Nucleation of Manganese Oxides in the Presence of Reactive Halogen Species

在NSF化学部环境化学科学项目的资助下，华盛顿大学的Young-Shin Jun教授研究了盐水中氧化锰颗粒的形成。锰氧化物在环境中是丰富的，并且在去除污染物方面是重要的。它们的形成可能受到人类活动产生的高盐浓度产品的影响，例如脱盐和石油和天然气回收。所涉及的化学反应知之甚少，包括卤素离子的作用（例如，氯化物和溴化物）和高反应性卤素物质。这项工作定量和定性地研究了盐水化学如何影响环境中锰氧化物的形成。该项目还为代表性不足或经济上处于不利地位的K-12学生开发环境化学外展计划。这种推广活动既鼓励高中生和本科生尽早参与研究，又通过纳入研究成果来改进大学课程，水和能源生产过程中产生的高含盐量废水的增加引起了人们对它们对环境影响的质疑。特别是，盐水中的卤化物可以极大地影响天然水生系统中的矿物形成和溶解过程。在阳光下，卤化物可进一步经历光化学反应以产生反应性自由基物质。然而，卤化物在阳光照射下对具有氧化还原活性的过渡金属离子及其固相形成的影响仍然不清楚。本项目研究活性卤素物种对水溶液锰（Mn）离子的氧化和锰颗粒的成核和生长的动力学的影响，有和没有天然有机物。据推测，从天然有机物和卤化物之间的反应在其光解过程中产生的反应物种可以促进光化学氧化的Mn 2+（aq）和促进形成更高的氧化态的锰氧化物。为了阐明新形成的锰氧化物的性质，并检查这些动态氧化还原反应行为，锰氧化物的固相和流体化学的特点。基于同步辐射的原位小角x射线散射提供了有关锰氧化物成核和生长的实时信息。该项目推进了高盐系统中锰氧化物成核机制和动力学的基础知识，这对于预测污染物去除和传输以及开发新的锰基材料非常重要。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Funded by the Environmental Chemical Sciences Program of the NSF Division of Chemistry, Professor Young-Shin Jun at Washington University examines the formation of manganese oxide particles in salt water. Manganese oxides are environmentally abundant and are important in removing contaminants. Their formation can be affected by products from human activities that have high salt concentrations, such as from desalination and oil and gas recovery. The chemical reactions involved are poorly understood, including the roles of halide ions (e.g., chloride and bromide) and highly reactive halogen species. This work quantitatively and qualitatively examines how salt water chemistry affects the formation of manganese oxides in the environment. The project also develops environmental chemistry outreach programs for underrepresented or economically disadvantaged K-12 students. This outreach both encourages the early involvement of high school and undergraduate students in research and improves university courses by incorporating research outcomes.The increased production of highly saline effluents from water and energy generating processes raises questions about their impacts on the environment. In particular, halides in brine can greatly affect mineral formation and dissolution processes in natural aquatic systems. With sunlight, halides may further undergo photochemical reaction to generate reactive radical species. However, the effects of halides under sunlight exposure on redox-active transition metal ions and their solid phase formation are still obscure. This project investigates the effects of reactive halogen species on the oxidation of aqueous manganese (Mn) ions and the kinetics of the nucleation and growth of Mn particles, with and without natural organic matter. It is hypothesized that reactive species generated from reactions between natural organic matter and halides during their photolysis can promote the photochemical oxidation of Mn2+ (aq) and facilitate the formation of higher oxidation states of manganese oxides. To elucidate the properties of newly formed manganese oxides and to examine these dynamic redox reaction behaviors, solid phases of manganese oxides and fluid chemistries are characterized. In situ synchrotron-based small angle x-ray scattering provides real-time information about the nucleation and growth of manganese oxides. The project advances fundamental knowledge regarding the nucleation mechanisms and kinetics of manganese oxides in highly saline systems, which is important for predicting contaminant removal and transport and for developing new manganese-based materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.