Abstract:

In order to realize the resource utilization of agricultural straw waste and strengthen the control of polycyclic aromatic hydrocarbons pollution in the ecological environment, the sunflower (Helianthus annuus) straw was used to prepare biochar in this paper. The carbonization temperature was set as 300 ℃, 500 ℃ and 700 ℃ (BC300, BC500 and BC700), while KOH modified biochar (A-BC500) was prepared at 500 ℃. Elemental composition, specific surface area, apparent morphology, phase structure, and functional group composition were characterized by elemental analyzer, specific surface area analyzer, scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectrometer. The sorption properties of phenanthrene on different biochar were studied by kinetic sorption experiments and isothermal sorption experiments. The results showed that carbonization temperature and alkali modification could affect the elemental composition of biochar, thereby changing its aromaticity, hydrophilicity, and polarity. The carbon skeleton structure of sunflower straw biochar gradually deformed and collapsed with the increase of carbonization temperature. Compared with BC500, the surface roughness of A-BC500 increased and the specific surface area increased to 529.14 m²∙g^-1. The kinetic sorption curve of phenanthrene by biochar conformed to the pseudo-second-order kinetic model (R²>0.99). Compared with BC500, the equilibrium sorption capacity of phenanthrene on A-BC500 increased by 12%, and the pseudo-second-order kinetic adsorption rate constant increased by about 2.3 times, and it could reach the equilibrium state of phenanthrene sorption quickly. Both the Freundlich model (R²>0.90) and the Langmuir model (R²>0.90) could be used to describe the sorption process of phenanthrene by biochar, and the process was relatively easy to be carried out. However, pH of solution had little effect on the sorption of phenanthrene by biochar. Meanwhile, FTIR spectra before and after sorption of phenanthrene by biochar showed that hydrogen bond and π-π interaction had a certain contribution to the sorption of phenanthrene by biochar. The free radical quenching experiment also proved that ·OH participates in the process of phenanthrene sorption. Specifically, the interaction mechanism between biochar and PAHs is complex, instead of a simple single molecular layer physical sorption, as it included the chemical reaction between PAHs and the surface of biochar.

Key words: temperature, KOH modification, biochar, polycyclic aromatic hydrocarbons phenanthrene, sorption

摘要：

为了实现农业秸秆废弃物的资源化利用,加强对生态环境中多环芳烃污染的控制,选取农业废弃物向日葵（Helianthus annuus）秸秆为原料,在不同温度条件下（300、500、700 ℃）烧制生物炭（BC300、BC500、BC700）,同时在500 ℃条件下制备KOH改性生物炭（A-BC500）,采用元素分析仪、比表面积分析仪、扫描电子显微镜、X射线衍射仪和傅里叶红外光谱仪分别对其元素组成、比表面积、表观形貌、物相结构和官能团组成进行表征,并采用动力学吸附实验和等温吸附实验研究不同生物炭对多环芳烃菲的吸附性能。结果表明,炭化温度及碱改性均会影响生物炭的元素组成,进而改变其芳香性、亲水性和极性。向日葵秸秆生物炭的炭质骨架结构随着炭化温度升高而逐步发生变形和坍塌;与BC500相比,A-BC500的表面结构粗糙程度增加且比表面积增加至529.14 m²∙g^-1。生物炭对菲的动力学吸附曲线符合准二级动力学模型（R²>0.99）,较BC500、A-BC500对菲的平衡吸附量提高了12%,且准二级动力学吸附速率常数提高了约2.3倍,能较快达到菲的吸附平衡状态;等温吸附曲线中Freundlich模型（R²>0.90）和Langmuir模型（R²>0.90）均可用于描述生物炭对菲的吸附过程,且该过程较容易进行;溶液pH对生物炭吸附菲的影响较小;生物炭吸附菲前后的FTIR谱图显示,氢键和π-π相互作用对生物炭吸附菲具有一定的贡献;自由基猝灭实验证明,∙OH参与了生物炭吸附菲的过程。生物炭与多环芳烃之间的相互作用机制较为复杂,并非简单的单分子层物理吸附,还包括多环芳烃与生物炭表面的化学反应。

关键词: 温度, KOH改性, 生物炭, 多环芳烃菲, 吸附