Efficient removal of organic dyes using electrospun nanofibers with Ce-based UiO-66 MOFs.

Cerium-based UiO-66 (Ce-UiO-66) metal-organic frameworks (MOFs) were synthesized via a facile solvothermal method and fully characterized using FTIR, XRD, BET, SEM, EDX, and zeta potential techniques. The synthesized Ce-UiO-66 particles were embedded into an electrospun cross-linked polyvinyl alcohol (PVA)/chitosan (CTS) nanofiber (EPCNF), and then employed to remove organic dyes from water. The adsorption results demonstrated that the adsorption capacities of both anionic (Congo Red (CR), Methyl Orange (MO) and Methyl Red (MR)) and cationic (Methylene Blue (MB)) dyes over the fabricated electrospun nanofibers (ENFs) increased with increasing the loadings of Ce-UiO-66 MOFs. Accordingly, the adsorption performance of EPCNF-10 (containing 10 wt% of Ce-UiO-66 MOFs) adsorbent toward these organic dyes is in the order of CR (102.04 mg/g) > MO (87.71 mg/g) > MR (65.35 mg/g) > MB (34.24 mg/g). Moreover, it was found that the Freundlich isotherm model and the pseudo-second-order kinetic model were appropriate for describing the adsorption behaviors of EPCNF-10 adsorbent toward both anionic and cationic dyes. Thus, it can be proposed that the fabricated EPCNF-10 adsorbent would be effective adsorbent materials for the removal of anionic and cationic dyes from water due to its excellent adsorption performance, facile preparation, good regeneration, and simple separation from aqueous solutions.

Magnetic Nitrogen-Rich UiO-66 Metal-Organic Framework: An Efficient Adsorbent for Water Treatment.

The postsynthetic modification of metal-organic frameworks (MOFs) has opened up a promising area to widen their water treatment application. However, their polycrystalline powdery state still restricts their widespread industrial-scale applications. Herein, the magnetization of UiO-66-NH2 is reported as a promising approach to facilitate the separation of the used MOFs after water treatment. A two-step postmodification procedure employing 2,4,6-trichloro-1,3,5-triazine (TCT) and 5-phenyl-1H-tetrazole (PTZ) agents was introduced to level up the adsorption performance of the magnetic nanocomposite. Despite a decrement in porosity and specific surface area of the designed MOFs (m-UiO-66-TCT) compared to neat UiO-66-NH2, it outweighs in adsorption capacity. It was observed that m-UiO-66-TCT has an adsorption capacity of ≈298 mg/g for methyl orange (MO) with facile MOF separation using an external magnet. Pseudo-second-order kinetic model and Freundlich isotherm models suitably interpret the experimental data. Thermodynamic studies showed that MO removal using m-UiO-66-TCT is spontaneous and thermodynamically favorable at higher temperatures. The m-UiO-66-TCT composite exhibited easy separation, high adsorption capacity, and good recyclability, rendering it an attractive candidate for the adsorptive removal of MO dye from aqueous environments.

Impact of scale, activation solvents, and aged conditions on gas adsorption properties of UiO-66.

This work reports on the potential application of UiO-66 in gas sweetening and its structural stability against water, air, dimethylformamide (DMF), and chloroform. The UiO-66 nanoparticles were solvothermally synthesized at different scales and activated via solvent exchange technique using chloroform, methanol, and ethanol. Thus prepared and aged MOFs were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), and nitrogen adsorption-desorption analysis. The chloroform-activated MOF showed the largest surface area among all activation solvents, and presented high uptakes of 8.8 and 4.3 mmol/g for CO2 and CH4, respectively, at 298 K and 30 bar. This might be due to removing all unreacted organic ligands and DMF molecules from the pores of the framework. The UiO-66 nanoparticles are stable at the experimental conditions with no significant loss in crystalline structure and gas adsorption ability even after aging under different conditions for one year. The UiO-66 could be easily regenerated at 373 K with no observed significant reduction in gas uptakes even after five consecutive adsorption-desorption cycles. The present findings suggest the excellent potential of the UiO-66-derived MOFs as the promising materials for CO2/CH4 separation at low pressures and results can be applied in practical natural gas sweetening.

Amino-silane-grafted NH2-MIL-53(Al)/polyethersulfone mixed matrix membranes for CO2/CH4 separation.

Mixed-matrix membranes (MMMs) are promising candidates for carbon dioxide separation. However, their application is limited due to improper dispersion of fillers within the polymer matrix, poor interaction of fillers with polymer chains, and formation of defects and micro-voids at the interface of both phases, which all result in the decline of the gas separation performance of MMMs. In this work, we present a new method to overcome these challenges. To this end, a series of MMMs based on polyethersulfone (PES) as the continuous polymer matrix and MIL-53-derived MOFs as the dispersed filler were prepared. FTIR-ATR, XRD, TGA, FESEM, and N2 adsorption/desorption analyses were employed to characterize the structural properties of the synthesized nanoparticles. The obtained results indicated that 3-aminopropyltriethoxysilane (APTES) molecules were successfully attached onto the surface of NH2-MIL-53(Al). Morphological characterization by FESEM and energy dispersive X-ray mapping (EDX) showed that desirable distribution within the whole membrane thickness, suitable nanoscale dispersion, and excellent interface were achieved by using amino-silane-grafted NH2-MIL-53(Al) (A-MIL-53(Al)) nanoparticles. The permeation results indicated that the permeability of two gases and the ideal CO2/CH4 selectivity enhanced by increasing the concentration of MOFs. In particular, comparing the experimental gas separation results of A-MMM-10 with those of pure PES membrane showed an 84% increase in the CO2 permeability and a 70% increase in CO2/CH4 selectivity. These results suggest that post-synthetic modification of MOF nanoparticles and strong interfacial adhesion between functionalized nanoparticles and polymer matrix could be a useful method to eliminate interfacial voids and improve gas separation efficiency.