The Strengthening Role of the Amino Group in Metal–Organic Framework MIL-53 (Al) for Methylene Blue and Malachite Green Dye Adsorption

Abstract

In this paper, two kinds of metal–organic frameworks (MOFs), MIL-53­(Al) and MIL-53­(Al)-NH2, were synthesized. Then these MOFs were used to remove methylene blue and malachite green dyes from aqueous solution. Characterizations of MOFs were carried out by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectrometry, and zeta potential. Experimental results showed that MIL-53­(Al)-NH2 can rapidly bind to the two kinds of cationic dyes from aqueous solution with high adsorption capacity. However, the adsorption capacity of MIL-53­(Al) for cationic dyes is extremely low. The adsorptive selectivity of MIL-53­(Al)-NH2 to the cationic dyes resulted from the hydrogen bonding interaction between amimo groups of the dyes molecule and the MIL-53­(Al)-NH2, while the extremely low adsorption capacity of MIL-53­(Al) for the dyes may be main caused by the “breathing” behavior of MIL-53­(Al). The factors including adsorption time, temperature, and the pH of solution that affected adsorption of the two dyes on MIL-53­(Al)-NH2 were studied. Pseudo first-order kinetic, pseudo second-order kinetic, and Weber–Morris models were used to fit the adsorption data, and the pseudo second-order kinetic model showed a better fit for the adsorption of methylene blue and malachite green than that of the pseudo first-order kinetic model. Furthermore, the internal diffusion model which represented by Weber-Morris model was involved in the step of speed control, but it was not the only speed control step, while out-diffusion also played an important role in the adsorption process. The adsorption isotherm and thermodynamics of methylene blue and malachite green on MIL-53­(Al)-NH2 were also studied. The adsorption of methylene blue and malachite green dyes on MIL-53­(Al)-NH2 can be fitted to both Langmuir and Freundlich isotherm, but the former was better than the latter. The adsorption thermodynamic experiments demonstrated that adsorption reaction was spontaneous and endothermic. Finally, according to the experimental phenomenon, the possible mechanism of adsorption was proposed. Besides, the used adsorbent can be reused for adsorptive removal through simply washing.

Synthesis of graphene oxide/metal–organic frameworks hybrid materials for enhanced removal of Methylene blue in acidic and alkaline solutions

“…The concentration of negative charge of the adsorbent increases with increasing pH of the MB solution, which is beneficial for improving the adsorption capacity because of electrostatic interaction. Interestingly, the adsorption amount increases with decreasing pH value (2–7), which is different from previous reports . The concentration of positive charge increases with decreasing pH, meaning that electrostatic interaction is no longer working because of charge repulsion between the surface of GO/MOFs and MB.…”

“…Interestingly, the adsorption amount increases with decreasing pH value (2-7), which is different from previous reports. 25,39,78 The concentration of positive charge increases with decreasing pH, meaning that electrostatic interaction is no longer working because of charge repulsion between the surface of GO/MOFs and MB. However, acid-base interaction may play an important part in improving the adsorption capacity when the pH values are 2-7.…”

Efficient Removal of Anionic Organic Dyes from Aqueous Solution with Cu‐Organic Frameworks

“…A similar increment was found for the NH 2 -MIL-101(Al) and MIL-101(Al) to adsorb methylene blue (MB) [25]. MIL-53(Al)-NH 2 could rapidly bind to two cationic dyes with high adsorption capacity [26]. MIL-100(Fe) was synthesized directly by aminoterephthalate and gave much higher adsorption capacity for malachite green [23].…”

Magnetic Control of MOF Crystal Orientation and Alignment

“…Above pH 2.8, the nanoparticles bear negative electrostatic charges. NH 2 ‐MIL‐53(Al) crystals, on the other hand, are positively charged below pH 10.5, likely due to protonation of the amine groups on the linker molecules . Aqueous suspensions of NH 2 ‐MIL‐53(Al) microneedles (8±2 μm in length, aspect ratio of 21±7) were mixed with the iron oxide nanoparticles at pH 3.5, whereby attractive electrostatic interactions between the two types of particles should prevail to allow nanoparticle attachment to the external MOF particle surfaces.…”