Ultra-small iron oxide nanoclusters with anti-self-adsorption properties activate peroxymonosulfate for the efficient degradation of rhodamine B

Although Fe 3 O 4 is widely employed in Fenton-like processes for wastewater treatment, its application is hindered by slow reaction kinetics and progressive performance decline due to self-adsorption-driven agglomeration over time. To address these challenges, this study presents the design and synthesis of 2-bromo-isobutyric acid (BMPA)-modified ultra-small iron oxide nanoclusters (5 nm, USIONC), which leverage their nanoscale low magnetism to mitigate self-aggregation and BMPA modification to enhance Fenton-like reactivity. Under optimal conditions (100 mg/L BMPA-USIONC, 2 mM peroxymonosulfate), 98% degradation of 20 mg/L rhodamine B is achieved within 3 minutes, with stable performance maintained over one month—significantly outperforming conventional Fe₃O₄, which exhibits a 15.2% degradation decline in the same period. Mechanistic analysis reveals that the superior activity of BMPA-USIONC arises from its high specific surface area and accelerated Fe(III)/Fe(II) cycling enabled by organic acid modification, facilitating the generation of multiple reactive oxygen species (SO 4 ⁻ , ·OH, O 2 ⁻ , 1 O 2 ) for multi-pathway pollutant degradation. Cell/hemolysis experiments confirm its non-toxicity, and successful degradation of pollutants in real dyeing wastewater highlights its practical potential as a low-cost, eco-friendly nanomaterial. This work provides an effective strategy to enhance the degradation efficiency and anti-agglomeration capability of Fe₃O₄-based materials for environmental remediation. • BMPA-USIONC has a larger specific surface area, allowing it to interact with more pollutants. • The ultrafine-sized ferric oxide (USIONC) can resist self-agglomeration over time. • An organic acid (BMPA-modified) ultrafine ferric oxide material (BMPA-USIONC) was designed for the efficient degradation of Rhodamine B. • Peroxymonosulfate is activated by BMPA-USIONC, generating various free radicals. • BMPA-USIONC is environmentally friendly and non-toxic to organisms.