Single-Molecule Investigation of Nanocatalysis

0851257陈此奖项是根据2009年美国复苏和再投资法案（公法111 - 5）资助的。知识产权纳米粒子催化有机合成，污染物去除和能源生产中的许多化学转化;因此，人们付出了巨大的努力来表征纳米粒子催化剂的结构和理解其催化性能。虽然单个纳米粒子的结构可以用先进的透射电子显微镜和扫描探针显微镜研究到原子分辨率，但它们的催化性能主要是在整体水平上测量的，获得平均性能。然而，由于纳米颗粒的结构分散性、表面位点的不均匀分布和表面重构动力学，纳米颗粒的催化性能本质上是不均匀的。为了解决这种异质性的挑战，并消除测量中的整体平均，PI率先在单粒子和单周转率分辨率下研究纳米粒子催化，使用荧光反应的单分子荧光显微镜。专注于胶体金纳米粒子的氧化还原催化，PI的初步研究表明，有可能在溶液中真实的时间内以单周转分辨率跟踪单个金纳米粒子的催化周转。我们发现，对于催化产物形成反应，所有Au纳米粒子遵循朗缪尔-欣谢尔伍德机制，但具有异质反应性;对于产物解离反应，存在三个纳米粒子亚群，其显示出异质反应性，在两个平行的产物解离途径之间具有不同的动力学。此外，单个Au纳米粒子显示出很大的时间活性波动，这归因于催化诱导和自发的表面重组动力学，这些动力学在表面催化和产物对接位点以不同的时间尺度发生。在这些成就的基础上，PI建议使用单粒子单周转方法：1）探测Au纳米颗粒的非均相反应性和表面重组动力学的性质，2）确定单个Au纳米颗粒催化的尺寸依赖性，3）确定单个Au纳米颗粒催化的形状依赖性。所获得的结果将揭示其非均相反应性的结构起源，揭示其表面重组动力学的性质，并在单粒子水平上深入了解其结构-活性相关性，更广泛的影响本提案中描述的单分子纳米催化研究为多相/纳米催化和单分子纳米催化开辟了新的方向。分子研究。如果设计了合适的荧光探针反应，单粒子方法也可推广到研究其他纳米级催化剂。所获得的知识将有助于理解纳米粒子催化活性的基本原理，这将有助于改进现有纳米催化剂和设计新的多相催化剂。金属纳米颗粒被广泛用作化学转化的催化剂，特别是用于燃料和太阳能电池中的能量转换。这些研究的基础知识将有助于了解化学工业、燃料和太阳能电池中使用的纳米粒子的活性，这将有助于找到改进它们的可能方法，从而使整个社会受益。PI的教育工作结合了他的单分子研究活动，促进了本科和研究生课程的跨学科教学和培训。PI积极扩大妇女和少数民族学生（本科生和研究生）参与研究的范围，并为本科生，包括四年制学院的学生提供培训。PI实验室的科学专业知识和技术仪器为当地社区的研究基础设施增添了力量。PI的外展活动将促进公众对前沿单分子研究的理解和支持，并促进K-12学生的科学教育。

0851257ChenThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Intellectual MeritNanoparticles catalyze many chemical transformations in organic synthesis, pollutant removal, and energy production; intense efforts are thus made to characterize the structure and understand the catalytic properties of nanoparticle catalysts. While structures of individual nanoparticles can be studied down to atomic resolution with advanced transmission electron microscopy and scanning probe microscopies, their catalytic properties have been mainly measured at the ensemble level, obtaining averaged properties. The catalytic properties of nanoparticles are intrinsically heterogeneous, however, due to their structural dispersions, heterogeneous distribution of surface sites, and surface restructuring dynamics. To address this heterogeneity challenge and to remove ensemble averaging in measurements, the PI has pioneered in studying nanoparticle catalysis at the single-particle and single-turnover resolution, using single-molecule fluorescence microscopy of fluorogenic reactions. Focusing on the redox catalysis by colloidal Au-nanoparticles, the PI's preliminary studies show it is possible to follow in real time in solution the catalytic turnovers of single Au-nanoparticles at single-turnover resolution. We found that for the catalytic product formation reaction, all Au-nanoparticles follow a Langmuir-Hinshelwood mechanism but with heterogeneous reactivity; for the product dissociation reaction, three nanoparticle subpopulations are present that show heterogeneous reactivity with distinct kinetics between two parallel product dissociation pathways. Moreover, individual Au-nanoparticles show large temporal activity fluctuations, attributable to catalysis-induced and spontaneous surface restructuring dynamics that occur with distinct timescales at the surface catalytic and product docking sites.Building on the achievements, the PI proposes to use the single-particle single-turnover approach to:1) probe the nature of the heterogeneous reactivity and surface restructuring dynamics of Au nanoparticles,2) determine the size dependence of single Au-nanoparticle catalysis, and 3) determine the shape dependence of single Au-nanoparticle catalysis. The results to be obtained will reveal the structural origins of their heterogeneous reactivity, unravel the nature of their surface restructuring dynamics, and gain insight into their structure-activity correlations at the single-particle level, much of which are beyond the reach of conventional ensemble measurements.Broader impactThe single-molecule nanocatalysis research described in this proposal opens new directions in both heterogeneous/nano-catalysis and single-molecule research. The single-particle methodology is also generalizable to study other nanoscale catalysts if a suitable fluorogenic probe reaction is designed. The knowledge to be gained will help understand the fundamental principles governing catalytic activities of nanoparticles, which will assist the efforts in improving current nanoscale catalysts and designing new ones for heterogeneous catalysis. Metal nanoparticles are widely used as catalysts for chemical transformations and in particular for energy conversion in fuel and solar cells. The fundamental knowledge from these studies will help understand the activity of nanoparticles used in the chemical industry and in fuel and solar cells, which will help in identifying possible means to improve them, thus benefiting the society as a whole.The PI's education efforts integrate his single-molecule research activities to promote interdisciplinary teaching and training in both undergraduate and graduate classes. The PI actively broadens the participation of women and minority students (both undergraduate and graduate) in research and offer training to undergraduate students, including those from four-year colleges. The scientific expertise and technical instrumentation of the PI's lab add strength to the research infrastructure of local community. The PI's outreach activities will advance the public understanding and support of frontier single-molecule research and promote science education in K-12 students.