Wilson Elizabeth A K, Kumar Prashant, Montjoy Douglas G, Kotov Nicholas A
Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States.
Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States.
ACS Nano. 2022 Sep 27;16(9):13942-13948. doi: 10.1021/acsnano.2c03058. Epub 2022 Aug 29.
Liquid and supercritical CO are nontoxic and nonflammable reaction media with pressure-variable physical properties. These states of CO 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 CO 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 CO 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 CO than those without or with less prominent nanoscale corrugation. For the particles of this size and liquid CO 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 CO 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.
液态和超临界CO是无毒且不可燃的反应介质，其物理性质随压力可变。CO的这些状态对气态和液态烃也有很高的溶解度极限，使其成为可持续化学技术中“绿色”疏水溶剂的理想选择。然而，亲水性胶体纳米级和微米级颗粒在CO中的分散具有挑战性，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。在此我们表明，天然亲水性半导体颗粒可以在不使用额外化学或机械分散技术的情况下，有效地分散在与乙腈（ACN）的液态CO混合物中。使用表面波纹作为防止聚集的方法，我们发现具有坚硬纳米级尖刺晕圈的几何形状复杂的颗粒比没有或纳米级波纹不明显的颗粒在液态CO中分散且保持悬浮的时间更长。对于这种尺寸的颗粒和液态CO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一个重要因素。使用紫外可见光谱、时域有限差分建模和电子显微镜相结合的方法证实了颗粒的分散和结构稳定性。助溶剂（ACN）的必要性表明颗粒在液态CO中的行为与在传统液相溶剂中的行为有很大不同，并突出了未来研究理解亲水性颗粒在高压非极性环境中润湿性的必要性。
