碳基吸附剂含氧基团-有机污染物之间“基团-极性”作用机理及其对吸附的贡献研究

Carbonaceous sorbents, with high surface areas and an abundance of oxygen-containing surface groups, are industrial products (e.g., activated carbon and carbon nanotubes) with extensive applications. They may also be derived from biomass pyrolysis (e.g., biochar). These materials are widely found in the environment and show high adsorptivity toward organic pollutants. Understanding of the interactions between carbonaceous sorbents and organic pollutants is significant for not only supporting their practical applications but also assessing their ecological risk. There are two shortages to overcome: (1) the underlying mechanisms behind the group-pollutant “group-polarity” interaction, and (2) the quantitive contribution to sorption of such interaction. This proposal is thus designed to determine the sorption of substituted aromatic compounds as sorbates on carbonaceous sorbents. The sorbents are carefully selected or prepared to contain different types and quantities of surface groups. The sorbates bear various groups of differential electron withdrawing or releasing abilities on the aromatic ring thereby causing electron density variation on the ring. Carbonaceous sorbents with sorbed aromatic molecules will be scanned by FTIR, XPS and XAFS to probe their surfaces, or directly “observed” by Cs-STEM (Spherical Aberration Corrected Scanning Transmission Electron Microscope), to obtain the configurations of both surface groups and sorbate molecules. The obtained sorption data and the “observed” surface information together will be used to evaluate the influence of sorbent surface groups and sorbate electron density on the “group-polarity” interaction, to deduce its underlying mechanism, and to quantify the contribution of such interaction to sorption. With these proposed work done, the above-mentioned two shortages in the carbonaceous sorbent-organic pollutant interaction will ultimately be resolved.

碳基吸附剂是一类应用广泛的工业制品（如碳纳米管和活性碳）或生物质的高温热解产物（如生物炭），具有表面积大、表面含氧基团丰富等特点，大量存在于环境中，对有机污染物具有高吸附性能。准确把握碳基吸附剂与有机污染物之间的作用不仅能够指导其工程应用，而且对于评估其生态风险具有重要意义。目前存在两大缺陷：（1）碳基吸附剂含氧基团-有机物之间“基团-极性”作用机理模糊，（2）该作用对有机物吸附的定量贡献未知。本课题据此立项，拟选取一系列含氧基团种类和数量不同的碳基吸附剂及带有不同取代基的苯系物，测定碳基吸附剂对苯系物的吸附，采用FTIR、XPS和XAFS探查及Cs-STEM（球差校正扫描透射电子显微镜）直接“观察”吸附样品表面，以期评估碳基吸附剂表面含氧基团和苯系物取代基引起的苯环电子性质变化对“基团-极性”作用的影响，揭示“基团-极性”作用机理，量化该作用对吸附的贡献率，从而解决上述两大缺陷。

碳基材料(CMs)通过工业排放和农业燃烧等途径广泛存在于环境中。CMs通常具有较大的表面积，具有较强的与各种污染物相互作用的能力，从而改变了污染物的命运、转运和生物利用度。含氧官能团(OFGs)是碳基材料中的结构成分，但对CMs与污染物的相互作用有显著影响。在项目中，我们研究了不同极性芳香族化合物与含有不同OFGs含量的CMs之间的相互作用。在CMs不同位置的OFGs对归一化单层的吸附容量有不同的影响。从吸附摩尔自由能的角度分析，介孔表面的OFGs通过水的竞争抑制了吸附，而外表面的OFGs通过增强的疏水和静电的相互作用促进了吸附。我们建立了标化的单层吸附量与介孔和外表面OFGs的多重线性关系。芳香族吸附物的性质、芳香族分子的极性面积对水的比值(PAad/w)、log Kow以及极性面积共同影响着OFGs的抑制或促进作用。通过理论计算和模拟，揭示了芳香化合物分子在含氧基团的碳基材料表面的吸附构型是平行于碳基材料的石墨烯片层的。通过SAPT能量分解，我们发现随着分子极性的增加，芳香化合物分子与CMs之间的静电相互作用增强。我们得出的结论是，由于外表面的含氧基团的存在使得静电作用得以增强。这项工作采用了包括光谱学和分子模拟在内的几种技术。这些结果是新颖的，为更好地理解CMs的环境作用和意义提供了机会。发表一篇论文、在投一篇，另两篇稿件在撰写中，共计可产生四篇论文。参加国际学术会议一人次。培养了一名硕士，一名博士研究生即将毕业。