Ferrate (Fe(VI))-Coated Sand Media for Simultaneous Oxidation of Organic Contaminants and Adsorption of Trace Metals in Water

在传统的水处理工艺中，氯和臭氧等化学氧化剂被广泛用作消毒剂和反应物来降解有害的微量有机化合物。然而，在水处理过程中，氯化和臭氧化也会导致有毒副产物的形成。高铁酸盐，即Fe（VI）氧化铁，由于其高氧化还原电位、良好的性质以及作为氧化剂、消毒剂、混凝剂和吸附剂的能力，已成为一种很有前途的多功能水处理试剂。然而，高铁酸盐在环境相关ph值的水溶液中迅速分解，这限制了其作为水处理氧化剂和功能试剂的反应性和有效性。前人的研究表明，硅胶可以延缓高铁酸盐的分解，催化生成高活性的高铁酸铁氧阴离子中间体。在这些有希望的发现的基础上，该项目的首席研究员（PI）建议测试沙子的假设，沙子主要由二氧化硅组成，可以稳定高铁酸盐在与环境相关的pH值的水溶液中的分解，并增强其反应性和作为多功能水处理试剂的部署。为了验证这一假设，PI和项目研究团队建议：1)设计、合成和表征高铁酸盐包覆砂复合材料；2)评估其作为非选择性水处理的化学氧化剂和吸附剂的性能。该项目的成功完成将通过产生基础知识来促进高效低成本高铁酸盐基多功能水处理材料的开发和应用，从而造福社会。通过学生教育和培训，包括指导华盛顿大学的一名研究生，将为社会带来额外的好处。高铁酸盐[Fe(VI)]是一种对环境无害的铁氧阴离子，可以氧化水溶液中的有机污染物，而其还原的无毒铁[Fe(III)]相可以吸附水中的重金属。然而，在与环境相关的ph值下，高铁酸盐迅速衰减，从而限制了其治疗效果。以往的研究表明，二氧化硅（SiO2）凝胶可以减缓高铁酸盐的电荷转移动力学，从而提高其作为氧化剂的反应活性和效率。然而，这些先前的研究依赖于非共价涂层和高铁酸盐与硅胶的物理混合。为了利用二氧化硅稳定高铁酸盐氧化和吸附的双重优势，首席研究员（PI）和项目研究团队将探索高铁酸盐在沙子上的共价附着，沙子是一种广泛使用的硅基水过滤介质，其目标是创造新的低成本多功能水处理材料。研究的具体目标是：1)合成并表征高铁酸盐-砂共价复合介质；2)探究介质在水溶液中的稳定性，研究介质与有机和无机污染物反应时铁（Fe）的形态；3)研究和阐明复合高铁酸盐-砂介质与已知影响水溶液中氧化还原反应和吸附过程的相关环境化合物和物质（如溶解的有机物和无机离子）之间的相互作用；4)研究高铁酸盐-砂复合介质的原位再生和再利用机会。该项目的成功完成将产生新的基础知识和材料，以指导设计和部署更有效和更具成本效益的多功能水处理介质，从而产生变革性影响。为了实现该项目的教育、培训和推广目标，PI建议利用华盛顿大学（UW）现有的项目，如工程日，吸引来自西雅图大都会地区的4 -8年级学生进行实验室演示实验，目的是让他们对STEM职业的机会感到兴奋。此外，PI还计划与非营利组织“嘻哈是绿色的”合作，领导一项教育推广活动，招募和指导高中生，让他们在PI在华盛顿大学的实验室研究高铁酸盐治疗介质时获得研究经验。该奖项反映了美国国家科学基金会的法定使命，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。

Chemical oxidants such as chlorine and ozone are widely utilized as disinfectants and reactants to degrade harmful trace organic compounds in conventional water treatment processes. However, chlorination and ozonation can also lead to the formation of toxic byproducts during water treatment. Ferrate, Fe(VI) iron oxide, has emerged as a promising multifunctional reagent for water treatment due to its high redox potential, benign nature and demonstrated ability to serve as an oxidant, disinfectant, coagulant, and sorbent. However, ferrate rapidly decomposes in aqueous solutions at environmentally relevant pHs, which limits its reactivity and effectiveness as oxidant and functional reagent for water treatment. Previous studies have shown that silica gels can delay the decomposition of ferrate and catalyze the production of highly reactive ferrate iron oxyanion intermediate species. Building upon these promising findings, the Principal Investigator (PI) of this project proposes to test the hypothesis that sand, which is primarily composed of silica, can stabilize ferrate decomposition in aqueous solutions at environmentally relevant pH and enhance its reactivity and deployment as multifunctional reagent for water treatment. To test this hypothesis, the PI and project research team propose to 1) design, synthesize, and characterize ferrate-coated sand composite materials and 2) evaluate their performance as chemical oxidants and sorbents for non-selective water treatment. The successful completion of this project will benefit society through the generation of fundamental knowledge to advance the development and deployment of efficient and low-cost ferrate-based multifunctional materials for water treatment. Additional benefits to society will be achieved through student education and training including the mentoring of one graduate student at the University of Washington. Ferrate [Fe(VI)], an environmentally benign iron oxyanion, can oxidize organic pollutants in aqueous solutions while its reduced, non-toxic ferric [Fe(III)] phase can sorb heavy metals in water. However, at environmentally relevant pHs, ferrate rapidly decays thus limiting its treatment effectiveness. Previous studies have demonstrated that silica (SiO2) gels can slow down the charge transfer kinetics of ferrate to enhance its reactivity and efficiency as oxidant. However, these previous studies relied on the non-covalent coating and physical mixing of silica gels with ferrate. To harness the dual benefits of SiO2-stabilized ferrate for oxidation and sorption, the Principal Investigator (PI) and project research team will explore the covalent attachment of ferrate onto sand, a widely used silica-based water filtration media, with the goal of creating novel and low-cost multifunctional materials for water treatment. The specific objectives of the research are to 1) synthesize and characterize covalent composite ferrate-sand media; 2) probe the media stability in aqueous solutions and investigate iron (Fe) speciation during media reactions with organic and inorganic contaminants; 3) investigate and elucidate the interactions between the composite ferrate-sand media with relevant environmental compounds and species (e.g., dissolved organic matter and inorganic ions) that are known to impact redox reactions and sorption processes in aqueous solutions; and 4) investigate opportunities for in-situ regeneration and reuse of the composite ferrate-sand media. The successful completion of this project has the potential for transformative impact through the generation of new fundamental knowledge and materials to guide the design and deployment of more efficient and cost-effective multifunctional media for water treatment. To implement the education, training, and outreach goals of the project, the PI proposes to leverage existing programs at the University of Washington (UW) such as Engineering Days to engage 4th -8th students from the greater Seattle metropolitan area to perform lab demonstration experiments with the goal of exciting them about opportunities in STEM careers. In addition, the PI plans to lead an educational outreach activity in partnership with the “Hip Hop is Green” nonprofit organization to recruit and mentor high school students to gain research experience while working on ferrate treatment media in the PI’s lab at UW.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.