Nam Jae Hyun, Nayak Gaurav, Exarhos Stephen, Mueller Chelsea M, Xu Dongxuan, Schatz George C, Bruggeman Peter J
Department of Mechanical Engineering, University of Minnesota Minneapolis MN-55455 USA.
Department of Chemistry, Northwestern University Evanston IL-60208 USA
Chem Sci. 2024 Jun 19;15(29):11643-11656. doi: 10.1039/d4sc01192a. eCollection 2024 Jul 24.
The interaction between low-temperature plasma and liquid enables highly reactive solution phase chemistry and fast reaction kinetics. In this work, we demonstrate the rapid synthesis of stabilizer-free, spherical and crystalline gold nanoparticles (AuNP). More than 70% of gold ion complex (AuCl ) conversion is achieved within a droplet residence time in the plasma of ∼10 ms. The average size of the AuNPs increases with an increase in the droplet residence time and the particle synthesis showed a power threshold effect suggesting the applicability of the classical nucleation theory. Leveraging UV-vis absorption and emission spectroscopy, and nanoparticle size distributions obtained from TEM measurements, we showed that the AuCl conversion exceeded by 250 times the maximum faradaic efficiency. We identified important roles of both short-lived reducing species including solvated electrons and possibly vacuum ultraviolet (VUV) photons, and long-lived species, HO, in the reduction of AuCl . A quantitative investigation was performed by a 1-D reaction-diffusion model which includes transport, plasma-enabled interfacial reduction of AuCl , classical nucleation, monomer absorption and autocatalytic surface growth enabled by HO. The model shows good agreement with the experimental results. The timescale analysis of the simulation revealed that nucleation is enabled by fast reduction of gold ions, and autocatalytic growth mainly determines the particle size and is responsible for the majority of the ion precursor conversion while also explaining the excessively large faradaic efficiency found experimentally.
低温等离子体与液体之间的相互作用能够实现高活性的溶液相化学和快速的反应动力学。在这项工作中，我们展示了无稳定剂、球形且结晶的金纳米颗粒（AuNP）的快速合成。在等离子体中液滴停留时间约为10毫秒的情况下，金离子络合物（AuCl）的转化率超过70%。AuNP的平均尺寸随着液滴停留时间的增加而增大，并且颗粒合成显示出功率阈值效应，这表明经典成核理论的适用性。利用紫外可见吸收和发射光谱以及从透射电子显微镜测量获得的纳米颗粒尺寸分布，我们表明AuCl的转化率比最大法拉第效率高出250倍。我们确定了包括溶剂化电子以及可能的真空紫外线（VUV）光子等短寿命还原物种和长寿命物种HO在AuCl还原过程中的重要作用。通过一维反应扩散模型进行了定量研究，该模型包括传输、等离子体驱动的AuCl界面还原、经典成核、单体吸收以及由HO实现的自催化表面生长。该模型与实验结果显示出良好的一致性。模拟的时间尺度分析表明，金离子的快速还原促成了成核，而自催化生长主要决定了颗粒尺寸，并负责大部分离子前驱体的转化，同时也解释了实验中发现的过大的法拉第效率。
