Yolk/shell nanoparticles (NPs), which integrate functional cores (likes Fe₃O₄) and an inert SiO₂ shell, are very important for applications in fields such as biomedicine and catalysis. An acidic medium is an excellent etchant to achieve hollow SiO₂ but harmful to most functional cores. Reported here is a method for preparing sub-100 nm yolk/shell Fe₃O₄@SiO₂ NPs by a mild acidic etching strategy. Our results demonstrate that establishment of a dissolution–diffusion equilibrium of silica is essential for achieving yolk/shell Fe₃O₄@SiO₂ NPs. A uniform increase in the silica compactness from the inside to the outside and an appropriate pH value of the etchant are the main factors controlling the thickness and cavity of the SiO₂ shell. Under our “standard etching code”, the acid-sensitive Fe₃O₄ core can be perfectly preserved and the SiO₂ shell can be selectively etched away. The mechanism of regulation of SiO₂ etching and acidic etching was investigated.

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卵黄/壳纳米颗粒（NPs）集成了功能性核（如Fe ₃ O ₄）和惰性SiO ₂壳，对于生物医学和催化等领域的应用非常重要。酸性介质是获得中空SiO ₂的极佳蚀刻剂，但对大多数功能性核有害。本文报道了一种通过温和的酸性蚀刻策略制备亚100 nm卵黄/壳Fe ₃ O ₄ @SiO ₂ NPs的方法。我们的结果表明，建立二氧化硅的溶解-扩散平衡对于获得蛋黄/壳Fe ₃ O ₄ @SiO ₂是必不可少的NP。二氧化硅从内部到外部的致密性的均匀增加以及蚀刻剂的适当pH值是控制SiO ₂壳的厚度和空腔的主要因素。按照我们的“标准蚀刻法”，可以很好地保存对酸敏感的Fe ₃ O ₄核，并可以选择性地蚀刻掉SiO ₂壳。研究了SiO ₂腐蚀和酸性腐蚀的调控机理。

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