A free-standing calcium alginate/polyacrylamide hydrogel nanofiltration membrane with high anti-fouling performance: Preparation and characterization

doi:10.1016/j.desal.2015.03.015

Desalination

Volume 365, 1 June 2015, Pages 234-241

https://doi.org/10.1016/j.desal.2015.03.015 Get rights and content

Highlights

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A free-standing calcium alginate/polyacrylamide nanofiltration membrane was prepared.
•
The CA/PAM hydrogel nanofiltration membrane exhibited excellent anti-fouling properties.
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The fabrication process is simple and low cost without producing organic wastewater.

Abstract

An anti-fouling, free-standing membrane was synthesized through the polymerization of acrylamide in the presence of sodium alginate using N,N′-methylene-bisacrylamide as the covalent crosslinker and CaCl₂ as the ionic crosslinker. The membranes were characterized via field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), and Thermal Gravity (TG). Bovine serum albumin (BSA) solution and yeast suspension were used to investigate the anti-fouling performance of the hydrogel filtration membrane. The calcium alginate/polyacrylamide (CA/PAM) filtration membrane exhibited 89.06% and 85.84% water flux recovery for yeast suspension and BSA solution, respectively, without washing the filtration membrane. The hydrogel filtration membrane showed limited adsorption and adhesion for BSA and yeast, and the rejection of BSA and yeast reached 98.53% and 99.64%, respectively. The results of dye rejection studies demonstrated potential applications of this material as a nanofiltration membrane. The free-standing CA/PAM hydrogel filtration membrane exhibits excellent anti-fouling properties and has promising application prospects in the fields of protein separation, microorganism filtration and removal of dyes.

Graphical abstract

Introduction

Membrane filtration has been widely used in many fields, including water treatment [1], [2], [3], protein separation or concentration [4], [5], and reverse osmosis pretreatment [6]. However, the relatively hydrophobic characteristic of membrane fouling causes significant flux decline. Many studies have focused on increasing the hydrophilicity of membranes via physical and chemical strategies such as surface and blending modifications [7], [8], [9], [10], [11], [12], [13], [5]. The grafting of zwitterionic polymers onto polymer membranes has been reported for the generation of nonfouling materials via radical graft copolymerization, endowing the membrane with high flux recovery and biofouling resistance [14], [15]. Correia et al. [16] combined different blends of chitosan and oxazoline-based antimicrobial oligomers on anti-biofouling 3D porous systems. The incorporation of ammonium quaternized oligo (2-oxazoline) into the composition of the scaffold enhanced the stability of the chitosan scaffold and its ability to repel protein adsorption. Ultrafiltration membranes prepared by incorporating nanoparticles into membranes also exhibited high hydrophilicity and anti-fouling properties [17]. Coating modification is another surface hydrophilic modification that significantly improves the stability and anti-fouling characteristics of membranes [18].

Surface hydrophilization by coating hydrogel onto membranes is a practical method to mitigate membrane fouling. Composite ultrafiltration membranes based on polyvinyl alcohol (PVA) prepared by depositing or coating PVA hydrogels on substrate membranes showed good hydrophilicity and anti-fouling properties [19], [20], [21]. The PVA coated ultrafiltration membrane exhibited high flux and high rejection for oil–water emulsion and protein. A polyhedral oligomeric silsesquioxane (POSS) derivative containing UV-curable methacrylate groups was used as the multi-functional cross-linker to form thin and durable hydrogel films with a hydrophilic comonomer, poly(ethylene glycol) methacrylate (PEGM), in the presence of a photoinitiator. The films showed excellent anti-fouling efficiency to oil–water emulsions and bovine serum albumin (BSA) solutions [8]. In another study, they synthesized bifunctional hydrogel materials through photopolymerization of polyethylene glycol diacrylate and a functional monomer containing ammonium salt. The polysulfone membranes coated with the hydrogel showed good anti-fouling efficiency and antimicrobial activity [22].

However, part of the pollutants that permeate through the hydrogel coating layer can still be adsorbed by the hydrophobic membrane matrix. Surface-coated hydrophilic substances can only alleviate the pollution but cannot solve the problem. A self-supporting membrane prepared with hydrogel materials may avoid membrane fouling fundamentally without using the hydrophobic substrate. Common hydrogels cannot be used as free-standing membranes because of their poor mechanical properties. Jeong-Yun Sun et al. [23] synthesized highly tough hydrogels from alginate and acrylamide, which formed ionically and covalently crosslinked networks. Given that the hybrid hydrogels are tough, they may be used directly as ultrafiltration membranes.

In this work, a free-standing calcium alginate/polyacrylamide (CA/PAM) hydrogel filtration membrane was synthesized via UV radiation-reduced polymerization using acrylamide as the monomer, sodium alginate as the matrix, urea as the pore-forming agent, N,N′-methylene-bisacrylamide (MBA) as the covalent crosslinker, and CaCl₂ as the ionic crosslinker. The prepared free-standing CA/PAM membrane showed excellent anti-fouling performance when BSA solution and yeast suspension were used as feed solutions in a cross-flow filtration system. The CA/PAM membrane also achieved good dye rejection performance.

Section snippets

Materials

Sodium alginate (SA) was purchased from Tianjin Yuanhang Chemical Company (Tianjin, China). Acrylamide (AAm), N,N′-methylenebisacrylamide (MBAA) and N,N,N′,N′-tetramethylethylenediamine (TEMED) were purchased from Chemistry Reagent Factory of Tianjin (Tianjin, China). Ammonium persulfate and urea were obtained from Institute of Tianjin Guangfu Fine Chemicals (Tianjin, China). Bovine serum albumin (BSA, M_W = 67 kDa) was purchased from Shanghai Lanji Science and Technology Development Company

Morphology of the CA/PAM nanofiltration membrane

Digital photographs of the CA/PAM membrane before and after the removal of urea are shown in Fig. 1 The thickness of the CA/PAM hydrogel nanofiltration membrane was 0.244 mm. The membrane before the removal of the porogen urea (Fig. 1(a)) was transparent, whereas the CA/PAM hydrogel nanofiltration membrane was translucent. Some pores were produced after the removal of porogen urea, and those pores reduced the transparency of the CA/PAM hydrogel membrane.

Fig. 2 shows the cross-sectional and

Conclusions

Highly fouling-resistant free-standing hydrogel nanofiltration membranes were prepared via the photo-induced copolymerization of acrylamide and sodium alginate in the presence of crosslinker MBAA and porogen, followed by crosslinking with calcium chloride and the extraction of the porogen. The prepared hydrophilic membrane could effectively resist protein adsorption and initial microbial adhesion. BSA and yeast filtration experimental results indicated that the CA/PAM membrane exhibited

Acknowledgments

The research is supported by the National Natural Science Foundation of China (51103102), Key Technologies R&D Program of Tianjin (13ZDSF00100), and Ministry of Education of the People's Republic of China doctoral new teacher fund (20111201120004).

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A free-standing calcium alginate/polyacrylamide hydrogel nanofiltration membrane with high anti-fouling performance: Preparation and characterization

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Morphology of the CA/PAM nanofiltration membrane

Conclusions

Acknowledgments

Chem. Eng. J.

J. Hazard. Mater.

Water Res.

J. Membr. Sci.

J. Membr. Sci.

Desalination

Desalination

J. Membr. Sci.

J. Membr. Sci.

J. Membr. Sci.

J. Membr. Sci.

J. Membr. Sci.

Desalination

Desalination