A novel polyethersulfone/modified activated carbon fiber composite membrane: potential for removal micropollutants from water under the electric field

In recent years, the micropollution of sulfanilamide antibiotics (SAs) has occurred frequently. SAs harm human beings by accumulating a specific concentration through the transfer of the biological chain (Chen et al. 2012). Sulfamethoxazole (SMZ) is chemically stable and difficult to biodegrade, which may induce mutated drug-resistant microbes (Pailler et al. 2009). Therefore, it is urgent to research new technologies to remove this micropollutant.

At present, the removal methods of SMZ mainly include the biological method, physical method, and chemical method (Wei et al. 2019). Carbon-based material adsorption and membrane treatment are widely used in the physical method (Şengül et al. 2018). Particularly, activated carbon fibers (ACF) shows the high adsorption rate and excellent adsorption performance because of its small particle diffusion resistance, short adsorption path, and longtime consumption (Zhang et al. 2020). However, the main problem of ACF is its limited hydrophilicity. Therefore, the modification of the ACF has been widely studied. For example, adding chemical groups or loading metals on the surface of ACF can improve the binding efficiency between pollutants and modified activated carbon fiber (MACF) (Liu et al. 2016; Shankar et al. 2017). Moreover, the traditional static adsorption (batch adsorption) has some defects, such as discontinuous adsorption (Stoquart et al. 2012). Therefore, it is essential to modify ACF and integrate it into the membrane to achieve dynamic continuous adsorption (Zhang et al. 2020).

Membrane separation technology has the advantages of high speed, low energy consumption (no phase change), etc. (Lalia et al. 2013). Polyethersulfone (PES) has been currently used as the primary polymer in the fabrication of commercial polymeric ultrafiltration (UF) membranes in water purification and blood purification (Goh et al. 2015). It is a widely used membrane material due to its thermal and mechanical strengths and chemical stability (Alenazi et al. 2019). However, the hydrophobic property of PES is one main drawback that causes a sharp decline of the water flux and shortens membrane lifetime (Aroon et al. 2010). Besides, micropollutants such as SAs were challenging to be retained by UF membranes due to the small molecular weights (Koyuncu et al. 2008). High pressure membrane processes such as nanofiltration or reverse osmosis are used to remove micropollutants, but the pollutants are difficult to remove, and the operation cost is high (Yoon et al. 2006; Semião et al. 2013). Therefore, many strategies, such as adding nano or porous adsorbents, have been adopted to improve the performance of the membrane (Daramola et al. 2017). In this case, UF membranes became the carrier of the adsorbent (Akanyeti et al. 2017). This enables the adsorption and filtration functions to be completed simultaneously, which will allow the membrane to have higher removal efficiency and better economic benefits for micropollutants (Lee et al. 2009).

There are many studies in composite PES membranes that have been channeled towards the integration of carbon-based material with casting solution to prepare polymer/carbon-based material composite membranes, which can combine the excellent membrane-forming ability of polymers with the unique properties of carbon-based (Salehi et al. 2016). Particularly, attention has been paid to hydrophilicity and absorbency. Many studies have focused on hydrophilic materials added in casting solution to regulate pore size distribution, hydrophilicity, and pollutant removal capacity (Liu et al. 2016; Mahlangu et al. 2017; Shankar et al. 2017). Ghiggi et al. (Ghiggi et al. 2017), demonstrated that the PES membranes with N-phthaloyl-chitosan were higher hydraulic permeance (27 ± 4 Lm^-2 h^-1bar^-1) and hydrophilicity (CA = 56 ± 5°). Similarly, the PES membrane had been modified by chitosan/chitosan-PAC composite material (Gafri et al. 2019). The membrane water flux increased with the increase of chitosan concentration, and the modified membranes of chitosan and chitosan-PAC reduced 28% and 45% of the total coliform bacteria, respectively. Furthermore, the CNT-RGO/PVDF composite membranes were prepared by combining flake rGO with filament carbon nanotubes (CNTS) in different ways (Wang et al. 2018a, 2018b).

In this work, the composite membrane material was combined with the electrochemical device, in which the cathode material is the composite membrane, and the anode material is a reticulated platinum electrode. Due to its excellent conductivity, ACF is used as a cathode in membrane materials/electrochemical systems to make better electrochemical degradation, and the ACF has the potential to improve the electrochemical performance of the original electrode (Rodrigues et al. 2019). The cathode can conduct a significant electrostatic repulsion to the negatively charged micropollutants (Zhao et al. 2019). Besides, because the electrophoretic force induced by the electric field can prevent fouling deposition on the membrane surface, coupling with the electric field is very effective in reducing membrane fouling (Weng et al. 2006). Moreover, membrane fouling can be further decomposed by reactive radicals produced by electrochemical anodization (Huotari et al. 1999). Therefore, it is worth studying that the electric field can enhance the anti-fouling ability of the membrane and thus improve the separation performance of the membrane.

The purpose of this study is to fabricate composite membranes with improved permeability, anti-fouling, and removal properties of micropollutants via a phase inversion method using modified ACF as an additive in the casting solution. ACF was modified with acid, Fe, and Mn, and the modification effect was analyzed. Also, the effect of MACF on the microstructure and properties of membranes was evaluated. The results show that the properties of the composite membranes have been improved significantly and have potential applications in membrane materials/electrochemical systems.

PES as membrane material was provided by Hohai University (Nanjing, China). ACF (average pore size of 2.165 nm, specific surface area of 1,200 m²/g) was obtained from Jiangsu Kejing Carbon Fiber Co. Ltd (Nantong, China). FeCl₃, MnSO₄, and LiCl were purchased from the Shanghai Chemical Reagent Company (Shanghai, China). N,N-dimethylacetamide (DMAC, ≥99.5%) as the solvent, was the commercially analytical grade. Polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA) was used as an additive. Bovine serum albumin (BSA) was supplied by Ruji Bio Co. Ltd (Shanghai, China). SMZ (≥98%), purchased from Brillway Technology Co., Ltd (Beijing, China). All other chemicals used in the experiments were commercially analytical graded and deionized (DI) water was used throughout all of the operations.

Before starting the modification, ACF was thoroughly boiled and washed with DI water, and dried. After drying, ACF was put into 1 mol/L H₂SO₄ and 1 mol/L HNO₃ mixed solution (the volume ratio of H₂SO₄ to HNO₃ solution is 4:1, and the rate is 1 g ACF with 5 mL mixed solution, soaking at 80 °C for 12 h), then washed and dried. Later on, the 1.0 g ACF was mixed with 2 mL 2 mol/L HNO₃ under ultrasound for 1 h. After drying, 0.5 g FeCl₃ and 175 mL absolute ethanol were added, to continue to be ultrasound for 1 h. Then 0.03 mL 3% PVA was added in every 2 mL mixture, ultrasonicated, thoroughly mixed, and dried to constant weight at 80 °C. The third modification method is that 1.0 g ACF was put into 100 mL 18% MnSO₄ solution in the oscillatory chamber at 25 °C for 12 h at the rate of 200 rap/min, dried to constant weight in 100 °C, and then activated in the tubular oven at 650 °C and nitrogen atmosphere for 2 h.

ACF-PES composite membranes were prepared by the phase inversion method. Table 1 showed the components of the casting solutions for membrane fabrication. In particular, the 19 wt% PES,5 wt% PVP,1 wt% LiCl was dissolved in 75 wt% DMAc solution, stirring at 60 °C for 24 h and degassing for 6 h at 25 °C. Next, certain content of MACF (0.8 wt% based on the quality of the solution ahead) was added and placed in an ultrasonic bath for 6 h to be uniformly dispersed and allowed to stand for 24 h a homogeneous casting solution is formed. Last, the casting solution was cast with 0.3 mm casting knife onto a glass plate and evaporated for the 30 s at 25 °C, and then immersed in DMAc/water (20/80 in volume) coagulation bath for 24 h. Finally, the prepared membranes were rinsed with DI water to remove the residual solvent and preserved in DI water until used.

The Brunauer–Emmett–Teller (BET) method-based specific surface area of the ACF material was calculated with the automatic adsorption apparatus (ASAP2010, Micromeritics, USA) using nitrogen as the adsorbent and helium is the carrier gas at −196 °C. The area and volume of the micropore are calculated by the t-plot method, and the pore size distribution was calculated using the Barrett–Joyner–Hacienda (BJH) model by adsorption branching. Each sample was analyzed at least three times to obtain an average value. FT-IR was used to characterize the functional group of ACF material. The ACF sample was mixed with potassium bromide and then tested by FT-IR-8400s (Shimadzu, Japan), with 32 scans and 4 cm² resolutions. A (S-3400N II, Hitachi, Japan) scanning electron microscope (SEM) was used to investigate the surface morphology of the ACF and MACF. The rotary target X-ray diffractometer (D/max-2500/PC, NSC, Japan) was used to measure the wavelength and intensity of characteristic X-ray generated in the interaction between the electron and the test sample to realize the analysis of material elements.

The surface characteristics measurement method of the membrane is the same as that in the section on ACF characterization. Surface morphology analysis of the prepared membranes was carried out on the SEM device (S-3400N II, Hitachi, Japan) after the gold-plating of the samples. The sample was first dried in ethanol and then soaked in liquid nitrogen for 60–90 s. After gold sputtering, the images were taken by SEM at 20 and 30 kV. The water contact angle of composite membrane was measured by the method of fixation using an automatic contact angle meter (OCA20, Dataphysics, Germany). Measurement of surface electrical potential difference calculation flow potential and zeta potential on the surface of the UF membrane using the SurPASS potential analyzer (SurPASS 3, Austria Anton pa, China). Two specimens of the membrane were separated by silica gel gaskets and placed in the test tank. Ag/AgCl phase reversal electrodes were placed on both sides of the UF membrane. Besides, the pH adjustment of electrolyte was carried out by using 0.1 mol/L HCl and KOH solution, and 0.001 mol/L KCl solution was used as the test electrolyte solution.

The basic properties of the UF membrane were analyzed using a stirred ultrafiltration cup (Millipore8200, Millipore, America) with a diameter of 62 mm and an effective membrane crossing area of 28.7 cm². The nitrogen bottle was connected to the ultrafiltration cup, and the valve door of the nitrogen bottle was controlled to keep the output pressure to the ultrafiltration cup at 0.1 MPa.

BSA solution was selected as ultrafiltration solution, and to measure BSA fluxes of 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120 min, respectively.

The membrane material was combined with the electrochemical device, the cathode material was a composite membrane, and the anode material was a reticulated platinum electrode. The cathode and anode materials are placed in parallel on the upper and lower sides of the electrode body, and the insulating silicone gasket is used in the middle to isolate the bipolar materials. Meanwhile, it can play a sealing role to prevent water leakage in the device. Figure 1 shows the schematic diagram of the device.

Under the electric field, the test water samples containing the target contaminant are placed separately in the inlet containers. SMZ test water sample was 500 ML, which was a mixture of 200 ug/L SMZ, 0.15 mol/L Na₂SO₄ and, 100 mg/L H₂O₂. The current operating density of the control device was 10 mA/cm², the speed of the wriggling pump was set at 100 r/min, and the water sample to be tested was obtained after 10 min of reaction. The reaction intermediates and final products are analyzed by a UPLC-MS/MS (Agilent, USA).

Table 2 shows that the average pore size of the composite membrane decreases, and the specific surface area and pore volume increase, which is contrary to the surface structure change of the pristine membrane. Large pore size materials are added into the casting solution to make the composite membrane have smaller pore size and larger specific surface area and pore volume. Also, this is similar to the change of the surface structure of ACF (Table 3). The membrane doped with different ACF materials has a smaller pore size and denser structure.

The images of ACF and MACF obtained from SEM are presented in Figure 2. There is a significant reduction in impurities on the surface of ACF-O, which may be caused by acid corrosion. On the surface of ACF-Fe there are flocs with irregular shapes superimposed on each other. The particles on the surface of ACF-Fe are small and densely distributed. Besides, the surface of MACF is relatively rough, indicating that the surface morphology of ACF changes after modification. In general, the increase of surface roughness can increase the effective filtration area and improve permeability (Wang et al. 2020).

The surface elemental analysis of ACF and MACF are shown in Table 4. The results illustrated that, after chemical modification, the elements were changed, and the extra elements were added to the ACF. The oxygen element of ACF-O was increased to 24.65%, indicating that acid modification of ACF increased the number of oxygen-containing functional groups. The surface oxygen content of ACF-Fe and ACF-Mn increased significantly, and the iron and manganese elements increased to 11.96% and 7.64%, respectively. Combined with the Figure 2, it is proved that the surface of ACF is successfully loaded with metal oxides (Chen et al. 2016; Chen et al. 2017).

SEM images of the surface and cross-section of the prepared membrane are shown in Figure 3 to evaluate different ACF effects. As can be seen, there is a difference between the PES membrane (Figure 3(a)) and composite membranes (Figure 3(b)–3(e)). Compared with the membrane without MACF, the surface of the MACF/PES composite membrane has a large number of pores, related to the hydrophilicity of MACF. Therefore, the penetration rate of water molecules on the surface of the composite membrane and the diffusion rate of solvent from the surface of the composite membrane to the aqueous phase is greatly increased by adding ACF materials. It can be seen from the SEM image of the cross-section of the membrane that the most apparent difference between the composite membranes is the finger-like support layer. The intermediate support layer of PES/MACF composite membranes is more regular, and the finger-like structure is complete. The addition of materials changed the structure of the supporting layer of the membrane and improved the hydrophilicity of the surface. Besides, the ordered arrangement of finger-like structures will improve the anti-fouling performance (Moideen et al. 2018).

Advancing contact angles of all PES/MACF composite membranes were less than 53° (Figure 4), demonstrating that they are all hydrophilic membranes. Compared with other experimental UF membranes (Dang et al. 2006), the water contact angle is lower.

The result shows that the largest contact angle was obtained to M1 due to ACF hydrophobic structure. After introducing MACF into the casting solution, a growth in membrane hydrophilicity resulted from reduced contact angle. The FT-IR of MACF is shown in Figure 5, and the results show that –OH, –COOH functional groups on the surface of ACF are significantly increased after modification. The increase of hydrophilic hydroxyl group, phenolic hydroxyl group and carboxyl group on the surface of MACF resulted in a decrease of the contact angle. According to the principle of similar phase dissolution, the hydrophilic material has a high affinity with the water-soluble material, and the transfer resistance of the solution water phase is small in the hydrophilic material, so the anti-fouling performance of the composite membrane is significantly enhanced.

As shown in Figure 6, the addition of ACF material facilitated the reduction of negative charge on the surface of the pristine membrane. Meanwhile, the surface zeta potential of the composite membranes decreases with the increase of pH. In general, the pH of surface water ranges from 6.5 to 8.5. Within this range, the zeta potential of both M3 and M4 decreased by more than 10 mV compared with the original membrane. This is due to the increase of the hydroxyl group and carboxyl group through the addition of MACF. Since the MACF has a stronger negative charge, the appearance of MACF on the surface of the PES membrane provided a reasonable explanation for the zeta potential reduction of the composite membrane.

This large negative zeta potential should induce electrostatic repulsion between the micropollutants and the membrane surface, conducive to the removal of target pollutants (Lee et al. 2013). It is expected, therefore, that the composite membrane can also effectively deter membrane fouling.

Porosity depends on many initial parameters, such as the viscosity of the casting solution. These parameters affect the resultant membrane pore distribution, affecting porosity (Sengur et al. 2015). Based on the data in Figure 7(a), the observed trend was that the porosity of the membranes (M1–M4) formed with ACF or MACF was lower than that formed with the pure polymer (M0). The addition of ACF or MACF to the polymer membrane reduces the porosity of the membrane. After MACF was added, the morphological structure of the membrane changed. The diameter of the membrane decreased, and the inner hole volume decreased, leading to a decrease of porosity. However, the hydrophobicity of ACF will increase the casting solution's viscosity, thus increasing the diffusion resistance of the casting solution in phase transformation, resulting in the increase of surface thickness of M1 and the minimum pore diameter (lowest porosity) (Sengur et al. 2015). In sum, porosity was generally greater for PES membranes than for membranes containing MACF, and porosity was generally greater for membranes composed of MACF than for membranes containing ACF.

Another parameter to determine membrane hydrophilicity is water content (Hosseini et al. 2020). Figure 7(b) indicates an incrementally trend in the membranes' water content with the addition of MACF. It manifests that the improvement of membrane water content depends on the hydrophilic properties of MACF. With the introduction of ACF-Fe, M3 obtained the highest water content. The results of water content also corresponded with the changes in the hydrophilicity.

In contrast with other composite membranes (Rahimi et al. 2020; Moochani et al. 2016), its porosity merely reached a moderate level, but water content has an obvious advantage.

As shown in Figure 8, the three fluxes of the composite membranes are all lower than the pristine membrane. As the pore size of the membrane decreases after MACF material is added, the water flux of the membrane decreases.

The variation trend of J_b and J_c of M2, M3, and M4 was different from J_a, J_b and J_c of the composite membrane are higher than those of the pristine membranes except M1. After adding MACF, the J_b and J_c of the composite membrane were significantly improved. This result indicates that the PES/MACF composite membrane has better impact resistance to BSA solution, and the membrane has improved fouling resistance. After the addition of MACF, the hydrophilicity of the membrane was developed, which effectively promoted the water phase transfer of the membrane and improved the fouling resistance. Specific pollution analysis is provided in a later section.

As shown in Figure 9, the rejection for BSA of composite membranes significantly increased, indicating that the introduction of ACF and MACF resulted in enhancing the separate performance. Figure 9 reveals that the BSA rejection rate of M1 is 95.3%, lower than that of M2–M4. And M3 displays the highest BSA rejection rate. Two factors can be used to explain high BSA rejection rate. Firstly, the charge of BSA molecules is about –20.5 electrons (pH = 7.4) (Taniguchi & Belfort 2004). Meanwhile, it was found from Figure 6 that the surface absolute zeta potential value of composite membranes increased with an addition of MACF material. Consequently, the electrostatic repulsion between the surface of composite membranes and BSA molecules led to a high BSA rejection (Huisman et al. 2000). Secondly, hydration layer would be formed on the composite membranes' surface due to the hydrophilicity of MACF, which hindered the BSA molecules through the membranes. Thus, composite membranes possess superior permeabilities and high BSA rejection.

Figure 10 presents the relationship between BSA flux and time. The BSA flux of the membrane was recorded at 0–120 min. All membranes experienced flux decline, with the pristine membranes showing the highest flux decline during filtration of the foulants containing feed solution. Due to the accumulation and deposition of BSA molecules distributed on the membrane surface, the pores of the membrane are blocked, so the flux of BSA decreases with time. Anti-fouling experimental data showed that M3 and M4 had the highest stability, which was better than the M0, M1, and M2.

Four anti-fouling indexes (FRR, R_r, R_ir, and total R_t) during the fouling process were calculated and shown in Figure 11(a). In general, high FRR value means that the UF membrane has a better anti-fouling performance. According to the data, the FRR of the composite membrane was prepared by adding different MACF, all increased. The FRR of M2, M3, and M4 has been greatly increased to about 95%. Compared with M0, the FRR value of M1 does not change significantly, while that of M3 is the largest. Besides, the R_ir values of the three composite MACF membranes all decreased significantly, and the R_ir values of the M3 and M4 were all less than 4%, indicating that the hydrophilicity of the modified membranes increased. PES/MACF composite membranes have better anti-fouling performance than the lowest R_ir (4.2%) reported from the previous investigation (Rahimi et al. 2019). The R_r values of the composite membranes did not change significantly. However, the Rt values of the membranes with MACF decreased significantly, and the anti-fouling properties of the composite membranes were significantly improved.

The proportion of the reversible and irreversible fouling rates of the composite membrane in the total fouling rates (R_r/R_t and R_ir/R_t) is shown in Figure 11(b). This part is complementary to the results of FRR, R_r, R_ir, and R_t of the membranes shown in Figure 11(a), which all reflect the anti-fouling performance of membranes. In general, when the R_ir of membrane decreased, Rr also reduced, and R_r/R_t increased, and R_ir/R_t decreased, indicating better anti-fouling performance (Rahimi et al. 2019). The R_r/R_t value of M2, M3, and M4 increased significantly, and it was noted that the membranes had a stronger anti-fouling performance.

In addition, the comparative results of the composite membranes in this work against different polymer membranes doped with different carbon-based materials were listed in Table 5. It could be observed that the PES/MACF composite membranes exhibited a general performance in pure water flux, but BSA rejection and FRR have an obvious advantage.

The SMZ pollutant treatment test was conducted in the membrane material/electrochemical cross-flow experimental facility. The electrification condition was controlled, and the effluent concentration of pollutants was detected at the cross-flow for 10 min. Finally, the removal rate of composite membrane was conditions was calculated through the influent concentration and effluent concentration, as shown in Figure 12.

Compared with the unenergized condition, the removal effect of SMZ was all improved by more than 10%, which was because the membranes doped with different MACF materials increase the groups of –OH, –COOH, Fe–O, Mn–O, Mn–O–Mn, etc. Functional groups, such as –OH, –COOH, are added to the surface of the membrane, which bond with SMZ molecules through hydrogen bonds and van der Waals forces, thus enhancing the adsorption performance of target pollutant SMZ. Moreover, the electric charge on the surface of the membrane can affect the separation effect of charged pollutants in water (Bildyukevich et al. 2018). The large negative zeta potential of the composite membrane (Figure 6) enhanced the electrostatic repulsion of the membrane to SMZ and promoted SMZ separation. Besides, as ACF-Fe and ACF-Mn successfully load metal oxides (Table 4), they are easy to form complexes with SMZ molecules, which enhance the chemical adsorption capacity (Yang et al. 2018), so the M3 and M4 are better to remove the SMZ.

As shown in Table 6, the removal rate of the PES/MACF composite membrane to micropollutant SMZ reached 90.1% in the presence of the electric field. Whether compared with commercial or other modified membranes, M3 has a high performance in the removal of micropollutants.

In order to further analyze the degradation of SMZ molecules under non-energized conditions and energized conditions, UPLC-MS/MS measurements of effluent from the four materials were conducted after 10 min. Table 7 shows the degradation products (possible intermediates).

As mentioned above, electrochemical degradation facilitated the removal of SMZ from the treatment system. During the treatment process, eight intermediates are produced, as shown in Figure 13. •OH directly attacks the methyl group and replaces it to get S-1 (m/z = 256). After •OH substituted SMZ with single hydroxyl on the benzene ring, SMZ's S-N bond was attacked, and the S-N bond was broken, and S-2 (m/z = 190) and S-3 (m/z = 99) were obtained. S-3 could continue to be reacted by hydroxyl, but no further products were detected in the water sample. Under the further action of •OH, s-2 breaks the S-C bond between the carbon atoms attached to the benzene ring, resulting in S-6 (m/z = 94) and S-7 (m/z = 159), while S-8 (m/z = 110) is the substitution product of the benzene ring hydroxyl of S-6. Besides, the double bond on the ring of the nitrogen atom in SMZ molecule is naturally attacked by the hydroxyl group and double bond addition reaction occurs to obtain polyhydroxy product, and then s-4 (m/z = 276) is obtained by opening the ring under the further action of •OH. Similarly, the benzene ring on S-4 is easily substituted by the hydroxyl reaction, resulting in the hydroxyl substitution product S-5 (m/z = 292) (Huang et al. 2012; Mitchell et al. 2013; Tzeng et al. 2016).

Based on the above analysis, we propose the possible degradation pathway of SMZ in the treatment system. Combined with the conclusion in the previous section, SMZ removal of M3 and M4 increased by 24.6% and 15.2%, respectively, under electrification, indicating that the presence of Fe and Mn oxide on MACF can promote electron transfer and REDOX reaction process (Du et al. 2020; Lian et al. 2020). The hydroxyl and carboxyl functional groups on the membrane can promote the decomposition of H₂O₂ to produce •OH for the REDOX of the SMZ, to improve the removal effect.

In this study, ACF-O, ACF-Fe, and ACF-Mn modified materials were successfully prepared from ACF raw materials. MACF was added to the casting solution, and the composite UF membrane was prepared by the phase inversion method. The FT-IR (Figure 5) and EDS results (Table 4) showed that the ACF was modified successfully. Also, the composite membrane characterization demonstrated that efficiency and performance could be improved by adding the MACF. The composite UF membrane was observed to have many small holes on the surface. The finger-like structure in the middle support layer (as seen on SEM images) was more regular and complete. The water contact angle of the membrane was significantly reduced, all of which decreased by more than 20°. It was shown that MACF could be introduced as effective for improving the hydrophilicity of the composite membranes. The composite UF membrane was combined with the electrochemical device. As expected, when the electric field is applied to the system, the removal performance of composite membranes achieves significantly improved because many reactive radicals such as •OH generated in the treatment process can decompose the SMZ. Considering the properties of the membrane and its performance in the coupling system, M3 is more suitable for SMZ removal. This study prepared a PES/MACF composite membrane for the high-efficiency treatment of SMZ wastewater and built a membrane-electric field coupling system to reveal the potential application of composite membrane removal micropollutants from water under the electric field.

This work was sponsored by the National Natural Science Foundation of China (Grant No. 51979077), the Fundamental Research Funds for the Central Universities (Grant No. 2019B42414), and PAPD, the Jiangsu Provincial Science and Technology Program Project (Grant Nos. SBA2018030430 and BE2019121). The authors are grateful to the editor, the anonymous reviewers, and Prof. Jianzhong Zhu (Hohai University) for the constructive comments, which led to major improvements of this paper.

All relevant data are included in the paper or its Supplementary Information.