多种因素对MIL-101(Cr)选择性吸附水溶液中染料的影响

在多种条件下研究了金属有机框架MIL-101(Cr)对阳离子型染料(亚甲基蓝、罗丹明B)和阴离子型染料(甲基橙、酸性铬蓝K)的吸附性质,主要研究了MIL-101(Cr)对亚甲基蓝和甲基橙的选择性吸附作用。结果表明,中性环境下无论在单组分还是双组分体系中MIL-101(Cr)对阴离子型染料的吸附能力均大于对阳离子型的吸附能力。在pH=3,T=300 K的条件下,选择性系数β可达5.9,但随着pH的增加,选择性系数逐渐降低。相比之下,温度对吸附的选择性影响不大。选择性吸附的机理可以解释为:由于表面带正电荷,MIL-101(Cr)对阴离子型染料产生静电吸引作用;相反,对阳离子型染料的排斥作用而降低了其吸附能力。另外,乙二胺改性提高了MIL-101(Cr)对阴离子型染料的选择吸附性能,而草酸改性降低了选择吸附性。

Effects of various factors on adsorption of MIL-101(Cr) for dyes in aqueous solutions

Under various conditions, the adsorption capacity of metal-organic framework, MIL-101(Cr), was measured for cationic dyes (methylene blue (MB), rhodamine B) and anionic dyes (helianthine B (HB), acid chrome blue K) in aqueous solutions. The effect of various factors on the adsorption selectivity of MIL-101(Cr) was studied for HB and MB in mixed solutions. The results show that the adsorption capacity to anionic dyes is higher than that to cationic dyes when the dyes exist solely or coexist. The selection coefficient b is 5.9 at T=300 K and pH=3, and it decreases obviously with the increase of pH value, while temperature has a little effect on adsorption selectivity. The mechanism for adsorption selectivity is that MIL-101(Cr) has positive surface potential, so there exist electrostatic attractive interactions between MIL-101(Cr) and anionic dye molecules while it is repulsion interaction for cationic dyes. Moreover, modification with ethyl diamine increases the adsorption selectivity of MIL-101(Cr) for anionic dyes, whereas with oxalic acid the selectivity decreases.