Superior selective adsorption of anionic organic dyes by MIL-101 analogs: Regulation of adsorption driving forces by free amino groups in pore channels

摘要

We herein report that the forces driving the adsorption of dyes onto MIL-101-NH2 micro/nanoparticles, which are electrostatic, hydrogen bonding, and n-ti stacking interactions, pore-volume, and steric hindrance, can be modulated by varying the molar ratio of terephthalic acid and 2-aminoterephthalic acid in the reaction system. The adsorption capacities of MIL-101-NH2-1 were determined to be 2967.1 mg g(-1) for Congo red (CR), 461.7 mg(-1) for methyl orange (MO), and 259.8 mg(-1) for acid chrome blue K (AC), which were higher by 117.0%, 102.2%, and -19.6%, respectively, compared with those of pristine MIL-101. This adsorption behavior could be rationalized based on the molecular structure of the dye, its zeta potential, BET specific surface area, and the adsorption characteristics of the dye. The study revealed that free -NH2 groups increase the hydrogen bonding and electrostatic interactions between MIL-101-NH2 micro/nanoparticles and linear anionic dyes. thereby improving the adsorption performance for linear anionic dyes by overriding the effect of pore-volume. On the other hand, the increased steric hindrance between MIL-101-NH2 micro/nanoparticles and a nonlinear anionic dye decreased the adsorption performance for the nonlinear dye, overriding the effects of hydrogen bonding, and electrostatic interactions. The adsorption uptakes of MIL-101-NH2-1 toward the linear anionic organic dyes (CR and MO) were found to be much higher than those of the other two MIL-101-NH2 adsorbents investigated herein. However, the adsorption uptake of MIL-101-NH2-1 toward the nonlinear anionic organic dye (AC) was the smallest owing to different adsorption mechanisms. The adsorption performance of MIL-101-NH2 is governed by the synergetic interplay between the hydrogen governed by the synergetic interplay between the hydrogen bonding, electrostatic and pi-pi stacking interactions, pore-volume, and the steric hindrance of the adsorbent. (C) 2020 Elsevier B.V. All rights reserved.