with the various challenges and future perspectives, aiming to provide a firm base for further progressions towards photocatalysis.