RUI: Heavy Metal Sorption/Co-precipitation Interactions with Nanoscale Iron Oxyhydroxides

纳米颗粒广泛存在于水环境体系中，在自然地球化学过程中发挥着重要作用，如金属污染物的封存。纳米粒子具有极高的比表面积，在表面能、反应性、相稳定性和其他化学/物理性质上与宏观粒子有很大的差异。由于这些独特的特征，重金属在这些高活性纳米颗粒上的吸附程度和机理可能与块体相相比有根本的不同。此外，现在有相当多的证据表明，许多纳米颗粒相是通过定向附着生长的，定向附着是一种特殊的聚集形式。这种生长机制可能会提供另一个强大的优势，通过基于聚集的生长诱导的(Co)沉淀过程将金属永久隔离到固相中。然而，尽管纳米粒子在环境中无处不在，而且现有的关于矿物/水界面金属吸附的丰富研究，对于当矿物颗粒是纳米级时，这些相互作用可能如何以及在多大程度上被改变，以及这可能对环境中金属的长期稳定性和流动性产生的相关影响，以及这可能对环境中金属的长期稳定性和流动性产生的相关影响，几乎没有基本的了解。拟议研究的主要目标是确定氢氧化铁纳米粒子与As(V)、Cu(II)、Hg(II)和Zn(II)的反应，As(V)、Cu(II)、Hg(II)和Zn(II)是一些环境污染地区中发现的有害(半)金属，在初始暴露和随后的纳米颗粒的老化/生长时。这将通过以下方式完成：a)合成氢氧化铁纳米颗粒，并现场收集酸性矿山排水区域的天然氢氧化铁纳米沉淀物；b)在基于聚集的纳米颗粒生长过程中对吸附的重金属的保留进行时间分辨测量，重点是新的(共)沉淀方法的证据；c)评估金属吸收对合成和天然纳米颗粒的生长和结构变化的影响；d)测定与合成和天然氢氧化铁纳米颗粒相关的重金属的化学形态，以确定老化过程不同阶段吸收的精确模式(S)；和e)使用老化的含金属纳米颗粒聚集体进行解吸研究，以评估和预测结合金属在与环境系统相关的pH和盐度变化时的长期稳定性和持久性。将合成直径为3 nm的氢氧化铁纳米颗粒，这些纳米颗粒先前已被表征为形貌、表面积、内部结构和表面结构，并用于宏观吸收实验，以确定在基于纳米颗粒聚集的渐进生长过程中As(V)、Cu(II)、Hg(II)和Zn(II)的吸附程度。这些时间分辨的信息将有助于区分含金属系统和无金属系统中生长速度和路径的变化。先进的X射线吸收光谱技术将被应用于研究金属吸收的精确模式(如间接吸收、直接吸收、(共)沉淀)(S)以及这些模式如何受颗粒大小和老化时间的差异的影响。解吸实验将研究纳米颗粒老化对金属再活化的影响，作为pH和离子强度的函数。结果将与现场收集的天然氢氧化铁沉淀物进行比较，以评估反应性和形态的相对差异。智力优势：拟议的研究将应用时间分辨的宏观和强大的同步加速器光谱方法，以发展对金属吸附和(共)与纳米级氢氧化铁沉淀的基本理解，这一过程发生在广泛的自然环境中，但尚未得到很好的记录。人们的期望是，这种纳米颗粒将通过以前尚未表征的新的吸收机制，相对于块状颗粒显示出更强的重金属吸收能力，并对这些污染物在环境中的未来移动性、生物有效性和命运产生重大影响。广泛影响：该项目将为化学和环境科学本科生提供独立研究和实地考察的机会，为学生提供接触国家同步加速器用户设施的机会，并启动查普曼大学和美国地质调查局之间的合作伙伴关系。查普曼大学是一家小型、独立、主要是本科的机构。学生将在区域和国家会议以及作者或合著者出版物上展示他们的工作，在同行评议的文献中传播他们的结果。这项研究的结果还可能导致在重金属污染引起环境问题的地区采取新的补救或处理策略。

Nanoparticles are widespread in aqueous environmental systems and play a significant role in natural geochemical processes such as the sequestration of metal contaminants. Nanoparticles possess exceptionally high surface areas and feature dramatic differences in surface energy, reactivity, phase stability, and other chemical/physical properties relative to macroscale particles. As a result of these unique features, the extent and mechanisms of heavy metal sorption to these highly reactive nanoparticles may be fundamentally different compared to bulk phases. Furthermore, there is now considerable evidence that many nanoparticulate phases grow by oriented attachment, a specialized form of aggregation. This growth mechanism may provide an additional powerful advantage in sequestering metals permanently into the solid phase through (co)precipitation processes induced by aggregation-based growth. Despite the pervasiveness of nanoparticles in the environment and the wealth of existing studies of metal sorption at the mineral/water interface, however, there is very little fundamental understanding of how and to what extent these interactions may be altered, perhaps dramatically, when the mineral particles are nanoscale, and the related effects this may have on the long-term stability and mobility of metals in the environment.The primary objective of the proposed research is to determine how iron oxyhydroxide nanoparticles react with As(V), Cu(II), Hg(II), and Zn(II), hazardous (semi-)metals found in a number of environmentally-polluted locales, upon initial exposure and with subsequent aging/growth of the nanoparticles. This will be accomplished by: a) synthesis of iron oxyhydroxide nanoparticles and field-based collection of natural iron oxyhydroxide nanosized precipitates from acid mine drainage (AMD) regions; b) timeresolved measurement of the retention of sorbed heavy metals during aggregation-based nanoparticle growth, focusing on evidence of novel methods of (co)precipitation; c) assessment of the effects of metal uptake on the growth and structural transformation of synthetic and natural nanoparticles over time; d) determination of the chemical speciation of heavy metals associated with the synthetic and natural iron oxyhydroxide nanoparticles to identify the precise mode(s) of uptake at different stages of the aging process; and e) desorption studies using aged metal-bearing nanoparticle aggregates to assess and predict the long-term stability and permanence of incorporated metals when exposed to changes in pH and salinity relevant to environmental systems.Iron oxyhydroxide nanoparticles of 3-nm diameter which have previously been characterized with respect to morphology, surface area, internal structure, and surface structure will be synthesized and used in macroscopic uptake experiments to determine the extent of As(V), Cu(II), Hg(II), and Zn(II) sorption during progressive nanoparticle aggregation-based growth. This time-resolved information will help distinguish changes in growth rate and pathway in metal-bearing systems compared to metal-free systems. Advanced X-ray absorption spectroscopy techniques will be applied to examine the precise mode(s) of metal uptake (e.g. indirect sorption, direct sorption, (co)precipitation) and how these modes are affected by differences in particle size and aging time. Desorption experiments will study the effects of nanoparticle aging on the remobilization of metals as a function of pH and ionic strength. Results will be compared with those using natural iron oxyhydroxide precipitates collected in the field to assess relative differences in reactivity and speciation.Intellectual Merit: The proposed research will apply both time-resolved macroscopic and powerful synchrotron-based spectroscopic methods to develop a basic understanding of metal sorption and (co)-precipitation with nanoscale iron oxyhydroxides, processes which occur in a wide range of natural environments yet have not been well-documented. The expectation is that such nanoparticles will display enhanced heavy metal uptake relative to bulk phases through novel mechanisms of uptake that have not been previously characterized and hold significant implications for the future mobility, bioavailability, and fate of these contaminants in the environment.Broader Impacts: This project will generate opportunities for independent research and fieldwork to chemistry and environmental science undergraduate students, provide students with exposure to national synchrotron user facilities, and initiate a collaborative partnership between Chapman University, a small, independent, primarily undergraduate institution, and the U.S. Geological Survey. Students will present their work at regional and national conferences and author or co-author publications disseminating their results in the peer-reviewed literature. Results from this research may also lead to new remediation or treatment strategies in areas where heavy metal contamination is cause for environmental concern.