Photocatalytic Reduction of Nitrate in Water

威斯特霍夫硝酸盐(NO3-)是北美和世界范围内最普遍的地下水污染物之一。它对人类健康构成风险，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保局的监管，因为它是高铁血红蛋白血症的已知原因，或蓝色婴儿？综合症，可能是致癌物质或内分泌干扰物。硝酸盐是一种可溶性离子，很难通过传统的混凝或吸附过程去除。氧化污染物的风险最好通过化学或生物还原为无害的形式(例如，NO3-中的氮气)来减轻。光催化还原已经报道了几十年，但还没有从工程上研究硝酸盐还原的方法。由本田-藤岛效应的光催化分解水(例如，生产氢气作为可再生燃料)的发现以及随后半导体金属负载的进展引发的研究表明，在近中性的pH条件下，硝酸盐的还原是可能的，而不需要添加牺牲剂。此外，现在看来，在水中光催化硝酸根还原可以产生无害的副产物(氮气)，而不是需要额外处理的不良副产物(例如氨)。在过去的十年里，光分解消毒在饮用水工业中很常见，光技术用于水处理的使用将继续发展，因为它们的有效性、占地面积小、能够在不产生废气的情况下运行等。化学、材料科学和物理领域的转化研究，其中还原光催化剂被开发用于分解水中的硝酸盐，建议应用于从水中去除硝酸盐的工程技术。皮S的初步数据证明了光催化还原硝酸盐和生成气态氮副产物的可行性。该项目的目标是探索和优化光催化剂作为一种还原技术在饮用水应用中处理硝酸盐的使用。潜在的假设是，在饮用水应用中，使用负载金属的光催化剂可以将硝酸盐转化为无害的水性物种。主要的研究目标是：(1)了解不同类型的光催化剂影响NO_3-还原为N_2的因素和机理；(2)将光催化剂应用于离子交换卤水和局部地下水中的NO_3-还原；(3)研究光反应器(浆料和固定膜光催化剂反应器)的实际操作方面，包括催化剂的作用、老化？(4)筛选用于硝酸盐和其他氧阴离子还原的新型光催化剂，并开发用于氧化污染物还原的新型光催化剂的选择框架。首选的结果是在环境条件(例如，pH)下实现硝酸盐处理，而不需要添加有机空洞清除剂。该项目专注于硝酸盐，这是美国和世界其他许多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面临的重大挑战之一。硝酸盐限制了地下水的饮用，是地表水富营养化的主要原因。该项目将为学生个人提供社会福利。其主要目的是传播有关饮用水中硝酸盐问题的知识和可信数据，以及处理饮用水的潜在战略。为此，该小组计划在会议上组织会议，并开发一个关于硝酸盐发生、健康风险和治疗的开放访问网站。这项研究将教育环境工程方面的博士生，并作为非博士学位授予机构的硕士研究生的毕业论文题目。该项目将作为几个顶峰高级项目的主题，作为以项目为导向的学习课程的一部分。该项目还将支持亚利桑那州立大学的奥巴马学者(第一次代表不足的本科生)，例如一名西班牙裔土木工程专业二年级的女学生，她在为这项提议获得初步数据方面发挥了重要作用。参与该项目的学生(S)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.