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

有机微污染物（OMPs）已成为美国乃至世界范围内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，在美国和世界各地的高级水回收和再利用工厂中越来越多地被用作去除omp的最终处理屏障。在典型的UV/AOP工艺中，UV- c光（波长254 nm）与氧化剂（例如过氧化氢）结合产生OH●自由基，可以破坏和矿化omp，包括个人护理产品，药品，杀虫剂，除草剂等。近年来，基于硫酸根自由基（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受到广泛的关注。硫酸盐自由基通常通过激活两种常见前体之一在现场产生：过氧单硫酸根（PMS）和过氧二硫酸根（PDS）使用催化剂或光解。最近的研究表明，PDS可以在不使用催化剂的情况下被可见光激活，从而为开发用于大规模水处理和废水回收的更具成本效益的AOPs提供了新的机会。本项目的总体目标是通过可见光活化促进对PDS产生硫酸盐自由基的机制的基本理解，并确定这种硫酸盐自由基基AOP降解和矿化不同类型omp的功效。该项目的成功完成将产生新的基础知识，以指导硫酸盐自由基基AOPs的设计和实施，用于去除和破坏废水和受污染的饮用水源中的omp。通过学生教育和培训，包括指导德克萨斯州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，将为社会带来额外的好处。与羟基自由基（OH●，20纳秒）相比，基于硫酸根（SO4●）的高级氧化过程（AOPs）具有更大的氧化还原电位和更长的半衰期（30-40微秒），因此尤其具有吸引力。此外，在SO4●-的初级前驱体过硫酸氢盐（PDS）中，O-O键的低键解离能表明，在没有催化剂的情况下，可见光活化PDS是可行的。然而，无催化剂和可见光激活的PDS AOP的实用性取决于SO4●-的量子产率和omp的性质，这些性质已被证明在含有阴离子（氯化物、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）建议使用无催化剂和可见光激活的PDS高级氧化工艺，对具有不同分子结构的六(6)个目标OMPs的降解动力学和机制进行基础研究。本研究的具体目标是：1)测量可见光在三个单色波长下活化PDS的量子产率；2)在广谱光谱下识别和量化活性物质，以确定可见光活化PDS比紫外光活化产生SO4●-自由基的潜在优势；3)确定6种目标OMPs在不同环境条件下的降解动力学；4)结合并整合多种实验分析/工具（例如，比色法和电子顺磁共振波谱法），以阐明和确认硫酸盐基AOPs中负责污染物降解的一级和二级反应物质。该项目的成功完成将产生新的基础知识，以指导设计更具成本效益和可持续性的水处理和废水回收aop，从而产生变革性影响。为了实现该项目的教育和培训目标，项目负责人建议利用德克萨斯农工大学（TAMU）和辛辛那提大学（UC）的现有项目，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，pi计划将这项研究的结果整合到TAMU和UC现有的环境工程研究生/本科生课程中。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。

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.