Elsevier

Applied Surface Science

Volume 345, 1 August 2015, Pages 301-309
Applied Surface Science

Surface modification of ultrafiltration membranes by grafting glycine-functionalized PVA based on polydopamine coatings

https://doi.org/10.1016/j.apsusc.2015.03.189Get rights and content

Highlights

  • Glycine-functionalized PVA was synthesized and grafted on PD-coated UF membranes.

  • The modification of PD-g-PVA reduced the surface roughness of membranes significantly.

  • The grafted PVA layer was fairly stable in acid and alkaline conditions.

  • The modification of PD-g-PVA improved the antifouling ability of UF membranes.

Abstract

Due to the ease of processing and stability during filtration, polydopamine (PD) coatings with grafted hydrophilic polymers have recently received significant attention. In this study, glycine-functionalized PVA was synthesized and grafted to a PD-coated ultrafiltration (UF) membrane to improve its performance during wastewater filtration. The membranes were modified by grafting PD with glycine-functionalized PVA (PD-g-PVA), and the resultant materials were characterized using surface morphology analyses, contact angle measurements, flux, oil/water emulsion separation tests, and grafted layer stability tests. The performance of the PD-g-PVA membrane was compared to that of the membrane modified with PD-g-polyethylene glycol (PEG). After grafting the PD-g-PVA, the surface roughness of the membranes decreased significantly. The grafted PVA layer, which was stable under acidic and alkaline conditions, protected the PD layer. The filtration experiments with an oil/water emulsion indicated that modifying the glycine-functionalized PVA by grafting can significantly improve the antifouling ability of membranes.

Introduction

Due to severe water shortages, membranes have been used increasingly in water purification and wastewater treatment. However, membrane fouling is the primary issue that impedes their application. Surface hydrophilic modification is a popular method used to improve the antifouling performance of membranes [1], [2], [3]. Many physical and chemical modification methods can be used to alter the characteristics of membrane surfaces and to improve the performances of these surfaces [4]. These methods include blending with a surface-modification additive, coating or adsorption, a chemical reaction with a contacting solution, plasma or corona treatment, and surface grafting after high-energy irradiation [5].

During a study inspired by biological adhesion, dopamine helped reduce oil/water emulsion-induced fouling because it produces a firm adhesive coating on solid surfaces [6], [7], [8]. In 2007, Lee et al. reported that in an aerobic aqueous solution, dopamine could form very thin surface-adherent polydopamine (PD) films on a solid surface through self-polymerization [9]; consequently, a PD film formed through a self-polymerization of dopamine under aerobic conditions [10]. Recently, a new method has been developed to prevent membrane fouling, gaining significant attention during studies of water purification by membranes [11], [12]. However, some researchers reported that PD coatings were not as effective as they expected [13], [14].

PD coatings on membrane surfaces containing reactive groups can provide a versatile platform for secondary reactions and can immobilize functional molecules with specific functional groups, such as single bondNH2 or single bondSH [15]. Consequently, some researchers attempted to graft hydrophilic material onto the membrane surface to improve its hydrophilicity and to increase its antifouling abilities. Jiang et al. prepared a hydrophilic membrane by immersing polyethylene (PE) porous membranes into aqueous dopamine solutions before heparin was covalently immobilized onto the reactive PD layer [16]. The results indicated that these modifications significantly suppressed the adhesion of platelet, enhancing the anticoagulation activity of the membranes. Zhu et al. immobilized bovine serum albumin (BSA) onto porous polyethylene (PE) membranes while using strongly attached PD as a spacer [17]. Their results revealed that the hydrophilicity of PE membrane improved significantly after coating with the PD and binding with the BSA. In addition, amine-terminated polyethylene glycol (mPEG-NH2), which is strongly hydrophilic, was used to improve the membrane surface functionalization after applying the PD coating. Bryan et al. coated the surfaces of reverse osmosis (RO), ultrafiltration (UF), and microfiltration (MF) membranes with PD before grafting them with poly(ethylene glycol) (PEG) [7], [18]. The membranes modified with PD exhibited a systematic reduction in protein adhesion [19], and the PD-g-PEG-modified membranes were slightly more resistant toward fouling when filtering oily water [20].

PVA is widely to modify the surfaces of membranes due to its high hydrophilicity, excellent chemical properties, thermal stability and low cost [21], [22], [23]. This material is produced through the polymerization of vinyl acetate and the hydrolysis of polyvinyl acetate, which replaces the ester groups with hydroxyl groups via ester exchange. Commercial PVA can be classified based on the extent of hydrolysis or hydrolysis degree as fully hydrolyzed (97.5–99.5%) and partially hydrolyzed (87–89%) materials. The hydrolysis degree of PVA significantly affects its water solubility. Partially hydrolyzed PVA is more hydrophobic than the fully hydrolyzed material because it still contains ester groups. The partially hydrolyzed PVA dissolves readily in water at ambient temperatures, while fully hydrolyzed PVA is soluble only at high temperatures. Due to its good solubility in water, the partially hydrolyzed PVA was suitable for coating membrane surfaces during hydrophilic modifications [22], [24], [25], [26].

Because mPEG-NH2 can be immobilized on the PD layer on membrane surface through nucleophilic addition [7], [9], we proposed that glycine-functionalized PVA could be grafted to a membrane surface coated with PD, thus improving the hydrophilicity of the membrane surface. The glycine-functionalized PVA could be prepared through an esterification reaction between PVA and amino acid while using an inorganic acid as a catalyst [27], as shown in Fig. 1.

In this paper, glycine-functionalized PVA, which was synthesized through an esterification between PVA and amino acids, was used to modify the surfaces of PES ultrafiltration membranes. Polyethersulfone (PES), which has good chemical resistance, thermal stability, mechanical and film-forming properties, is broadly manufactured for industrial applications. However, the intrinsic poor hydrophilic property limited the performance and application of PES membranes. When PES UF membranes were used in water treatment, unavoidable water flux decrease and fouling occurred in filtration. The glycine-functionalized PVA was grafted on the membrane surface by the covalent bonds between single bondNH2 group and the coated PD layer. The membrane surface was characterized using Fourier transform infrared (FT-IR) spectrometry and surface morphology analysis to confirm that the PVA layer was present. The membrane modified with mPEG-NH2 was compared to glycine-functionalized PVA in this investigation. An oil/water emulsion was separated to test the antifouling ability of the PD-g-PVA-modified membrane.

Section snippets

Materials

Glycine was used as the amino acid during this study. The glycine, dimethyl sulfoxide (DMSO), PVA (1788, molecular weight 77,000, hydrolysis degree 88%), Trizma hydrochloride (i.e., tris buffer), alcohol and sulfuric acid were purchased from Sinopharm Chemical Reagent Co., Ltd. The dopamine hydrochloride and mPEG-NH2 (CH3O(CH2CH2O)nCH2CH2NH2, MW = 10,000 Da, CAS: 80506-64-5) were purchased from Aladdin (Shanghai, China). The acetone and isopropanol (IPA) were obtained from Lingfeng Chemical Co.,

FTIR analysis of PVA and glycine-functionalized PVA

The FTIR spectra of the net PVA and glycine-functionalized PVA are shown in Fig. 2. The peaks corresponding to the typical Osingle bondH and Csingle bondH (2910–2942 cm−1) bands were obvious in the spectra of the pure PVA [26]. The adsorption peaks at approximately 1708 cm−1 and 1631 cm−1 are more obvious in the glycine-functionalized PVA than the net PVA, which can be attributed to the formation of the Csingle bondOsingle bondC and Cdouble bondO groups after the reaction between the hydroxyl group of the PVA and glycine [21]. The strength of the peak

Conclusions

The characteristics and performance of PES UF membranes modified with PD-g-PVA were investigated in this paper. The presence of glycine-functionalized PVA grafts on the PD-modified membrane was confirmed using FT-IR and pure water flux measurements. During the AFM analysis, the roughness of the PD-g-PVA-modified membrane surface decreased obviously after it was modified. The proposed structure of glycine-functionalized PVA layer immobilized on the membrane surface is horizontal. A significant

Acknowledgments

This work is supported by the National Natural Science Foundation of China (Grant No. 51478099, 51108266) and the Fundamental research Funds for the Central Universities ((Grant No. 2232015A3-04).

References (42)

  • L.P. Zhu et al.

    Immobilization of bovine serum albumin onto porous polyethylene membranes using strongly attached polydopamine as a spacer

    Colloids Surf. B: Biointerfaces

    (2011)
  • B.D. McCloskey et al.

    A bioinspired fouling-resistant surface modification for water purification membranes

    J. Membr. Sci.

    (2012)
  • F. Li et al.

    Surface modification of PES ultrafiltration membrane by polydopamine coating and poly(ethylene glycol) grafting: Morphology, stability, and anti-fouling

    Desalination

    (2014)
  • D.J. Miller et al.

    Fouling-resistant membranes for the treatment of flowback water from hydraulic shale fracturing: A pilot study

    J. Membr. Sci.

    (2013)
  • C.H. Zhang et al.

    Preparation and characterization of hydrophilic modification of polypropylene non-woven fabric by dip-coating PVA (polyvinyl alcohol)

    Sep. Purif. Technol.

    (2008)
  • A. Saraf et al.

    Poly(vinyl) alcohol coating of the support layer of reverse osmosis membranes to enhance performance in forward osmosis

    Desalination

    (2014)
  • E. Salehi et al.

    Novel chitosan/poly(vinyl) alcohol thin adsorptive membrane modified with amino functionalized multi-walled carbon nanotubes for Cu(II) removal from water: Preparation, characterization, adsorption kinetics and thermodynamics

    Sep. Purif. Technol.

    (2012)
  • J.R. Du et al.

    Modification of poly(vinylidene fluoride) ultrafiltration membranes with poly(vinyl alcohol) for fouling control in drinking water treatment

    Water Res.

    (2009)
  • L. Liu et al.

    TiO2 and polyvinyl alcohol (PVA) coated polyester filter in bioreactor for wastewater treatment

    Water Res.

    (2012)
  • C. Cheng et al.

    The hydrodynamic permeability and surface property of polyethersulfone ultrafiltration membranes with mussel-inspired polydopamine coatings

    J. Membr. Sci.

    (2012)
  • P. Le-Clech et al.

    Fouling in membrane bioreactors used in wastewater treatment

    J. Membr. Sci.

    (2006)
  • Cited by (0)

    View full text