The roles of oxygen-containing functional groups in modulating water purification performance of graphene oxide-based membrane

Journal Pre-proofs The roles of oxygen-containing functional groups in modulating water purification performance of graphene oxide-based membrane Hao Yu, Yi He, Guoqing Xiao, Yi Fan, Jing Ma, Yixuan Gao, Ruitong Hou, Xiangying Yin, Yuqi Wang, Xue Mei PII: DOI: Reference:

S1385-8947(20)30366-1 https://doi.org/10.1016/j.cej.2020.124375 CEJ 124375

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

6 November 2019 4 February 2020 6 February 2020

Please cite this article as: H. Yu, Y. He, G. Xiao, Y. Fan, J. Ma, Y. Gao, R. Hou, X. Yin, Y. Wang, X. Mei, The roles of oxygen-containing functional groups in modulating water purification performance of graphene oxide-based membrane, Chemical Engineering Journal (2020), doi: https://doi.org/10.1016/j.cej.2020.124375

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2020 Published by Elsevier B.V.

The roles of oxygen-containing functional groups in modulating water purification performance of graphene oxide-based membrane Hao Yu 1, 2, Yi He 1, 2,*, Guoqing Xiao 2,*, Yi Fan 1, 3,*, Jing Ma 1, 2, Yixuan Gao 1, 2, Ruitong Hou 1, 2,

Xiangying Yin1, 2, Yuqi Wang1, 2, Xue Mei 1, 4

1

State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Southwest Petroleum

University, Chengdu, Sichuan 610500, China. 2

College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu,

Sichuan 610500, China. 3

Chengdu Graphene Application Institute of Industrial Technology, Chengdu, Sichuan 611130, P

R of China 4

Northwest Division of Petrochina Southwest Oil＆Gas Field Company, Jiangyou, Sichuan 621700,

China

* Correspondence to this author. Prof., Ph.D.; Tel,: +86-02883037315. E-mail address: [email protected] (Yi He) [email protected] (Guoqing Xiao） [email protected] (Yi Fan）

ABSTRACT Due to the excellent mechanical properties and tunable inter-layer distance spacing (Dspacing), graphene oxide based nanofiltration membranes (GONMs) have attracted tremendous attention for wastewater treatment and seawater desalination. However,

GONMs with different reduction degrees or originate from different graphite resources present totally distinct purification performance. The principal consideration of the differences between those GONMs is the oxygen-containing functional groups (carboxyl (-COOH), hydroxyl (-OH) and epoxy (-COC-)). While, it is still not fully understood what role do different oxygen-contained functional groups play. Herein, in order to reveal this knowledge gap, we fabricated and systematically studied three oxygen-containing functional groups dominant (C-GO, H-GO and E-GO) GO membranes. Zeta potential was measured to analysis the surface properties of C-GO, H-GO and E-GO nanosheets. Furthermore, XRD was used to observe the D-spacing of GONMs. The results showed that the oxygen-contained functional groups with different hydrophilicity and electricity modulated the D-spacing of GONMs effectively, which resulted in different water permeance and sieving performance of the GONMs. Besides, C-GONMs with abundant negative charges exhibited excellent antifouling capacity for Trypan blue (dye) owing to the electrostatic interaction effect. Such differences between GONMs with three kinds of oxygen-contained functional groups pave a powerful platform to better understand and design the GO based separation membrane. Keywords: graphene oxide; carboxyl; hydroxyl; epoxy; water purification; membrane

Graphical Abstract

2

1.

Introduction With the rapid expansion of industrialization and population, water consumption

is soaring astonishingly, thus the purification of industrial organic wastewater and desalination of seawater to obtain potable water is of current interest.[1] However, some traditional methods for water purification, such as multistage flash distillation (MSF), multi-effect distillation (MED), and reverse osmosis (RO) technologies, suffer the huge energy consumption. Therefore, the development of efficient and low-cost water treatment technologies is particularly urgent[2–5]. Recently, nanofiltration membrane separation technologies[6,7] gain special attention driven by their low-energyconsumption and relative high efficiency[8–10]. Among the diverse materials used in nanofiltration membrane, graphene oxide (GO) has attracted more and more attentions from both theoretical researchers and experimental investigators due to its excellent mechanical properties, low cost[11–13], and the tunable inter-layer spacing of adjacent nanosheets, which enable membrane to sieve solute accurately[7,14–18]. These properties lead GO to be natural nanofiltration membrane materials for organic 3

molecules separating and seawater desalinating[2,6,8,19,20]. However, GONMs originate from different graphene present totally distinct water purification performance. For example, Xu, Weiwei L et al fabricated a GONM with 41% C-O bond and 10% C=O bond, such a membrane exhibited accepted water permeance around 20 L m-2 h-1 bar-1 and MgSO4 rejection about 60%[21]. While, Kunli Goh et al described a GONM with 48 L m-2 h-1 bar-1 water permeance and 67% methylene blue rejection, and the water transport capacity is more than twice of above[22]. Interestingly, Dae Woo Kim reported a homemade GONM by the same Hummers’ method, but the methylene blue rejection reached above 90%[12]. The GONMs prepared by same material and method, but exhibited distinct water purification performance, the principle consideration is the graphite source, as graphite with different configuration would produces various GO during the oxide process[23]. Besides, GONMs with different reduced degrees also represent diverse water purification properties. As our previous work[24] showed that weak reduced GONMs by UV-irradiation possess higher water permeance and dyes rejections than pristine membranes. More than that, Jin-Hyeok Jang et al[25] described a heat treated rGONM with deeper reduced degree, which shows slower water permeance and heavy metal rejections but better dyes removal rates. To summarize, the oxygen-containing functional groups make major changes to the GONMs water purification performance, and it maybe a effective approach to control the membrane properties by adjusting oxygen-containing functional groups. Although the impact of oxygen-containing functional groups of GONMs on water 4

purification has increasingly attracted the attention of researchers, such as Ruosang Qiu et al[26] studied how edge functional groups of GO lattices affect water transport in GONM by numerically method. Dongshuai Hou et al[27] also used molecular dynamics method to simulate the effect of functional groups of GO nanosheets surface on water and ions. But it is worth noting that the reports about the effect of different oxygencontained functional groups on water separation are all studied by simulation methods which usually worked under confined boundary conditions, and it is undeniable that some objective conditions in real word have been neglected. In this work, in order to reveal how different oxygen-containing functional groups affect GONMs on water purification performance more objective and practical, we fabricated carboxyl dominant GO (C-GO), hydroxyl dominant GO (H-GO) and epoxy dominant GO (E-GO), then made three kinds of GO membranes on Polyvinylidene fluoride (PVDF) support by vacuum filtration method. After that, SEM, Raman, XPS, XRD, FTIR, TGA, Zeta potential were used to characterize the chemical and physical properties of the three kinds of GO and GONMs. Such membranes also had been employed for water transport and waste water (dye and salt solution) treatment study by dead-end filtration facility to reveal how oxygen-contained functional groups affect membrane performance. Meanwhile, the cyclic experiment of different charged and molecule weight dyes solution had also been tested to study the contribution of -OH, COC- and -COOH on membrane antifouling performance. Hope such differences between GONMs with three kinds of oxygen-contained functional groups to pave a powerful platform to better understand and design the GO based separation membrane. 5

2.

Experimental

2.1. Materials GO was purchased from the sixth element (Changzhou, China) Materials Technology Co., Ltd. The specifications for GO: oxygen content (atomic %): ≤ 31.0%, average lateral dimension: ˂15µm, monolayer probability: ˃90%. HCl (36.0%~ 38.0%), HBr (40%), Oxalic acid (AR, ≧99.0%), H2O2 (35%), FeSO4·7H2O (AR, ≧99.0%), Na2SO4 (AR, ≧99.0%), Methylene blue (MB, positively charged, Mw 319.85, AR, ≧99.0%), Eriochrome black T (EBT, negatively charged, Mw 461.38, AR, ≧99.0%), Trypan blue (TB, negatively charged, Mw 960.81, AR, ≧99.0%), Rhodamine B (RB, neutral[2], Mw 479.01, AR, ≧99.0%), all the details of dyes are shown in Table 1. MgSO4 (AR, ≧99.0%), AgNO3 (AR, 99.8%) were purchased from Kelong Chemical Co., Ltd. (Chengdu, China). Commercial Polyvinylidene Fluoride (PVDF) membrane (form: square, diameter: 5cm, thickness: 200µm, pore size: 0.05µm) was purchased from

RisingSun

Membrane

Technology

(Beijing)

Co.,

Ltd.

(https://www.risingsunmem.com/)[28] Table 1 The basic information of four kinds of organic dyes.

2.2. Carboxyl dominant GO (C-GO) fabrication GO purchased was already hydroxyl dominant GO (H-GO) as XPS result showed 6

(Figure 1b), and the C-GO and E-GO were modified from H-GO. The C-GO was fabricated as following steps: the H-GO dispersion (2.5 mg mL-1, 30mL) with 5mL HBr was firstly vigorously stirring for 12h at room temperature, then added 1.50g oxalic acid for another 4h[29], and purified by centrifugation method. Finally, the obtained CGO was diluted to 0.05mg mL-1 to the follow-up experiments.

Scheme 1 Schematic illustration of C-GO preparation process. 2.3. Epoxy dominant GO (E-GO) fabrication The H-GO dispersion (2.5 mg mL-1) was treated by 16.66 mg/L H2O2 and 13.62 mg/L FeSO4·7H2O mixed solution (pH≤3) for more than half an hour to obtained the polyhydroxylated GO nanosheets. As the adjacent hydroxyl groups were easily lost to became epoxy groups, the E-GO could be obtained by dried polyhydroxylated GO[28]. Finally, the obtained E-GO powder was diluted to 0.05mg mL-1 to the follow-up experiments.

7

Scheme 2 Schematic illustration of E-GO preparation process. 2.4. GO membranes fabrication 1.6mL GO dispersion (0.05 mg mL-1) was diluted with 50 mL deionized water, then ultrasonicated the obtained dispersion with stirring for 10 minutes to fully disperse. Next, transferred the dilute dispersion from beaker to filter cup. Finally, GO membrane was vacuum filtrated (S1) on PVDF support membrane (effective diameter: 3.91cm). In which, the mass loading of GO was 66.67 mg m-2. Besides, we also fabricated thick GO membranes above 2 g m-2 to analyze the XRD. 2.5. Materials characterization UV-vis absorption spectroscopy (UV-1800, SHIMADZU) was used to evaluate the dyes rejection performance of GONMs over 400~800 nm. Scanning electron microscopy (FSEM, FEI Inspect F50) was used to characterize the surface morphology of GO membranes (~1cm2). The D-spacing of GO membranes was determined by Xray diffractometer (XRD, PANalytical, The Netherlands, Cu Kα radiation source) in the 2θ range between 5 and 15˚. LabRAM HR800 (532 nm laser, spot size~1 µm2) was taken to characterize Raman spectra of GONMs. The content of chemical composition of different GO dispersion (0.05 mg/mL) was measured on X-ray photoelectron 8

spectroscopy (XPS, Kratos, XSAM800, Al Kα excitation source). Fourier transform infrared (FTIR) spectrometer (Beijing Rayleigh Analytical Instrument, WQF‐520, China) and thermogravimetric analysis (TGA) (STA449F3, Netzsch) were used to affirm the formation of C-GO, H-GO and E-GO. Zeta potential was used to characterize the surface charge of GO nanosheets and dispersibility of GO dispersion (0.05mg mL1,

pH=7) by a Brookhaven Instruments Corporation phase analysis light scattering

(PALS) zeta potential analyzer. The conductivities of the salt solutions were measured by the conductivity meter (FE38, METTLER TOLEDO Instruments (Shanghai) Co., Ltd, China). 2.6. Permeance and rejection properties of the membranes In this work, the permeance and rejection properties of GONMs were measured on a homemade dead-end pressure filtration equipment (S2) with an effective area of 7.07 cm2 at room temperature (5 bar). The concentration of feed dye solution was 20 mg/L, that of feed salt solution was 1000 mg/L. The permeance 𝐽(L m-2 h-1 bar-1) and rejection 𝑅(%) were calculated by equations (1) and (2), respectively. 𝑉

(1)

𝐽 = 𝐴∆𝑡𝑃 𝐶𝑝

(2)

𝑅 = 1 ― 𝐶𝑓 × 100%

where 𝑉(L) was the volume of feed solution, 𝐴(m2) was the effective area of membrane, ∆𝑡(h) was the permeate time, 𝑃(bar) was the applied pressure, and 𝐶𝑝 and 𝐶𝑓 were the concentration of permeate and feed solutions, respectively. 3.

Results and discussion

3.1. Characteristics of C-GO, H-GO and E-GO 9

The XPS results (Figures 1a-c) of C-GO, H-GO and E-GO depicted the relative content of different oxygen-contained functional groups. For H-GO (Figure 1b), the content of hydroxyl group was more than that of epoxy and carboxyl groups. Compared to H-GO, the epoxy content of E-GO (Figure 1a) increased obviously and exceeded the other groups. During C-GO reaction process, the hydroxyl groups of H-GO turned into carboxyl groups, and occupied the dominated position (Figure 1c). All the data listed in S3 indicated that we fabricated three kinds of GO successfully. Then, TGA analysis was carried out to confirm the difference between each kind of GO. Generally for GO, below 100 ℃, the main mass loss is associated with the residual water molecules[30]. Till 185 ℃, the removal of few physiosorbed water molecules[30] and labile oxygencontained functional groups[31,32] lead the slight weight loss. Further increased the temperature to 225 ℃, the relatively stable oxygen-contained functional groups began to decomposed[33]. As Figure 1d showed that the curves of three kinds of GO below 100℃ have little difference. But between ~100 to 185℃, the mass loss order was EGO > C-GO > H-GO, this result indicated that the labile oxygen-contained functional groups content is E-GO > C-GO > H-GO. Around 225℃, the mass loss order was CGO ≈ H-GO > E-GO, due to the total O content of three different GO. The FTIR spectra was following to characterize the C-GO, H-GO and E-GO. As presented in Figure 1e, the absorption bands around 1729cm-1 and 1399 ~1064cm-1 were ascribed to the C=O stretching of -COOH and the C-O stretching of the C-OH/C-O-C groups[15], respectively. Between the different GO, E-GO has stronger C-O stretching absorption[28]. Moreover, the CO2 absorption (2200 ~2400 cm-1) of E-GO was also 10

stronger than that of H-GO and C-GO, this is because the adsorption energy for C-O-C is greater than that of both -COOH and -OH[34]. In addition, after esterified H-GO by oxalic acid, the C=O absorption of C-GO around 1729 cm-1 is enhanced dramatically, and it is consistent with the experimental design. For Raman spectra of GONMs in our study, G band at 1600cm-1 means order degree of GONMs. Contrarily, D band at 1350cm-1 refers to the disorder degree of GONMs and defect degree of GO lattice[35], the intensity ratio of D and G band (ID/IG) represents the relative disorder and defect degree of each GONMs. As shown in Figure 1f, the ID/IG of C-GO, H-GO and E-GO were 0.9955, 0.9975 and 0.9898, respectively. The little difference of disorder and defect degree between three kinds of GONMs indicated that (a) modified reaction did not introduce any defect and (b) different content of various oxygen-contained functional groups had little influence on GONMs structure. And these similar structures also provided an objective and scientific condition for comparing the differences among different oxygen-contained functional groups on GONMs properties. Furthermore, as shown in figure 1 g, the zeta potential order C-GO (-35.06 mV) H-GO > E-GO, due to the different polarity of those various GO lattices[23].

11

Figure 1. High-resolution C 1s XPS spectra of (a) E-GO, (b) H-GO, (c) C-GO dispersions. (d) TGA plot, (e) FTIR spectra of C-GO, H-GO and E-GO powders. (f) Raman spectra, (g) Zeta potentials of 0.05 mg/mL C-GO, H-GO and E-GO dispersions.

3.2. Membrane characterization In order to study the effect of three different kinds of oxygen-contained functional groups on D-spacing of GONMs, we fabricated E-GO, H-GO and C-GO membranes with the area density of 2g m-2, respectively, for XRD detecting. As shown in Figure 2a, the 2θ of E-GO, H-GO and C-GO membranes were all around 10˚ with tiny difference, and the D-spacing (Calculated through Bragg formulation as follow: λ = 2dsin 𝜃. where λ is the wavelength of the Cu X-ray beam about 0.154056nm, d is the interlayer spacing between contiguous GO layers, 𝜃 is the diffraction angle.) were 8.80, 8.86 and 8.92 Å, respectively. These tiny differences may be mainly derived from 12

the size of different oxygen-contained functional groups, which act as supports between adjacent GO nanosheets in dry state. But in wet state (Figure 2b), the 2θ of each kind of GO membrane shifted left compare to that in dry state. The D-spacing of E-GO, HGO and C-GO membranes presented an obvious distinction and were 13.46, 14.27 and 15.06 Å, respectively, due to the combined action of hydrophilicity (water molecules fill in the interlayer space of GO nanosheets and enlarge the D-spacing) and electrostatic repulsion of different oxygen-contained functional groups[26]. To further study the importance of electrostatic action on D-spacing of GONMs, we also tested CGO membrane in different pH conditions. As shown in Figure 2c, after successively soaked the C-GO membrane into the solution with pH of 1, 7 and 13 for 30min (in order to avoid the GONMs be reduced by strong alkaline solution for long-term immersion[36]), the C-GONM exhibited more distinct D-spacing, which was 12.85 and 13.7Å when the pH was 1 and 7, respectively. Interestingly, when the C-GO membrane was immersed into the strong alkaline solution, the 2θ was lower than 5˚ and could not be tested (test range was 5~15˚), it was indicated that the D-spacing of C-GO membrane at pH=13 exceeded 17.66 Å (2θ=5˚)[18]. It was intuitively proved that the carboxyl groups have a great influence on the D-spacing. We then used SEM to observe the surface morphology of C-GO, H-GO and E-GO membranes. Obviously, there were many folds exhibit on the H-GO membrane surface (Figure 2e), which formed the water transport nanochannels. Different from H-GO membrane, C-GO membrane exhibited less folds on the surface (Figure 2d), due to the abundant of -COO- that made C-GO nanosheets more flatter during the filtrate membrane process. As shown in Figure 2f, 13

few folds could be observed on the E-GO membrane surface, attributed to the weaker H-bond of -COC- groups that made E-GO nanosheets more facile to stack compacted.

Figure 2. XRD pattern of C-GO, H-GO and E-GO membranes in (a) dry state and (b) wet state. (c) XRD pattern of C-GO at different pH conditions. SEM images of (d) C-GO, (e) H-GO, (f) E-GO membranes

3.3. Membrane evaluation Next, we fabricated C-GO, H-GO and E-GO membrane, respectively, with the area density of 66.67 mg m-2 to study the influence of different oxygen-contained functional groups on membrane performance. As shown in Figure 3a, the water permeance of C-GO, H-GO and E-GO membranes were 9.19, 7.22 and 5.94 L m-2 h-1 bar-1, respectively. Considering the water molecules confined in real GONMs nanochannels (not strictly parallel plate) cannot form consecutive ice-like state as previously study reported[37–42], liquid state water migration may be the dominant effect on water transport rate. In addition, the type of oxygen-contained functional groups affect water molecules migration little, due to the sp2 domains were the main 14

frictionless channels of water transport[18,43,44]. According to above reasons, the Dspacing of GONMs were the main factor affecting water transport. However, the salt rejection rates of different GONMs were all around 15% under low pressure, it was indicated that different types of oxygen-contained functional groups had little influence on GONMs salt rejection performance, due to the main factor affect salt rejection were applied pressure and channel length[45–47]. Furthermore, we used three different charged and molecule weight dyes (MB, EBT and TB) to estimate our GONMs purification performance. In this section, the volume of each dye feed solution (20mg/L) was 60mL, during the filtration process, every 10 mL filtrate would be collected to test the UV spectra. As Figure 3b showed that the MB filtrate rejection rates of three kinds of GONMs were all near 100% at first, then decreased gradually with the increase of filtrate volume, also the differential of that became more and more obvious. Finally, the MB rejection rates of E-GO, H-GO and C-GO membranes were 98.85%, 95.33% and 83.46%, respectively. More than this, the rejection curves of EBT and TB also had the same trend of that of MB. The final EBT rejection rates of E-GO, H-GO and C-GO membranes were 99.14%, 93.28% and 85.73%, respectively. The final TB rejection rates of that were 99.25%, 99.12% and 99.10%, respectively. The results indicated that, for GONMs, the D-spacing affect water permeance and dye rejection performance critically. With the D-spacing of GONMs increased, the water permeance improved and the dye rejection rate decreased. Besides, for dye molecule weight, the final rejection rates increased when we used larger molecule weight dye, due to the size sieving action that larger size molecule would be rejected easier. 15

Figure 3. (a) The water permeance, NaSO4 solution (1000 mg/L) rejection, (b) MB solution (20 mg/L) rejection, (c) EBT solution (20mg/L) rejection and (d) TB solution (20 mg/L) rejection of C-GO, H-GO and E-GO membranes (66.67 mg m-2). Interestingly, we also observed that different oxygen-contained functional groups dominated GONMs possess distinct antifouling performance. In this antifouling experiment, we placed three kinds of GONMs in the home-made equipment, as Figure 4a-c showed that the initial appearance of C-GO, H-GO and E-GO membranes were completely cleaning. We then filtrated 60 mL TB solution (20 mg/L), as shown in Figure 4d-f, the GONMs were polluted seriously, particularly the E-GO membrane was obviously darker than other two kinds of GONMs. After that, the GONMs were rinsed with pure water, and exhibited different surface appearance. As Figure 4g showed, the C-GO membrane almost return to original appearance. The H-GO membrane remained some dye spots (Figure 4h), and the E-GO membrane could not be clean at all (Figure 16

4i). The different antifouling performance of various oxygen-contained functional groups dominated GONMs may attribute to electrostatic interaction that larger negative charge density conduces to repel the like charged dye molecules (TB, negative). In order to prove this view, we further used three different electrical charged (positive charged MB, negative charged EBT and neutral charged RB) dyes with similar molecule weight to test the antifouling property of C-GO membrane. As Figure S5 showed, after rinsing with pure water, the membrane polluted with negatively charged EBT was basic returned to original appearance, but the membranes polluted with neutral and positively charged dyes were still be polluted. The results reconfirmed that the electrostatic action is helpful to improve the membrane antifouling performance to the same charged dyes.

Figure 4. The digital images of C-GO, H-GO and E-GO membranes before, after TB 17

filtration and after rinsing. Finally, cyclic tests were carried out to examine the effect of different oxygencontained functional groups on long-term performance. In this section, we totally conducted five cycle tests that each cycle test contained 60 mL TB feed (20 mg/L) solution. As Figure 5a-c showed, the TB rejection trend of different GONMs were all gradually decreased with the test going on. Before next cycle experiment, we rinsed the GONMs with pure water, and the TB rejection rate would be returned partially and then continue decreased. The cycle then repeated itself. At the end of the cyclic tests (Figure 5d), the TB solution permeance order of different GONMs was consistent with our previous work (C-GO > H-GO > E-GO), however, the TB rejection rate (92.29%) of C-GO membrane was unexpectedly higher than that (74.58%) of H-GO, and this phenomenon cannot be simply explained by D-spacing theory. Therefore, the electrostatic exclusion action[48] may be the main reason that C-GO membrane possessed higher TB rejection rate than that of H-GO[49]. These results indicated that size sieving action and electrostatic interaction play an important role during the dye molecule rejection process by GONMs.

18

Figure 5. The cyclic test results of TB dye solution treated by C-GO, H-GO and EGO membrane. 4.

Conclusion In summary, we successfully fabricated carboxyl dominant GO (C-GO), hydroxyl

dominant GO (H-GO) and epoxy dominant GO (E-GO), respectively, to study how the different oxygen functional groups of GONMs affect water purification performance. It was found that, the different oxygen-contained functional groups affected the Dspacing of GONMs extremely in water condition, and the D-spacing order of GONMs was C-GO > H-GO > E-GO, due to the combined effect of hydrophilicity and electrostatic action of each kind of oxygen-contained functional groups. Because of the trade-off effect, such GONMs exhibit distinct water transport and solute sieving performance. Besides, we also found that the enrichment of large amount of charge 19

conduce to improve the rejection and antifouling performance of the same charged pollutants. However, the results of salt rejection experiment showed that the different oxygen-contained functional groups have little effect on desalination property of low metal salt ion. Herein, our study disclosed the mechanism of different oxygen-contained functional groups adjusting GONMs purification performance by affect the D-spacing and electric density of that, hoping to pave a powerful platform to better understand and design the GO based nanofiltration membranes in the future water treatment.

ACKNOWLEDGEMENTS This work was financially supported by National Natural Science Foundation of China (51774245), National Natural Science Foundation of China (51874255), Applied Basic Research Program of Science and Technology Department of Sichuan Province (No.2018JY0517), Open Fund (PLN161) of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation and Research Center of Energy Polymer Materials (Southwest Petroleum University). All the test provided by College of Chemistry and Chemical

Engineering

(Southwest

Petroleum

University)

and

‘ceshigo’

(www.ceshigo.com). REFERENCES [1]

M.A. Eltawil, Z. Zhengming, L. Yuan, A review of renewable energy technologies integrated with desalination systems, Renew. Sustain. Energy Rev. 13 (2009) 2245–2262.

[2]

P. Zhang, J.L. Gong, G.M. Zeng, B. Song, S. Fang, M. Zhang, H.Y. Liu, S.Y. 20

Huan, P. Peng, Q.Y. Niu, D.B. Wang, J. Ye, Enhanced permeability of rGO/SGO layered membranes with tunable inter-structure for effective rejection of salts and dyes, Sep. Purif. Technol. 220 (2019) 309–319. doi:10.1016/j.seppur.2019.03.041. [3]

J. Hou, C. Bao, S. Qu, X. Hu, S. Nair, Y. Chen, Graphene oxide membranes for ion separation: detailed studies on the effects of fabricating conditions, Appl. Surf. Sci. 459 (2018) 185–193.

[4]

R. Ni, Y. Wang, X. Wei, J. Chen, P. Xu, W. Xu, J. Meng, Y. Zhou, Ionic liquid modified molybdenum disulfide and reduced graphene oxide magnetic nanocomposite for the magnetic separation of dye from aqueous solution, Anal. Chim. Acta. 1054 (2019) 47–58. doi:10.1016/j.aca.2018.12.037.

[5]

A. Abdel-Karim, J.M. Luque-Alled, S. Leaper, M. Alberto, X. Fan, A. Vijayaraghavan, T.A. Gad-Allah, A.S. El-Kalliny, G. Szekely, S.I.A. Ahmed, S.M. Holmes, P. Gorgojo, PVDF membranes containing reduced graphene oxide: Effect of degree of reduction on membrane distillation performance, Desalination. 452 (2019) 196–207. doi:10.1016/j.desal.2018.11.014.

[6]

A.W. Mohammad, Y.H. Teow, W.L. Ang, Y.T. Chung, D.L. Oatley-Radcliffe, N. Hilal, Nanofiltration membranes review: Recent advances and future prospects, Desalination. 356 (2015) 226–254. doi:10.1016/j.desal.2014.10.043.

[7]

Y. Mo, X. Zhao, Y. xiao Shen, Cation-dependent structural instability of graphene oxide membranes and its effect on membrane separation performance, Desalination. 399 (2016) 40–46. doi:10.1016/j.desal.2016.08.012. 21

[8]

L. Shao, X. Cheng, Z. Wang, J. Ma, Z. Guo, Tuning the performance of polypyrrole-based solvent-resistant composite nanofiltration membranes by optimizing polymerization conditions and incorporating graphene oxide, J. Memb. Sci. 452 (2014) 82–89. doi:10.1016/j.memsci.2013.10.021.

[9]

J. Liu, Z. Cui, L. Hou, D. Li, Y. Gao, L. Shuai, J. Liu, J. Jin, N. Wang, Y. Zhao, Bioinspired membranes for multi-phase liquid and molecule separation, Sci. China Chem. 62 (2019) 14–23. doi:10.1007/s11426-018-9332-2.

[10]

K. Rahaoui, L.C. Ding, L.P. Tan, W. Mediouri, F. Mahmoudi, K. Nakoa, A. Akbarzadeh, Sustainable Membrane Distillation Coupled with Solar Pond, Energy Procedia. 110 (2017) 414–419.

[11]

S.G. Kim, S.H. Wang, C.M. Ok, S.Y. Jeong, H.S. Lee, Lateral diffusion of graphene oxides in water and the size effect on the orientation of dispersions and electrical conductivity, Carbon N. Y. 125 (2017) 280–288. doi:10.1016/j.carbon.2017.09.054.

[12]

D.W. Kim, J. Choi, D. Kim, H.T. Jung, Enhanced water permeation based on nanoporous multilayer graphene membranes: the role of pore size and density, J. Mater. Chem. A. 4 (2016) 17773–17781. doi:10.1039/C6TA06381K.

[13]

W. Ren, H.-M. Cheng, The global growth of graphene, Nat. Nanotechnol. 9 (2014) 726–730. doi:10.1038/nnano.2014.229.

[14]

H. Qiu, M. Xue, C. Shen, Z. Zhang, W. Guo, Graphynes for Water Desalination and Gas Separation, Adv. Mater. 1803772 (2019) 1–16. doi:10.1002/adma.201803772. 22

[15]

Y. Liu, R. Deng, Z. Wang, H. Liu, Carboxyl-functionalized graphene oxide– polyaniline composite as a promising supercapacitor material, J. Mater. Chem. 22 (2012) 13619–13624. doi:10.1039/c0xx00000x.

[16]

K.S. Andrikopoulos, G. Bounos, D. Tasis, L. Sygellou, V. Drakopoulos, G.A. Voyiatzis, The Effect of Thermal Reduction on the Water Vapor Permeation in Graphene Oxide Membranes, Adv. Mater. Interfaces. 1 (2014) 1–8. doi:10.1002/admi.201400250.

[17]

E. Yang, M.H. Ham, H.B. Park, C.M. Kim, J. ho Song, I.S. Kim, Tunable semi-permeability of graphene-based membranes by adjusting reduction degree of laminar graphene oxide layer, J. Memb. Sci. 547 (2018) 73–79. doi:10.1016/j.memsci.2017.10.039.

[18]

S. Zheng, Q. Tu, J.J. Urban, S. Li, B. Mi, Swelling of Graphene Oxide Membranes in Aqueous Solution: Characterization of Interlayer Spacing and Insight into Water Transport Mechanisms, ACS Nano. 11 (2017) 6440–6450. doi:10.1021/acsnano.7b02999.

[19]

Y. Han, Z. Xu, C. Gao, Ultrathin graphene nanofiltration membrane for water purification, Adv. Funct. Mater. 23 (2013) 3693–3700.

[20]

Y. Wei, Y. Zhu, Y. Jiang, Photocatalytic self-cleaning carbon nitride nanotube intercalated reduced graphene oxide membranes for enhanced water purification, Chem. Eng. J. 356 (2019) 915–925. doi:10.1016/j.cej.2018.09.108.

[21]

W.L. Xu, C. Fang, F. Zhou, Z. Song, Q. Liu, R. Qiao, M. Yu, Self-Assembly: 23

A Facile Way of Forming Ultrathin, High-Performance Graphene Oxide Membranes for Water Purification, Nano Lett. 17 (2017) 2928–2933. [22]

K. Goh, W. Jiang, H.E. Karahan, S. Zhai, L. Wei, D. Yu, A.G. Fane, R. Wang, Y. Chen, All-carbon nanoarchitectures as high-performance separation membranes with superior stability, Adv. Funct. Mater. 25 (2015) 7348–7359.

[23]

D.R. Dreyer, S. Park, Christopher W. Bielawski, Rodney S. Ruoff, The chemistry of graphene oxide, Chem. Soc. Rev. 39 (2010) 228–240. doi:10.1039/B917103G.

[24]

H. Yu, Y. He, G. Xiao, Y. Fan, J. Ma, Y. Gao, R. Hou, J. Chen, Weakreduction graphene oxide membrane for improving water purification performance, J. Mater. Sci. Technol. (2019). doi:10.1016/j.jmst.2019.08.024.

[25]

J.H. Jang, J.Y. Woo, J. Lee, C.S. Han, Ambivalent Effect of Thermal Reduction in Mass Rejection through Graphene Oxide Membrane, Environ. Sci. Technol. 50 (2016) 10024–10030. doi:10.1021/acs.est.6b02834.

[26]

R. Qiu, S. Yuan, J. Xiao, X.D. Chen, C. Selomulya, X. Zhang, M.W. Woo, Effects of Edge Functional Groups on Water Transport in Graphene Oxide Membranes, ACS Appl. Mater. Interfaces. 11 (2019) 8483–8491. doi:10.1021/acsami.9b00492.

[27]

D. Hou, Q. Zhang, M. Wang, J. Zhang, P. Wang, Y. Ge, Molecular dynamics study on water and ions on the surface of graphene oxide sheet: Effects of functional groups, Comput. Mater. Sci. 167 (2019) 237–247. doi:10.1016/j.commatsci.2019.05.038. 24

[28]

J.L. Han, D. Zhang, W. Jiang, Y. Tao, M.J. Liu, M.R. Haider, R.Y. Ren, H. cheng Wang, W.L. Jiang, Y.C. Ding, Y.N. Hou, B. Zhang, H.Y. Cheng, X. Xia, Z. Wang, A.J. Wang, Tuning the functional groups of a graphene oxide membrane by ·OH contributes to the nearly complete prevention of membrane fouling, J. Memb. Sci. 576 (2019) 190–197. doi:10.1016/j.memsci.2018.12.055.

[29]

Y. Liu, R. Deng, Z. Wang, H. Liu, Carboxyl-functionalized graphene oxide– polyaniline composite as a promising supercapacitor material, J. Mater. Chem. 22 (2012) 13619–13624. doi:10.1039/c0xx00000x.

[30]

A. Alhadhrami, S. Salgado, V. Maheshwari, Thermal reduction to control the spacing in graphene oxide membranes: Effect on ion diffusion and electrical conduction, RSC Adv. 6 (2016) 70012–70017. doi:10.1039/c6ra16400e.

[31]

L. Guardia, J.I. Paredes, P. Solı, J.M.D. Tasco, Vitamin C Is an Ideal Substitute for Hydrazine in the Reduction of Graphene Oxide Suspensions, (2010) 6426– 6432. doi:10.1021/jp100603h.

[32]

M. Wojtoniszak, X. Chen, R.J. Kalenczuk, A. Wajda, J. Łapczuk, M. Kurzewski, M. Drozdzik, P.K. Chu, E. Borowiak-Palen, Synthesis, dispersion, and cytocompatibility of graphene oxide and reduced graphene oxide, Colloids Surfaces B Biointerfaces. 89 (2012) 79–85. doi:10.1016/j.colsurfb.2011.08.026.

[33]

N. Rubio, K.C. Mei, R. Klippstein, P.M. Costa, N. Hodgins, J.T.W. Wang, F. Festy, V. Abbate, R.C. Hider, K.L.A. Chan, K.T. Al-Jamal, Solvent-Free 25

Click-Mechanochemistry for the Preparation of Cancer Cell Targeting Graphene Oxide, ACS Appl. Mater. Interfaces. 7 (2015) 18920–18923. doi:10.1021/acsami.5b06250. [34]

M. Lalitha, S. Lakshmipathi, Gas adsorption efficacy of graphene sheets functionalised with carboxyl, hydroxyl and epoxy groups in conjunction with Stone-Thrower-Wales (STW) and inverse Stone-Thrower-Wales (ISTW) defects, Phys. Chem. Chem. Phys. 19 (2017) 30895–30913. doi:10.1039/c7cp06900f.

[35]

† Konstantin N. Kudin, ‡ Bulent Ozbas, ‡ Hannes C. Schniepp, ‡ Robert K. Prud’homme, ‡ and Ilhan A. Aksay, † Roberto Car*, Raman Spectra of Graphite Oxide and Functionalized Graphene Sheets, Nano Lett. 8 (2008) 36– 41.

[36]

X. Fan, W. Peng, Y. Li, X. Li, S. Wang, G. Zhang, F. Zhang, Deoxygenation of exfoliated graphite oxide under alkaline conditions: a green route to graphene preparation, Adv. Mater. 20 (2008) 4490–4493. doi:10.1002/adma.200801306.

[37]

R.J. Mashl, S. Joseph, N.R. Aluru, E. Jakobsson, Anomalously Immobilized Water: A New Water Phase Induced by Confinement in Nanotubes, (2003) 0– 3.

[38]

D.W. Boukhvalov, M.I. Katsnelson, Y.W. Son, Origin of anomalous water permeation through graphene oxide membrane, Nano Lett. 13 (2013) 3930– 3935. doi:10.1021/nl4020292.

[39]

H. Zeng, K. Wu, X. Cui, Z. Chen, Wettability effect on nanoconfined water 26

flow: Insights and perspectives, Nano Today. 16 (2017) 7–8. doi:10.1016/j.nantod.2017.05.001. [40]

Y. Liu, Q. Wang, L. Zhang, T. Wu, Dynamics and density profile of water in nanotubes as one-dimensional fluid, Langmuir. 21 (2005) 12025–12030. doi:10.1021/la0517181.

[41]

M. Ma, F. Grey, L. Shen, M. Urbakh, S. Wu, J.Z. Liu, Y. Liu, Q. Zheng, Water transport inside carbon nanotubes mediated by phonon-induced oscillating friction, Nat. Nanotechnol. 10 (2015) 692–695. doi:10.1038/nnano.2015.134.

[42]

K. Wu, Z. Chen, J. Li, X. Li, J. Xu, X. Dong, Wettability effect on nanoconfined water flow, Proc. Natl. Acad. Sci. 114 (2017) 3358–3363. doi:10.1073/pnas.1612608114.

[43]

Q. Zhang, X. Qian, K.H. Thebo, H.M. Cheng, W. Ren, Controlling reduction degree of graphene oxide membranes for improved water permeance, Sci. Bull. 63 (2018) 788–794.

[44]

L. Huang, J. Chen, T. Gao, M. Zhang, Y. Li, L. Dai, L. Qu, G. Shi, Reduced Graphene Oxide Membranes for Ultrafast Organic Solvent Nanofiltration, Adv. Mater. 28 (2016) 8669–8674.

[45]

P. Sun, M. Zhu, K. Wang, M. Zhong, J. Wei, D. Wu, Z. Xu, H. Zhu, Selective ion penetration of graphene oxide membranes, ACS Nano. 7 (2013) 428–437.

[46]

P. Sun, R. Ma, H. Deng, Z. Song, Z. Zhen, K. Wang, T. Sasaki, Z. Xu, H. Zhu, Intrinsic high water/ion selectivity of graphene oxide lamellar membranes in concentration gradient-driven diffusion, Chem. Sci. 7 (2016) 6988–6994. 27

[47]

L. Chen, G. Shi, J. Shen, B. Peng, B. Zhang, Y. Wang, F. Bian, J. Wang, D. Li, Z. Qian, G. Xu, G. Liu, J. Zeng, L. Zhang, Y. Yang, G. Zhou, M. Wu, W. Jin, J. Li, H. Fang, Ion sieving in graphene oxide membranes via cationic control of interlayer spacing, Nature. 550 (2017) 1–4.

[48]

D.W. Kim, J. Jang, I. Kim, Y.T. Nam, Y. Jung, H.T. Jung, Revealing the Role of Oxygen Debris and Functional Groups on the Water Flux and Molecular Separation of Graphene Oxide Membrane: A Combined Experimental and Theoretical Study, J. Phys. Chem. C. 122 (2018) 17507–17517. doi:10.1021/acs.jpcc.8b03318.

[49]

L. Chen, N. Li, Z. Wen, L. Zhang, Q. Chen, L. Chen, P. Si, J. Feng, Y. Li, J. Lou, L. Ci, Graphene oxide based membrane intercalated by nanoparticles for high performance nanofiltration application, Chem. Eng. J. 347 (2018) 12–18. doi:10.1016/j.cej.2018.04.069.

28