改性蒙脱土颗粒吸附直接染料的分形特征

研究了改性蒙脱土颗粒(050823和MMT35)吸附2种直接染料(直接耐晒黑G和直接大红4BE)的吸附特性,并从类分形动力学规律、颗粒吸附染料前后的表面分形特征变化等方面对上述吸附过程进行了探讨.结果表明,颗粒对染料的吸附可分为快速的边缘覆盖和缓慢的晶层吸附2个过程.整个吸附过程符合准-二级反应动力学方程,并且染料进入晶层的吸附阶段具有类分形特征.除MMT35-直接大红4BE染料吸附体系外,Freundlich、Langmuir吸附等温模型的非线性方程、不同形式的线性方程及分形Langmuir模型对其余3个吸附体系(050823-直接耐晒黑G、050823-直接大红4BE、MMT35-直接耐晒黑G)等温线数据的模拟均取得了较好的效果,其中,非线性方程是获得统一模型参数较好的方法.此外,染料分子主要通过静电引力/斥力和范德华引力的综合作用吸附在颗粒上,并通过晶层膨胀和开孔作用,使颗粒表面粗糙度增加,相应的表面分形维数Ds升高.

Fractal characteristics of adsorption of direct dye compounds onto modified montmorillonite particles

The adsorption process of two direct dye compounds (direct fast light black G, direct scarlet 4BE) onto modified montmorillonite particles (050823 and MMT35) was studied with fractal methods. The results showed that the adsorption process could be divided into two stages, one was high-speed boundary coverage, and another was low-speed interlayer adsorption. A pseudo second-order reaction kinetic equation was applicable for the entire process, and fractal-like properties were found in the main interlayer adsorption stage. Classical non-linear equations and linear equations were used to simulate the Freundlich, Langmuir and fractal Langmuir adsorption isotherms for direct dye compound adsorption onto the modified montmorillonite particles, and the experimental data fit well with these isotherms, except for the adsorption of direct scarlet 4BE onto MMT35. The simulation results indicated that the non-linear method was a better way to estimate the desired parameters. In addition, the surface fractal dimension Ds for particles with dye adsorption was higher than that without dye adsorption because of the increase of surface roughness. The increase of surface roughness may be attributed to the absorption of dye compounds onto the modified montmorillonite particles by electrostatic attraction/repulsion and Van der Waals attraction, as well as the interlayer expansion and pore opening effect.