CAREER: Molecular Electrocatalysts and Reactive Separations for Wastewater Nitrogen Refining

氮肥的利用对于最大限度地提高农业和农业产量以养活不断增长的世界人口至关重要。不幸的是，农业径流和污水处理厂释放的过量氮（硝酸盐）也导致了广泛的地下水污染和地表水系统的营养物质富集，这一过程通常被称为富营养化。在含氮有限的地表水系统中，包括湖泊、河流和河口，富营养化已被证明会导致水质下降、氧气消耗、水生生物群的丧失和有害藻华的发生。这个CAREER项目的总体目标是探索利用电化学精炼从废水中回收硝酸盐，并将其转化为有价值的产品，如氨，氨是氮肥的关键成分。为了实现这一目标，首席研究员建议结合并整合化学分离（膜），电催化（硝酸盐还原反应），过程建模，技术经济分析（TEA）和生命周期评估（LCA）来设计，开发和优化反应和分离系统，这些系统可以捕获，浓缩并将废水中的硝酸盐转化为高纯度氨。该项目的成功完成将通过产生新的基础知识和技术来促进硝酸盐污染的缓解并实现循环氮经济，从而造福社会。通过教育和培训，包括斯坦福大学的一名研究生的指导，将为社会带来额外的好处。全球氮循环的管理已被美国国家工程院确定为14大工程挑战之一。电化学精炼已经成为一项很有前途的技术，可以促进循环氮经济，因为它可以用来调整氧化态，从废水中运输和转化氮污染物到有价值的产品，与现有的商业技术相比，它可能以更低的成本减少化学投入和排放。这个CAREER项目将研究电化学还原废水中的硝酸盐以产生氨，氨是氮肥的关键成分。为了实现这一目标，首席研究员（PI）建议设计、合成、评估和优化一种新的均相分子催化剂[M（DIM）催化剂，其中M是位于二甲基配体（DIM）中心的过渡金属（Co, Fe, Mn, Cu, Ni）]，可以实现快速、选择性、廉价和节能的电化学硝酸还原为高纯度氨。本研究的具体目标是：1)设计和合成分子M（DIM）催化剂，并阐明其在各种废水基质中还原硝酸盐的机理；2)设计和设计萃取系统，从处理过的废水中分离催化剂及其反应产物（氨）；3)设计、开发和优化电力驱动的反应和分离系统，这些系统可以集成到废水处理厂中，以回收硝酸盐并将其转化为高纯度氨。该项目的成功完成有可能产生变革性影响，通过产生新的基础知识，推动设计和开发更有效和更具成本效益的废水处理工艺和系统，以回收并将硝酸盐转化为有价值的产品。为了实施该CAREER项目的教育和推广活动，PI建议利用斯坦福大学现有的项目和资源，设计并启动一个年度湾区电化学（BAE）训练营，培训早期研究生学习电化学方法和循环水处理应用。此外，PI还建议：1)开发和实施一个REU项目，其中包括社会公平研讨会，以招募和留住来自代表性不足群体的本科生；2)设计和组织与水相关的科学博览会项目，以吸引和指导来自代表性不足群体的高中生。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。

The utilization of nitrogen (N) fertilizers has been critical to maximizing crop yields in agriculture and farming to feed a growing world population. Unfortunately, the release of excess N (nitrate) from agricultural runoffs and wastewater treatment plants has also led to widespread groundwater pollution and nutrient enrichment in surface water systems, a process commonly referred to as eutrophication. In nitrogen-limited surface water systems including lakes, rivers, and estuaries, eutrophication has been shown to cause a decrease in water quality, oxygen depletion, a loss of aquatic biota, and the occurrence of harmful algal blooms. The overarching goal of this CAREER project is to explore the utilization of electrochemical refining to recover nitrate from wastewater and convert it into valuable products such as ammonia which is a critical component of N fertilizers. To advance this goal, the Principal Investigator proposes to combine and integrate chemical separations (membranes), electrocatalysis (nitrate reduction reactions), process modeling, technoeconomic analysis (TEA), and life cycle assessment (LCA) to design, develop, and optimize reaction and separation systems that can capture, concentrate, and convert nitrate from wastewater sources to high purity ammonia. The successful completion of this project will benefit society through the generation of new fundamental knowledge and technology to advance the mitigation of nitrate pollution and enable a circular nitrogen economy. Additional benefits to society will be achieved through education and training including the mentoring of one graduate student at Stanford University. The management of the global nitrogen cycle has been identified as one of the 14 Grand Challenges for Engineering by the US National Academy of Engineering. Electrochemical refining has emerged as a promising technology to advance a circular nitrogen economy as it can be utilized to tune the oxidation states, transport, and conversion of nitrogen pollutants from wastewater to valuable products at potentially lower cost with reduced chemical inputs and emissions than existing commercial technologies. This CAREER project will investigate the electrochemical reduction of nitrate from wastewater to produce ammonia, a critical component of nitrogen fertilizers. To advance this goal, the Principal Investigator (PI) proposes to design, synthesize, evaluate, and optimize a new family of homogenous molecular catalysts [M(DIM) catalysts, where M is a transition metal (Co, Fe, Mn, Cu, Ni) at the center of a dimethyl ligand (DIM)] that could enable the rapid, selective, inexpensive, and energy-efficient electrochemical nitrate reduction to high-purity ammonia. The specific objectives of the research are to 1) design and synthesize molecular M(DIM) catalysts and elucidate their mechanisms of nitrate reduction in various wastewater matrices; 2) design and engineer extraction systems to separate the catalysts and their reaction products (ammonia) from treated wastewater; and 3) design, develop, and optimize electrically driven reactive and separation systems that could be integrated into wastewater treatment plants to recover and convert nitrate to high-purity ammonia. The successful completion of this project has the potential for transformative impact through the generation of new fundamental knowledge to advance the design and development of more efficient and cost-effective wastewater treatment processes and systems to recover and convert nitrate to valuable products. To implement the educational and outreach activities of this CAREER project, the PI proposes to leverage existing programs and resources at Stanford University to design and launch an annual Bay Area Electrochemistry (BAE) Bootcamp to train early-stage graduate students on electrochemical methods and circular water treatment applications. In addition, the PI proposes to 1) develop and implement an REU program augmented with seminars on societal equity to recruit and retain undergraduate students from underrepresented groups and 2) design and organize water-related science fair projects to engage and mentor high school students from underrepresented groups.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.