低温空气氧化生物炭吸附苯系污染物的作用机制

为进一步明晰低温空气氧化生物炭吸附苯系污染物的作用机制，以竹屑为原料、CaCl₂为活化剂，通过两步活化法制备低温空气氧化生物炭，并综合吸附试验、炭结构表征和密度泛函理论（density functional theory， DFT）计算，解析低温空气氧化生物炭吸附苯酚、苯胺、对苯二酚、对硝基苯酚等4种苯系污染物的过程与行为。结果表明：低温空气氧化生物炭对苯系污染物的吸附性能受生物炭孔隙结构和表面官能团的协同作用影响，生物炭通过微孔结构的孔隙填充作用在空间几何尺度调控苯系污染物的吸附存储过程。低温空气氧化生物炭后，氧原子以羟基、醛基和羧基的形式赋存于生物炭碳骨架表面，从电子尺度影响碳骨架的电子结构排布、改变碳骨架与苯系污染物间的吸附位置及作用类型，通过静电引力及氢键等作用，显著增强生物炭对苯系污染物的吸附能力，其中，羟基和羧基的氢原子作为氢键的供体，醛基的氧原子作为氢键的受体。

Adsorption mechanism of low-temperature air oxidation biochar for benzene pollutants

Biochar is an efficient adsorption carrier for benzene pollutants， but the adsorption capacity of directly carbonized biochar for benzene pollutants is limited. Low-temperature air oxidation is effective in modifying the structure of biochar and enhancing its adsorption capacity of benzene pollutants. However， the adsorption behavior and mechanism of low-temperature air oxidation biochar for benzene pollutants still needs to be further clarified. Herein， low-temperature air oxidation biochar was prepared by a two-step activation method using bamboo chips as raw material and CaCl₂ as activator. The adsorption processes and behaviors of low-temperature air oxidation biochar for four benzene pollutants including phenol， aniline， hydroquinone， and p-nitrophenol were deeply analyzed with comprehensive adsorption experiments， biochar structure characterization， and density flooding theory（DFT） calculations. The adsorption properties and mechanisms of oxygen-modified biochar for benzene pollutants were studied. The results showed that the adsorption performance of low-temperature air oxidation biochar for benzene pollutants was influenced by the synergistic effect of the pore structure and surface functional groups of biochar. Biochar regulated the adsorption and storage process of benzene pollutants at a spatial geometric scale through the pore filling effect of microporous structure. Oxygen atoms were assigned to the surface of the carbon skeleton of biochar in the form of hydroxyl， aldehyde and carboxyl groups after the oxidation of biochar by low temperature air. The electronic structure of the carbon skeleton was influenced by the electronic scale， modifying the adsorption position and type of interaction between the carbon skeleton and benzene pollutants. The adsorption capacities of biochar for benzene pollutants were significantly enhanced through mechanisms such as electrostatic attraction and hydrogen bonding. Among them， the hydrogen atoms of the hydroxyl and carboxyl groups in the carbon skeleton are easy to become donors of hydrogen bonds， while the oxygen atoms of the aldehyde group are easy to become acceptors of hydrogen bonds.