生物碳表面含氧基团的形成机制、定量表征及污染阻控作用

Biochar exhibits great potential in carbon sequestration, soil reclamation and soil contamination remediation. The oxygen-containing groups on the surface of biochars, such as carboxyl group, play a critical role in the properties and environmental applications of biochars, because they composite the main adsorption sites of biochars for heavy metals and organic pollutants, and control many other key physicochemical properties of biochars, like surface charges, hydrophobicity/hydrophilicity, and pH buffering property. The primary objective of current proposal is to elucidate the formation mechanism of oxygen-containing groups on biochar surface and their effects on the performance of biochars in soil pollution control. Multi characterizing methods, such as Fourier infrared spectra and X-ray photoelectron spectroscopy (XPS) are employed to quantitatively identify the category, contents and dissociation property of oxygen-containing groups on biochars. The effects of raw biomass property and pyrolysis condition on the development of oxygen-containing groups and biochar physiochemical properties are investigated to elucidate the formation characteristics of oxygen-containing groups on the surface of biochars and their relationship with biochar surface properties. Then, the sorption properties and mechanisms of biochars for Pb, Cd, sulfa-antibiotics, phenols and anilines, and the effect of biochar amendment on the leaching, plant uptake and extraction property of pollutants in soil are studied to elucidate the interactions between biochar oxygen-containing groups and contaminants as well as their effects on soil pollution control. These results would be worthy for understanding the structure-performance of biochars, and for optimizing biochars production and utilization, which help protect environmental quality and safety of soil in China.

生物碳（Biochar）在土壤固碳、土壤改良和土壤污染控制中应用潜力巨大。生物碳表面的含氧基团（如羧基）是生物碳吸附溶液中Pb、Cd等污染物的重要位点，决定生物碳的表面带电性、亲疏水性、pH缓冲性和离子交换性。本项目旨在探明生物碳表面含氧基团的形成机制及对土壤污染的阻控作用。结合红外光谱、XPS等多种手段以定量表征生物碳表面含氧基团的种类、含量与解离性质，考察原料种类和裂解条件对生物碳组成与理化性质影响，探明生物碳表面含氧基团的形成机制、调控因子及与表面性质的定量联系；调节生物碳表面含氧基团组成性质，分析生物碳对Pb、Cd、磺胺类抗生素、酚类和胺类污染物的吸附作用、构效关系及对土壤中污染物的溶出、动植物吸收和可萃取性影响，探讨生物碳表面含氧基团与污染物相互作用的定量关系及污染阻控机制，试图为深入认识生物碳的组成性质、优化生物碳的生产使用以保障我国土壤环境质量安全提供理论依据和技术支撑。

由于组成结构特殊，生物碳（Biochar）在土壤固碳、土壤改良和土壤污染控制中应用潜力巨大。生物碳表面的含氧基团（如羧基）是生物碳吸附溶液中Pb、Cd等污染物的重要位点，决定生物碳的表面带电性、亲疏水性、pH缓冲性和离子交换性。为了探明生物碳表面含氧基团的形成机制及对土壤污染的阻控作用，本研究主要开展了三个方面的探索：1）制备条件（主要是裂解温度、裂解气氛和裂解时间）对生物碳表面含氧基团含量、组成与理化性质（表面带电性、亲疏水性和pH缓冲性）的影响；2）空气中热氧化处理对生物碳吸附固定Pb(II)和Cd(II)性能的影响；3）生物碳吸附胺类、酚类和磺胺类抗生素等可离子化有机污染物的影响因素（溶液pH、化合物的形态和生物碳表面含氧基团的种类、含量和pKa值）和作用机理（特别是氢键作用的定量化分析）。结果表明，将生物碳放置于空气氛围中加热氧化可显著提高生物碳表面的羧基和酚羟基含量，增强生物碳对有机碱类有机污染物（芳香胺类和喹啉）和重金属离子（Pb(II)和Cd(II)离子）的吸附能力。生物碳吸附芳香酸类和酚类可离子化有机污染物前后溶液pH的上升与生物碳-化合物之间的氢键作用无直接相关性。因此，文献中报导的采用监测吸附前后pH变化的方法难以定量反映生物碳表面含氧官能团与有机污染物之间氢键的形成。造成吸附前后pH变化的主要原因是，生物碳的芳香性表面对离子态和分子态有机污染物的差异性吸附引发的水相中离子态和分子态之间的失衡和形态转化。因此，通过分析吸附前后的pH可解决化合物不同形态共存时（即pH接近化合物pKa时）各形态吸附量难以区分的难题，并且可预测化合物的吸附量以替代分析吸附后溶液浓度的方法。根据氢键作用-pH响应关系与其他吸附作用的差异，建立了分析生物碳吸附可离子化有机化合物中氢键作用和生物碳表面酸碱官能团贡献的定量模型。受化合物和生物碳pKa调控的单重氢键和双重氢键对生物碳吸附磺胺类抗生素均有重要贡献。