CAREER: Molecular Electrocatalysts and Reactive Separations for Wastewater Nitrogen Refining

氮肥的利用对于农业和农业中最大限度地提高作物产量以养活日益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N(硝酸盐)也导致了广泛的地下水污染和地表水系统的养分浓缩，这一过程通常被称为富营养化。在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、氧气枯竭、水生生物丧失，以及有害藻华的发生。这个职业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，这是氮肥的关键成分。为了推进这一目标，首席研究员建议将化学分离(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)结合起来，以设计、开发和优化反应和分离系统，这些系统可以捕获、浓缩废水来源的硝酸盐，并将其转化为高纯度的氨。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和实现循环氮经济，从而造福社会。还将通过教育和培训，包括指导斯坦福大学的一名研究生，为社会带来更多好处。全球氮循环的管理已被美国国家工程院确定为工程学的14大挑战之一。电化学精炼已成为一种很有前途的循环氮经济技术，因为它可以用比现有商业技术更少的化学投入和排放，以潜在更低的成本调整氧化状态，将氮污染物从废水中转移和转化为有价值的产品。这个职业项目将研究从废水中电化学还原硝酸盐来生产氨，氨是氮肥的关键成分。为了推进这一目标，首席调查员(PI)建议设计、合成、评估和优化一系列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)]，能够快速、选择性、廉价和节能地将硝酸盐电化学还原为高纯度的氨。这项研究的具体目标是：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，从处理后的废水中分离催化剂及其反应产物(氨)；以及3)设计、开发和优化可集成到污水处理厂中的电驱动反应和分离系统，以回收硝酸盐并将其转化为高纯氨。这一项目的成功完成有可能产生变革性的影响，通过产生新的基本知识来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，以回收硝酸盐并将其转化为有价值的产品。为了实施这一职业项目的教育和外展活动，PI建议利用斯坦福大学现有的课程和资源，设计并推出一年一度的湾区电化学(BAE)训练营，以培训早期研究生有关电化学方法和循环水处理应用的知识。此外，PI建议1)开发和实施REU计划，并辅之以社会公平研讨会，以招收和留住代表不足群体的本科生，以及2)设计和组织与水相关的科学博览会项目，以吸引和指导代表不足群体的高中生。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.