Collaborative Research: Hollow Nanoparticle Synthesis - Templating Electrochemically Evolved Hydrogen Nanobubbles

德克萨斯大学阿灵顿分校和布林莫尔学院之间的这项合作研究将对气泡模板合成方法——一种新的纳米颗粒合成工艺——有一个基本的了解。在该方法中，电化学演化的氢纳米泡被用作还原剂和模板来形成金属空心纳米颗粒。这种新的合成概念有可能成为制造各种纳米结构的通用途径。本项目由固体与材料化学计划资助，将利用原位同步x射线衍射、原子力显微镜（AFM）和电子显微镜（SEM和TEM）研究纳米气泡和纳米颗粒在不同生长阶段的形成，并研究从不同材料合成结构更复杂的纳米颗粒。首先，利用同步x射线衍射原位监测氢纳米泡周围的金属沉积，研究氢纳米泡周围金属还原的反应机理和动力学。通过电子显微镜对不同合成参数下形成的纳米颗粒进行分析，验证“气泡越小反应速率越高”的假设。然后，利用原子力显微镜原位检测条形电极表面非导电区纳米气泡的形成，研究电化学演化氢纳米气泡的形成机理。以金纳米颗粒为指示剂，利用电子显微镜分析研究了电解质中载体和添加剂（如表面活性剂和析氢促进剂）的表面性质对纳米气泡形成的影响。最后，探讨了Pt、Pd、Ag等不同化学沉积金属的空心纳米粒子的合成以及多壳、半球等更复杂结构的纳米粒子的合成。纳米技术被认为是美国在全球经济竞争中最有潜在价值的技术之一。金属纳米粒子作为纳米技术的重要组成部分，在能量转化和化学工业中被广泛用作催化剂，在生物医学应用中被用作显像和治疗剂，在电子和光电子器件中被用作构件，以及其他许多领域。通过对一种新的纳米颗粒合成工艺-气泡模板合成的系统研究，这个由固态和材料化学计划资助的研究项目将导致对纳米颗粒形成机制的理解的进步，为控制合成过程提供必要的信息，以实现纳米颗粒的预期性能。此外，该合成方法还可作为研究液体中微小气泡（纳米气泡）的便捷工具。这将对气泡相关的广泛应用产生许多重要影响，从制氢和水电解到流体微通道和纳米器件的设计。该研究项目与一个多层次的教育和推广项目相结合，包括本科纳米技术教育的课程开发、跨学科的学生培训、K-12学生的夏令营，以及为费城当地中学女生举办的年度“扩展你的视野”（EYH）会议的推广活动。特别强调扩大妇女和代表性不足的西班牙裔学生在科学和工程领域的参与，为布林莫尔学院的女本科生和德克萨斯州的西班牙裔高中生和大学生提供机会，在该项目中进行最先进的纳米技术研究。

TECHNICAL SUMMARY This collaborative research between the University of Texas at Arlington and Bryn Mawr College will develop a fundamental understanding of the bubble template synthesis method, a new nanoparticle synthesis process. In this method, electrochemically evolved hydrogen nanobubbles are used as reducing agents and templates to form metal hollow nanoparticles. This new synthesis concept possesses the potential to become a general route to varieties of nanostructures. In this project funded by the Solid State and Materials Chemistry Program, in situ synchrotron x-ray diffraction, atomic force microscopy (AFM) and electron microscopy (SEM and TEM) will be employed to investigate the formation of nanobubbles and nanoparticles at different growth stages, and the synthesis of nanoparticles with more complicated structures and from different materials will be studied. First, the reaction mechanism and kinetics of metal reduction around hydrogen nanobubbles will be investigated by in situ monitoring the metal deposition using synchrotron X-ray diffraction. The hypothesis of "the reaction rate is higher for smaller bubbles" will be tested through electron microscopy analysis of nanoparticles formed with different synthesis parameters. Then, the formation mechanism of electrochemically evolved hydrogen nanobubbles will be studied by in situ detecting the formation of nanobubbles on non-conductive areas on stripe pattern electrode surfaces using AFM. With Au nanoparticles as an indicator, the effects of the surface properties of supports and additives in electrolytes (such as surfactants and hydrogen evolution enhancers) on nanobubble formation will be studied using electron microscopy analysis. Finally, the synthesis of hollow nanoparticles of different electroless-depositable metals such as Pt, Pd and Ag and nanoparticles with more complicated structures such as multi-shells and half spheres will be explored. NON-TECHNICAL SUMMARY Nanotechnology is considered as one of the most potentially valuable technologies for U.S. in the global economic competition. As an important part of nanotechnology, metallic nanoparticles are widely used as catalysts in energy conversion and chemical industry, as imaging and therapeutic agents in biomedical applications, as building blocks in electronic and optoelectronic devices, and in many other areas. Through a systematic study on a new nanoparticle synthesis process - the bubble template synthesis, this research project funded by the Solid State and Materials Chemistry Program will lead to advances in the understanding of nanoparticle formation mechanisms, providing essential information for controlling the synthesis process to achieve the desired properties of nanoparticles. In addition, the new synthesis process can also be utilized as a convenient tool for studies on very small gas bubbles (nanobubbles) in liquid. This will have many important impacts on a wide range of bubble-related applications, from hydrogen generation and water electrolysis to the design of fluidic microchannels and nanodevices. This research program is integrated with a multi-layered education and outreach program, including course development for undergraduate nanotechnology education, interdisciplinary student training, summer camps for K-12 students, and outreach activities through annual "Extending Your Horizon" (EYH) conference for Philadelphia local middle school girls. Special emphasis has been placed on broadening the participation of both women and underrepresented Hispanic students in science and engineering by providing opportunities to women undergraduate students in Bryn Mawr College and Hispanic high school and college students in Texas with conducting state-of-the-art nanotechnology research in this project.