老化的生物质炭性质变化及对菲吸持的影响

Structural Changes of Aged Biochar and the Influence on Phenanthrene Adsorption

将稻壳分别在350℃和550℃热解温度下制备成生物质炭,避光条件下恒温培养300 d,通过傅里叶变换红外光谱、扫描电镜和核磁共振等技术手段及平衡吸附实验,探究生物质炭老化前后的动态结构变化及对菲吸持作用的影响.结果表明,生物质炭老化过程中氧含量增加,含氧基团增多,对菲的非线性吸附行为显著增强.热解温度的不同决定了生物质炭老化过程中性质变化的差异,350℃热解的生物质炭,老化后极性增强,芳香性减弱,而550℃热解的生物质炭,老化后脂肪族碳类物质增加,羧基减少,芳香性增强,Langmiur预测的菲在350℃热解的生物质炭上老化前后的最大吸附量分别为3.57 mg·g-1、2.35mg·g-1,主要是老化后性质变化抑制了表面吸附作用,而550℃热解的生物质炭上老化前后的最大吸附量分别为0.42mg·g-1、4.17 mg·g-1,老化后吸附量的显著增加主要是生物质炭性质变化促进了对菲的分配作用与表面吸附作用.研究生物质炭在自然环境中的老化行为对环境污染物固定的稳定性有着重要意义.

Biochars prepared by pyrolysis of rice husk at 350℃ and 550℃ were incubated in the lucifugal thermostat for 300 d. Diffuse Reflectance Infrared Fourier Transform Spectroscopy（ DRIFTS）,Scanning Electron Microscopy（ SEM）,and Nuclear Magnetic Resonance（ NMR） techniques were applied to explore the structural change before and after incubation. It was found that the oxygen content was increased after incubation,suggesting the formation of oxygen-containing functional groups. Incubation of the biochars also enhanced their nonlinear adsorption of phenanthrene. Structural change subjected to incubation was in fact affected by the pyrolysis temperatures at which the biochars were synthesized. Increase of polarity and decrease of aromaticity were found for biochars prepared at 350℃. In contrast,incubation of biochars prepared at 550℃ resulted in increased aliphatic contents and aromaticity,as well as decrease of carboxyl group. The adsorption capacity of phenanthrene predicted by Langmuir model was 3. 57 and 2. 35 mg·g^- 1for new and aged biochar with lower pyrolysis temperature,respectively. It was assumed that change of the surface structure of the biochars due to aging inhibited the adsorption. On the contrary,aging of biochares prepared at 550℃ resulted in enhanced adsorption capacity of phenanthrene from 0. 42 to 4. 17 mg·g^- 1,which was probably correlated to the partition effect due to enhanced aromaticity. The data obtained in this research suggested that aging of biochars potentially affected the fate of the pollutants in environment.