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

纳米颗粒广泛存在于水环境系统中，并在自然地球化学过程中发挥重要作用，如金属污染物的螯合。纳米颗粒具有非常高的表面积，并且相对于宏观颗粒在表面能、反应性、相稳定性和其他化学/物理性质方面具有显著差异。由于这些独特的功能，重金属吸附到这些高反应性的纳米粒子的程度和机制可能是根本不同的相比，体相。此外，现在有相当多的证据表明，许多纳米颗粒相生长的定向附着，一种专门的形式的聚集。这种生长机制可以提供额外的强大的优势，在螯合金属永久进入固相通过（共）沉淀过程引起的基于聚集体的生长。尽管纳米颗粒在环境中的普遍性和矿物/水界面处金属吸附的现有研究的丰富性，但是，当矿物颗粒是纳米级时，对于这些相互作用如何以及在多大程度上可能被改变（可能是戏剧性的）的基本理解很少，以及这可能对长期-金属在环境中的长期稳定性和流动性。拟议研究的主要目标是确定羟基氧化铁纳米粒子如何与As（V）、Cu（II）、Hg（II）和Zn（II）是在许多环境污染地区发现的危险（半）金属，在初始暴露和随后的纳米颗粒老化/生长时。这将通过以下方式实现：B）在基于聚集的纳米颗粒生长期间吸附的重金属的保留的时间分辨测量，集中于新的（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随时间的生长和结构转化的影响; d）测定与合成和天然羟基氧化铁纳米颗粒相关的重金属的化学形态，以鉴定在老化过程的不同阶段的精确吸收模式;和e）使用老化的含金属纳米颗粒聚集体的解吸研究，以评估和预测当暴露于与环境系统相关的pH和盐度的变化时，掺入的金属的长期稳定性和持久性。将合成先前已经关于形态、表面积、内部结构和表面结构表征的直径为100 nm的纳米颗粒，并将其用于宏观吸收实验以确定在基于渐进纳米颗粒聚集体的生长期间As（V）、Cu（II）、Hg（II）和Zn（II）吸附的程度。这种时间分辨的信息将有助于区分与无金属系统相比，含金属系统中生长速率和途径的变化。先进的X射线吸收光谱技术将用于检查金属吸收的精确模式（例如间接吸附，直接吸附，（共）沉淀）以及这些模式如何受到粒度和老化时间差异的影响。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值和离子强度的函数。结果将与使用在现场收集的天然羟基氧化铁沉淀物的结果进行比较，以评估反应性和形态的相对差异。拟议的研究将应用时间分辨宏观和强大的基于同步加速器的光谱方法，以发展对金属吸附和纳米级氢氧化铁（共）沉淀的基本理解，在广泛的自然环境中发生的过程尚未得到很好的记录。预计这种纳米颗粒将通过先前未被表征的新的吸收机制显示出相对于体相增强的重金属吸收，并对这些污染物在环境中的未来流动性、生物利用度和归宿产生重大影响。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，并启动查普曼大学，一个小型的，独立的，主要是本科院校之间的合作伙伴关系，和美国地质调查局。学生将在区域和国家会议上展示他们的工作，并在同行评审的文献中传播他们的成果。这项研究的结果也可能导致在重金属污染引起环境问题的地区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.