Effect of Synergistic Interplay between Surface Charge, Crystalline Defects, and Pore Volume of MIL-100(Fe) on Adsorption of Aqueous Organic Dyes

We herein report that the morphology, size, and surface charge status of MIL-100(Fe) micro/nanoparticles can be tailored by adding a coordination modulator (HF or tetramethylammonium hydroxide) to the reaction system. Interestingly, the adsorption capacities of low-crystallinity MIL-100(Fe) and MIL-100(Fe)-TMA toward Congo red (CR) and acid chrome blue K (AC) were found to be significantly larger than that of the high-crystallinity MIL-100(Fe)-HF adsorbent, whereas there was little difference in the adsorption capacities of the three MIL-100(Fe) toward methyl orange (MO) and methylene blue (MB). The adsorption uptake of MIL-100-(Fe)-TMA toward the anionic dyes (CR, AC, and MO) was found to be highest, whereas the adsorption uptake of MIL-100(Fe) toward the cationic dye (MB) was the highest owing to different adsorption mechanisms. This adsorption behavior could be rationalized based on the morphological characteristics and crystal structure defects, zeta potential, and pore volume of MIL-100(Fe) and the adsorption characteristics and molecular structure of the dye. It was revealed that the adsorption performance of MIL-100(Fe) micro/nanoparticles is governed by the synergistic interplay between electrostatic, hydrophobic, and pi-pi stacking interactions, pore volume, crystal structure defects, and steric hindrance of the adsorbent.