Interfacial Free Energy of Nanominerals in Solutions, Biofilms and Microbial Cells

该奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。界面现象在低温、地球化学和生物环境中很常见。界面自由能是控制纳米矿物热力学相稳定性、影响生物矿化、决定在环境中(例如，在土壤中、在生物修复过程中)沉淀的矿物的形式和活性以及直接影响表面反应动力学(例如，吸附和溶解)的关键参数。了解这些量如何随环境类型变化对于理解和控制这些过程至关重要。本研究的目的是测定针铁矿这一重要的天然纳米矿物在不同表面环境下的界面自由能，并用其分析成核、吸附和反应活性。针铁矿纳米颗粒由矿物风化和酸性矿山废水的中和形成，经常与微生物细胞共生，有时是微生物新陈代谢的副产品。针铁矿纳米颗粒在不同环境中的界面自由能的测定需要一种非破坏性且不改变纳米颗粒或其周围环境的技术。传统的量热法和接触角测量无法满足这一要求。这一挑战将使用研究人员最近开发的基于衍射的方法来解决，该方法表明，依赖于尺寸的界面自由能可以通过积分从衍射实验获得的表面应力数据来获得。研究人员将使用常规和基于同步加速器的X射线衍射来测量晶格参数，从而测量表面应力随颗粒大小的变化。(脱气)针铁矿纳米颗粒和纳米颗粒，在水中，在含有小有机分子的溶液中，附着在细菌细胞(Gebacter sp.)上，并被脂质双层覆盖。界面自由能与尺寸和环境有很强的相关性。针铁矿的成核将通过修改经典理论来分析，以纳入界面自由能与环境和尺寸的关系。将研究结合强度和界面自由能之间的关系，并将结果作为环境类型的函数来预测反应活性。这项拟议的研究将为研究自然环境中涉及纳米颗粒的界面现象提供一个新的模板。广泛影响：纳米颗粒界面现象是地球附近许多地球化学和生物过程的关键？S地表。由于纳米粒子的界面自由能决定了它们的相稳定性、反应性和转化动力学，因此新的见解将在地球化学、环境、医学科学和工程以及环境友好型纳米技术的发展方面具有广泛的意义。拟制定的方法也应具有广泛的适用性。本科生研究是该项目的一个中心主题。实验决定是直截了当的，使学生能够充分参与最先进的研究。通过研究，学生在获得实际研究经验的同时，还将发展批判性和创造性的思维能力。科学概念及其在生物修复中的实际应用将通过与一名当地教师的互动向高中生传达，这名教师将参加在Rifle CO现场的暑期实地考察。从研究中获得的知识将通过专业出版物和专题介绍、为感兴趣的团体举办研讨会以及张贴在纳米地球科学网站和开放的维基百科网站上供公众查阅，向广大受众传播。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Interfacial phenomena are common in low temperature geochemical and biological environments. Interfacial free energy is a key parameter that controls the thermodynamic phase stability of nanominerals, impacts biomineralization, determines the form and reactivity of minerals precipitated in the environment (e.g., in soils, during bioremediation), and directly impacts surface reaction kinetics (e.g., sorption and dissolution). Knowledge about how this quantity varies with environment type is essential for understanding and controlling these processes. The purpose of the present research is to determine the interfacial free energy of goethite, an important natural nanomineral, in various surface environments, and to use the results to analyze nucleation, adsorption and reactivity. Goethite nanoparticles form by mineral weathering and neutralization of acid mine drainage and are often associated with microbial cells, sometimes as byproducts of their metabolism. Determination of interfacial free energy of goethite nanoparticles in various environments necessitates a technique that is non-destructive and does not modify the nanoparticles or their surroundings. This requirement is not fulfilled with conventional calorimetry and contact angle measurements. This challenge will be addressed using a diffraction-based method developed recently by the investigators, which shows that the size-dependent interfacial free energy can be derived from integration of surface stress data obtained from diffraction experiments. The investigators will use both conventional and synchrotron-based x-ray diffraction to measure the lattice parameters and hence the surface stress as a function of particle size for ?dry? (degassed) goethite nanoparticles and nanoparticles in water, in solution containing a small organic molecule, attached to bacterial cells (Geobacter sp.), and coated by lipid bilayers. Strong size- and environment-dependence of the interfacial free energy is expected. Goethite nucleation will be analyzed by modifying classical theory to incorporate the environment- and size-dependence of interfacial free energy. The relationship between binding strength and interfacial free energy will be examined and the results used to predict reactivity as a function of environment type. The proposed research will serve as a new template for study of interfacial phenomena involving nanoparticles in natural environments.Broader Impacts: Nanoparticle interfacial phenomena are key to many geochemical and biological processes near the Earth?s surface. Because the interfacial free energy of nanoparticles determines their phase stability, reactivity and transformation kinetics, new insights will be broadly relevant in geochemistry, environmental and medical sciences and engineering, and for development of environment-compatible nanotechnologies. The methodology to be developed should also be broadly applicable. Undergraduate research is a central theme of the project. The experimental determinations are straightforward, enabling full participation of students in state-of-the-art research. Through the research, students will develop critical and creative thinking skills in addition to obtaining practical research experience. Science concepts and their practical applications in bioremediation will be conveyed to high school students through interactions with a local teacher who will participate in summer fieldwork at the Rifle CO site. The knowledge acquired from the research will be disseminated to a broad audience through professional publications and presentations, seminars to interested groups, and posting to the Nanogeoscience web site and the open Wikipedia web site for public access.