ABSTRACT
The mixed ligand synthetic approach offers an alternative to engineering a specific character in metal-organic framework (MOFs) materials. Herein, we synthesized and characterized a well-known prototype zirconium-based-MOF, so-called UiO-66, and its mixed ligand derivatives UiO-66-xATA, where x is mole fraction (0.5, 0.75, and 1.0) and ATA is 2-animoterephthalate. The study investigates whether the dye adsorption capacity can be tuned/enhanced by the ATA ligand substitution into the framework. We found that, at room temperature, UiO-66-0.75ATA shows the highest adsorption capacity toward various dye solutions, including methylene blue (MB), indigo carmine (IC), and congo red (CR). The optimum adsorption conditions in all four materials were in a common trend where their adsorption capacities can be increased with decreasing pH and adsorbent dose, increasing IC concentration, contact time, and temperature. Pseudo-second order kinetics model fits best with their adsorption data, where UiO-66-ATA has the fastest adsorption rate. Langmuir and Freundlich isotherms were found best to describe adsorption behavior in ATA-containing UiO-66 and UiO-66, respectively, where adsorption processes were found to be physisorption. Confirming by thermodynamic studies, the adsorption in all four materials occurred spontaneously, driven by entropy. Computational studies showed ligand to metal charge transfer where the distribution of electron densities was varied with the amount of functionalized ligand. Adsorption mechanism is proposed as a synergistic interplay between electrostatic interaction and hydrogen bonding. The findings in this work broaden the potential strategy to fine-tune the dye adsorption capacity in MOF materials.
ABSTRACT
In this research, for the first time, a series of Co(II) doped copper terephthalate (CoX-CuBDC, where X is doping percentage) were successfully synthesized via solvothermal method and were tested for dye removal application. The physical properties of CoX-CuBDC were studied by several techniques including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) surface area analysis. The incorporation of Co(II) dopant leads to isomorphic substitution of Cu(II) in the CuBDC framework with the maximum doping percentage of 22. Doping and parent MOFs which are non-porous were used for removal of Methylene Blue (MB) from aqueous solution. Adsorption capacity of Co22-CuBDC and CuBDC are 52 and 58â¯mg/g, respectively, both of which are higher than the adsorption capacity recorded from several high porosity MOFs. Adsorption kinetic studies indicate that adsorption process follows pseudo-second order model while the adsorption mechanism is dominated by electrostatic attraction. Overall, even though these materials show non-porous characteristic, it can be used effectively in wastewater treatment application.
