Purpose

This study aimed to explore the adsorption behaviors and mechanisms of chlorobenzene compounds (CBs; monochlorobenzene (MCB); 1,2-dichlorobenzene (1,2-DCB); pentachlorobenzene (PeCB); and hexachlorobenzene (HCB)) on corn straw-based biochar.

Materials and methods

The adsorption kinetics and isotherms of the four CBs were investigated in mono- or multi-CB adsorption experiments with the corn straw–based biochar which was pyrolyzed at 500 °C and modified with 1 mol/L HCl. Moreover, the surface morphology and porosity of the biochar were characterized. The molecular orbitals, electron cloud distribution, and configuration of the CBs were calculated by the quantum chemical method. The relationships were investigated among the adsorption behaviors and quantum chemical parameters of the CBs as well as the morphology characteristics of the biochar to explore the adsorption mechanisms of the CBs on the biochar.

Results and discussion

The results showed that in both mono- and multi-adsorbate systems, the adsorption of the CBs was well fitted by the pseudo-second-order, Elovich, and the Freundlich model. The adsorption rates, affinities, and amounts indicated that the biochar preferably absorbed highly chlorinated CBs (PeCB and HCB) over low-chlorinated CBs (MCB and 1,2-DCB). The absolute electronegativity (χ), electrophilicity index (ω), polarizability (α), and molecular volume (V_m) followed the increasing order MCB < 1,2-DCB < PeCB < HCB. The values of energy gap of molecular frontier orbitals (ΔE_Gap) and molecular hardness (η) decreased with increasing halogen number of the CBs. The lower energy gap of molecular frontier orbitals, the less molecular stability, and higher deformability could favor the adsorption of highly chlorinated CBs (PeCB and HCB) on the biochar.

Conclusions

During the adsorption process of the CBs on the biochar, physisorption and pore filling might be the two associated mechanisms. The biochar with properties (aromatization and porosity) matchable to the CBs in energy gap of molecular frontier orbitals, electrophilicity, and polarizability is available to enhance adsorption capacity to the greatest extent. The competitive adsorption might enhance the risk of CB mobility and bioavailability by reducing the adsorption amount and delaying the equilibrium time.

中文翻译：

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氯苯化合物在生物炭上的单/多吸附：氯苯分子和生物炭性质的影响

目的

本研究旨在探讨氯苯类化合物（CBs；一氯苯（MCB）；1,2-二氯苯（1,2-DCB）；五氯苯（PeCB）；六氯苯（HCB））在玉米秸秆基材料上的吸附行为和机理。生物炭。

材料和方法

使用在 500 °C 下热解并用 1 mol/L HCl 改性的玉米秸秆基生物炭，在单 CB 或多 CB 吸附实验中研究了四种 CB 的吸附动力学和等温线。此外，表征了生物炭的表面形态和孔隙率。通过量子化学方法计算了 CB 的分子轨道、电子云分布和构型。研究了炭黑的吸附行为、量子化学参数与生物炭的形貌特征之间的关系，探讨了炭黑对炭黑的吸附机理。

结果与讨论

结果表明，在单吸附物和多吸附物体系中，CBs 的吸附均符合伪二级、Elovich 和 Freundlich 模型。吸附速率、亲和力和吸附量表明，生物炭比低氯化 CB（MCB 和 1,2-DCB）更喜欢吸收高氯化 CB（PeCB 和 HCB）。绝对电负性 (χ)、亲电性指数 (ω)、极化率 ( α ) 和分子体积 ( V _m ) 遵循 MCB < 1,2-DCB < PeCB < HCB 的递增顺序。分子前线轨道的能隙值（ΔE _Gap) 和分子硬度 (η) 随着 CB 卤素数的增加而降低。较低的分子前线轨道能隙、较低的分子稳定性和较高的变形能力可能有利于高度氯化的 CB（PeCB 和 HCB）在生物炭上的吸附。

结论

在 CBs 在生物炭上的吸附过程中，物理吸附和孔隙填充可能是两个相关的机制。分子前线轨道能隙、亲电性和极化率等性能（芳构化和孔隙率）与炭黑相匹配的生物炭可最大程度地提高吸附能力。竞争吸附可能通过减少吸附量和延迟平衡时间来提高CB流动性和生物利用度的风险。