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的热力学相稳定性、影响生物矿化、确定在环境中沉淀的矿物的形式和反应性（例如，在土壤中，在生物修复过程中），并直接影响表面反应动力学（例如，吸附和溶解）。了解这一数量如何随环境类型而变化，对于理解和控制这些过程至关重要。本研究的目的是确定针铁矿，一种重要的天然纳米矿物，在不同的表面环境中的界面自由能，并使用结果来分析成核，吸附和反应性。针铁矿纳米颗粒通过矿物风化和酸性矿井排水的中和而形成，并且通常与微生物细胞相关，有时作为其代谢的副产物。针铁矿纳米粒子在各种环境中的界面自由能的测定需要一种非破坏性的技术，不修改纳米粒子或其周围环境。传统的量热法和接触角测量无法满足这一要求。这一挑战将使用最近开发的基于衍射的方法来解决的研究人员，这表明，尺寸依赖的界面自由能可以来自从衍射实验获得的表面应力数据的整合。研究人员将使用传统的和同步加速器为基础的X射线衍射来测量晶格参数，因此作为粒度的函数的表面应力？干吗？（脱气的）针铁矿纳米颗粒和在水中的纳米颗粒，在含有小有机分子的溶液中，附着于细菌细胞（Geophylla sp.），并被脂质双层包覆。强烈的尺寸和环境依赖性的界面自由能是预期的。针铁矿成核将通过修改经典理论进行分析，将环境和尺寸依赖的界面自由能。结合强度和界面自由能之间的关系将被检查和结果用于预测作为环境类型的函数的反应性。拟议中的研究将作为一个新的模板，研究涉及纳米粒子在自然environments.broader影响的界面现象：纳米粒子界面现象的关键是许多地球化学和生物过程附近的地球？s表面。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，因此新的见解将广泛适用于地球化学、环境和医学科学与工程，以及开发与环境相容的纳米技术。拟制定的方法也应广泛适用。本科生研究是该项目的中心主题。实验测定是直接的，使学生充分参与国家的最先进的研究。通过研究，学生将发展批判性和创造性思维能力，除了获得实际的研究经验。科学概念及其在生物修复中的实际应用将通过与当地教师的互动传达给高中学生，该教师将参加步枪CO现场的夏季实地考察。从研究中获得的知识将通过专业出版物和演示文稿，向感兴趣的团体举办研讨会，并张贴到Nanogeoscience网站和开放的维基百科网站供公众访问，传播给广大受众。

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.