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

本项目由美国国家科学基金化学分部环境化学科学项目资助。它是康涅狄格农业实验站的Joseph Pignatello博士、布兰代斯大学的Klaus Schmidt-Rohr教授和Old Dominion大学的Jingdong Mao教授的合作成果。他们与博士后和研究生一起研究环境中生物质炭的性质和行为。生物炭颗粒是部分燃烧后表面变黑的植物物质。木炭是自然和人为纵火产生的，是土壤和水生沉积物的常见成分。活性炭（木炭的一种形式）和生物炭可以作为有益的土壤添加剂用于农业生产过程。炭的重要属性包括其强结合污染物和改变污染物分子特性的能力。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。空气中的氧气可以对木炭的物理和化学性质产生重大影响，并可以影响它们作为吸收和改变污染物的材料的功能。本研究通过精心控制的实验，在室温和高温下研究了生物炭表面污染物的吸收和变化。该项目通过研究生物质炭如何影响环境中污染物的命运来造福社会。它还提供了宝贵的信息，可能对清理受污染场地的努力以及农业应用有用。除了培养学生和博士后之外，该项目还包括针对博士生和教授的访问学者计划，针对本科生的实习计划，促进本科生参与积极研究的荣誉学院计划，以及针对高中生的指导计划。该项目有很强的外联和教育组成部分，旨在吸引历史上处于不利地位的群体，特别是在老道明大学，这是一个拥有大量少数民族人口的城市校园。生物质炭是火灾土壤和沉积物中普遍存在的成分，也引起了农业和环境修复中土壤改质的兴趣。炭的重要属性包括它们有效吸附有机和无机化合物的能力，以及介导与有机物质之间或与有机物质之间的电子转移反应。在热解过程中或之后存在的空气会对影响这些功能的木炭的物理化学性质产生重大影响，但这一主题很少受到关注。该项目的目标是确定由热氧化和环境空气氧化（AO）引起的木炭的潜在结构和化学变化，并确定这些变化对其与新出现的污染物相互作用至关重要的影响。在实验室里炭是由木头和柳枝稷制成的。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（双菊酯和百草枯）和模型有机化合物。采用先进的固体核磁共振（NMR）技术鉴定和量化了官能团组成和融合芳环大小的变化。这也允许检测来自表面基团和弱酸吸附物之间形成的异常强氢键的信号。利用富含13c的柳枝稷作为生物质前体，用13c标记的化合物作为吸附剂，提高了核磁共振灵敏度。该项目调查了空气氧化对形成异常强氢键的影响。它还研究了阳离子交换相互作用、溶解有机物对吸附位点的竞争、木炭介导的氧化还原反应以及热解过程中形成的持久性自由基的浓度。这一发现有望为碳结构和弱酸溶质在环境中的行为提供新的见解。该项目包括外联和教育内容，旨在吸引历史上处于不利地位的群体中的学生。

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.