Elsevier

Applied Surface Science

Volume 427, Part A, 1 January 2018, Pages 38-47
Applied Surface Science

Full Length Article
Improved antifouling performance of ultrafiltration membrane via preparing novel zwitterionic polyimide

https://doi.org/10.1016/j.apsusc.2017.08.004Get rights and content

Highlights

  • Zwitterionic polyimide (Z-PI) was successfully prepared by solution polycondensation and quaternary amination reaction.

  • Z-PI membrane exhibited enhanced hydrophilicity and water permeability.

  • Z-PI membrane showed improved antifouling property and long-term residence stability.

  • This approach is facile and scalable for the large-scale preparation of antifouling ultrafiltration membranes.

Abstract

On the basis of the outstanding fouling resistance of zwitterionic polymers, an antifouling ultrafiltration membrane was fabricated through phase inversion induced by immersion precipitation method, directly using the novel zwitterionic polyimide (Z-PI), which was synthesized via a two-step procedure including polycondensation and quaternary amination reaction, as membrane material. The chemical structure and composition of the obtained polymer were confirmed by using FTIR, 1H NMR and XPS analysis, and its thermal stability was thoroughly characterized by TGA measurement, respectively. The introduction of zwitterionic groups into polyimide could effectively increase membrane pore size, porosity and wettability, and convert the membrane surface from hydrophobic to highly hydrophilic. As a result, Z-PI membrane displayed significantly improved water permeability compared with that of the reference polyimide (R-PI) membrane without having an obvious compromise in protein rejection. According to the static adsorption and dynamic cycle ultrafiltration experiments of bovine serum albumin (BSA) solution, Z-PI membrane exhibited better fouling resistant ability, especially irreversible fouling resistant ability, suggesting superior antifouling property and long-term performance stability. Moreover, Z-PI membrane had a water flux recovery ratio of 93.7% after three cycle of BSA solution filtration, whereas only about 68.5% was obtained for the control R-PI membrane. These findings demonstrated the advantages of Z-PI membrane material and aimed to provide a facile and scalable method for the large-scale preparation of low fouling ultrafiltration membranes for potential applications.

Introduction

Nowadays, there are several problems worldwide associated with water pollution, energy shortages and environmental challenges. Membrane technology, especially ultrafiltration (UF), can solve these problems mentioned above since it involves a number of attractive advantages including low energy consumption, competitive operating cost, mild operating condition, unique separation principle and transport selectivity, high separation efficiency and its environmentally benignity [1]. Ultrafiltration has gained an important place and made great progress in numerous industries and used in a broad range of applications, particularly in wastewater treatment. Membrane material is the decisive factor for determining various membrane properties, such as hydrophilicity, morphology, surface charge and allowable pH range, which gives a direct influence on membrane performance including permeability and selectivity as well. Ultrafiltration fueling this progress and obtaining the high efficiency are urgent need to meet the growing demand for high performance membrane materials. To date, ultrafiltration membranes have made from a wide variety of chemically and thermally stable synthetic polymers, including polyvinyl chloride (PVC), polyacrylonitrile (PAN), polysulfone (PSf), polyethersulfone (PES), polyimides (PIs) and polyvinylidene fluoride (PVDF) [2]. However, these membrane materials are not ideal candidates due to their inherent hydrophobic properties, which restrict the permeate flux in aqueous phase system and result in serious membrane fouling [3]. In particular, membrane fouling is a major obstacle to the widespread use of membrane technology, which can cause severe flux decline and affect productivity, alter membrane selectivity, shorten membrane life, require intense chemical cleaning or frequent membrane replacement, and significantly enhance the operating cost by increasing osmotic pressure and circulating the feed solution [4], [5], [6]. Therefore, much attention has been attracted to preparing and modifying membrane materials with tailorable chemical structures or groups in an attempt to improve their antifouling performance [7], especially the recent development of zwitterionic membrane materials [8].

Zwitterionic polymers, containing typically the same number of anionic and cationic groups, and the overall charge is zero under normal condition despite the high density of ion pairs attached to the polymer backbones, which are particularly attractive as a promising alternative to pave the way for antifouling ultrafiltration membrane [9]. In general, the chemical structures of zwitterionic polymers are commonly hydrophilic, overall electrically neutral, hydrogen-bond acceptors but not hydrogen-bond donors [10], [11]. Due to these unique characteristics, zwitterionic polymers can form the hydration layer near the membrane surface to avoid the adsorption of solutes and confer to various materials excellent biocompatibility and resistance to nonspecific protein adsorption, bacterial adhesion, and (bio)fouling [12]. Recently, much effort had been given to preparing zwitterionic-based ultrafiltration membrane by two strategies primarily including surface grafting or coating of zwitterionic polymers after membrane preparation (surface modification method) [13], [14], [15] and synthesis of novel zwitterionic polymers before membrane preparation (chemical synthesis method) [16]. The former has narrow potential window for large-scale application since surface grafting and coating involve complicated preparation process and limited production, as well as often block the membrane pores and suffer flux reduction, all the reported applications of zwitterionic surface are still at experimental stage [13], [17]. There is thereby an urgent need but it is still a significant challenge to the development of zwitterionic surface. In contrast, the future looks bright for incorporating zwitterionic structure and high performance synthetic polymer into a single membrane material by the chemical synthesis method to facile and large-scale fabricate the desired antifouling ultrafiltration membrane through conventional phase inversion method, which is regarded as an efficient way to promote the development of membrane technology. Currently, numerous significant researches had exploited different types of zwitterionic polymer membrane material with superior antifouling property and high permeability, such as zwitterionic chitosan [18], zwitterionic cellulose acetate [19], zwitterionic polyvinyl chloride [20], polyacrylonitrile-based zwitterionic copolymers (PAN-DMAEMA, PAN-DMMSA and PAN-MPDSAH) [21], [22], [23], polymethylmethacrylate-based zwitterionic copolymers (P(MMA-co-SBVIM)and P(MMA-co-CBVIM)) [24], zwitterionic tertiary amine modified polyethersulfone [25], zwitterionic sulfobetaine poly(arylene ether sulfone) (PES-SB) and carboxybetaine poly(arylene ether sulfone) (PES-CB) [26], etc. However, achieving excellent antifouling property and separation performance of membrane materials, while retaining their thermal and chemical stability, remains a challenge.

Polyimides (PIs) are a class of high performance engineering plastics and composed of aromatic dianhydride and diamine monomers. Due to excellent thermal and dimensional stability, chemical resistance, and mechanical strength, polyimides can meet a number of key requirements for ideal membrane materials [27]. However, their inherent hydrophobicity raises serious concerns over insufficient wettability, which could directly impair permeability and antifouling property of the liquid filtration membrane. Owing to the multiple possible synthetic approaches and various available dianhydride and diamine monomers, a wide variety of polyimides with desired chemical structures can be prepared by an accurate molecular design and functionalized with respect to the applicative purposes [28]. It is expected that zwitterionic polyimide provide a good approach to improve permeability and antifouling property of ultrafiltration membrane. Zwitterionic polymers are commonly prepared using free radical polymerization and ring opening of lactone [12], [29]. In this study, zwitterionic polyimide (Z-PI) was successfully synthesized by employing a two-step procedure consist of polycondensation and quaternary amination reaction. Z-PI was then extensively characterized in terms of chemical structure, chemical composition, thermal stability and solubility behavior. Subsequently, the hydrophilicity, morphology and pore statistic of Z-PI membrane were thoroughly studied, and the protein static adsorption of Z-PI membrane was examined to provide a better understanding of the effect of zwitterionic groups on membrane antifouling performance. Furthermore, the protein separation and long-term performance stability of Z-PI membrane were investigated by dynamic cycling ultrafiltration experiment and the results were compared in detail with those obtained by using the reference polyimide (R-PI) membrane.

Section snippets

Materials

4,4′-Diamino-4′′-(dimethylamino)triphenylamine (TPA-NMe2) was synthesized according to a previously reported procedure [30]. 4,4′-Oxydiphthalic dianhydride (ODPA) was purchased from Tokyo Chemical Industry (TCI, Japan) and purified by recrystallization from acetic anhydride. 4,4′-diaminodiphenyl ether (ODA), polyethyleneglycol (PEG) with a molecular weight of 400 Da, sodium bromoacetate (SBA), isoquinoline and m-cresol were purchased from Aladdin Reagent (China). Dimethyl sulfoxide (DMSO) was

Characterization of zwitterionic polyimide

The polymer preparation processes are outlined in Scheme 1, the polyimide bearing pendant tertiary amine groups (TA-PI) was synthesized by a one-pot, high-temperature polycondensation of TPA-NMe2 and ODPA in the m-cresol/isoquinoline system. Then, TA-PI was converted to zwitterionic polyimide (Z-PI) by quaternary amination reaction, and the mole ratio of SBA to the tertiary amine group was set to 2:1 to ensure complete conversion of the tertiary amine group into zwitterionic group. For the

Conclusions

In this work, a novel zwitterionic polyimide (Z-PI) membrane material was successfully synthesized by solution polycondensation and quaternary amination reaction, which was confirmed by FTIR, 1H NMR and XPS measurements. Subsequently, Z-PI membrane was prepared via phase inversion induced by immersion precipitation method, which processed several advantages such as high hydrophilic, high water permeation property, excellent fouling resistant ability and performance stability. Furthermore, the

Acknowledgements

This work is financially supported by the Fundamental Research Funds for the Central Universities (No. 2572016BB03), Youths Science Foundation of Heilongjiang Province, China (No. QC2014C044), and National Innovation Training Program for Undergraduates of Northeast Forestry University (201710225051).

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    H.T. Huang and J.Y. Yu contribute equally to this work.

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