Collaborative Research: Catalyst Free Activation of Peroxydisulfate under Visible Light to Degrade Contaminants in Water: Elucidation of Kinetics and Mechanism

在美国和世界范围内，有机微污染物(OMP)已经成为对人类和生态系统健康的主要威胁。传统的水处理工艺不能有效地去除许多OMP。高级氧化工艺(AOPS)，如商业UV/AOP工艺，正越来越多地被用作去除美国和世界各地高级水回收和再利用工厂的OMP的最终处理屏障。在典型的UV/AOP过程中，UV-C光(波长为254 nm)与氧化剂(如过氧化氢)相结合，生成可破坏和矿化OMP的OH自由基，包括个人护理产品、药品、农药、除草剂等。最近，基于硫酸盐自由基(SO4-)的AOPS因其比OH自由基具有更高的氧化还原电位和更长的寿命而在全球范围内广受欢迎。硫酸盐自由基通常是通过使用催化剂或光解激活两种常见的前体之一在现场生成的：过氧单硫酸盐(PMS)和过氧二硫酸盐(PDS)。最近的研究表明，PDS可以在可见光下被激活，而不需要使用催化剂，从而为开发更具成本效益的AOPS提供了新的机会，用于大规模水处理和废水回收。本项目的主要目标是促进对可见光活化PDS生成硫酸盐自由基的机理的基本了解，并确定这种基于硫酸盐自由基的AOP降解和矿化不同类别OMP的效果。该项目的成功完成将产生新的基本知识，指导设计和实施基于硫酸根的AOPS，用于去除和销毁废水和受污染的饮用水水源中的OMPS。还将通过学生教育和培训为社会带来更多好处，包括指导德克萨斯农工大学的一名本科生和两名研究生，以及辛辛那提大学的一名研究生。基于硫酸根(SO4)的高级氧化工艺(AOPS)由于其更大的氧化还原电位和比羟基自由基(OH，20纳秒)更长的半衰期(30-40微秒)而特别吸引人。此外，SO4-的主要前体过氧二硫酸盐(PDS)中O-O键的低键离解能表明，在没有催化剂的情况下，利用可见光活化PDS是可行的。然而，无催化剂和可见光活化的PDS AOP的实用性取决于SO4-的量子产率和OMPs的性质，这已被证明在含有阴离子(氯离子、碳酸盐和磷酸盐)和天然有机物的水溶液中促进其他自由基物种的形成，包括OH、超氧化物(O2)和单线态氧(1O2)。为了应对这些挑战，该项目的首席研究员(PI)建议利用无催化剂和可见光激活的PDS高级氧化过程对六(6)个具有明显不同分子结构的目标OMP的降解动力学和机理进行基础研究。本研究的具体目标是1)测量活化的PDS在三个单色波长的可见光下的量子产率；2)鉴定和定量广谱光中的反应物种，以确立可见光激活PDS产生SO4-自由基的潜在优势；3)确定六(6)个靶标有机磷在不同环境条件下的降解动力学；以及4)结合多种实验分析/工具(如比色法和电子顺磁共振光谱)，以阐明和确认导致硫酸盐自由基AOPS中污染物降解的主要和次要反应物种。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指导为水处理和废水回收设计更具成本效益和可持续的AOPS。为了实现该项目的教育和培训目标，私人投资机构建议利用德克萨斯农工大学(TAMU)和辛辛那提大学(UC)现有的项目，从代表性不足的群体中招募和指导本科生参与该项目。此外，PIS计划将这项研究的结果整合到TAMU和加州大学现有的环境工程研究生/本科生课程中。这一奖项反映了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。

Organic micropollutants (OMPs) have become major threats to human and ecosystem health in the United States and worldwide. Many OMPs are not efficiently removed by conventional water treatment processes. Advanced oxidation processes (AOPs) such as the commercial UV/AOP process are increasingly being utilized as a final treatment barrier to remove OMPs in advanced water reclamation and reuse plants in the United States and worldwide. In a typical UV/AOP process, UV-C light (254 nm in wavelength) is combined with an oxidant (e.g., hydrogen peroxide) to generate OH● free radicals that can destroy and mineralize OMPs including personal care products, pharmaceuticals, pesticides, herbicides, etc. Recently, AOPs based on sulfate radicals (SO4●-) have gained worldwide popularity due to the higher redox potential and longer lifetime of SO4●- radicals compared to those of OH● radicals. Sulfate radicals are typically generated on site by activating one of two common precursors: peroxymonosulfate (PMS) and peroxydisulfate (PDS) using a catalyst or photolysis. Recent studies have shown that PDS can be activated by visible light without using catalyst thereby providing new opportunities to develop more cost-effective AOPs for large-scale water treatment and wastewater reclamation. The overarching goal of this project is to advance the fundamental understanding of the mechanisms of sulfate radical generation from PDS by visible light activation and determine the efficacy of this sulfate radical-based AOP to degrade and mineralize different classes of OMPs. The successful completion of this project will generate new fundamental knowledge to guide the design and implementation of sulfate radical-based AOPs for the removal and destruction of OMPs from wastewater and contaminated drinking water sources. Additional benefits to society will be achieved through student education and training including the mentoring of one undergraduate and two graduate students at Texas A&M University and one graduate student at the University of Cincinnati. Sulfate radical (SO4●)-based advanced oxidation processes (AOPs) are particularly attractive due to their larger redox potential and much longer half-life (30-40 microseconds) compared to those of hydroxyl radicals (OH●, 20 nanoseconds). In addition, the low bond dissociation energy of the O-O bond in peroxydisulfate (PDS), a primary precursor of SO4●-, suggests that activation of PDS is feasible by visible light without a catalyst. However, the practicality of a catalyst-free and visible light activated PDS AOP depends on the quantum yield of SO4●- and the properties of OMPs, which have been shown to promote the formation of other radical species including OH●, superoxide (O2●), and singlet oxygen (1O2) in aqueous solutions containing anions (chloride, carbonate, and phosphate) and natural organic matter. To address these challenges, the Principal Investigators (PIs) of this project propose to carry out a fundamental study of the kinetics and mechanisms of degradation of six (6) target OMPs with distinctively different molecular structures using a catalyst free and visible light activated PDS advanced oxidation process. The specific objectives of this research are to 1) measure the quantum yields of activated PDS by visible light at three monochromatic wavelengths; 2) identify and quantify reactive species in a broad spectrum of light to establish the potential advantage of visible light activation of PDS over UV light activation for the generation of SO4●- radicals ; 3) determine the degradation kinetics of six (6) target OMPs under different environmental conditions; and 4) combine and integrate multiple experimental assays/tools (e.g., colorimetry and electron paramagnetic resonance spectroscopy) to elucidate and confirm the primary and secondary reactive species responsible for contaminant degradation in sulfate radical-based AOPs. The successful completion of this project has the potential for transformative impact through the generation of new fundamental knowledge to guide the design of more cost-effective and sustainable AOPs for water treatment and wastewater reclamation. To implement the education and training goals of the project, the PIs propose to leverage existing programs at Texas A&M University (TAMU) and the University of Cincinnati (UC) to recruit and mentor undergraduate students from underrepresented groups to work on the project. In addition, the PIs plan to integrate the findings from this research into existing environmental engineering graduate/undergraduate courses at TAMU and UC.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.