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，化学氧化剂如氯和臭氧被广泛用作消毒剂和反应物以降解有害的痕量有机化合物。 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，Fe（VI）氧化铁，由于其高氧化还原电位、良性性质和表现出的作为氧化剂、消毒剂、凝结剂和吸附剂的能力，已成为用于水处理的有前途的多功能试剂。然而，高铁酸盐在环境相关pH的水溶液中迅速分解，这限制了其作为水处理的氧化剂和功能试剂的反应性和有效性。此前的研究表明，硅胶可以延缓高铁酸盐的分解，并催化产生高活性高铁酸盐铁氧阴离子中间体物种。在这些有希望的发现的基础上，该项目的主要研究者（PI）提出了一个假设，即主要由二氧化硅组成的沙子可以在环境相关的pH值下稳定高铁酸盐在水溶液中的分解，并增强其反应性和作为水处理多功能试剂的部署。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涂层砂复合材料，2）评估其作为非选择性水处理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和低成本的高铁酸盐多功能水处理材料的开发和部署，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，将为社会带来更多的好处。高铁酸盐[Fe（VI）]是一种环境友好的铁氧阴离子，可以氧化水溶液中的有机污染物，而其还原、无毒的三价铁[Fe（III）]相可以吸附水中的重金属。然而，在环境相关的pH值下，高铁酸盐迅速衰减，从而限制了其处理效果。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，以提高其作为氧化剂的反应性和效率。 然而，这些先前的研究依赖于硅胶与高铁酸盐的非共价涂层和物理混合。为了利用SiO2稳定的高铁酸盐在氧化和吸附方面的双重好处，主要研究者（PI）和项目研究团队将探索高铁酸盐与沙子（一种广泛使用的硅基水过滤介质）的共价连接，目的是创造新型低成本的多功能水处理材料。研究的具体目标是：1）合成和表征共价复合高铁砂介质; 2）探测水溶液中的介质稳定性，并研究介质与有机和无机污染物反应期间的铁（Fe）形态; 3）研究和阐明复合高铁砂介质与相关环境化合物和物种（例如，溶解的有机物和无机离子），已知其影响水溶液中的氧化还原反应和吸附过程;以及4）研究复合高铁酸盐-砂介质的原位再生和再利用的机会。该项目的成功完成有可能通过产生新的基础知识和材料来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）的现有计划，如工程日，让来自大西雅图大都市区的第4 - 8名学生进行实验室演示实验，以激发他们对STEM职业机会的兴趣。此外，PI计划与“Hip Hop is绿色”非营利组织合作，领导一项教育推广活动，招募和指导高中生，在PI位于UW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NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

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.