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Arch Hyg Sci 2019, 8(1): 56-65 |
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Ghasemi Kochameshki M, Mahmoudian M, Marjani A. Mixed-Matrix Membranes Containing Metal Organic Frameworks (MOFs) for Separation of Dyes and Heavy Metals from Water. Arch Hyg Sci 2019; 8 (1) :56-65
URL: http://jhygiene.muq.ac.ir/article-1-322-en.html
URL: http://jhygiene.muq.ac.ir/article-1-322-en.html
1- Department of Chemistry, Islamic Azad University, Arak Branch, Arak, Iran
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| Abstract (HTML) (3649 Views)
Background
Environmental contamination of water with heavy metals and dyes is a source of mounting concern for global public health, (1). To minimize the amount of metals released into the environment, the development of selective solid-phase sorbents is an essential pursuit for industrial applications and environmental remediation (2). Polymeric membranes are more effective, environmental friendly and energy saving technique in separation technology (3-11). Various types of polymeric membranes have been developed for gas and liquid separation (12-24). Polyethersulfone has many attractive properties as, it is a high-Tg (glass-transition temperature) polymer of high mechanical, thermal and chemical resistances and shows wide range of tolerated pH, physiological neutrality and can be used for food, water and medical applications (25). Besides having many advantages, polyethersulfone (PES) membranes have a major drawback of fouling when used in water treatment, which leads to deposition of particles on the surface or in membrane pores leading to its fouling and consequently to reduced flow and membrane lifetime (26). Introducing hydrophilic nanoparticles into PES material through common blending method has demonstrated another strategy to enhance the hydrophilicity of PES membranes (27).
MOFs are branch of materials having many virtues such as thermal stability, discrete ordered structure, ultra-low densities, large internal surface area extending beyond 6000 m2/g, ease of synthesis and with broad-spectrum of properties suited for physical and chemical applications (28). The synthesis of metal-organic frameworks (MOFs) has attracted immense attention during the last two decades due to the possibility to obtain a large variety of aesthetically interesting structures that could also be of great interest for applications in a number of fields related to porous materials (29-32). Metal-Organic Frameworks (MOFs) is gaining much more interest as nanofiller because of its high surface area and multiple potential applications (33). Because of the easy synthesis and low regeneration cost related to the usual physisorption mechanism, porous metal organic frameworks (MOFs) that adsorb heavy metals have received increasing attention in recent years in water purification (34,35). MOFs have emerged as an extensive class of crystalline materials with high porosity in nature. Precipitation process is a conventional method for removal heavy metals and others metals from aqueous solutions, while the most useful technique is filtration with membranes (36). The modifying agent added to the polymer solution includes surfactants, mineral fillers, or nonsolvent (37). These substances were added to increase hydrophilicity, increase or decrease the number of generated macropores, and increase the number of pores and improve connections between them (38,39).
Aims of the study: In this study, the MOFs was synthesized via the hydrothermal method and the structure, w:as char:acterized by X-ray powder diffraction (XRD), Field-Emission Scanning Electron Microscope (FESEM), and Fourier transform infrared spectroscopy (FTIR). Then, the effect of MOFs dispersed in the mixed matrix membrane on the membrane performance, the matrix structure and surface hydrophilicitity was investigated by FESEM. In this research, a MOF-PES membrane for removal of hazardous materials such as Hg, Pb, Cd, Cr, Methylene blue, and Methyle orange is presented.
Materials
T erephthalic acid (H2BDC) was purchased from Merck. Zn(NO3)2•6H2O, Polyethersulfone (PES, Ultrason® E 6020 P) was supplied by Sigma-Aldrich. Methanol (synthetic grade, Merck, Mumbai) was used as received, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), acetone, were purchased from Dae Jung, South Korea. Bovine serum albumin (BSA) was supplied by Sigma-Aldrich. Doubly distilled water was made in the laboratory and was used throughout the experiments.
Characterizations
FTIR spectra were acquired using a WQF-510A spectrophotometer in the range of 500–4000 cm-1 to analyse the functional groups. Field Emission Scanning Electron Microscope (FE-SEM) images was obtained to study the surface structure, cross-section and morphology of prepared nanocomposite membranes a using HITACHI S-4160, operating 30kV. All samples were fractured in liquid nitrogen and then coated with a thin gold layer.
Preparations of functionalized MOFs
Synthesized MOFs was prepared via the hydrothermal method. Zn(NO3)2.6H2O (0.321 g, 1 mmol), terephthalic acid (H2BDC, 0.490 g, 1 mmol) were dissolved in 20 mL DMF at room temperature. The mixture was transferred into a 50 mL Teflon-lined autoclave, which was sealed and maintained at 120 °C for 24 h. The reaction mixture was allowed to cool to 25 °C, and washed several times with methanol.
Preparations of the membranes
Flat-sheet polyethersulfone (PES) membranes were prepared by phase inversion technique. In this study, various ratios of MOFs (3 wt%, 5 wt%, 7 wt%) were used as additives. They were added to N-methyl-2-pyrrolidone (NMP) and stirred vigorously to provide a homogeneous solution. Polysetherulfone was then added to prepare a casting solution. Polyethylene glycol (PEG) was used as pore forming agent (10 wt%). The composition of the membranes and their abbreviations are listed in Table 1. These solutions were flatted on smooth glass plate by doctor blade with 200 µm thickness. The casting film was immediately immersed into non-solvent (usually distilled water bath) and kept there for 24 hour until most of the solvent was removed.
Figure 4) FE-SEM images of the cross section of membrane Neat (a), 3 wt% (b), 5 wt% (c), 7 wt% (d) from additive according Table 1.
The efficiency of membrane processes in removing of Pb+2, Cd+2, Cr+2 and Hg+2 from wastewater are represented in Figure 6.
Figure 6) Performance of membrane in rejection of Heavy metal solutions including Pb+2, Cd+2, Cr+2 and Hg+2.
Figure 7 depicts the dye removal efficiency of the membranes for methylene blue (MB) and methyl orange (MO) organic dyes solution as a function of additive percentage.
Figure 7) Dye rejection including (MO and MB) by unmodified and modified PES membranes.
Structural analysis
According to Figure 1, the IR spectrum of the synthesized Zn-BDC is dominated by the bands associated with organic part. In the paddlewheel structure, the carboxylate ion is coordinated to two Zn atoms and made a unit cell of crystal. The intense bands at 1418.80 cm-1 appear in the spectrum which confirms the paddle-wheel type unit of MOF. IR spectra of MOF-5 show the expected strong characteristic adsorptions for the symmetric and asymmetric vibrations of BDC (1642.77, 1025.36 and 1418.80 cm-1) and adsorbed water (3,500–3,200 cm-1) (40).
X-ray diffraction (XRD) is an effective method to investigate crystalline properties of a synthesized material. According to Figure 2, the extremely high intensities of the diffraction peaks indicate the good crystallinity of sample. The peak of highest intensity in image at 2θ= .5ᵒ is indexed as the d200 for zinc metals (40, 41).
The SEM micrograph (Figure 3) show distribution of particles in MOFs as clusters of irregular shaped flakes arranged as flower-like clusters. SEM of MOFs, Figure 3 at the magnifications shown, show irregular flake particles. A high magnification Figure 3 confirm these flakes-like particles having irregular shapes (42).
Membrane morphology
As shown in Fig. 4, a finger-like structure was formed when NMP/water was used as the solvent/nonsolvent pair with PES. The hydrophilic nature of MOFs increased the mass transfer rate between the solvent and the nonsolvent during phase inversion process and led to the formation of larger pore channels.
This further demonstrated that addition of MOFs changed the structure of membrane. Gradually, it can be said that the presence of a large amount of MOFs caused a remarkable hydrophilicity improvement in the prepared membranes and increased permeation rate of water molecules into the cast solution.
Membrane Performance
Pure water fluxes
The achieved improvement in hydrophilicity (discussed later) was due to the presence of MOFs. As shown in Figure 5, water flux through unmodified and modified membranes were changed by increasing MOFs as an additive up to 7 wt%. For 5 bar pressure, the maximum and minimum rates of pure water flux was observed in 7 wt% MOFs and neat PES, respectively. This behavior could be explained in this manner which by increasing of polymer concentration in membrane formulation, the pore size of membrane decreased strongly. On the other hand, addition of MOFs amount in membrane causes larger channels, more porosity and subsequently makes them more hydrophilic in nature (43).
In this study, the fouling properties of membranes and the effect of MOFs on fouling, the dynamic fouling analysis (flux recovery ratio), static fouling analysis (surface protein adsorption) and rejection tests were done for prepared membrane. (Table 2). It was found that, the flux recovery ratio (FRR) increased from 43.4 % to 78.3%, when weight percent of MOFs increased from 0 to 5 wt.%, while for membranes with 7 wt.% MOFs obtained FRR (%) was 70.8%. This finding can be related to different parameters such as surface hydrophilicity and roughness. Surface roughness can play a key role due to protein molecules irreversible deposition into the surface pores. Static protein adsorption on the membranes surface decreased, which is in good agreement with FRR results and only a decrease was observed for membrane with 7 wt.% MOFs likely due to surface roughness which caused more adsorption of BSA.
The initial concentration of the used heavy metals for these experiments (Pb(NO3)2, Cd(NO3)2, Cr(NO3)2 and HgCl2) was 50 ppm of metal ions. The percentage of heavy metal rejection improved by increasing additive (MOFs) from 0 to 5 wt%, while with further increase of MOFs in the membrane matrix, the removal of heavy metals decreased (see Figure 6). As mentioned in the previous section, two parameters (pore size and the extent of interaction between metal ions and functional groups on the MOFs surface) acted in the opposite direction (44). Therefore, it can be argued that the initial increase in rejection was due to more and stronger interactions; however, at higher percentage of additive, strengthening of the pore size is weakened the interactions effect, thus rejection of heavy metals decreased.
The rejection of dyes was measured using a lab scale nanofiltration cell (operating pressure= 0.5 MPa, pH=7.0 and the dye concentration= 100 mg/L). As it can be observed in Figure 7, the MO rejection was more than the MB for all of the prepared membranes. As shown in Figure 7, the rejection performance in all of the MOFs modified membranes was better than the neat PES membrane that confirmed the effective filtration performance of the prepared nanocomposite membranes. The better rejection efficiency of the modified mixed matrix membranes can be related to the repulsion forces between negative surface of the membranes and negatively charged surface in the dye molecules (45). In other words, it can be concluded that rejection was improved by addition of MOFs to 5 wt.% and then decreased which could be related to contrast between pore size and the extent of interactions. The prepared mixed matrix membranes were negatively charged due to the presence of several carboxylic functional groups from MOFs additive. Increasing MOFs additive concentration from 1 wt.% to 5 wt.% improved dye removal while higher percentage of MOFs decreased removal efficiency slightly. This may be due to an increase in surface negative charge by MOFs to 5 wt% but higher percentage of MOFs increased the pore diameter of the membrane and reduced removal efficiency. The results were in agreement with heavy metal removal and the highest dye removal was observed for the sample with 5 wt% MOFs additive concentration.
In this study, metal organic frameworks (MOFs) was synthesized via the hydrothermal technique. This MOFs as additive was incorporated to the mixed matrix membrane. The surface and cross-section morphology of MOFs and the neat and the modified membranes were investigated by FE-SEM. Effect of MOFs on the performance’s properties (heavy metals and dye removal) was investigated. Base on the results, hydrophilicity, water flux, and antifouling properties were improved by hybrid membranes. Addition of MOFs also improved the rejection of heavy metal and dyes more efficiently than neat PES membrane and membrane with 5 wt.% of MOFs suggested better properties. Additionally excellent heavy metal separation behavior was observed among rejection tests.
Conflict of Interest:
The authors declared no conflict of interest.
Full-Text: (1516 Views)
Background
Environmental contamination of water with heavy metals and dyes is a source of mounting concern for global public health, (1). To minimize the amount of metals released into the environment, the development of selective solid-phase sorbents is an essential pursuit for industrial applications and environmental remediation (2). Polymeric membranes are more effective, environmental friendly and energy saving technique in separation technology (3-11). Various types of polymeric membranes have been developed for gas and liquid separation (12-24). Polyethersulfone has many attractive properties as, it is a high-Tg (glass-transition temperature) polymer of high mechanical, thermal and chemical resistances and shows wide range of tolerated pH, physiological neutrality and can be used for food, water and medical applications (25). Besides having many advantages, polyethersulfone (PES) membranes have a major drawback of fouling when used in water treatment, which leads to deposition of particles on the surface or in membrane pores leading to its fouling and consequently to reduced flow and membrane lifetime (26). Introducing hydrophilic nanoparticles into PES material through common blending method has demonstrated another strategy to enhance the hydrophilicity of PES membranes (27).
MOFs are branch of materials having many virtues such as thermal stability, discrete ordered structure, ultra-low densities, large internal surface area extending beyond 6000 m2/g, ease of synthesis and with broad-spectrum of properties suited for physical and chemical applications (28). The synthesis of metal-organic frameworks (MOFs) has attracted immense attention during the last two decades due to the possibility to obtain a large variety of aesthetically interesting structures that could also be of great interest for applications in a number of fields related to porous materials (29-32). Metal-Organic Frameworks (MOFs) is gaining much more interest as nanofiller because of its high surface area and multiple potential applications (33). Because of the easy synthesis and low regeneration cost related to the usual physisorption mechanism, porous metal organic frameworks (MOFs) that adsorb heavy metals have received increasing attention in recent years in water purification (34,35). MOFs have emerged as an extensive class of crystalline materials with high porosity in nature. Precipitation process is a conventional method for removal heavy metals and others metals from aqueous solutions, while the most useful technique is filtration with membranes (36). The modifying agent added to the polymer solution includes surfactants, mineral fillers, or nonsolvent (37). These substances were added to increase hydrophilicity, increase or decrease the number of generated macropores, and increase the number of pores and improve connections between them (38,39).
Aims of the study: In this study, the MOFs was synthesized via the hydrothermal method and the structure, w:as char:acterized by X-ray powder diffraction (XRD), Field-Emission Scanning Electron Microscope (FESEM), and Fourier transform infrared spectroscopy (FTIR). Then, the effect of MOFs dispersed in the mixed matrix membrane on the membrane performance, the matrix structure and surface hydrophilicitity was investigated by FESEM. In this research, a MOF-PES membrane for removal of hazardous materials such as Hg, Pb, Cd, Cr, Methylene blue, and Methyle orange is presented.
|
Materials & Methods
|
Materials
T erephthalic acid (H2BDC) was purchased from Merck. Zn(NO3)2•6H2O, Polyethersulfone (PES, Ultrason® E 6020 P) was supplied by Sigma-Aldrich. Methanol (synthetic grade, Merck, Mumbai) was used as received, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), acetone, were purchased from Dae Jung, South Korea. Bovine serum albumin (BSA) was supplied by Sigma-Aldrich. Doubly distilled water was made in the laboratory and was used throughout the experiments.
Characterizations
FTIR spectra were acquired using a WQF-510A spectrophotometer in the range of 500–4000 cm-1 to analyse the functional groups. Field Emission Scanning Electron Microscope (FE-SEM) images was obtained to study the surface structure, cross-section and morphology of prepared nanocomposite membranes a using HITACHI S-4160, operating 30kV. All samples were fractured in liquid nitrogen and then coated with a thin gold layer.
Preparations of functionalized MOFs
Synthesized MOFs was prepared via the hydrothermal method. Zn(NO3)2.6H2O (0.321 g, 1 mmol), terephthalic acid (H2BDC, 0.490 g, 1 mmol) were dissolved in 20 mL DMF at room temperature. The mixture was transferred into a 50 mL Teflon-lined autoclave, which was sealed and maintained at 120 °C for 24 h. The reaction mixture was allowed to cool to 25 °C, and washed several times with methanol.
Preparations of the membranes
Flat-sheet polyethersulfone (PES) membranes were prepared by phase inversion technique. In this study, various ratios of MOFs (3 wt%, 5 wt%, 7 wt%) were used as additives. They were added to N-methyl-2-pyrrolidone (NMP) and stirred vigorously to provide a homogeneous solution. Polysetherulfone was then added to prepare a casting solution. Polyethylene glycol (PEG) was used as pore forming agent (10 wt%). The composition of the membranes and their abbreviations are listed in Table 1. These solutions were flatted on smooth glass plate by doctor blade with 200 µm thickness. The casting film was immediately immersed into non-solvent (usually distilled water bath) and kept there for 24 hour until most of the solvent was removed.
Table 1) Compositions of casting solution for PSf membrane with MOF 1-NH2 as additive
|
Pure water flux
Pure water flux measurements were carried out by loading the membranes in a batch type, dead-end cell at a pressure of 0.5 MPa. A membrane with an effective surface area of 7.065 cm2 was used as sample. Nitrogen gas was utilized to force the water through the membrane. Water flux was determined on the basis of permeate mass divided by effective surface area and filtration time, in L.m-2.h-1 unit. The water flux was calculated by the following equation (1):
(1)
Where J is the permeation flux of the membrane for pure water (L.m-2.h-1), V is the permeate volume measured (L), A is the effective membrane area (m2) and t is the permeation time (hour).
Heavy metals and dyes removal
The membranes were characterized by rejection of salt solutions, removal of heavy metals and dyes rejection. The separation performance tests were carried out with a 50 ppm of heavy metal (Pb(NO3)2, Cr(NO3)2, Cd(NO3)2, HgCl2) under 0.5 MPa operating pressures. The methylene blue (MB) and methyl orange (MO) rejections were recorded using a UV spectrophotometer PG (china) with 1 cm quartz cell. The concentration of metal ions in the aqueous solutions was determined using a Shimadzu AA-670 atomic absorption spectrophotometer with a hallow cathode lamp using an air–acetylene flame.
The rejection R (%) was calculated by using equation (2):
(2)
Where Cp and Cf are the concentration of permeate and feed solutions, respectively.
Antifouling properties
Dynamic fouling test for the prepared membranes was conducted using, bovine serum albumin (BSA) solution in PBS (100 ppm, 50 mM, pH=7) buffer. Each membrane was pressed for an initial 20 min at 0.4 MPa. Pure water flux of the membrane, Jw1 (L.m-2h-1), was determined over a period of 1 minute. After that, BSA was fed inside cell to be passed through the membrane for 30 minute. Then the membrane was washed with water and pure water flux Jw2 (L.m-2.h-1) was measured again. Finally, the membrane antifouling property was determined which named flux recovery ratio (FRR) according to Equation (3):
(3)
To assess static protein adsorption of the membranes, surface of samples washed with phosphate buffered saline (PBS) solution for 2 hour and then put into tubes filled with BSA in PBS solution (5 ml of 100ppm). These tubes were put on water bath for 24 hour at 30ºC to reach equilibrium. The amount of protein adsorbed on the membrane was calculated by adsorption intensity of solutions at 280 nm (recorded by a UV–Vis spectrometer).
Figure 1 indicates the IR spectrum of the synthesized Zn-BDC. Also, the XRD patterns for zinc MOFs are presented in Figure 2.
Figure 1) FT-IR spectra of MOFs
Figure 2) XRD diagrams for the prepared MOFs
Scanning electron micrograph of MOFs is presented in Figure 3. Scanning electron microscopy is a technique that enables the study of the microstructure of nanoparticles of matter.
Figure 3) FE-SEM images of the MOFs
To study the effect of MOFs on morphological changes of the membranes, the cross-sectional morphology w:as char:acterized using FE-SEM as shown in Figure 4. The effect of additive content on the membrane structure has been investigated using SEM analysis.
Pure water flux measurements were carried out by loading the membranes in a batch type, dead-end cell at a pressure of 0.5 MPa. A membrane with an effective surface area of 7.065 cm2 was used as sample. Nitrogen gas was utilized to force the water through the membrane. Water flux was determined on the basis of permeate mass divided by effective surface area and filtration time, in L.m-2.h-1 unit. The water flux was calculated by the following equation (1):
(1)
Where J is the permeation flux of the membrane for pure water (L.m-2.h-1), V is the permeate volume measured (L), A is the effective membrane area (m2) and t is the permeation time (hour).
Heavy metals and dyes removal
The membranes were characterized by rejection of salt solutions, removal of heavy metals and dyes rejection. The separation performance tests were carried out with a 50 ppm of heavy metal (Pb(NO3)2, Cr(NO3)2, Cd(NO3)2, HgCl2) under 0.5 MPa operating pressures. The methylene blue (MB) and methyl orange (MO) rejections were recorded using a UV spectrophotometer PG (china) with 1 cm quartz cell. The concentration of metal ions in the aqueous solutions was determined using a Shimadzu AA-670 atomic absorption spectrophotometer with a hallow cathode lamp using an air–acetylene flame.
The rejection R (%) was calculated by using equation (2):
(2)
Where Cp and Cf are the concentration of permeate and feed solutions, respectively.
Antifouling properties
Dynamic fouling test for the prepared membranes was conducted using, bovine serum albumin (BSA) solution in PBS (100 ppm, 50 mM, pH=7) buffer. Each membrane was pressed for an initial 20 min at 0.4 MPa. Pure water flux of the membrane, Jw1 (L.m-2h-1), was determined over a period of 1 minute. After that, BSA was fed inside cell to be passed through the membrane for 30 minute. Then the membrane was washed with water and pure water flux Jw2 (L.m-2.h-1) was measured again. Finally, the membrane antifouling property was determined which named flux recovery ratio (FRR) according to Equation (3):
(3)
To assess static protein adsorption of the membranes, surface of samples washed with phosphate buffered saline (PBS) solution for 2 hour and then put into tubes filled with BSA in PBS solution (5 ml of 100ppm). These tubes were put on water bath for 24 hour at 30ºC to reach equilibrium. The amount of protein adsorbed on the membrane was calculated by adsorption intensity of solutions at 280 nm (recorded by a UV–Vis spectrometer).
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Results
|
Figure 1 indicates the IR spectrum of the synthesized Zn-BDC. Also, the XRD patterns for zinc MOFs are presented in Figure 2.
Figure 1) FT-IR spectra of MOFs
Figure 2) XRD diagrams for the prepared MOFs
Scanning electron micrograph of MOFs is presented in Figure 3. Scanning electron microscopy is a technique that enables the study of the microstructure of nanoparticles of matter.
Figure 3) FE-SEM images of the MOFs
To study the effect of MOFs on morphological changes of the membranes, the cross-sectional morphology w:as char:acterized using FE-SEM as shown in Figure 4. The effect of additive content on the membrane structure has been investigated using SEM analysis.
Figure 4) FE-SEM images of the cross section of membrane Neat (a), 3 wt% (b), 5 wt% (c), 7 wt% (d) from additive according Table 1.
The permeated water flux through unmodified and modified membranes are shown in Figure 5 for different contents of additive to understand the effect of additives on membrane permeation, and mass transfer. It is seen that the highest mass transfer flux has been obtained for the membrane prepared with 7 wt. % of additive.
Figure 5) The pure water flux of PES composite membranes containing different percent of MOFs as additive in 5 bar pressure operating.
The fouling properties of the prepared membranes as well as the effect of MOFs percentage on flux recovery ratio, and adsorption intensity are listed in Table 2.
Figure 5) The pure water flux of PES composite membranes containing different percent of MOFs as additive in 5 bar pressure operating.
The fouling properties of the prepared membranes as well as the effect of MOFs percentage on flux recovery ratio, and adsorption intensity are listed in Table 2.
Table 2) Flux recovery ratio (FRR) and static protein adsorption for the prepared membranes
| adsorption intensity (UV) | Flux recovery ratio (%) | Jw2(L.m-2.h-1) | Jw1(Lm-2.h-1) | Membrane |
| 0.071 | 43.4 | 41.6 | 95.8 | Neat PES |
| 0.079 | 73.7 | 85.2 | 115.6 | 3 wt.% MOFs |
| 0.087 | 78.3 | 125.3 | 160.1 | 5 wt.% MOFs |
| 0.082 | 70.8 | 134.2 | 189.7 | 7 wt.% MOFs |
The efficiency of membrane processes in removing of Pb+2, Cd+2, Cr+2 and Hg+2 from wastewater are represented in Figure 6.
Figure 6) Performance of membrane in rejection of Heavy metal solutions including Pb+2, Cd+2, Cr+2 and Hg+2.
Figure 7 depicts the dye removal efficiency of the membranes for methylene blue (MB) and methyl orange (MO) organic dyes solution as a function of additive percentage.
Figure 7) Dye rejection including (MO and MB) by unmodified and modified PES membranes.
|
Discussion
|
Structural analysis
According to Figure 1, the IR spectrum of the synthesized Zn-BDC is dominated by the bands associated with organic part. In the paddlewheel structure, the carboxylate ion is coordinated to two Zn atoms and made a unit cell of crystal. The intense bands at 1418.80 cm-1 appear in the spectrum which confirms the paddle-wheel type unit of MOF. IR spectra of MOF-5 show the expected strong characteristic adsorptions for the symmetric and asymmetric vibrations of BDC (1642.77, 1025.36 and 1418.80 cm-1) and adsorbed water (3,500–3,200 cm-1) (40).
X-ray diffraction (XRD) is an effective method to investigate crystalline properties of a synthesized material. According to Figure 2, the extremely high intensities of the diffraction peaks indicate the good crystallinity of sample. The peak of highest intensity in image at 2θ= .5ᵒ is indexed as the d200 for zinc metals (40, 41).
The SEM micrograph (Figure 3) show distribution of particles in MOFs as clusters of irregular shaped flakes arranged as flower-like clusters. SEM of MOFs, Figure 3 at the magnifications shown, show irregular flake particles. A high magnification Figure 3 confirm these flakes-like particles having irregular shapes (42).
Membrane morphology
As shown in Fig. 4, a finger-like structure was formed when NMP/water was used as the solvent/nonsolvent pair with PES. The hydrophilic nature of MOFs increased the mass transfer rate between the solvent and the nonsolvent during phase inversion process and led to the formation of larger pore channels.
This further demonstrated that addition of MOFs changed the structure of membrane. Gradually, it can be said that the presence of a large amount of MOFs caused a remarkable hydrophilicity improvement in the prepared membranes and increased permeation rate of water molecules into the cast solution.
Membrane Performance
Pure water fluxes
The achieved improvement in hydrophilicity (discussed later) was due to the presence of MOFs. As shown in Figure 5, water flux through unmodified and modified membranes were changed by increasing MOFs as an additive up to 7 wt%. For 5 bar pressure, the maximum and minimum rates of pure water flux was observed in 7 wt% MOFs and neat PES, respectively. This behavior could be explained in this manner which by increasing of polymer concentration in membrane formulation, the pore size of membrane decreased strongly. On the other hand, addition of MOFs amount in membrane causes larger channels, more porosity and subsequently makes them more hydrophilic in nature (43).
In this study, the fouling properties of membranes and the effect of MOFs on fouling, the dynamic fouling analysis (flux recovery ratio), static fouling analysis (surface protein adsorption) and rejection tests were done for prepared membrane. (Table 2). It was found that, the flux recovery ratio (FRR) increased from 43.4 % to 78.3%, when weight percent of MOFs increased from 0 to 5 wt.%, while for membranes with 7 wt.% MOFs obtained FRR (%) was 70.8%. This finding can be related to different parameters such as surface hydrophilicity and roughness. Surface roughness can play a key role due to protein molecules irreversible deposition into the surface pores. Static protein adsorption on the membranes surface decreased, which is in good agreement with FRR results and only a decrease was observed for membrane with 7 wt.% MOFs likely due to surface roughness which caused more adsorption of BSA.
The initial concentration of the used heavy metals for these experiments (Pb(NO3)2, Cd(NO3)2, Cr(NO3)2 and HgCl2) was 50 ppm of metal ions. The percentage of heavy metal rejection improved by increasing additive (MOFs) from 0 to 5 wt%, while with further increase of MOFs in the membrane matrix, the removal of heavy metals decreased (see Figure 6). As mentioned in the previous section, two parameters (pore size and the extent of interaction between metal ions and functional groups on the MOFs surface) acted in the opposite direction (44). Therefore, it can be argued that the initial increase in rejection was due to more and stronger interactions; however, at higher percentage of additive, strengthening of the pore size is weakened the interactions effect, thus rejection of heavy metals decreased.
The rejection of dyes was measured using a lab scale nanofiltration cell (operating pressure= 0.5 MPa, pH=7.0 and the dye concentration= 100 mg/L). As it can be observed in Figure 7, the MO rejection was more than the MB for all of the prepared membranes. As shown in Figure 7, the rejection performance in all of the MOFs modified membranes was better than the neat PES membrane that confirmed the effective filtration performance of the prepared nanocomposite membranes. The better rejection efficiency of the modified mixed matrix membranes can be related to the repulsion forces between negative surface of the membranes and negatively charged surface in the dye molecules (45). In other words, it can be concluded that rejection was improved by addition of MOFs to 5 wt.% and then decreased which could be related to contrast between pore size and the extent of interactions. The prepared mixed matrix membranes were negatively charged due to the presence of several carboxylic functional groups from MOFs additive. Increasing MOFs additive concentration from 1 wt.% to 5 wt.% improved dye removal while higher percentage of MOFs decreased removal efficiency slightly. This may be due to an increase in surface negative charge by MOFs to 5 wt% but higher percentage of MOFs increased the pore diameter of the membrane and reduced removal efficiency. The results were in agreement with heavy metal removal and the highest dye removal was observed for the sample with 5 wt% MOFs additive concentration.
|
Conclusion
|
In this study, metal organic frameworks (MOFs) was synthesized via the hydrothermal technique. This MOFs as additive was incorporated to the mixed matrix membrane. The surface and cross-section morphology of MOFs and the neat and the modified membranes were investigated by FE-SEM. Effect of MOFs on the performance’s properties (heavy metals and dye removal) was investigated. Base on the results, hydrophilicity, water flux, and antifouling properties were improved by hybrid membranes. Addition of MOFs also improved the rejection of heavy metal and dyes more efficiently than neat PES membrane and membrane with 5 wt.% of MOFs suggested better properties. Additionally excellent heavy metal separation behavior was observed among rejection tests.
|
Footnotes
|
Conflict of Interest:
The authors declared no conflict of interest.
References
1. 1. Schwarzenbach RP, Escher BI, Fenner K, Hofstetter TB, Johnson CA, von Gunten U, et al. The challenge of micropollutants in aquatic systems. New York: Science; 2006. p. 313,1072-1077. Link [DOI:10.1126/science.1127291]
2. Marjani A, Shirazi Y, Shirazian S. Investigation on the best conditions for purification of multiwall carbon nanotubes, Asian J Chem 2011;23(7):3205-7. Link
3. Mahmoudi E, Ng LY, Ba-Abbad MM, Mohammad AW. Novel nanohybrid polysulfone membrane embedded with silver nanoparticles on graphene oxide nanoplates, Chem Eng J 2015;277:1-10. Link [DOI:10.1016/j.cej.2015.04.107]
4. Marjani A, Shirazian S, CFD simulation of dense gas extraction through polymeric membranes. World Academy Sci Eng Technol 2010;4(1):127-31. Link
5. Marjani A, Shirazian S. Simulation of heavy metal extraction in membrane contactors using computational fluid dynamics. Desalination 2011;281:422-428. Link [DOI:10.1016/j.desal.2011.08.032]
6. Marjani A, Shirazian S. Hydrodynamic investigations on heavy metal extraction in membrane extractors. Oriental J Chem 2011;27(4):1311-6. Link
7. Marjani A, Shirazian S. Investigation on numerical simulation of acetone and ethanol separation from water by using membrane. Asian J Chem 2011;23(7):3293-4. Link
8. Marjani A, Shirazian S. Computational fluid dynamics simulation of ammonia removal from wastewaters by membrane. Asian J Chem 2011;23(7):3299-300. Link
9. Marjani A, Shirazian S. Investigation on copper extraction using numerical simulation. Asian J Chem 2011;23(7):3289-3290. Link
10. Moghadassi A, Marjani A, Shirazian S, Moradi S. Gas separation properties of hollow-fiber membranes of polypropylene and polycarbonate by melt-spinning method. Asian J Chem 2011;23(5):1922-1924. Link
11. Sohrabi MR, Marjani A, Moradi S, Davallo M, Shirazian S. Theoretical studies on membrane-based gas separation using Computational Fluid Dynamics (CFD) of mass transfer. J Chem Soc Pakistan 2011;33(4):464-73. Link
12. Sohrabi MR, Marjani A, Moradi S, Davallo M, Shirazian S. Preparation and simulation of polycarbonate hollow-fiber membrane for gas separation. Asian J Chem 2011;23(1):302-304. Link
13. Sohrabi MR, Marjani A, Shirazian S, Moradi S. Simulation of ethanol and acetone extraction from aqueous solutions in membrane contactors. Asian J Chem 2011;23(9):4229-30. Link
14. A Marjani, Mohammadi P, Shirazian S. Preparation and characterization of poly (vinyl alcohol) membrane for pervaporation separation of water-organic mixtures. Orient J Chem 2012;28(1):97-102. Link [DOI:10.13005/ojc/280114]
15. Marjani A, Shirazian S. Theoretical studies on copper extraction by means of polymeric membrane contactors. Orient J Chem 2012;28(1):23-28. Link [DOI:10.13005/ojc/280104]
16. Marjani A, Shirazian S. Mathematical modeling and cfd simulation of hydrocarbon purification using membrane technology. Orient J Chem 2012;28(1):123-129. Link [DOI:10.13005/ojc/280118]
17. Marjani A, Shirazian S. Modeling of organic mixtures separation in dense membranes using finite element method (FEM). Orient J Chem 2012;28(1):41-46. Link [DOI:10.13005/ojc/280106]
18. Marjani A, Shirazian S. CFD simulation of mass transfer in membrane evaporators for concentration of aqueous solutions. Orient J Chem 2012;28(1):83-87. Link [DOI:10.13005/ojc/280112]
19. Marjani A, Shirazian S. Application of CFD Techniques for Prediction of NH3 transport through porous membranes. Orient J Chem 2012;28(1):67-72. Link [DOI:10.13005/ojc/280110]
20. Marjani A, Shirazian S, Ranjbar M, Ahmadi M. Mathematical modeling of gas separation in flat-sheet membrane contactors. Orient J Chem 2012;28(1):13-18. Link [DOI:10.13005/ojc/280102]
21. Pishnamazi M, Marjani A, Shirazian S, Samipurgiri M. Mathematical modeling and numerical simulation of wastewater treatment unit using CFD. Orient J Chem 2012;28(1):51-58. Link [DOI:10.13005/ojc/280108]
22. Shirazian S, Marjani A, Rezakazemi M. Separation of CO2 by single and mixed aqueous amine solvents in membrane contactors: Fluid flow and mass transfer modeling. Eng Comput 2012;28(2):189-198. Link [DOI:10.1007/s00366-011-0237-7]
23. Shirazian S, Pishnamazi M, Rezakazemi M, Nouri A, Jafari M, Noroozi S, et al. Implementation of the Finite Element Method for Simulation of Mass Transfer in Membrane Contactors. Chem Eng Technol 2012;35(6):1077-1084. Link [DOI:10.1002/ceat.201100397]
24. Shirazian S, Rezakazemi M, Marjani A, Moradi S. Hydrodynamics and mass transfer simulation of wastewater treatment in membrane reactors. Desalination 2012;286:290-295. Link [DOI:10.1016/j.desal.2011.11.039]
25. Meng N, Wang Z, Low Z-X, Zhang Y, Wang H, Zhang X. Impact of trace graphene oxide in coagulation bath on morphology and performance of polysulfone ultrafiltration membrane. Sep Purif Technol 2015;147:364-371. Link [DOI:10.1016/j.seppur.2015.02.043]
26. Khan A, Sherazi TA, Khan Y, Li S.A.R. Naqvi, Z. Cui. Fabrication and characterization of polysulfone/modified nanocarbon black composite antifouling ultrafiltration membranes. J Membrane Sci 2018;554:71-82. Link [DOI:10.1016/j.memsci.2018.02.063]
27. Liu Z, Mi Z, Chen C, Zhou H, Zhao X, Wang D. Preparation of hydrophilic and antifouling polysulfone ultrafiltration membrane derived from phenolphthalin by copolymerization method. Appl Surf Sci 2017;401:69-78. Link [DOI:10.1016/j.apsusc.2016.12.228]
28. Janiak C, Vieth JK. MOFs, MILs and more: concepts, properties and applications for porous coordination networks (PCNs). New J Chem 2011;11:2366-2388. Link [DOI:10.1039/c0nj00275e]
29. Vakili R, Xu S, Al-Janabi N, Gorgojo P, Holmes SM, Fan X. Microwave-assisted synthesis of zirconium-based metal organic frameworks (MOFs): Optimization and gas adsorption. Microporous Mesoporous Mater 2018;260:45-53. Link [DOI:10.1016/j.micromeso.2017.10.028]
30. Kang Y-S, Lu Y, Chen K, Zhao Y, Wang P, Sun W-Y. Metal-organic frameworks with catalytic centers: From synthesis to catalytic application. Coordination Chem Rev 2019;378:262-280. Link [DOI:10.1016/j.ccr.2018.02.009]
31. Gharib M, Safarifard V, Morsali A. Ultrasound assisted synthesis of amide functionalized metal-organic framework for nitroaromatic sensing. Ultrason Sonochem 2018;42:112-118. Link [DOI:10.1016/j.ultsonch.2017.11.009]
32. Duan C, Li F, Luo S, Xiao J, Li L, Xi H. Facile synthesis of hierarchical porous metal-organic frameworks with enhanced catalytic activity. Chem Eng J 2018;334:1477-1483. Link [DOI:10.1016/j.cej.2017.11.086]
33. Gholami F, Zinadini S, Zinatizadeh AA, Abbasi AR. TMU-5 metal-organic frameworks (MOFs) as a novel nanofiller for flux increment and fouling mitigation in PES ultrafiltration membrane. Sep Purif Technol 2018;194:272-280. Link [DOI:10.1016/j.seppur.2017.11.054]
34. Abney CW, Gilhula JC, Lu K, Lin W. Metal-Organic Framework Templated Inorganic Sorbents for Rapid and Efficient Extraction of Heavy Metals. Adv Mater 2014;26 (47):7993-7997. Link [DOI:10.1002/adma.201403428]
35. Rudd ND, Wang H, Fuentes-Fernandez EMA, Teat SJ, Chen F, Hall G, Chabal YJ, Li J. Highly Efficient Luminescent Metal-Organic Framework for the Simultaneous Detection and Removal of Heavy Metals from Water. ACS Appl Mater Interfaces 2016;8 (44):30294-30303. Link [DOI:10.1021/acsami.6b10890]
36. Mansourpanah Y, Amiri Z. Preparation of modified polyethersulfone nanoporous membranes in the presence of sodium tripolyphosphate for color separation; characterization and antifouling properties. Desalination 2014;335(1):33-40. Link [DOI:10.1016/j.desal.2013.12.008]
37. Wang Y, He G, Shao Y, Zhang D, Ruan X, Xiao W, et al. Enhanced performance of superhydrophobic polypropylene membrane with modified antifouling surface for high salinity water treatment. Sep Purif Technol 2018;214:11-20. Link [DOI:10.1016/j.seppur.2018.02.011]
38. Lai GS, Yusob MHM, Lau WJ, Gohari RJ, Emadzadeh D, Ismail AF. Novel mixed matrix membranes incorporated with dual-nanofillers for enhanced oil-water separation. Sep Purif Technol 2017;178:113-121. Link [DOI:10.1016/j.seppur.2017.01.033]
39. Vatanpour V, Madaeni SS, Rajabi L, Zinadini S, Derakhshan AA. Boehmite nanoparticles as a new nanofiller for preparation of antifouling mixed matrix membranes. J Membr Sci 2012;401-402:132-143. Link [DOI:10.1016/j.memsci.2012.01.040]
40. Zhang S-Y, Li D, Guo D, Zhang H, Shi W, Cheng P, et al. Synthesis of a chiral crystal form of MOF-5, CMOF-5, by chiral induction. J Am Chem Soc 2015;137(49)15406-15409. Link [DOI:10.1021/jacs.5b11150]
41. Tranchemontagne DJ, Hunt JR, Yaghi OM. Room temperature synthesis of metal-organic frameworks: MOF-5, MOF-74, MOF-177, MOF-199, and IRMOF-0. Tetrahedron 2008;64(36):8553-8557. Link [DOI:10.1016/j.tet.2008.06.036]
42. Zhu L, Jia X, Bian H, Huo T, Duan Z, Xiang Y, Xia D. Structure and adsorptive desulfurization performance of the composite material MOF-5@ AC, New J Chem 2018;42:3840-3850. Link [DOI:10.1039/C7NJ04192F]
43. Dechnik J, Nuhnen A, Janiak C. Mixed-Matrix Membranes of the Air-Stable MOF-5 Analogue Co4 (μ4-O)(Me2pzba) 3. with a Mixed-Functional Pyrazolate-Carboxylate Linker for CO2/CH4 Separation. Cryst Growth Des 2017;17(8):4090-4099. Link [DOI:10.1021/acs.cgd.7b00202]
44. Rao Z, Feng K, Tang B, Wu P. Surface Decoration of Amino-Functionalized Metal-Organic Framework/Graphene Oxide Composite onto Polydopamine-Coated Membrane Substrate for Highly Efficient Heavy Metal Removal. ACS Appl Mater Interfaces 2017;9(3):2594-2605. Link [DOI:10.1021/acsami.6b15873]
45. Sani N, Lau W, Ismail A. Polyphenylsulfone-based solvent resistant nanofiltration (SRNF) membrane incorporated with copper-1, 3, 5-benzenetricarboxylate (Cu-BTC) nanoparticles for methanol separation. RSC Adv 2015;17:13000-13010. Link [DOI:10.1039/C4RA14284E]
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