生物炭对极性与非极性有机污染物的吸附机理
Sorption mechanisms of polar and apolar organic contaminants onto biochars
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摘要: 以玉米秸秆为原料,分别在200、400、600、700℃下制备了不同性质的生物炭,对其性质进行了表征.研究了极性物质普萘洛尔和非极性物质萘在生物炭上的吸附,并对不同物质的吸附机理进行了探讨.结果表明,随裂解温度的升高,生物炭芳香性增强,极性降低,比表面积增大.普萘洛尔和萘的吸附都随生物炭裂解温度的升高而增大,普萘洛尔的lgKoc由3.10(低平衡浓度3 mg·L-1)和2.88(高浓度10 mg·L-1)增加到3.89和3.67;萘的lgKoc由2.74(低平衡浓度3 mg·L-1)和2.65(高浓度15 mg·L-1)增加到4.59和4.05.疏水分配作用对萘在低温生物炭上的吸附起主要作用,而随裂解温度升高,表面吸附和孔填充所占贡献逐渐增强.除了以上机理,普萘洛尔还可通过静电吸引进行吸附,而且在BC200上,由于大量极性官能团的作用,有利于静电吸附,其对普萘洛尔的吸附显著大于对萘的吸附;而且存在分子的倾斜吸附或多分子层吸附,单位表面积的吸附量远远大于单分子层吸附预测值.而在高温生物炭上,由于萘的分子较小而憎水性较高有利于孔填充作用,其对萘的吸附大于对普萘洛尔的吸附.Abstract: Biochars were prepared by pyrolyzing corn straw under temperatures of 200, 400, 600 and 700℃. Elemental component, surface area, pore volume and Fourier transform infrared spectroscopy of the biochars were characterized. Sorption of polar propranolol and non-polar naphthalene onto the biochars were studied and sorption mechanisms were discussed. With the increase of pyrolytic temperature, aromaticity of biochars increased, polarity decreased, and surface area increased. Sorption of propranolol and naphthalene increased with increasing pyrolytic temperature and the values of lgKoc increased from 3.10 (at low equilibrium concentration of 3 mg·L-1) and 2.88 (at high equilibrium concentration of 10 mg·L-1) to 3.89 and 3.67 for propranolol and increased from 2.74 (at low equilibrium concentration of 3 mg·L-1) and 2.65 (at high equilibrium concentration of 15 mg·L-1) to 4.59 and 4.05 for naphthalene. Hydrophobicity played a major effect on naphthalene sorption on low pyrolytic temperature biochars, and the contribution of surface adsorption and pore filling increased with the increase of pyrolytic temperature. Besides the above mechanism, electrostatic attraction played an important role in the sorption of propranolol. There were plentiful polar functional groups on BC200, which favored the electrostatic attraction, leading to a greater sorption of propranolol compared to naphthalene. The actual adsorption amount calibrated by surface area on BC200 was greater than the value predicted by monolayer adsorption, and hence, oblique attachment or multilayer adsorption may occur on BC200 due to the presence of a large number of polar functional groups. On the other sides, the sorption of naphthalene was greater than propranolol on biochars obtained at high pyrolytic temperature, where the pore filling mechanism was enhanced by the relative smaller size and greater hydrophobicity of naphthalene molecules.
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Key words:
- sorption /
- biochar /
- naphthalene /
- propranolol
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