NaBH4-induced oxygen vacancy engineering in NiFe2O4: linking charge dynamics with reactive oxygen species generation for enhanced photocatalysis

초록

This study presents a defect-engineering strategy to enhance visible-light-driven photocatalytic biomass oxidation using NiFe2O4 nanoparticles (NPs) enriched with surface oxygen vacancies (OV) via NaBH4 reduction. Pristine NiFe2O4 possesses suitable band energetics for reactive oxygen species (ROS) generation but exhibits limited activity due to the scarcity of surface OV. In contrast, NaBH4-treated NiFe2O4 (r-NiFe2O4) retains favorable ROS-related band alignment while achieving a significantly increased OV concentration, as confirmed by X-ray photoelectron spectroscopy (XPS) and OV-associated spectroscopic features. As a result, r- NiFe2O4 demonstrates markedly enhanced photoconversion efficiency and oxidation rates under visible-light irradiation. In situ XPS under illumination reveals reversible shifts in the Ni 2p, Fe 2p, and O 1 s spectra, indicating dynamic charge redistribution at OV sites. Magnetic measurements show that although the magnetization of r-NiFe2O4 is approximately 40% lower than that of Fe3O4, it remains sufficient for rapid magnetic separation and efficient catalyst recyclability at room temperature. Control experiments further confirm that the enhanced activity primarily arises from OV-mediated charge separation and surface reactivity, rather than defect-induced sub-band state. These findings demonstrate that NaBH4 reduction is an effective approach for tailoring surface defects in NiFe2O4, enabling the development of efficient and magnetically recoverable photocatalysts for visible-light-driven biomass oxidation and related environmental applications.

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