Effect of TiO2 content on the properties of polysulfone nanofiltration membranes modified with a layer of TiO2–graphene oxide

doi:10.1016/j.seppur.2020.116770

Separation and Purification Technology

Volume 242, 1 July 2020, 116770

https://doi.org/10.1016/j.seppur.2020.116770 Get rights and content

Highlights

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The d-spacing of GO sheets can be tuned by adjusting the TiO₂ loading.
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The antifouling property of the membrane is related to the amount of TiO₂ loading.
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NFG-2 membrane exhibited a high rejection for dyes and low Na₂SO₄ retention.

Abstract

Graphene oxide (GO)-based membranes have been widely used for molecular separation due to their size exclusion effect. However, it remains a challenge to prepare a structurally stable, freestanding GO-based membrane that exhibits efficient separation. Herein, GO nanofiltration (NF) membranes with different loadings of TiO₂ (TiO₂@GO) were successfully prepared on top of a polysulfone (PSF) support layer and showed high efficiency in dye separation/desalination, along with antifouling and antibacterial activity. The resulting TiO₂@GO NF membranes also showed excellent structural stability. The membrane prepared with the same contents of GO and TiO₂ (NFG-2) exhibited high dye rejection (>98%) and low Na₂SO₄ rejection (<6%) and thus could be applied in the treatment of dye wastewater. Moreover, its permeation flux (3.6 L·m⁻²·h⁻¹·bar⁻¹) and dye rejection (98.0%) remained constant at high levels after 9 h of operation. Antifouling and antibacterial properties were also observed. This new kind of NF membrane may be a promising candidate for use in dye separation and desalination applications.

Graphic abstract

Introduction

With industrial development and population growth, many pollutants, such as dyes, are released into rivers and lakes and cause serious water pollution [1], [2]. Current treatment technologies to separate dyes and salts from water are precipitation, ion exchange, solvent extraction, salting out, adsorption, and membrane separation [3], [4], [5], [6]. Among these technologies, membrane separation has been extensively used to remove dyes from wastewater due to its low energy consumption, high separation efficiency and environmentally friendly characteristics [6]. Of particular significance are nanofiltration (NF) membranes, which have an average pore size of 0.5–2.0 nm and have been widely used in water treatment in recent years [6], [7], [8]. Compared with ultrafiltration (UF) membranes and reverse osmosis (RO) membranes, NF membranes can be used to effectively separate small solutes at low pressures. Therefore, NF has attracted increasing interest for water purification, dye separation/desalination and other applications [9], [10]. Although flexible NF membranes can be simply prepared and are relatively low cost, their application is hindered by organic fouling of the membrane and their poor antibacterial properties [11]. Herein, to improve the antifouling and antibacterial performance of NF membranes, we explore the separation performance of a GO-based NF membrane with different contents of TiO₂.

GO has recently attracted great interest due to its large specific surface area, good water-dispersion ability and high adsorption capacity [12], [13], [14]. Additionally, GO sheets can be a proper host for decoration and dispersion of other inorganic nanoparticles, which make it more appropriate for the modification of polymeric membranes [15], [16], [17]. Doped nanoparticles can adjust the interlayer spacing of GO to improve the permeability of the membrane [18], [19]. Many studies have verified that the antibacterial and antifouling properties of porous polymer membranes can be significantly improved by modification with nanoparticles, such as TiO₂ [20], [21], [22], [23], [24], [25], [26]. TiO₂ particles have unique physical and chemical properties and can be assembled on the membrane surface and in the membrane pores. Adding TiO₂ particles to GO nanosheets may allow us to efficiently impart antibacterial, antifouling and selectivity characteristics to the sheets [17].

GO-based membranes can be fabricated by spin coating [27], vacuum filtration [22], layer-by-layer (LbL) assembly [26], phase inversion [19], [25] and interfacial polymerization [7], [9]. Among these methods, the vacuum filtration was widely used due to its simple operation and controllable film thickness with adjusted concentration of GO nanocomposite suspension. The vacuum filtration process continuously filtrates a GO suspension with a strong vacuum pressure and the lamellar GO sheets can be uniformly deposited. The continuous suction force from vacuum pump is able to move water rapidly, which contribute to a strong electrostatic repulsion among GO flakes to overcome the agglomeration of GO and the formation of ordered laminated GO membranes.

In this study, we proposed a facile vacuum filtration approach to deposit TiO₂ and GO on a polysulfone (PSF) UF membrane to prepare GO-based NF. The effect of different TiO₂ contents on the properties of membranes was investigated based on pure water flux, static water contact angle, Zeta potential, surface and cross-section morphology, fouling tests and biocidal activity experiment. Separation performance of the prepared membranes was studied by rejection of three reactive dyes with different molecular weight, while the effect of salt concentration on dye/salt separation performance was also investigated. The stability of the NFG-2 membrane was evaluated by measuring the permeation and rejection for Chrome black T and salt over a 9-hour filtration process.

Section snippets

Materials

Chrome black T (IND, M_W = 461.38) was purchased from Xilong Chemical Co., Ltd. (China). Congo red (IND, M_W = 696.68) and Brilliant Blue R250 (AR, M_W = 825.97) were purchased from Aladdin Industrial Corporation (China). Anhydrous sodium sulfate (Na₂SO₄, AR) was purchased from Shanghai Lingfeng Chemical Reagent. The structures and molecular dimensions of the dye molecules are listed in Table 1. Titanium oxide (TiO₂, anatase 60 nm) and bovine serum albumin (BSA) were purchased from Aladdin

Membrane characterization

GO has a typical FTIR spectrum with many distinct, strong absorption peaks corresponding to oxygen functional groups [21]. As shown in Fig. 1b, a wide peak at approximately 3422 cm⁻¹ can be attributed to the O single bond H stretching vibration of GO and water [25], [36]. The GO curve shows a stretching vibration of C double bond O at 1660 cm⁻¹, and the three absorption peaks at 1406, 1237 and 1074 cm⁻¹ are induced by the COH, CO and COC vibrations, respectively [26]. Fig. 1a shows that the spectra of the NFG-0, NFG-1,

Conclusion

In this study, novel TiO₂@GO NF membranes were prepared by modifying PSF UF membrane surfaces with GO nanosheets and TiO₂ nanoparticles. The interlayer spacing of the GO nanosheets was controlled by the amount of TiO₂ nanoparticles. Compared with the NF membrane only containing GO (NFG-0), the NF membrane containing the same amount of TiO₂ and GO (NFG-2) had a decreased contact angle (from 57.6° to 43.4°, respectively) and increased water permeability (from 2.6 to 6.2 L·h⁻¹·m⁻²·bar⁻¹,

CRediT authorship contribution statement

Lifang Zhu: Conceptualization, Methodology, Writing - original draft, Investigation, Validation. Mengyao Wu: Software, Writing - original draft, Investigation. Bart Van der Bruggen: Writing - review & editing. Lecheng Lei: Writing - review & editing. Lizhong Zhu: Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This project was supported by the National Key Research and Development Program of China (2017TFA0207002) and the National Natural Science Foundation of China (21621005). We thank Wang Hefei for his kind assistance with the fluorescence microscopy analysis and Zhao Yan for his suggestion about the experiment and revision of the manuscript.

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Effect of TiO2 content on the properties of polysulfone nanofiltration membranes modified with a layer of TiO2–graphene oxide

Highlights

Abstract

Graphic abstract

Introduction

Section snippets

Materials

Membrane characterization

Conclusion

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgements

J. Ind. Eng. Chem.

J. Hazard. Mater.

J. Hazard. Mater.

Chem. Eng. J.

J. Water Process Eng.

J. Membr. Sci.

Appl. Surf. Sci.

J. Membr. Sci.

Sep. Purif. Technol.

J. Membr. Sci.

J. Membr. Sci.

Carbon

Chem. Eng. J.

J. Membr. Sci.

J. Ind. Eng. Chem.

J. Membr. Sci.

Carbon

J. Membr. Sci.

J. Membr. Sci.

Desalination

J. Membr. Sci.

J. Membr. Sci.

J. Membr. Sci.

Desalination

J. Membr. Sci.

Effect of TiO₂ content on the properties of polysulfone nanofiltration membranes modified with a layer of TiO₂–graphene oxide