Size Control of Highly Monodisperse Citrate-Stabilized Magnetite Nanoparticles in Aqueous Media: The Role of Cerium Cations

Abstract

Magnetite nanoparticles; Cerium cations

Nanopartículas de magnetita; Cationes de cerio

Nanopartícules de magnetita; Cations de ceri

Controlling the nucleation and growth of magnetite nanoparticles (NPs) via aqueous coprecipitation at room temperature is inherently challenging due to kinetic and thermodynamic constraints. Rapid pH increases trigger a burst nucleation event that depletes precursors before significant growth occurs, while NP surfaces are quickly passivated by water and hydroxyl ions, forming a dewetting barrier that impedes further growth. To address these challenges, we developed an innovative synthesis approach that incorporates lanthanide (Ln) cations, mainly Ce3+, together with sodium citrate into the coprecipitation process. These additives act synergistically to lower surface energy and stabilize both precursors and reaction intermediates, thereby facilitating controlled crystal growth. We systematically investigated the impact of Ln cations by fine-tuning the Ce3+ concentration, which enabled precise control over NP size, yielding diameters from 13 to 46 nm. Notably, at higher Ce3+ concentrations, multidomain nanowires are formed, with diameters reaching up to 90 nm and lengths on the micron scale. Moreover, the synthesized NPs exhibit enhanced performance in magnetic hyperthermia (MH) and peroxidase-like activity compared with those produced without Ce3+. The improved catalytic activity is attributed to accelerated Fe2+ regeneration in the reaction, mediated by the presence of the Ce4+/Ce3+ redox couple, which boosts •OH radical production. Importantly, this strategy is versatile and can be extended to other Ln cations (Eu3+, Gd3+, Er3+, Yb3+, and Lu3+), yielding single-crystal magnetite NPs of comparable sizes. Collectively, Ln-assisted synthesis addresses longstanding challenges in magnetite NP coprecipitation, providing a scalable route to high-performance magnetic NPs with tunable size and morphology. This approach not only improves control over NP growth but also broadens their potential applications in MH and catalysis.

K.M.-C., M.F.G., V.P., and N.G.B. gratefully acknowledge financial support from the MCIN/AEI International Joint Research Projects Program (CONCORD, PCI2019-103436), cofunded by the European Union and the Generalitat de Catalunya (2021-SGR-00878), as well as funding from project PID2023-148967OB-C22. ICN2 is supported by the Severo Ochoa program of the Spanish MCIN/AEI (CEX2021-001214 S) and receives institutional support from the CERCA Programme/Generalitat de Catalunya. K.M.-C. acknowledges a predoctoral fellowship (PRE2019-090084) from MCIN. P.G. acknowledges support from MCIN/AEI/10.13039/501100011033 (CNS2022-135583 and PID2021-122645OB-I00) and from the Ramón y Cajal program “FSE invierte en tu futuro” (RYC2019-028414). M.C.S. and J.A. acknowledge support from the Generalitat de Catalunya (2021SGR00457). This study is part of the Advanced Materials Programme and was supported by the MCIN with European Union NextGenerationEU funding (PRTR-C17.I1). ICN2 is a founding member of e-DREAM.