Reducing MOF particles to the nanoscale size range is beneficial due to their increased surface-to-volume ratio, higher defects exposing metals and ligands, and short diffusion path. While great efforts have been made to reduce the particle sizes by controlling the reaction kinetics or terminating the particle growth, large-scale, rapid synthesis of MOF nanoparticles (NPs) remains a challenge. Here, we report supercritical (sc) CO₂-assisted synthesis of HKUST-1 NPs in a continuous flow reactor, which yielded pure and thermally stable MOFs with median sizes of 110–250 nm and BET surface areas of 1610–1890 m² g⁻¹ under 10 seconds synthesis time. ScCO₂ and ethanol with a molar ratio of 9 : 1 are used as co-solvents for the fast nucleation of HKUST-1 and crystal formation. A typical dry yield of 53.7 wt% is achieved with 0.1 M Cu precursor under mild conditions at 75 °C and 13 MPa. The space–time yields and surface area production rates are 5668 kg m⁻³ d⁻¹ and 1.0 × 10¹⁰ m² m⁻³ d⁻¹. Particle size and morphology analyses indicate that aggregation of nascent structures occurs in the aerosolized state, leading to a non-classical crystal growth mechanism and enabling multiple pathways for tuning the synthesis process. With the ability to recycle CO₂, solvents, and unreacted precursors, the method can be used for the scalable production of MOFs.

中文翻译：

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HKUST-1 MOF 纳米颗粒：超临界 CO2 中的非经典结晶路线


将 MOF 颗粒还原到纳米级尺寸范围是有益的，因为它们的表面体积比增加，暴露出金属和配体的缺陷更高，扩散路径短。虽然已经做出了巨大的努力通过控制反应动力学或终止颗粒生长来减小颗粒尺寸，但 MOF 纳米颗粒 （NPs） 的大规模、快速合成仍然是一个挑战。在这里，我们报道了在连续流反应器中超临界 （sc） CO₂ 辅助合成 HKUST-1 NPs，在 10 秒合成时间内产生中位尺寸为 110-250 nm，BET 表面积为 1610-1890 m^{2 g-1} 的纯热稳定 MOF。ScCO₂ 和乙醇的摩尔比为 9：1 用作助溶剂，用于 HKUST-1 的快速成核和晶体形成。在 75 °C 和 13 MPa 的温和条件下，使用 0.1 M Cu 前驱体可实现 53.7 wt% 的典型干产量。时空产额和表面积产生率分别为 5668 kg ^{m-3 d-1} 和 1.0 × 10¹⁰ m^{、2 m-3 d-1}。粒度和形态分析表明，新生结构的聚集发生在雾化状态下，导致非经典晶体生长机制，并为调整合成过程提供了多种途径。该方法能够回收 CO₂、溶剂和未反应的前驱体，可用于 MOF 的放大生产。