Fabrication of graphene oxide incorporated polyethersulfone hybrid ultrafiltration membranes for humic acid removal

Separation and Purification Technology 223 (2019) 17–23

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Fabrication of graphene oxide incorporated polyethersulfone hybrid ultrafiltration membranes for humic acid removal ⁎

T

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Mohammad Saad Algamdia, , Ibrahim Hotan Alsohaimib, , Jenny Lawlerc, Hazim M. Alib, Abdullah Mohammed Aldawsarid, Hassan M.A. Hassanb,e a

King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia Chemistry Department, College of Science, Jouf University, Sakaka, Saudi Arabia c Membrane and Environmental Technologies Laboratory, School of Biotechnology and DCU Water Institute, Dublin City University, Dublin 9, Ireland d Chemistry Department, College of Arts & Science-Wadi Al-dawaser, Prince Sattam bin Abdulaziz University, Alkharj, Saudi Arabia e Department of Chemistry, Faculty of Science, Suez University, Suez, Egypt b

A R T I C LE I N FO

A B S T R A C T

Keywords: Humic acid removal Graphene oxide Ultrafiltration Antifouling Polyethersulfone

In this study, hybrid polyethersulfone membranes incorporated with graphene oxide were synthesized by a nonsolvent induced phase separation approach. The influence of graphene oxide content on the membrane efficiency and fouling durability was elucidated, with emphasis on water flux, natural organic matter (NOM) rejection using humic acid as a model for NOM, and flux reduction due to fouling. The results revealed that the water flux increased with increasing GO content. It is worth noting that the MGO-5 membrane exhibits the highest Jw value (340 L m−2 h−1) among all the fabricated membrane, while the greatest JHA (193.78 L m−2 h−1) value was obtained for MGO-3 membrane. NOM rejection was improved significantly by the incorporation of GO. The best rejection value of HA solution using the membranes was observed for MGO-3 at pH 7. The presence of GO also improved the membrane reusability and antifouling capabilities, due to the enhancement of the hydrophilicity of the GO-membrane surface.

1. Introduction

NOM membrane contamination can take place: (i) reversible fouling due to adsorption on the membrane surface, which can be eliminated by adopting a facile hydraulic cleaning, and (ii) irreversible fouling stemming from NOM’s strong interaction on the surface or inside the membrane pores [14–17]. Many approaches have been widely investigated to enhance the hydrophilic nature and antifouling capability of polymeric membranes, such as (i) the deposition of an antifouling coating on the surface of the fabricated membrane, (ii) combination of hydrophobic polymer with a small percentage of functionalized copolymers, (iii) nanofillers and (iv) incorporating of functionalized polymer with hydrophilic moieties onto the hydrophobic membrane surface by polymerization [14–22]. Nanofiller grafting within the polymer molding for the synthesis of low fouling ultrafiltration membrane composites has acquired much research interest. Hence, titanium oxide, zeolite, zirconium oxide, carbon nanotubes, and graphene oxide have been exploited as nanofillers to synthesize membranes with reduced fouling properties [23,24]. Graphene oxide (GO) and other graphene based composites have gained tremendous attention in the fabrication of hybrid ultrafiltration membranes due to its distinct characteristics, such as a single atomic layered

Natural organic matter (NOM) is considered as a complex of organic substances found in natural surface water sources. Disinfection byproducts (such as trihalomethanes) can be produced during drinking water treatment such as chlorination, leading to detrimental health impacts [1,2] and NOM is one of the main contaminants [3,4]. Therefore, the removal of NOM from natural surface water and wastewater is of great interest to avoid the production of disinfection by-products and to provide safe drinking water [5–8]. Humic acid (HA) is one of the main constituents of dissolved organic matter in natural waters. Humic acid exhibits a complicated structure with three functional moieties, namely, methoxyl, phenolic alcohol and carboxylic acid. Conventional treatment of contaminated water by chlorination causes the interaction of chlorine with humic acid producing a series of human carcinogenic constituents. It is therefore necessary to remove humic acid before traditional chlorination of drinking water [9,10]. While ultrafiltration (UF) has been received much attention for use in drinking and wastewater treatment [11], flux reduction due to membrane fouling is a crucial problem for effective application of UF [12,13]. Two kinds of

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Corresponding authors. E-mail addresses: [email protected] (M.S. Algamdi), [email protected] (I.H. Alsohaimi).

https://doi.org/10.1016/j.seppur.2019.04.057 Received 5 March 2019; Received in revised form 14 April 2019; Accepted 17 April 2019 Available online 19 April 2019 1383-5866/ © 2019 Elsevier B.V. All rights reserved.

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Table 1 The composition of casting solutions for the fabrication of hybrid ultrafiltration membranes. Total Mass (g) Mass PESa

100 % GO (% of PES mass)b

Mass GO

Mass (or %) NMPc

18 18 18 18 18

1 2 3 4 5

0.18 0.36 0.54 0.72 0.9

81.82 81.64 81.46 81.28 81.1

a

Polyethersulfone. The percentage of GO is based on the total fraction of PES polymer in the casting solution, i.e. 1% of 18%. c N-methylpyrrolidone. b

Scheme 1. Schematic representation for the interaction of PES with GO.

graphite was mixed with 250 ml of sulfuric acid under stirring in a three-neck flask. Next, 10 g of KMnO4 was gradually added to the mixture in an ice bath to produce a purple-green cake. The suspension was then transferred to a 40 °C water bath with stirring for 90 min. The dark brown colored cake was further diluted with the addition of 200 ml of deionized water and stirred for a further 10 min. A 100 ml portion of H2O2 was gradually poured to minimize the residual KMnO4 forming a golden-brown cake. The formed cake was separated and rinsed with hot water several times until pH ∼6 was achieved. Finally, the powder was dried at 100 °C for 24 h.

with two-dimensional nanostructure, high surface area, outstanding adsorption performance, good thermal and mechanical stability [25,26]. Hence, the surface decoration of GO with hydrophilic moieties containing oxygen (eOH, eC]O, eCOOH) can offer extraordinary characteristics providing a novel opportunity for tailored membrane composites [27,28]. GO will also be beneficial to enhance the retention ability of hybrid ultrafiltration membranes towards natural organic matter due to the electrostatic exclusion of NOM from the same charged membranes [29,30]. N-methyl-2-pyrrolidone is a non-toxic, colorless, biodegradable and odorless liquid used as a solvent in various industries [31], and it is possible to recover NMP for re-use from aqueous solutions. The polar nature of n-methyl-2-pyrrolidone can also enable it to interact with GO through many hydrophilic moieties during the preparation of the casting solutions, causing a longer dispersability of GO and increasing the membrane hydrophilicity. In this work, low fouling hybrid ultrafiltration membranes were successfully fabricated from graphene oxide and polyethersulfone (PES) (Scheme 1) by a non-solvent induced phase separation approach. The fabricated membranes were applied for the efficient removal of humic acid from synthetic surface water samples. While GO has been incorporated into the dope solution previously [32], evaluation of humic acid removal has only been assessed for GO-PES membranes prepared by vacuum deposition [33,34] and chemical binding [35], representing the novelty of the presented work.

2.3. Membrane fabrication PES and GO incorporated membranes were synthesized by nonsolvent induced phase separation (NIPS) approach [14,15,24]. Membrane casting solutions were prepared by adding varied contents of GO (0–5 wt%; Table 1) relative to the total amount of PES polymer in Nmethylpyrrolidone (NMP) and then sonicated in an ultrasonic bath for 30 min. An increase of GO above 5 wt% led to difficulties in fabrication. Thereafter, PES was dissolved into the solutions with constant stirring at room temperature until a homogeneous solution was obtained. The casting mixture was then stirred for 24 h to attain a good homogeneity of GO powder in the precursor solutions, with degassing by sonication for 1 hr prior to the membrane casting. The polymer solution was cast onto a clean glass plate using an Elcometer 3580 (Elcometer Ltd., UK) to achieve a membrane thickness of ∼200 μm, then transferred to a DI water bath until a free detached membrane was obtained. The membrane films were then washed with DI, followed by drying for 12 h at room temperature and finally kept in DI water for further measurements. The as-fabricated GO/PES membranes with 1, 2, 3, 4 and 5 wt% GO powder are designed as MGO-0, MGO-1, MGO-2, MGO-3, MGO-4, and MGO-5, respectively.

2. Experimental 2.1. Materials Veradel Polysulfone (PES) was obtained from Solvay, Belgium. Polyvinylpyrrolidone (PVP) was purchased from Sigma–Aldrich, Ireland. N-methyl-2-pyrrolidone (NMP) and toluene were purchased from Applichem, GmbH, Germany. Sodium chloride and calcium chloride were obtained from Fisher Scientific, Ireland. Expandable graphite flakes (1721, Asbury Graphite Mills, US) with average flake size > 500 µm were used as starting material for GO synthesis. Other chemicals for GO synthesis including KMnO4, H2SO4 (97%), HCl (37%) and H2O2 (35 wt%) were obtained from Sigma–Aldrich, Ireland. Humic acid (HA) was obtained from Sigma–Aldrich, Ireland. 1 M HCl and 1 M NaOH for pH adjustment was obtained from VWR, Ireland. Water purified with a Milli-Q system (Millipore) (DI water) was adopted in this work. All materials were used as received.

2.4. Membranes characterization The MGO membrane surface and cross-section images were obtained adopting a scanning electron microscope (Quanta 400 FEG, Czech Republic) operating at 20 kV. The cross-section images were acquired after the fracturing of the fabricated membranes in liquid nitrogen followed by coating with gold for 30 s at 30 mA (Emitech, UK). ATR-FTIR spectra were obtained using a Varian 3100 spectrophotometer in the range of 600–4000 cm−1. The contact angle assessment performed applying a sessile drop approach on FTA° 200 contact angle analyzer (First Ten Angstroms, Inc., USA) equipped with a video camera. Five assessments were obtained at different sites for each sample to acquire the averaged result. The thermal stability of the fabricated membranes was examined by thermal gravitational analysis (TGA) using Q50. The fabricated membranes were heated in the range 25–700 °C in nitrogen. The flow rate was set to pass over the sample at a rate of 50 ml min−1 and a heating rate of 20 °C min−1. The water

2.2. Synthesis of graphene oxide Graphene Oxide (GO) was synthesized using a modified Hummer’s approach [36,37]. Firstly, 2 g of graphite flakes were heated in 700 W microwave for about 20 s to form expandable graphite as the starting material for the fabrication of graphene oxide. 2 g of expandable 18

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content of the synthesized membranes was carried out using a Q200 series differential scanning calorimeter (TA instrument, USA) within the temperature in the range of −30 ± 30 °C under nitrogen and a heating rate of 10 °C min−1. Water uptake (φ) and porosity (ε) of the membranes were estimated using gravimetric methods [14]. A 2 cm × 2 cm dry membrane pieces was cut to size and the weight recorded using an analytical balance. The pieces of the membrane were subsequently soaked in DI water at RT for 24 h. The wet membrane pieces were ejected, gently blotted with a clean filter paper to remove excess water droplets from the membrane surface, and immediately weighed. The water uptake values for each membrane sample was replicated three times to evaluate the reproducibility of the obtained data. The water uptake φ (%) was determined using Eq. (1):

φ (%) =

ww − wd wd

Rr =

Rir =

Jw1 − Jw 2 × 100 Jw1

(7)

2.6. Humic acid adsorption The quantity of HA adsorbed on the hybrid membranes at pH 7 was assessed. The fabricated membranes in the form of the circle with the area of 2 cm2 were submerged into a vial containing 10 ml of HA solution (100 mg L−1), with stirring for 24 h with constant stirring speed. After that, the membranes were removed, and the supernatant solutions containing HA were assessed using a Cary 50 Probe UV–Vis spectrophotometer (Varian Inc.) at 280, 254 and 200 nm, respectively. The adsorbed quantity of HA was evaluated in accordance with the below Eq. (8):

(1)

ww − wd ρw × A × δ

(6)

where J x is the HA solution flux.

where Ww is the wet membrane weight (kg) and Wd is the dry membrane weight (kg). For porosity determination, square pieces of hybrid membranes were soaked in DI water at RT for 24 h, excessive water was blotted from the surface using a filter paper, and the weight immediately measured. The wet pieces of hybrid membranes were then dried in a vacuum oven at 60 °C for 24 h, and the weights of the dried membrane pieces were measured. The porosity ε (%) was evaluated according to Eq. (2):

ε (%) =

Jw 2 − Jx × 100 Jw1

q=

(Co − Ca) × V A

(8)

where q adsorption capacity (mg/g), Co and Ca were the initial and supernatant quantity of HA (mg/L), respectively, V is the volume (L), and A is the actual membrane area. The final results have been calculated based on the average of all measurements for each sample. 3. Result and discussion

(2)

where ρw is the density of water (kg/m ), A is the effective membrane area (m2), and δ is the membrane thickness (m). 3

3.1. Membrane fabrication and physicochemical assessment Composite GO/PES membranes with varied quantity of GO were synthesized by solution casting and non-solvent induced phase separation method [36,37]. In this work, NMP was used as a dispersion medium for the GO as well as in the membrane preparation. The water uptake (φ) and porosity (ε) of the membranes are presented in Table 2. Water uptake plays a decisive role in the transportation mechanism and stability of the membranes; principally, high water uptake could lead to a reduction in the durability of the membrane. As such, a suitable water uptake as well as swelling level should be preserved to ensure efficiency of the membranes. Table 2 shows the water uptake of all hybrid membranes is increased in comparison with the pure PES under the same experimental conditions. This could be attributed to (i) Water molecules are small enough to pass easily through the GO nano-channels within the membrane surfaces, (ii) GO contains considerable hydrophilic moieties (eOH, eCOOH and eOe), providing additional water storage spaces and increasing their powerful ability to attract water molecules. (ii) The polar characteristics of N-methyl-2-pyrrolidone enable it to interact with GO via the hydrophilic moieties during the fabrication of the casting solutions, causing a longer dispersability of GO and increasing the membrane hydrophilicity. The porosity was also systematically improved with increasing quantity of GO (Table 2). The highest porosity (64.93%) was achieved for membrane MG-5. This could be attributed to the hydrophilic effect of GO nanosheets and the casting solution viscosity during phase inversion process. Additionally,

2.5. Ultrafiltration and water flux assessment The filtration efficiency of the synthesized membranes was performed using a stirred UF cell (Amicon 8050; Millipore). The fabricated membrane was pre-compacted by passing distilled water at a feed pressure of 2 bar for about 30 min. Thereafter, the pressure was decreased to 1 bar and water was again passed for 1 h. The pure water flux (Jw) of the fabricated membranes was calculated from the collected permeate mass using Eq. (3):

Jw =

m ρ×t×A

(3)

where m (g) is the permeate mass, ρ is the water density, A (m ) is the area of membrane and t (h) is the filtration time. Ultrafiltration experiments were performed at room temperature at approximately 400 rpm to assess the capability of the organic matter antifouling by filtering 500 ml solution of humic acid solution at pH = 7 and concentrations of 10, 20, 50 and 100 mg L−1, at a feed pressure of 1 bar. After each UF experiment, the membranes were thoroughly cleaned with distilled water for one hour. The water flux of the regenerated membranes was again evaluated by passing distilled water through the cleaned membranes. The flux recovery ratio (FRR) of the membranes was evaluated adopting Eq. (4) [36,37]: 2

FRR (%) =

Jw2 × 100 Jw1

Table 2 Physicochemical properties for the hybrid ultrafiltration membranes: water uptake; φ, porosity; ε, and contact angles; θ.

(4)

where Jw2 is the water flux of the fabricated membrane following membrane cleaning and Jw1 is the initial water flux of the membrane. To give more insight on the fouling mechanism of the fabricated membrane, the total fouling ratio (Rt), reversible fouling ratio (Rr) and irreversible fouling ratio (Rir) were estimated adopting the following Eqs. (5), (6) and (7)

Rt =

Jw1 − Jx × 100 Jw1

(5) 19

Membrane

φ (%)

ε (%)

θ°

MGO-0 MGO-1 MGO-2 MGO-3 MGO-4 MGO-5

70.49 72.82 77.62 77.86 78.67 79.46

39.19 41.70 42.01 47.12 52.21 64.93

80.59 70.25 68.53 67.09 61.73 56.02

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Fig. 1. The cross-section SEM images at high and low resolution for the PES/GO membranes prepared with varied fraction of GO (Table 1): (A) MGO-0; (B) MGO-1; (C) MGO-2; (D) MGO-3 and (E) MGO-5.

membrane, indicating an enhancement of the thermal stability. The DSC profiles for MGO-0, MGO-1, MGO-2, MGO-3, and MGO-5 membranes in the swollen state are shown in Fig. 3. All membranes exhibit one peak in the range of 0–5 °C due to the presence of the water molecules within the membranes. Additionally, the membrane’s peak area was significantly increased with GO content, supporting the hydrophilicity increase observed via water contact angle, water uptake and porosity (Table 2).

the rate of solvent exchange with nonsolvent during phase-inversion process could be enhanced by hydrophilic GO nanosheets with matrix of polymers. Water contact angle measurements are depicted (inset in Fig. 1) and the obtained magnitude are presented in Table 2. The results indicated that the values of the water contact angle were based mainly on the GO content in the membranes. The contact angle of 80.59° for the pristine membrane MGO-0 decreases to 57.6° for the membrane containing 5 wt% GO (MGO-5) associated with an increase in the content of GO. These observations suggest that a powerful hydration layer was formed on the membrane surface owing to the robust tendency of C]O and OeH moieties to water molecules along with water binding tendency to GO. Furthermore, the membrane MGO-5 exhibits a contact angle of 57.6°, which could explain the enhancement in the hydrophilicity of the hybrid membrane as indicated from water uptake values (Table 2). The results revealed that the hybrid membranes surface exhibit more hydrophilicity with increasing GO quantity.

3.3. Membrane permeability Fig. 4 shows the water and humic acid solution flux of the composite membranes comprising different contents of GO versus the pristine membrane. The Jw values gradually increased for the modified membranes with increasing GO content. The MGO-5 membrane exhibits the highest Jw value (340 L m−2 h−1) among all the hybrid membrane, which can be related to (i) the highest hydrophilicity, (ii) water uptake and (iii) porosity (Table 2). The hybrid membrane having 1 wt% GO (MGO-1) exhibit the lowest Jw value (149 L m−2 h−1). Humic acid solution flux (JHA) was also based on the content of GO in the fabricated membranes (Fig. 4). The values of humic acid flux (JHA) increased robustly with an increasing GO content up to 3 wt% GO and then declined with further increase in the quantity of GO up to 5 wt%. The addition of GO above 3 wt% can lead to a high rate of demixing with higher GO content, due to it’s hydrophilicity. This can then compete with the thermodynamic effects of GO inclusion with increased viscosity and higher GO loading, explaining the decline in flux. The greatest JHA (193.78 L m−2 h−1) value was obtained for MGO-3 membrane. Furthermore, the values of humic acid flux were found to be lower than water flux values for all of the fabricated membranes. This could be attributed to concentration polarization close to the membrane surface and membrane fouling which are principally responsible for lowering JHA values than Jw values for all hybrid membranes. It was further observed that the solution rejection values slightly increased with an increase of GO content, however above a certain porosity level, the rejection of HA was decreased. The highest rejection value was acquired for MGO-2 membrane (Fig. 5).

3.2. Membrane characterization The cross-sections of the hybrid membranes are depicted in Fig. 1. Overall, the morphology resembles that for typical UF membranes, without defects. As the GO quantity increased in the casting solutions, the porosity of the membrane became more significant. The membrane MGO-5 exhibited the highest porosity among all the synthesized membranes. This could be attributed to the substitution rate of the solvent (NMP) with water in the phase inversion method. The substitution rate of NMP with water during the membrane fabrication in phase inversion method was improved with raising the hydrophilicity of the dope solution. The ATR-FTIR spectra for the membranes are shown in Fig. 2a. The absorption peaks at 1727 cm−1 and 2921 cm−1 correspond to the stretching modes of C]O and OeH peaks of carboxylic moieties of GO, respectively. By comparing the unmodified with functionalized GO, it can be observed that the PES membrane spectrum did not possess that peak, confirming that GO was successfully integrated into the PES membranes. Thermogravimetric analysis was performed to examine the thermal stability of the fabricated membranes (Fig. 2b). The fabricated membranes exhibit three distinct weight loss steps: (i) the first stage is assigned to the desorption of remaining solvents (NMP) and water in the range of 50–200 °C; (ii) the second step attributed to the decomposition of sulfonic acid moiety on PES around 250–450 °C; (iii) the third step is the disintegration of polymeric skeleton in the range of 450–700 °C. Compared with pure PES membrane, the incorporation of GO modifies the thermal degradation behavior of the composite

3.4. Antifouling performance The antifouling efficiency of the hybrid membranes was estimated in relation to HA capturing and flux recovery ratio of hybrid membranes after UF of these solutions. The adsorbed quantity of HA for the pristine membrane and GO incorporated membranes at pH = 7 are 20

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Fig. 2. (a) ATR-FTIR Spectra for pristine recast PES/GO hybrid membranes (b) TGA profiles of PES/GO hybrid membranes.

Fig. 3. DSC profiles for PES/GO hybrid membranes with different water content at temperature range −30–+30 °C.

Fig. 5. Rejection of Humic acid (HA) on PES/GO ultrafiltration membranes at pH = 7.

Fig. 4. Pure water flux and Humic acid solution flux for PES/GO hybrid ultrafiltration membranes containing various content of GO, pH = 7, 1 bar applied pressure and a stirring speed of 400 rpm.

Fig. 6. Adsorption of Humic acid solution (50 mg L−1) on PES/GO ultrafiltration membranes at pH = 7.

presented in Fig. 6. The adsorbed quantity of HA remained reasonably static with slight decrease for the membranes with an increasing content of GO up to 3 wt% GO (MGO-3), then increased when the content of GO increased especially for the hybrid membrane having 5 wt% GO

(MGO-5), mirroring the trend in water contact angle (Table. 2), indicating that surface roughness may play a role. The effective reduction occurred in the quantity of adsorption of HA owing to the production of a hydration layer on the surface of the membrane. The MGO-3 membrane shows a less tendency to HA adsorption as compared to other 21

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surface waters containing NOM at pH 7. The flux recovery ratio (FRR) for all the synthesized membranes after the ultrafiltration process of HA at pH 7 are depicted in Fig. 7. The FRR value for pristine membrane (MGO-0) was estimated to be 75%, the smallest value among all the synthesized membranes. This due to the interaction between HA solution and PES was hydrophobic, leading to membrane fouling. The FRR value was further increased with increasing GO content. Overall, FRR values for the membranes containing GO were greater than that of the pristine membrane (MGO-0) as the antifouling capability of the PES blend membranes was improved by GO incorporation. High FRR values for the hybrid membranes indicate that NOM on the membrane surface could be easily removed by simple washing, and mitigated by applying tangential flow. The fouling behavior of the membranes was further examined by assessment of the total fouling ratio (Rt), reversible fouling ratio (Rr), and irreversible fouling ratio (Rir) (Fig. 8). It worth noting that Rt value for HA solution was substantially reduced with increasing content of GO in the fabricated membranes indicating low fouling by HA. The reversible fouling ratio (Rr) values increased with a content of GO, which give rise to the decline in the irreversible solutions fouling ratio values (Rir) from 22.3 to 2.4% with increasing the content of GO (1–5 wt%). The lower total fouling and irreversible fouling ratio for the membrane MGO-5 indicate that the weakly binding HA over the surface and/or within the membranes porosity could be taken away simply by facile cleaning with water flow.

Fig. 7. Flux recovery ratio for PES/GO hybrid membranes after ultrafiltration of 500 ml Humic acid solution (50 mg L−1) and subsequent washing with DI water.

3.5. Membrane transportation mechanism The selective transportation manner of graphene membranes which allow separation is via the nano-pore structure located within the basal of the hexagonal structure. Alternatively, molecules can be selectively transported through the interstitial space of multi-layered 2D materials. Stacked sheets of GO form a multilayer laminate that shows remarkable mechanical strength for use in pressure-driven water filtration operation due to the strong hydrogen bonds between individual sheets. Functional moieties having oxygen deposited irregularly along the edges of GO plates retain large spacing between layers and empty spaces between non-oxidized regions, creating a network of nano-capillaries inside the film. These nano-capillaries allow the permeation of water molecules and subsequent transport along the hydrophobic zone of the membrane, helping to accelerate the flow of water [38].A summarized comparison of the humic acid removal adopting different membranes taking into consideration the ultrafiltration conditions is given in Table 3.

Fig. 8. Collection of total fouling ratio (Rt), the reversible fouling ratio (Rr) and the irreversible fouling ratio (Rir) for PES/GO hybrid membranes.

membranes under the same working conditions. The adsorbed quantity of HA solution using MGO-3 membrane at pH = 7 was obtained to be 7.8 µg cm−2, which is the lowest obtained value (Fig. 6). It can be seen that all fabricated membranes show comparable adsorption performance of HA solution compared to the pristine membrane (MGO-0), apart from MGO-5 which is significantly increased. Thus, the hybrid membranes with low fouling capability would be suitable for UF of

4. Conclusions Hybrid ultrafiltration membranes were successfully fabricated from a combination of (GO) and polyethersulfone (PES) by non-solvent induced phase separation approach. The fabricated membranes displayed a typical asymmetric structure having a thin skin layer and a porous

Table 3 Comparison of humic acid removal cited in the literature with the fabricated membrane in this work. Membrane material

Membrane type

Challenge HA

Pure water flux of pristine membrane (LMH)

HA rejection (%)

Reference

PES/XA (0.5–1.5 wt%) PES & 8% 3,5-diaminobenzoic acid (DBA) PES & 6% Gallic acid (GA) Polysulfone/2% Titanium Dioxide TiO2/Pebax/(PSf‐PES) PEI/PEG PAN/CS-Fe3O4 RC/negatively charge (sulfonic acid group) RC/negatively charge (carboxylic acid group) Cellulose acetate MGO-5

UF UF, flatsheet UF, flatsheet UF, hollow fibre Thin Film UF UF UF UF UF UF

– 1000 ppm 1000 ppm 1000 ppm 10–30 ppm – 10–50 ppm 2 ppm 2 ppm – 10–100 ppm

4.83@ 200 KPa 60 @ 3 bar 35 78 @1 bar 3 and 5 188@ 3 bar 25.5 @ 5.5 1 bar @ 1 bar 160@ 3 bar @ 2 bare

90 34 28 90 96–98 56 96.5 91 96 95.1 94.5

[39] [40] [40] [41] [42] [43] [44] [45] [45] [46] Present work

22

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sub-layer. The incorporation of GO played an important point of interest in the membrane ultrafiltration efficiency owing to their features as charges on the membrane surface, surface functional moieties, and active centres quantity. The membrane porosity and hydrophilicity can be adjusted by changing the content of GO in the dope solutions proportional to membrane polymer. The fouling propensity of the membranes was significantly decreased with raising GO content. Thus, HA removal and fouling of the fabricated membranes could be adjusted by varying the content of GO. Flux during filtration of HA solutions was mainly based on the GO content; the highest values were acquired for MGO-5. This maximum assignment of GO content is related to the porosity as well as cross-section morphology. The best rejection value of HA solution using the membranes was observed for MGO-3 at pH 7. The antifouling tendency measured in terms of the FRR and rejection values of pristine and the hybrid membranes, showed that membrane performance is enhanced with incorporation of GO. Furthermore, the improved membranes can be suitable for removing organic matter from natural water sources.

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