Collaborative Research: Air-Oxidation of Biomass Chars - Structural Changes and Implications for Retention and Reactions of Contaminants

该项目由美国国家科学基金会化学部环境化学科学项目资助。它代表了康涅狄格州农业实验站的Joseph Pignatello博士、Brandeis大学的Klaus Schmidt-Rohr教授和Old Dominion大学的毛京东教授的合作。他们与博士后和研究生一起，研究生物质焦在环境中的性质和行为。生物炭颗粒是部分燃烧的植物物质，表面变黑。焦炭是自然和故意设置的火灾的产物，是土壤和水生沉积物的常见成分。活性碳(木炭的一种形式)和生物炭可以在农业过程中用作有益的土壤添加剂。焦炭的重要属性包括它们能够强烈结合污染物并改变污染物分子的身份。在炭化过程中，空气可能存在也可能不存在。它通常存在于环境中木炭的风化过程中。空气中的氧气可能会对焦炭的物理和化学性质产生重大影响，并可能影响其作为吸收和改变污染物的材料的功能。这项研究通过在室温和更高温度下仔细控制的实验，考察了污染物在生物炭表面的吸收和变化。该项目通过研究生物质焦如何影响环境中污染物的去向，为社会提供了好处。它还提供了宝贵的信息，这些信息可能有助于清理受污染的场地，以及在农业应用中。除了培养学生和博士后研究员外，该项目还包括面向博士生和教授的访问学者计划、面向本科生的实习计划、旨在促进本科生参与积极研究的荣誉学院计划，以及面向高中生的导师计划。该项目具有强大的宣传和教育部分，旨在吸引潜在的科学家进入历史上处于不利地位的群体，特别是在老多米尼恩大学，这是一个城市校园，有相当多的少数民族人口。生物质炭是土壤和火灾沉淀物中普遍存在的成分，也引起了人们对农业和环境修复中的土壤改良剂的兴趣。焦炭的重要属性包括能够有效地吸附有机和无机化合物，以及在有机物种之间或与有机物种之间进行电子转移反应。在热解过程中或热解后存在的空气会对焦炭的物理化学性质产生重大影响，从而影响这些功能，但这个课题很少受到关注。该项目的目标是确定热氧化和环境空气氧化引起的焦炭潜在的结构和化学变化，并确定这些变化对其与新出现的污染物相互作用的关键影响。在实验室里，木炭是由木头和柳枝草制成的。测试化合物是磷酸盐、砷酸盐、亚砷酸盐、亚硒酸盐、水生除草剂(敌草快和百草枯)，以及模型有机化合物。先进的固体核磁共振波谱被用来识别和量化官能团组成和稠合芳环大小的变化。这也允许检测来自表面基团和弱酸吸附之间形成的极强氢键的信号。以富含~(13)C的柳枝草为生物体前驱体，以~(13)C标记的化合物为吸附物，提高了核磁共振的灵敏度。该项目调查了空气氧化对形成异常强烈的氢键的影响。它还讨论了阳离子交换作用，溶解有机物对吸附位置的竞争，焦炭介导的氧化还原反应，以及热解过程中形成的持久自由基的浓度。这一发现有望为环境中的焦炭结构和弱酸溶质行为提供新的见解。该项目有外展和教育部分，目的是让学生参与历史上处于不利地位的群体。

This project is funded by the Environmental Chemical Sciences Program in the Chemistry Division at the National Science Foundation. It represents a collaboration between Dr. Joseph Pignatello at the Connecticut Agricultural Experiment Station, Professor Klaus Schmidt-Rohr at Brandeis University, and Professor Jingdong Mao at Old Dominion University. Together with their postdocs and graduate students, they investigate properties and behavior of biomass chars in the environment. Biochar particles are partially burned plant matter with blackened surfaces. Char results from natural and deliberately-set fires and are common components of soil and aquatic sediments. Activated carbon (a form of charcoal) and biochar can be beneficial soil additives for use in agricultural processes. Important attributes of chars include their ability to strongly bind pollutant and to change the identity of the pollutant molecules. Air may be present or absent during the charring process. It is usually present during the weathering of chars in the environment. The oxygen in air can have major effects on the physical and chemical properties of chars and can impact their functions as materials that absorb and change pollutants. This research examines the absorption and change in pollutants on biochar surfaces using carefully controlled experiments at both room temperatures and higher temperatures. This project provides benefits to society by studying how biomass chars affect the fate of pollutants in the environment. It also provides valuable information that may be useful in efforts to clean up contaminated sites, as well as in agricultural applications. In addition to fostering the training of students and postdoctoral fellows, this project incorporates a visiting scholars program for PhD students and professors, an internship program for undergraduate students, an Honors College program to foster involvement of undergraduate students in active research, and mentorship programs for high school students. The project has strong outreach and education components directed at engaging prospective scientists among historically disadvantaged groups, especially at Old Dominion University, which is an urban campus with a significant minority population.Biomass chars are ubiquitous components of soil and sediment from fires and also have attracted interest as soil amendments in agriculture and environmental remediation. Important attributes of chars include their ability to effectively adsorb organic and inorganic compounds and to mediate electron transfer reactions to/from or between organic species. Air present during or after pyrolysis can have major effects on the physical-chemical properties of chars that impact these functions, yet this subject has receivedlittle attention. The objectives of this project are to determine the underlying structural and chemical alterations of char caused by both thermal and ambient air oxidation (AO), and to determine the effects of these alterations critical to their interactions with emerging pollutants. In the laboratory chars are made from wood and switchgrass. The test compounds are phosphate, arsenate, arsenite, selenite, aquatic herbicides (diquat and paraquat), and model organic compounds. Advanced solid-state nuclear magnetic resonance (NMR) spectroscopy is employed to identify and quantify changes in functional group composition and fused aromatic ring size. This also allows detection of signals coming from exceptionally strong hydrogen bonds formed between surface groups and weak acid adsorbates. NMR sensitivities are enhanced by using 13C-enriched switchgrass as the biomass precursor and 13C-labelled compounds as adsorbates. The project investigates the consequences of air oxidation on the formation of exceptionally strong hydrogen bonds. It also addresses cation exchange interactions, dissolved organic matter competition for adsorption sites, oxidation-reduction reactions mediated by chars, and the concentrations of persistent free radicals formed by the pyrolysis process. The findings are expected to provide novel insights for char structure and weak acid solute behavior in the environment. The project has outreach and education components and aims to engage students among historically disadvantaged groups.