Applications in biomedicine and ferrofluids, for instance, require long‐term colloidally stable, concentrated aqueous dispersions of magnetic, biocompatible nanoparticles. Iron oxide and related spinel ferrite nanoparticles stabilized with organic molecules allow fine‐tuning of magnetic properties via cation substitution and water‐dispersibility. Here, we synthesize≤5 nm iron oxide and spinel ferrite nanoparticles, capped with citrate, betaine and phosphocholine, in a one‐pot strategy. We present a robust approach combining elemental (CHN) and thermal gravimetric analysis (TGA) to quantify the ratio of residual solvent molecules and organic stabilizers on the particle surface, being of particular accuracy for ligands with heteroatoms compared to the solvent. SAXS experiments demonstrate the long‐term colloidal stability of our aqueous iron oxide and spinel ferrite nanoparticle dispersions for at least 3 months. By the use of SAXS we approved directly the colloidal stability of the nanoparticle dispersions for high concentrations up to 100 g L⁻¹.

中文翻译：

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≤5 nm 尖晶石铁氧体纳米颗粒的长期胶体稳定水分散体

例如，在生物医学和铁磁流体中的应用需要磁性、生物相容性纳米粒子的长期胶体稳定、浓缩水分散体。用有机分子稳定的氧化铁和相关尖晶石铁氧体纳米颗粒可以通过阳离子取代和水分散性来微调磁性。在这里，我们通过一锅法合成了≤5 nm的氧化铁和尖晶石铁氧体纳米颗粒，并用柠檬酸盐、甜菜碱和磷酸胆碱封端。我们提出了一种结合元素（CHN）和热重分析（TGA）的稳健方法来量化颗粒表面上残留溶剂分子和有机稳定剂的比率，与溶剂相比，对于具有杂原子的配体具有特别的准确性。SAXS 实验证明我们的水性氧化铁和尖晶石铁氧体纳米颗粒分散体具有至少 3 个月的长期胶体稳定性。通过使用 SAXS，我们直接证实了纳米颗粒分散体在高达 100 g L ^-1的高浓度下的胶体稳定性。