Photocatalytic Reduction of Nitrate in Water

1132779硝态氮（NO3-）是北美和世界范围内最普遍的地下水污染物之一。它对人类健康构成威胁，并对自然氮循环产生很大影响。饮用水中的硝酸盐受到美国环境保护局的管制因为它是导致高铁血红蛋白血症的已知原因，还是？蓝色的婴儿?可能是一种致癌物质或内分泌干扰物。硝酸盐是一种难以通过传统的混凝或吸附方法去除的可溶性离子。氧化污染物的风险最好通过化学或生物还原为无害形式（例如，从NO3-转化为N2）来减轻。光催化还原已经报道了几十年，但还没有从工程方法研究硝酸盐还原。光催化水分解的Honda-Fujishima效应的发现（例如，作为可再生燃料的氢的生产）和半导体金属负载的后续进展表明，在不添加牺牲剂的情况下，在接近中性pH下还原硝酸盐是可能的。此外，现在看来，光催化水中NO3-还原可能产生无害的副产物（N2），而不是需要额外处理的不良副产物（例如氨）。在过去的十年中，用于消毒的光解在饮用水工业中很常见，并且由于其有效性，占地面积小，能够在没有废水流的情况下运行等原因，使用基于光的水处理技术将继续发展。从化学、材料科学和物理领域的转化研究，其中还原性光催化剂用于分解水，建议应用于工程技术从水中去除硝酸盐。π吗?初步数据证明了光催化还原硝态氮并产生气态氮副产物的可行性。本项目的目的是探索和优化光催化剂作为一种还原技术在处理饮用水中硝酸盐的应用。潜在的假设是硝酸盐可以转化为无害的水在饮用水应用中使用金属负载的光催化剂。主要研究目标是：(1)了解不同类型光催化剂对NO3-还原为N2的影响因素和机制；(2)在离子交换盐水和当地地下水中应用光催化剂还原NO3-；(3)研究光反应器操作的实际方面（浆状和固定膜光催化剂反应器），包括催化剂的作用？老化？催化剂还原NO3-性能及催化剂回收率；(4)筛选硝酸盐和其他氧阴离子还原的新型光催化剂，建立新型氧化污染物还原光催化剂的选择框架。首选结果是在环境条件下（例如，pH值）实现硝酸盐处理，而不需要添加有机孔清除剂。该项目的重点是硝酸盐，这是美国和世界上许多其他地区最普遍的地下水污染物。管理氮循环是美国国家工程院的重大挑战之一。硝酸盐限制了地下水的饮用用途，是地表水富营养化的主要原因。该项目将为社会和学生个人带来好处。主要目的是传播有关饮用水中硝酸盐问题的知识和可靠数据以及处理水的潜在战略。为此，该团队计划在会议上组织会议，并开发一个与硝酸盐发生、健康风险和治疗有关的开放访问网站。该研究将教育环境工程专业的博士研究生，并作为非博士学位授予机构的硕士研究生的论文题目。该项目将作为几个顶级高级项目的主题，作为项目导向学习课程的一部分。该项目还将支持亚利桑那州立大学的奥巴马学者（首次未被充分代表的本科生），例如一名西班牙裔土木工程大二女生，她在获得本提案的初步数据方面发挥了重要作用。参与该项目的学生将在华盛顿特区参加为期两周的体验，在那里他们将学习科学如何成为政策。

1132779WesterhoffNitrate (NO3-) is one the most prevalent ground-water contaminants in North America and world-wide. It poses a risk to human health and has a large impact on the natural nitrogen cycle. Nitrate is regulated by the USEPA in drinking water because it is a known cause of methemoglobinemia, or ?blue baby? syndrome, and could possibly be a carcinogen or endocrine disruptor. Nitrate is a soluble ion that is difficult to remove by traditional coagulation or adsorption processes. Risks from oxidized pollutants are best mitigated through chemical or biological reduction to innocuous forms (e.g., N2 from NO3-). Photocatalytic reduction has been reported for decades, yet has not been investigated from an engineering approach for nitrate reduction. Research initiated by the discovery of Honda-Fujishima effect for photocatalytic water splitting (e.g., production of hydrogen as a renewable fuel) and subsequent advances in metal loading of semiconductors suggest that nitrate reduction in near neutral pH without addition of sacrificial agents is possible. Furthermore, it now appears possible that photocatalytic NO3- reduction in water could yield innocuous by-products (N2) instead of undesirable by-products that require additional treatment (e.g., ammonia). Photolysis for disinfection is commonplace in the drinking water industry over the past decade and use of light-based technologies for water treatment will continue to evolve because of their effectiveness, small size footprint, ability to operate without wastestreams, etc. Translational research from the fields of chemistry, material science and physics, where reductive photocatalysts are developed for splitting water, is proposed to be applied towards engineered technologies for nitrate removal from water. The PI?s preliminary data demonstrate the feasibility to photocatalytically reduce nitrate and yield gaseous-N by-products. The goal of this project is to explore and optimize the use of photocatalysts as a reductive technology for treating nitrate in drinking water applications. The underlying hypothesis is nitrate can be converted to innocuous aqueous species in drinking water applications using metal-loaded photocatalysts. The primary research objectives will be to: (1) Understand factors and mechanisms affecting NO3- reduction to N2 for different types of photocatalysts; (2) Apply photocatalyst for NO3- reduction in ion exchange brines and local groundwaters; (3) Investigate practical aspects of photoreactor operation (slurry and fixed film photocatalyst reactors) including role of catalyst ?aging? on catalyst performance in reducing NO3- and catalyst recovery; (4) Screen novel photocatalysts for nitrate and other oxo-anion reduction and develop a framework for selecting emerging photocatalysts for reduction of oxidized pollutants. The preferred outcome is to achieve nitrate treatment under ambient conditions (e.g., pH) and without the need of adding an organic hole scavenger.The project focuses on nitrate, the most prevalent groundwater contaminant in the USA and throughout many other parts the world. Managing the nitrogen cycle is one of the National Academy of Engineering Grand Challenges. Nitrate limits the use of the groundwater for potable purposes, and is a major cause of eutrophication in surface waters. The project will provide societal benefits as well as benefits to individual students. The primary intent is to disseminate knowledge and credible data on issues related to nitrate in drinking water and potential strategies to treat the water. Towards this end the team plans to organize sessions at conferences and develop an open-access website related to nitrate occurrence, health risks and treatment. The research will educate PhD students in environmental engineering and serve as a thesis topic for MS students at a non PhD-degree granting institution. The project will serve as a theme for several capstone senior projects, as part of a project oriented learning curriculum. This project also will support Obama Scholars at ASU (first-time underrepresented undergraduate student), such as a female Hispanic sophomore Civil Engineering student who has been instrumental in obtaining preliminary data for this proposal. Student(s) working on this project will participate in an experience in Washington, DC for 2 weeks where they will learn how science becomes policy.