生物碳质吸附剂的结构特征与吸附机理

02-0-005

生物碳质吸附剂的结构特征与吸附机理

陈宝梁*，周丹丹，朱利中

浙江大学环境科学系，杭州310028, E-mail: blchen@

我国水体有机微污染(如PAHs、PCBs、芳香硝基化合物)日趋严重, 对饮用水安全和人群健康构成严重威胁[1]。寻找经济高效、环境友好的新型吸附剂已成为了环境科学与工程领域关注的焦点之一[2]。森林火灾常以针叶树木为代价，松针作为森林中典型落叶之一, 其干燥后极易燃烧, 产生的生物碳质则大量积累于土壤中, 成为土壤碳黑的重要来源[3-4]。本文以松针为生物质代表，在8个不同炭化温度(100、200、250、300、400、500、600、700˚C)下，制备了一系列生物碳质吸附剂[3]，用元素分析、比表面积、红外谱图和电镜扫描表征其结构特征；研究其吸附水中硝基苯、4-硝基甲苯、间二硝基苯和萘的性能, 探讨其机理与吸附剂结构之间的定量关系，为制备经济高效吸附剂提供理论依据。结果表明，生物碳质吸附剂的芳香性随炭化温度的升高而急剧增加、极性指数((N+O)/C)则急剧降低, 逐渐从“软碳质”过渡到“硬碳质”, 同时其比表面积则迅速增大；生物碳质吸附剂对水中有机污染物具有强的吸附能力, 等温吸附曲线符合Freundlich方程, N指数和log K f与其芳香性呈良好的线性关系。定量描述了分配作用与表面吸附对生物碳质总的吸附作用的贡献。表面吸附贡献量随炭化温度升高而迅速增大，表面饱和吸附量(Q max,SA)与吸附剂的比表面积呈良好的正关系，硬碳质吸附剂的Q max,SA与单层平铺理论计算值相当；对极性化合物，软碳质吸附剂的Q max,SA值则高于理论值，而对非极性化合物则相反。生物碳质的分配作用(K om)取决于分配介质与有机污染物的“匹配性”和“有效性”，随(N+O)/C降低呈现先升高后降低的趋势。

关键词：生物碳质吸附剂；有机污染物；分配作用；表面吸附作用；废水处理。

参考文献：

[1] Baoliang Chen, Xiaodong Xuan, Lizhong Zhu, et al. Water Research, 2004, 38, 3558-3568

[2] 霍金仙, 刘会娟, 曲久辉, 茹加, 刘海宁, 李国亭. 科学通报, 2005, 50(18), 1957-1961

[3] Chun Y, Sheng G Y, Chiou C T, and Xing B S. Environ Sci Technol, 2004, 38(17), 4649-4655

[4] Masiello C A, and Druffel E R M. Science, 1998, 280 (19)，1911-1913

Structural Characteristics of Carbonaceous Biosorbents on Sorption mechanisms with Organic Contaminants

*Bao-Liang Chen, Dan-Dan Zhou, Li-Zhong Zhu

Department of Environmental Science, Zhejiang University, Hangzhou 310028

The combined adsorption and partition effects of bio-chars with varying fractions of non-carbonized organic matter have not been clearly defined. The carbonaceous biosorbents, produced by pyrolysis of pine needles at different temperatures (100˚C-700˚C, referred as P100-P700), were characterized by elemental analysis, surface areas, FTIR and SEM. Sorption isotherms of naphthalene, nitrobenzene, m-dinitrobenzene and p-nitrotoluene from water to the biosorbents were compared. Sorption parameters (N and log K f) are linearly related to sorbent aromaticities, which increase with the pyrolytic temperature. Sorption mechanisms are evolved from partitioning-dominant at low pyrolytic temperatures to adsorption-dominant at higher pyrolytic temperatures. The quantitative contributions of adsorption and partition are determined by the relative carbonized and non-carbonized fractions and their surface and bulk properties. The partition of P100-P300 originates from an amorphous aliphatic fraction, which is enhanced with a reduction of the substrate polarity; for P400 to P600, the partition occurs with a condensed aromatic core that diminishes with a further reduction of the polarity. Simultaneously, the adsorption component exhibits a transition from a polarity-selective (P200-P400) to a porosity-selective (P500-P600) process, and displays no selectivity with P700 and AC in which the adsorptive saturation capacities are comparable to predicted values based on the monolayer surface coverage of molecule. These observations will provide a theoretical reference to design a cost-effective and high-efficient sorbent, and to accurately predict sorption properties and mechanisms of a given sorbent.

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