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In this study, NH2-MIL-101(Al) metal-organic frameworks (MOFs) covered with 3-aminopropyltriethoxysilane (APTES) were incorporated into the polyethersulfone (PES) to produce mixed-matrix membranes (MMMs) for CO2 separation. The APTES functionalization was performed to improve the MOF dispersion in the PES matrix. Different analyses such as X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM) revealed that the MOFs surface successfully functionalized with APTES. An improvement in CO2/CH4 separation efficiency was observed in MMMs, and the performance shifted towards Robeson upper bounds. Notably, the membrane containing 10 wt.% S-MIL-5 (NH2-MIL-101(Al) functionalized with 5.0 mL of APTES) showed an increment in CO2 permeability (50%), and ideal CO2/CH4 selectivity (80%) compared to the PES membrane. The FTIR, TGA, FESEM, and DSC analyses constituted an excellent dispersion of MOFs within the PES phase, which led to significant development in gas permeability and selectivity.

In this study, we present results of a mathematical model in which the governing equations of electroforming process were solved using a robust finite element solver (COMSOL Multiphysics). The effects of different parameters including applied current density, solution electrical conductivity, electrode spacing, and anode height on the copper electroforming process have been investigated. An electroforming experiment using copper electroforming cell was conducted to verify the developed model. The obtained results show that by increasing the applied current density, the electroforming process takes place faster, thereby resulting in a higher thickness of the electroformed layer. In addition, higher applied current density led to non-uniformity of the coated layer. It was revealed that by increasing electrolytic conductivity from 5 to 20 S/m, the electroformed layer became thicker. By considering three different anode heights, it was found that if the cathode and anode are the same height, the process will be more effective. Finally, it was concluded that there is an optimum value of anode-cathode spacing: above it, energy consumption and plating time are high; while below it, the resultant layer is non-uniform. The present study demonstrates that the developed model can accurately capture the physics of electroforming with a reasonable computational time.

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.

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.

In this work, the addition of a novel polyaniline (PANI)/silica (SiO2) nanostructure (PSn) in chitosan/polyvinyl alcohol nanofibers (CP) was evaluated to enhance the dye removal capacity of CP. Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) results confirmed the chemical grafting of SiO2 on PANI nanoparticles. Brunauer-Emmett-Teller (BET) results showed a specific surface area of 61 m2 g−1 for the PSn filled CP nanofiber (CP-PSn). FE-SEM and EDS-elemental mapping results showed the uniform dispersibility of PSn in CP nanofibers. After the addition of PSn into CP, the adsorption capacity of CP increased from 48 to 110 mg g−1 (from 0.069 to 0.158 mmol g−1), 40 to 90 mg g−1 (from 0.122 to 0.274 mmol g−1), and 31 to 45.2 mg g−1 (from 0.097 to 0.141 mmol g−1) for Congo red (CR), methyl orange (MO), and methylene blue (MB) dyes, respectively. The optimum anionic dye (CR and MO) uptake was observed at pH 5, while for the cationic dye (MB), the optimum uptake was detected at pH 9. The isotherm experiments results showed that the Sips isotherm model could well describe the adsorption process (R2 > 0.98). Thermodynamic studies at 298 and 328 K verified that the adsorption process is spontaneous with ΔG ranging between −10.44 and − 2.83 kJ mol−1. Also, ΔH was found to be 34.16, 22.25, and 17.05 kJ mol−1 for CR, MO, and MB adsorption, respectively. The highest recovery after 5 cycles was observed for a sodium hydroxide solution (NaOH, 0.1 M), which were 74, 68, and 55% of the adsorption capacity of the first cycle for CR, MO, and MB dyes, respectively.

Human society is becoming more intransigent on removing organic dyes from polluted water before discharging to the environment. To fulfill this goal, a magnetic metal-organic framework adsorbent based on functionalized magnetic Fe3O4 nanoparticles and highly water stable UiO-66 with high porosity and sensitivity to the external magnetic field was designed and synthesized via an easy step-by-step self-assembly technique. The synthesized adsorbent magnetic nanoparticles (Fe3O4@UiO-66) were applied to remove organic dyes, i.e., methyl orange (MO) and methylene blue (MB), from a contaminated aqueous solution. The experiments displayed that magnetic Fe3O4@UiO-66 has good adsorption uptake for MO (244 mg/g) and MB (205 mg/g). The influence of several factors, including contact time, dye concentration, initial solution pH, the temperature of adsorption, and salt concentration, on the adsorption capacities of these dyes was assessed. The adsorption kinetic investigation demonstrated that the experimental adsorption data for both dyes well fitted the pseudo-second-order model. The thermodynamic research illustrated that the adsorption of both cationic and anionic organic dyes onto Fe3O4@UiO-66 was a thermodynamically spontaneous and endothermic process, and thermodynamically derived by entropy change rather than an enthalpy impact. Accordingly, the maximum adsorption capacities of Fe3O4@UiO-66 for MO increased from 243.9 to 303.0 mg/g with increasing the adsorption temperature from 25 to 45 °C. The excellent adsorption capacity, good water stability, excellent adsorption selectivity, proper regeneration, as well as good behavior in magnetic separation endorsed that the magnetic Fe3O4@UiO-66 could be a suitable adsorbent for dye elimination from aqueous solutions.

The Zr-based metal-organic framework (MOF, UiO-66) was synthesized solvothermally. The synthesized UiO-66 was activated using different solvents (acetone, chloroform, and ethanol) via two activation methods of centrifugation and Soxhlet extraction over different periods (1–10 days). The crystalline structure and morphology of the synthesized UiO-66s were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, and field-emission scanning electron microscopy (FESEM) techniques. The adsorption behaviors of the synthesized UiO-66s were then investigated by selecting anionic methyl red (MR) and cationic methylene blue (MB) as the model dyes. It was found that a change in activation solvent and activation method would alter the physical properties of UiO-66, such as surface area, pore-volume, pore diameter, and surface charge. Experimental adsorption tests demonstrated that UiO-66 activated by ethanol via the Soxhlet extraction method for five days (abbreviated as ES-5) presented higher MR uptake capacity (243 mg/g) than the other synthesized UiO-66s, ascribed to its large surface area and total pore volume. Furthermore, it was found that the uptake capacity of ES-5 for cationic MB and anionic MR dyes increased and decreased, respectively, with raising the solution pH. This resulted in superior adsorption selectivity of MB over MR at pH 9.1. All in all, the findings of this work showed that the Soxhlet extraction method holds great promise for the activation of different MOFs.

The presence of dyes as pollutants in wastewater sources from textile industries can cause significant health issues if they are not adequately treated. Dye adsorption to entrap contaminants in nanoparticle pores has created considerable attention in recent years due to the environmental concerns occurring as a result of spillage of dyes in water bodies. In efforts to understand adsorption capability UiO-66, metal-organic frameworks (MOFs) were developed and examined for the separation of four pollutant dyes containing methyl red (MR), methyl orange (MO), malachite green (MG), and methylene blue (MB), which are widely used in textile industries. The adsorbent structural stability in water, chloroform, and dimethylformamide (DMF) was studied for one year period to understand their chemical stability. The UiO-66 crystalline structure remained unchanged in water and chloroform, while XRD patterns of UiO-66 aged in DMF showed only a minor change, which might be due to the partially exterior framework collapse. The maximum adsorption capacities of pristine UiO-66 for anionic methyl red (MR) (384 mg/g) and methyl orange (MO) (454 mg/g) dyes were slightly higher than those of the cationic malachite green (MG) (133 mg/g) and methylene blue (MB) (370 mg/g) dyes, particularly at lower pH values. The partition coefficients of pristine UiO-66 for MR, MO, MG, and MB dyes were found to be 1.137, 2.208, 0.070, and 1.345 mg/g µM, respectively, which indicated that pristine UiO-66 had a good affinity to MO dye. The adsorption results perfectly matched the pseudo-second-order kinetic model. The MR, MO, and MB adsorption isotherms have matched the Langmuir model, while MG isotherms are in line with the Freundlich model. The distinctive features of the UiO-66 framework make it potentially applicable for the treatment of wastewater.