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Article

A High-Permeance Organic Solvent Nanofiltration Membrane via Polymerization of Ether Oxide-Based Polymeric Chains for Sustainable Dye Separation

by
Beibei Zhang
1,
Chunhai Yi
2,*,
Dongyun Wu
2,
Jie Qiao
2 and
Lihua Zhang
1,*
1
Shaanxi Province Key Laboratory of New Drugs and Chinese Medicine Foundation Research, Pharmacy College, Shaanxi University of Chinese Medicine, Xianyang 712046, China
2
Shaanxi Key Laboratory of Energy Chemical Process Intensification, School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an 710049, China
*
Authors to whom correspondence should be addressed.
Sustainability 2023, 15(4), 3446; https://doi.org/10.3390/su15043446
Submission received: 1 December 2022 / Revised: 16 January 2023 / Accepted: 5 February 2023 / Published: 13 February 2023
(This article belongs to the Section Resources and Sustainable Utilization)
Browse Figures
Versions Notes

Abstract

:
The widely used dyes in the pharmaceutical, chemical, and medical industries have brought about an intensive concern for the sustainable development of the environment. Membrane separation offers a versatile method for classified recycling and the reuse of residual components. In this work, polyimide membranes were synthesized via the polymerization of 4,4′-(hexafluor-isopropylidene) diphthalic anhydride and 1,4-bis (4-aminophenoxy) benzene diamine. The organic solvent nanofiltration membrane was prepared by casting onto a glass plate and precipitating in the non-solvent phase. The properties of the membranes were recorded by FTIR, 1HNMR, TGA, and GPC. The molecular simulations were carried out to analyze the affinity between the membrane and different solvents. The membrane was used in the removal of Rose Bengal, methyl blue, Victoria blue B, and crystal violet from methanol. The effects of the feed liquid concentration, operating pressure, swelling degree, organic solvent resistance, and long-term running on the membrane performance were studied. Results showed that membranes prepared in this work demonstrated high solvent permeation and dye rejection due to the sieving effect and solvent affinity. For methyl blue, the solvent performance achieved a permeability of 2.18 L∙m−2∙h−1∙bar−1 corresponding to a rejection ratio of 94.2%. Furthermore, the membrane exhibited good stability over 60 h of continued testing. These results recommend a potential strategy in the development of a suitable monomer to prepare a polyimide membrane for dye separation.

1. Introduction

The high development of the chemical, petroleum, and pharmaceutical industries has caused serious environmental pollution [1,2,3]. It was reported that approximately 700,000 tons of dyes are produced annually and almost 5% of dyes are discharged into the environment [4]. For example, the emission of dyes from the textile process induces the eutrophication and disturbance of aquatic life [5]. Therefore, dye pollution in wastewater or organic solvent must be restrained to realize the sustainable development of the environment [6,7].
Recently, nanofiltration separation has presented great advantages in the rejection of dyes from organic solvents [8,9] and has been successfully used as an alternative for wastewater purification. Dye separation relies on the molecular size, steric hindrance, and Donnan exclusion [7,10,11]. Li et al. [12] fabricated nanofiltration membranes using PEEK as the matrix modified with polar ether groups. The ether groups endowed the membrane with ultra-wettability and excellent stability in the organic solvents. Bruggen et al. [13] studied a series of nanofiltration membranes (NF70, NTR7450, UTC-20, Zirfon@VITO) for dye separation where the results showed that the charge effect dominated the sieving process when the dyes were much smaller than the size of the membrane pores. However, the influence of charge on the performance was reduced when the dyes had an approximate size with the membrane pore size. Abdulhamid et al. [14,15] prepared organic solvent nanofiltration (OSN) membranes using PEEK as a parent matrix. The results showed that the solvent permeance increase was significantly related to their binding energy. The polar solvent molecule exhibited a higher binding interaction and permeance than the non-polar solvent molecule.
The ideal membrane separation material is expected to have remarkable performance in solvent flux and dye rejection. It should also have excellent mechanical strength and permeability stability [16,17]. Therefore, the design and development of new membrane with superior comprehensive performance for dye separation is still a challenge [18,19].
Aromatic polyimide membrane materials have great potential for industrial wastewater separation [20,21,22] and are synthesized using diamine and dianhydride via polycondensation and chemical imidization. The versatile designable structure could endow membranes with different properties by changing different monomers or groups. Feng et al. [23] modified commercial polyimide membranes by the heating treatment. The evolution groups from benzyl to benzene carbonyl tune the microstructure of the membranes, which lead to a superior performance. The ethanol permeability of the polyimide membrane achieved 0.76 L·m−2·h−1·bar−1 along with premium sieving for small molecules. Farahani et al. [24,25] fabricated P84 polyimide nanofiltration membranes for dye separation, which showed a molecular weight cut-off (MWCO) of 390 Da. The membrane achieved an ethanol permeance of about 2.8 L·m−2·h−1·bar−1 with 98% Rose Bengal rejection. Gao et al. [26] prepared polyimide membranes using Matrimid®5218 (BASF, Ludwigshafen, Germany) to separate dyes with different molecular sizes. The results demonstrated a high-performance of isopropanol (IPA) permeance of 21.37 L·m−2·h−1·bar−1 and a RB rejection of 70.41%.
The above studies showed that the solvent separation performance was closely related to the membrane material, dyes, and solvent properties. It inspired us to develop a membrane material by making full use of its membrane–dye–solvent affinity, hydrophilicity, hydrogen bonding interaction, and charge interaction. Herein, we designed a polyimide membrane through the incorporation of the ether oxide-containing monomer into polymer chains, which was expected to provide the membrane with a versatile tunning function. The fluorine (–CF3) containing diacid anhydride was used as another monomer due to its large bulk steric hindrance. The characterization by FTIR, 1HNMR, TGA, and GPC was measured to investigate the structure and properties of the membrane. Four types of dyes containing Rose Bengal 94 (RB, 1017 Da), methyl blue (MB, 799.8 Da), Victoria blue B (VBB, 506.1 Da), and crystal violet (CV, 408 Da) were employed to understand the solvent permeance and dye rejection of the membrane. In addition, the various influences containing the feed concentration, operating pressure, swelling degree, organic solvent resistance, and long-time running on the dye separation performance of the membrane were systematically studied. The developed polyimide material demonstrated a new design mentality for the OSN membrane with enhanced separation performance.

2. Materials and Methods

2.1. Chemicals

Dianhydride (6FDA) and diamine (BAP) were bought from J&K Scientific Co. Ltd. (Beijing, China). N,N-dimethylformamide (DMF), triethylamine (TEA), methanol (MeOH), and iso-propyl alcohol (IPA) were obtained from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Acetic anhydride (Ac2O) was produced by Xilong Scientific Co. Ltd. (Shantou, China). The dyes of Rose Bengal (1017 Da), methyl blue (MB, 799.8 Da), Victoria blue B (VBB, 506.1 Da), and crystal violet (CV, 408 Da) were purchased from Shanghai Macklin Biochemical Co. Ltd. (Shanghai, China). The intuitive ball-stick model of the dyes are shown in Figure 1.

2.2. Membrane Preparation

The polyimide material was synthesized as per our previous work [27,28]. First, equimolar 6FDA and BAP were added into DMF, forming a homogeneous solution. The viscous polyamide acid (PAA) solution was obtained after being continuously stirred under N2 purge for 24 h. Second, the transparent solution was subjected to the catalysis of triethylamine. To obtain high molecular weight polyimide chains, the Ac2O was added as the dehydrating agent. Finally, the white fibrous polyimide was precipitated in the amount of methanol. The obtained white fibrous material was collected by the following steps: (1) filtration; (2) washed with methanol; and (3) drying in a vacuum oven. The synthesis route of the polyimide material is described in Scheme 1.
The OSN membrane was prepared through casting and immersed phase inversion. First, the synthesized polyimide fibers were dissolved into DMF with a mechanical stirrer at room temperature. Then, the polyimide solution was filtered and cast flattened on a plate, followed by immersion in a non-solvent. The membrane was peeled off and soaked in a solution consisting of PEG400/IPA (60:40 wt%) overnight. Finally, the fresh membrane was dried to remove any residual solvents and subjected to a thermal annealing treatment for further testing. The preparation of the polyimide nanofiltration membranes is shown in Figure 2.

2.3. Characterization

FTIR was used to analyze the chemical bond and group through an iS50 (Thermo Fisher Scientific, NICOLET, Townsend, MA, USA) instrument. 1HNMR spectroscopy was recorded to confirm the structure of the polyimide membrane using a Bruker Avance 600 MHz Spectrometer instrument. Chloroform (CDCl3-d6) was adopted as the solvent. TGA curves were conducted on STA 449F5 (NETZSCH, Waldkraiburg, Germany) under a N2 covered flow. Gel permeation chromatograph (GPC) was performed with a DAWN HELEOS-II (Wyatt, Santa Barbara, CA, USA) instrument with DMF as the eluent. Ultraviolet spectrophotometer (UV) was performed on an UV-1800 (Shimadzu, Kyoto, Japan) instrument.

2.4. Membranes Performance Testing

Separation Testing: The separation evaluation was conducted using an apparatus built in-house (Figure 3). First, each prepared sample was mounted and flattened into the cell with a solvent pre-pressure. Afterward, these membranes were subjected to different concentrations of dye solution for testing. The concentration of dye was detected by a UV instrument. The membrane flux J at pressure P was calculated from Equation (1) [29,30]:
J = V A × T × P
where J refers to the flux of each sample (L·m−2·h−1·bar−1); V refers to the solvent permeation volumetric flow rate (m3) at time (h); A is the effective area of testing membrane (m2); P is the operating pressure (bar).
The dye rejection (R) was calculated as per Equation (2) [31]:
R = 1 − C p C f × 100 %
where R represents the dye rejection of the sample (%); Cp refers to the concentration of the permeate side (mg·L−1); Cf refers to the concentration of the feed side (mg·L−1).
Membrane Swelling Test: The whole procedure of the swelling test was carried out at a constant temperature (~30 °C). All samples were dried in a vacuum oven overnight. Afterward, these samples were soaked in different solvents for 60 h. In this work, four different types of organic solvents containing n-hexane, toluene, ethyl acetate, and ethanol were chosen for investigation. The membrane swelling degree was quantitatively evaluated using Equation (3) [32]:
S D = W 1 − W 2 W 1
where SD represents the swelling degree (%); W1 is the weight of membrane before soaking in the solvent (mg); W2 is the weight of the membrane after being saturated in the solvent (mg).

2.5. Molecular Simulation

Molecular simulation was carried out to analyze the microstructure of the membranes as it could provide insights into analyzing the properties of the membrane material such as the energy change, inter- and intra- molecular force, van der Waals energy, etc. Recently, molecular simulation has expressed advances in predicting the separation process, especially for the binding energy evaluation and solvent transport [33,34]. The molecular simulation was carried out using the Material Studio 8.0 software package with the COMPASS force field analysis. The polymer chains were constructed by connecting the repeat unit of dianhydride (6FDA)-diamine (BAP). Then, hydrogen atoms were automatically calculated and geometry optimization was carried out in these molecular chains. The simulations were conducted in four steps: (1) Construct the monomers (6FDA and BAP) and connect molecular chains; (2) set the head-tail atom and build the homopolymer; (3) construct the amorphous cell following a series of geometric and dynamic balance; and (4) calculate the sorption energy between the polymer chain and different solvents.

3. Results

3.1. Characterization Analysis

Figure 4a exhibits the FTIR characterization results of the membranes. As revealed in Figure 4a, the present C=O vibration was located at 1780 cm−1 and 1720 cm−1 [33]. The aromatic rings in the main chains of the polyimide appeared at the wavenumber of 1500 cm−1 [35]. The stretching peak presented at 1372 cm−1 was due to the C–N bond [36]. The characteristic peak of the –CF3 group in 6FDA was supported by the 1296 cm−1 absorption values. The ether bond stretching vibration appeared at 1050 cm−1. These FTIR spectra of the resulting membrane presented a typical polyimide structure. Figure 4b displays the 1HNMR spectra of the 6FDA/BAP polyimide membrane. The chemical shift peaks located at about 7.8~8.2 ppm was the proton vibration in 6FDA. The proton vibration of BAP diamine was concluded at 7.0~7.5 ppm. Figure 4c illustrates the thermal properties of the polyimide membrane, which showed an excellent thermal stability for the membrane with an initial pyrolysis temperature higher than 200 °C (as shown in the DTG curve). These were higher than the separation demand of the OSN. The GPC results are depicted in Figure 4d, and the high molecular weight for both the average molecular weight (Mw = 2.794 × 106 g·mol−1) and average molecular number (Mn = 1.998 × 106 g·mol−1) was obtained. The polydispersity index (PDI = 1.398) was reasonable for the membrane. The SEM image in Figure 4e,f shows a typical nanofiltration membrane structure.
The exploration of molecular simulations is vital to study the microstructure properties of polymeric materials. The amorphous cell was constructed with a lattice parameter size of 49.80 Å for each side. The sorption affinity between the polymer chains and separate solvents is recorded in Figure 5 where the view of the periodic boundary cell for polymeric sorption with different solvents is presented. The sorption capacities of amorphous cell for toluene, ethyl acetate, ethanol, and n-hexane were 158.66 (8.09 × 10−6·Å−3), 144.10 (8.09 × 10−6·Å−3), 138.58 (8.09 × 10−6·Å−3), and 125.64 (8.09 × 10−6·Å−3), respectively. The larger adsorption amount represented the stronger affinity between the polymer segment and the solvent.

3.2. Performance Testing

3.2.1. The Separation on Different Dyes

The membrane performance testing was evaluated by four different dyes containing RB, MB, VBB, and CV. The testing was carried out at room temperature (20 ppm dye in methanol). The membrane presented a dye rejection of 94.6%, 94.2%, 63.2%, and 58.2% for RB, MB, VBB, and CV, respectively (Figure 6a). The physical and chemical parameters of the dyes are listed in Table 1. As shown in Table 1, MB and CV possessed the same molecular charge but presented different dye rejections. This was due to the difference in the molecular weight. The molecular weight of RB, MB, VBB, and CV were 1017.64 g·mol−1, 799.80 g·mol−1, 506.08 g·mol−1, and 407.98 g·mol−1, respectively, following the order of RB > MB > VBB > CV. The sequence of rejection was in good accordance with their molecular weight, which revealed a typical molecular sieve mechanism. The permeabilities of RB, MB, VBB, and CV solution were 2.05 L∙m−2∙h−1∙bar−1, 2.18 L∙m−2∙h−1∙bar−1, 3.28 L∙m−2∙h−1∙bar−1, and 3.35 L∙m−2∙h−1∙bar−1, respectively (Figure 6b). These solvent permeability trends were contrary to their rejections. MB had the optimum performance for both rejection and permeability among all of these investigated dyes. Therefore, the MB separation was further studied in the following section.

3.2.2. Performance of Different Concentrations

It is essential for nanofiltration membranes to be treated with different dye solutions in practical applications. These membranes were also observed after treatment with different feed concentrations of the dyes. These results are presented in Figure 7. As shown in this figure, the permeability indicated a dramatic reduction with the elevated feed concentration. For example, the MB solution permeability decreased by 46.9% (from 2.18 L∙m−2∙h−1∙bar−1 to 1.16 L∙m−2∙h−1∙bar−1) with the feed concentration elevated from 20 ppm to 120 ppm. However, the dye rejection was almost constant (91.5%~94.2%). This phenomenon was mainly due to the concentration polarization, which appeared most at the membrane separation process. Notably, the permeability decreased about 35.5% (from 60 ppm to 120 ppm), and was higher than the permeability decrement of the increased concentration from 20 ppm to 60 ppm (about 17.4%). This is because the dye was well-dissolved and could easily pass through in the low concentration instead of the high concentration. Therefore, it is more favorable for the separation of low concentration dyes.

3.2.3. Filtration Performance versus Operation Pressure

The membrane performance under different operation pressure was recorded to understand its flux and microstructure stability. The results are shown in Figure 8. The operation pressure of the membrane testing was elevated from 5 bar to 11 bar at room temperature. Obviously, the membrane flux presented a linearly increase at the operating pressure of 5~7 bar. When the operating pressure exceeded 7 bar, the permeate flux of the membrane showed a slight change with the elevated feed side pressure. The presence of different slopes can be attributed to the compaction effect [39]. The nanofiltration membrane has abundant porous structure, so the increased feed pressure would cause an extrusion deformation within the membrane [40]. Consequently, it would lead to a reduction in the porosity diameter and flux.

3.2.4. Swelling Degree and Solvent Resistance of Nanofiltration Membrane

The solvent flux of the membrane for ethanol, toluene, ethyl acetate, and n-hexane expressed a difference over time. The solvent flux of the membrane was related to their viscosity, kinetic diameter, and polarity [41]. The solvent properties are listed in Table 2. As shown in the table, n-hexane had the lowest viscosity and relative polarity, and it achieved the highest solvent flux. The solvent permeance followed the order of n-hexane > ethanol > ethyl acetate > toluene. Toluene had the largest kinetic diameter, which led to the lowest solvent flux. A comprehensive affinity between the solvent and membrane was also systematically studied. The swelling degree testing meaningfully expressed the stability of the polyimide membrane. The swelling degrees of the polymeric membrane were investigated. Four different organic solvents were selected in this experiment: ethanol, toluene, ethyl acetate, and n-hexane.
The samples were soaked into different organic solvents for 60 h with continuous immersion to calculate its swelling degree. As shown in Figure 9a, the highest swelling degree was recorded in toluene (about 130%) and ethyl acetate (80%). However, the membrane swelling with ethanol (60%) and n-hexane (30%) was relatively low. The higher swelling degree in toluene was mainly attributed to the high-affinity between the polymer chains and solvent, which was confirmed by the result of the molecular dynamic simulations (as shown in Figure 5). The affinity was in the sequence of toluene > ethyl acetate > ethanol > n-hexane. This means that the toluene molecule can be easily adsorbed into the polymer chains, which leads to a relatively higher swelling degree. Figure 9b show the permeability results of the membrane after immersion in four different solvents over time. Obviously, the membrane permeability was decreased with the extension of the immersion time regarding all of these solvents. The sequence of the sorption capacities was in good accordance with that of their swelling degree. The swelling degree exerted the large influence on the permeability. For example, the permeability of the membrane decreased by 67% and 63.3% in toluene and ethyl acetate, respectively. However, the membrane permeability decreased only by 28.2% and 15.6% after immersion in ethanol and n-hexane, respectively. It was speculated that the porosity changes after swelling. Membranes with high swelling would cause a high distortion degree for the macropore structures. Therefore, the membrane presented a deficient solvent resistance for this penetrant. Wang et al. [46] prepared an OSN membrane using a P84 polyimide matrix by the phase separation method. It was spun to prepare a hollow fiber membrane for the separation of Rhodamine B. The crucial factor of solvent resistance on the membrane was studied. The results showed that the permeance was decreased with a further increasing swell (in DMF) and an extension in the immersion time. This trend of membrane performance was similar to our results.

3.2.5. Long Time Stability Test

Long-term testing was further evaluated to explore the membrane stability. The membrane was tested by being subjected to 20 ppm solutions (MB in methanol) for a total of about 60 h. As shown in Figure 10, the permeance of the membrane displayed a slight decrease in the initial 10 h and then gradually tended to be flat. The flux achieved 1.25 L∙m−2∙h−1∙bar−1 after 60 h of continuous testing. This was because the polymer chains were not in equilibrium as a result of the glassy features. The glassy chains and pore structure gradually reached stabilization over time, which resulted in a chain relaxation, thus causing the decreased performance in permeability [47,48]. In addition, the stacking of the filter layer would induce a concentration polarization over time. In summary, the membranes prepared in this work presented good stability, which was confirmed as a promising separation material for dye separation.

3.2.6. Comparison of the Separation Performance with Reported Research

The separation performance of this work and the related polyimide membrane for OSN are summarized in Table 3. The polyimide membrane prepared in this work presented superiority in both the permeability and rejection. As listed in this table, compared with the most widely used commercial material and analogous membrane materials, the membrane fabricated in this study showed higher permeability and had great potential for dye separation [40,44,49,50,51,52,53,54,55,56,57,58,59]. Hence, it is a promising material for organic solvent nanofiltration.

4. Conclusions

In this work, a polyimide membrane was synthesized for OSN. Characterizations of the material through FTIR, 1HNMR, TGA, and GPC provided insights into the membrane structure and properties. The effects of the dye types, feed concentration, operation pressure, swelling degree, and long-term running stability of the polyimide nanofiltration membrane were studied. The rejection ratio of dyes was in good agreement with their molecular weight, which showed a sieving mechanism in dye separation. The study also revealed that the membrane is recommended for MB separation, especially with a low concentration of dye. The polyimide membrane exhibited an excellent MB solution permeability of about 2.18 L∙m−2∙h−1∙bar−1, which was superior to most commercial polyimide materials. The solvent permeance of the membrane was proven to increase with the feed liquid pressure. Molecular dynamic simulations showed that the sorption capacities of the amorphous cell for toluene, ethyl acetate, ethanol, and n-hexane were 158.66 (8.09 × 10−6·Å−3), 144.10 (8.09 × 10−6·Å−3), 138.58 (8.09 × 10−6·Å−3), and 125.64 (8.09 × 10−6·Å−3), respectively. The swelling degree was significantly related to the affinity between the polymer chains and solvent molecule, and the membrane exhibited excellent solvent resistance in ethanol or n-hexane. The membrane also exhibited good stability in methanol for more than 60 h of continuous testing.

Author Contributions

Conceptualization, B.Z., C.Y. and L.Z.; Methodology, D.W.; Investigation, D.W. and J.Q.; Data acquisition, B.Z. and J.Q.; Writing, J.Q.; Writing—revising and editing, B.Z., C.Y., and L.Z.; Funding support, C.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the National Key R&D Program of China (2021YFB3801201); the National Natural Science Foundation of China (22108215); and the Education Department of Shaanxi Province (CN) (20JS034). The calculations were performed at the Shenzhen Cloud Computing Center.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available.

Conflicts of Interest

The authors declare no conflict of interest.

Nomenclature

6FDA4,4′-(Hexafluoroisopropylidene) diphthalic anhydride
OSNOrganic solvent nanofiltration
PEEKPoly (ether-ether-ketone)
PAAPolyamide acid
PEGPolyethylene glycol
PIPolyimide
Matrimid@52183,3′,4,4′-Benzophenone tetracarboxylic dianhydride and diaminophenylindane
BAP1,4-Bis (4-aminophenoxy) benzene
PEIPoly(ethylene imine)
P84Polyimide 84
PDIPolydispersity
poly-TaDbPoly(butyl acrylamide-co-divinylbenzene)
PPyPolypyrrole
DDM4,4′-Diaminodiphenylmethane
TMCTrimesoyl chloride
DHAQ2,6-Dihydroxyanthraquinone
RES1,3-Benzenediol, resorcinol monomer
POSSPolyhedral oligomeric silsesquioxane
PANPolyacrylonitrile
PIPPiperazine
XP84Cross-linked polyimide
CACellulose acetate
PDAPolydopamine

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Figure 1. The intuitive model of dyes. (a–d) presents the Rose Bengal, crystal violet, victoria blue B, and methyl blue, respectively.
Figure 1. The intuitive model of dyes. (a–d) presents the Rose Bengal, crystal violet, victoria blue B, and methyl blue, respectively.
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Scheme 1. Preparation procedure of the polyimide nanofiltration membranes.
Scheme 1. Preparation procedure of the polyimide nanofiltration membranes.
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Figure 2. Graphic description of the membrane preparation process.
Figure 2. Graphic description of the membrane preparation process.
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Figure 3. Nanofiltration equipment: (1) nitrogen tank, (2) pressure reducing valve, (3) feed liquid tank, (4) membrane cell, (5) support platform, (6) measuring cylinder.
Figure 3. Nanofiltration equipment: (1) nitrogen tank, (2) pressure reducing valve, (3) feed liquid tank, (4) membrane cell, (5) support platform, (6) measuring cylinder.
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Figure 4. The characterization results of the membranes: (a−f) FTIR spectrum, 1HNMR, TGA curves, GPC scale, SEM image, and enlarge SEMcross section image, respectively.
Figure 4. The characterization results of the membranes: (a−f) FTIR spectrum, 1HNMR, TGA curves, GPC scale, SEM image, and enlarge SEMcross section image, respectively.
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Figure 5. The orthographic view of the sorption capacity between polymeric chains with (a) toluene, (b) ethyl acetate, (c) ethanol, and (d) n-hexane. The 45° perspective view for the sorption capacity between polymeric chains with (e) toluene, (f) ethyl acetate, (g) ethanol, and (h) n-hexane.
Figure 5. The orthographic view of the sorption capacity between polymeric chains with (a) toluene, (b) ethyl acetate, (c) ethanol, and (d) n-hexane. The 45° perspective view for the sorption capacity between polymeric chains with (e) toluene, (f) ethyl acetate, (g) ethanol, and (h) n-hexane.
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Figure 6. The performance of the membrane on different dyes in methanol. (a) Dye rejection, (b) solvent performance.
Figure 6. The performance of the membrane on different dyes in methanol. (a) Dye rejection, (b) solvent performance.
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Figure 7. The relationship between the membrane performance and feed concentration for the MB solution (feed concentration: 20 ppm to 120 ppm).
Figure 7. The relationship between the membrane performance and feed concentration for the MB solution (feed concentration: 20 ppm to 120 ppm).
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Figure 8. OSN performance versus the elevated operation pressure for the MB solution (from 5 bar to 11 bar at room temperature).
Figure 8. OSN performance versus the elevated operation pressure for the MB solution (from 5 bar to 11 bar at room temperature).
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Figure 9. Effect of the swelling degree and solvent resistance on the membrane performance. (a) Swell degree; (b) solvent performance.
Figure 9. Effect of the swelling degree and solvent resistance on the membrane performance. (a) Swell degree; (b) solvent performance.
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Figure 10. Long-time operation stability of the polyimide membrane for MB in methanol (feed concentration: 20 ppm).
Figure 10. Long-time operation stability of the polyimide membrane for MB in methanol (feed concentration: 20 ppm).
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Table
Table 1. The basic physical parameters of the dyes.
Table 1. The basic physical parameters of the dyes.
CodeMolecular FormulaMolecular Weight (g·mol−1)Molecular Charge [37]Molar Volume (cm3·mol−1)
Rose BengalC20H2Cl4I4Na2O51017.64−2272.8
Methyl blueC37H27N3Na2O9S3799.80+1 [38]241.9
Victoria blue BC33H32ClN3506.08--
Crystal violetC25H30N3Cl407.98+1231
Table
Table 2. The basic physical parameters of the solvents.
Table 2. The basic physical parameters of the solvents.
SolventMolecular FormulaMolecular Weight (g·mol−1)Viscosity at 25 °C (mPa·s) [42,43,44]Molar Volume (g·mol−1) [42]Stokes Diameter (nm)Kinetic Diameter (nm) [45]Relative Polarity [45]
TolueneC7H892.150.55106.30.910.550.099
Ethyl acetateC4H8O288.120.4298.50.860.520.228
EthanolC2H6O46.071.0858.50.620.440.654
n-HexaneC6H1486.20.33130.7-0.510.009
Table
Table 3. The comparison of the polyimide membranes in this work with other related membrane materials.
Table 3. The comparison of the polyimide membranes in this work with other related membrane materials.
CodeSeparation DyesPerformance (L∙m−2∙h−1∙bar−1)Rejection (%)Reference
Poly-TaDbBrilliant Blue R (BB, 825.9 g·mol−1), 0.4 MPa1.70>90[49]
PPy/H-PANRose Bengal (1017 g·mol−1) 5 bar, room temperature1.46 (0.79~1.03)>90 (96~98)[50]
DDM-TMC/C-PEIErythrosin B1.05>90[51]
Matrimid 5218 PI dual-layer HFRemazol brilliant blue R (627 g·mol−1)1.596[52]
PEEKWCRose Bengal (1017 g·mol−1)1.690[44]
PAR-DHAQ/PICrystal violet (CV, 408 g·mol−1) 30 bar, 30 °C0.697.7[53]
PAR-RES/PICrystal violet (CV, 408 g·mol−1) 30 bar, 30 °C0.699.7[53]
PA/crosslinked P84 PIStyrene oligomers (236 g·mol−1)1.598[54]
Catechol/POSS/PIRose Bengal2.2384.2[55]
Catechol/PEI/PANBromothymol blue (624 g·mol−1)1.868[56]
Crosslinked polyimide XP84 PIP-0.1%-10minAcid fuchsin (585.5 g·mol−1) 30 °C, 10 bar1.1799.1[57]
Crosslinked polyimide XP84 PIP-0.1%-10min-ACTAcid fuchsin (585.5 g·mol−1) 30 °C, 10 bar1.5999.5[57]
[(PDDA/PAA-CSH)2.5]PFOMethyl blue, 0.4 MPa, 100 mg/L dye/ethanol solution6~68[59]
CAMethyl blue, aq. solution, 25 ppm,4~82[40]
PDA/PIMethyl blue, in ethanol, 5 bar, 25 °C0.9199[58]
BAP/6FDAMethyl blue (20 ppm) 0.7 MPa2.1894.2This work
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Zhang, B.; Yi, C.; Wu, D.; Qiao, J.; Zhang, L. A High-Permeance Organic Solvent Nanofiltration Membrane via Polymerization of Ether Oxide-Based Polymeric Chains for Sustainable Dye Separation. Sustainability 2023, 15, 3446. https://doi.org/10.3390/su15043446

AMA Style

Zhang B, Yi C, Wu D, Qiao J, Zhang L. A High-Permeance Organic Solvent Nanofiltration Membrane via Polymerization of Ether Oxide-Based Polymeric Chains for Sustainable Dye Separation. Sustainability. 2023; 15(4):3446. https://doi.org/10.3390/su15043446

Chicago/Turabian Style

Zhang, Beibei, Chunhai Yi, Dongyun Wu, Jie Qiao, and Lihua Zhang. 2023. "A High-Permeance Organic Solvent Nanofiltration Membrane via Polymerization of Ether Oxide-Based Polymeric Chains for Sustainable Dye Separation" Sustainability 15, no. 4: 3446. https://doi.org/10.3390/su15043446

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