亲水性“Hedgehog”微粒在液体CO2混合物中的分散

https://doi.org/10.1021/acsnano.2c03058

 

Abstract

Liquid and supercritical CO2 are nontoxic and nonflammable reaction media with pressure-variable physical properties. These states of CO2 also have high solubility limits for gas and liquid hydrocarbons, making them good candidates for “green” hydrophobic solvents in sustainable chemical technologies. However, the dispersion of hydrophilic colloidal nanoscale and microscale particles in CO2 is challenging due to the tendency of polar particles to aggregate in nonpolar media, limiting their available surface area and catalytic efficiencies. Here we show that native hydrophilic semiconductor particles can be effectively dispersed in a liquid CO2 mixture with acetonitrile (ACN) without additional chemical or mechanical dispersion techniques. Using surface corrugation as a method to prevent aggregation, we find that geometrically complex particles with a halo of stiff nanoscale spikes disperse and remain suspended longer in liquid CO2 than those without or with less prominent nanoscale corrugation. For the particles of this size and liquid CO2 mixtures, individual particle mass remains a prominent factor determining particle sedimentation rate even in the absence of aggregation. Particle dispersion and structural stability are confirmed using a combination of UV–vis spectroscopy, finite-difference time-domain modeling, and electron microscopy. The necessity of the cosolvent (ACN) indicates that particle behavior in liquid CO2 is vastly different than in traditional liquid-phase solvents and highlights the need for future studies to understand the wetting behavior of hydrophilic particles in high-pressure nonpolar environments.

 

液体和超临界CO2是无毒和不可燃的反应介质，具有可变压力的物理性质。这些状态的二氧化碳对气体和液体碳氢化合物也有很高的溶解极限，使其成为可持续化学技术中“绿色”疏水溶剂的良好候选者。然而，亲水性胶体纳米级和微米级颗粒在CO2中的分散是具有挑战性的，因为极性颗粒倾向于在非极性介质中聚集，限制了它们的可用表面积和催化效率。在这里，我们证明了天然亲水性半导体颗粒可以有效地分散在含有乙腈（ACN）的液体CO2混合物中，而无需额外的化学或机械分散技术。使用表面波纹作为一种防止聚集的方法，我们发现，与没有或没有不太明显的纳米级波纹的颗粒相比，具有刚性纳米级尖峰光环的几何复杂颗粒在液体CO2中分散和悬浮的时间更长。对于这种尺寸的颗粒和液态CO2混合物，即使在没有聚集的情况下，单个颗粒质量仍然是决定颗粒沉降速率的重要因素。使用紫外-可见光谱、时域有限差分建模和电子显微镜的组合来确认颗粒分散和结构稳定性。共溶剂（ACN）的必要性表明，颗粒在液态CO2中的行为与在传统液相溶剂中的行为大不相同，并强调了未来研究的必要性，以了解亲水颗粒在高压非极性环境中的润湿行为。

KEYWORDS: nanocomposites， spiky particles， colloidal stability， liquid carbon dioxide， UV−vis spectroscopy

关键词：纳米复合材料，尖锐颗粒，胶体稳定性，液态二氧化碳，紫外-可见光谱