颗粒活性炭吸附染料时的表面分形分析

Fractal surface analysis of granular activated charcoal adsorbing dye compounds

采用N2吸附脱附实验研究了颗粒活性炭吸附染料前后表面特征的变化,运用表面分形维数表征了表面屏蔽效应和表面粗糙性等性质。结果表明,颗粒活性炭的孔结构是倾斜板交错重叠而形成四面开放的缝隙,桃红、绿色、天蓝、耐晒黑可以撑开颗粒活性炭的孔隙,增大平均孔径;耐晒翠蓝具有降低孔径的能力;大红却有些微孔阻塞作用。FHH理论计算出的相应的7个颗粒活性炭样品吸附6种染料前后的孔隙表面分形维数Ds很接近,为2.97左右,证明颗粒活性炭上吸附的染料并没有发生表面屏蔽效应,也没有使颗粒活性炭表面的粗糙性降低。分形吸附等温线法与基于N2吸附脱附的FHH理论法计算出的Ds相差较大,这与两种算法的理论基础和码尺大小有关。而热力学模型计算出的D远大于3,与Sahouli等的研究不符。

The present paper is aimed to give a detailed analysis of the pore structure properties of granular activated charcoal which can be determined by N2 adsorption-desorption data. As is found, the dye compounds of pink red, acid green, ink blue, direct fast light black G can actually serve as ＂pillars＂ to expand the pores of granular activated charcoal （ pore open effect）, and lead to the increase of pore radius. On the contrary, the adsorbed direct fast light turquoise blue GL dye are likely to decrease pore radius. The adsorbed direct scarlet 4BE as a kind of dye has some pore blocking effect, that is to say, it can clog some smaller pores and prevent nitrogen from sneaking into such pores. With FHH theory, the calculated surface fractal dimensions Ds of granular activated charcoal samples before and after absorbing 6 kinds of dye compounds are all very close to and about 2.97. All the above properties indicate that the dye compounds wouldn＇t screen out any surface rugosity, which still remain accessible to the nitrogen molecules. The big difference between Ds values calculated by both fractal adsorption isotherm and FHH theory may be accredited to the theoretical base of the two methods and the absorbates. The calculated Ds value much bigger than the three through the thermodynamic model proves to have discrepancy from Sahouli et al＇ s results.