Elsevier

Desalination

Volume 286, 1 February 2012, Pages 99-107
Desalination

Novel functionalized carbon nanotubes for improving the surface properties and performance of polyethersulfone (PES) membrane

https://doi.org/10.1016/j.desal.2011.10.039Get rights and content

Abstract

Amine functionalized Multi-walled carbon nanotubes (F-MWCNTs)/polyethersulfone (PES) membranes were prepared using phase inversion induced by immersion precipitation. Crude MWCNTs were chemically treated using strong acids (H2SO4/HNO3) and 1,3-phenylenediamine (mPDA) to produce the functional amine groups (single bondNH2) on their surfaces. F-MWCNTs with different concentration were blended in the casting solution containing PES, polyvinylpyrrolidone (PVP) and dimethylacetamide (DMAC). Pure water was used as non-solvent. The FTIR spectra indicated that the amine functional groups were produced on the surface of MWCNTs. The membranes prepared with different concentrations of F-MWCNTs were characterized using contact angle, field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and permeation tests. The surface hydrophilicity of membranes was significantly improved by addition of F-MWCNTs in the casting solution. An increment in the porosity, pore size and surface roughness of the membranes was observed by increasing F-MWCNTs content up to 1 wt.%. Further addition of F-MWCNTs caused a reduction in porosity and roughness of formed membrane. The membranes prepared with 0.5 and 1 wt.% of F-MWCNTs showed higher performance than neat membrane. Addition of F-MWCNTs in the casting solution improved the BSA rejection and antifouling properties of PES membrane.

Highlights

► Amine functionalization of MWCNTs was carried out using strong acid and mPDA. ► Hydrophilic PES membranes were prepared by blending with F-MWCNTs via phase inversion via immersion precipitation technique. ► F-MWCNTs/PES membranes showed high antifouling properties compared to PES membrane.

Introduction

Polyethersulfone (PES) is classified as a transparent amorphous and high-Tg polymer, which has high mechanical, thermal and chemical resistances. These properties are adequate factors to wide application of PES in manufacturing asymmetric membranes with different pore sizes in surfaces [1], [2], [3], [4]. Due to the low hydrophilic properties of PES among other membrane materials such as polyacrylonitrile, cellulose acetate, polyamide, polyamide-imide, PES membrane is known as high fouling membrane for aqueous filtration [1], [2], [3], [4], [5]. Therefore, many investigations have been done to change the surface properties of this hydrophobic membrane [6], [7], [8]. Methods such as blending, surface graft polymerization, chemical grafting, and radiation induced grafting have been developed in attempts to increase the surface hydrophilicity of membranes [9], [10], [11], [12]. In addition, organic–inorganic hybrid membranes have been favored recently as next generation of membranes [13], [14]. Inorganic fillers and additives especially nano-sized materials such as zeolite, titanium dioxide, and silica were also embedded in polymeric membranes to improve their performances because of their enhanced properties, such as high perm-selectivity, higher hydrophilicity, and enhanced fouling resistance [15], [16], [17].

Carbon nanotubes (CNTs) have gained more attention as one of these additives recently. In some literatures, the increments in special parameters like modulus and tensile strength, water flux and permeability, and rejection have been studied because of adding CNTs to polymeric membranes [16], [17], [18], [19]. However, the efficient utilization of CNTs in composite applications depends on the ability to disperse the CNTs homogeneously throughout the matrix and the compatibility between CNTs and the matrix. These two factors are important in the utilization of fillers in polymer composites as well as CNTs [20], [21].

The main problem of using pristine CNTs is their insolubility in solvents and weak affinities for most polymers [22], [23]. Thus, surface functionalization is carried out in order to improve their dispersion capability and performance [21], [24], [25]. Surface oxidation and introduction of hydrophilic functional groups into the surface of the CNTs can also be helpful to obtain better dispersion of carbon nano-materials into relevant matrices [26]. Amine group has a high reactivity, a wealth of chemistry and can react with many chemicals such as polymers [27], [28], [29].

In this research, novel functionalized MWCNTs (F-MWCNTs) containing amine groups were fabricated and blended with polyethersulfone (PES) casting solution for improving the surface properties and performance of ultrafiltration membranes. The conventional method to functionalize CNTs with amine groups is generally a process involving a reaction, toxic coupling reagents (SOCl2), but in this study we prefer to use phenylendiamine directly. It is predicted that the amine F-MWCNTs are able to improve the hydrophilicity of PES membranes. The influences of F-MWCNT concentrations in the casting solution on the membrane morphology and performance were investigated. Moreover, in this paper the changes in PES membrane surface composition, hydrophilicity and antifouling properties were discussed with addition of F-MWCNTs in the casting solution.

Section snippets

Materials

Polyethersulfone (PES Ultrason E6020P with Mw = 58,000 g/mol) as membrane polymer and N,N-dimethylacetamide (DMAC) as solvent were supplied from BASF. Multiwall Carbon nanotubes (O.D. × I.D. × L 5 nm × 1.3–2.0 nm × 50 μm) manufactured by CVD method were purchased from Sigma-Aldrich. Polyvinylpyrrolidone (PVP, with Mw = 25,000 g/mol), nitric acid 65% (HNO3), Sulfuric acid 96% (H2SO4), 1,3-phenylenediamine (mPDA), N,N-dimethylformamide (DMF), tetrahydrofuran (THF) and Bovin Serum Albumin powder (BSA, MW ~ 66 KDa)

Characteristics of F-MWCNTs

FTIR spectra of pristine and F-MWCNTs containing carboxylic and amine groups are shown in Fig. 3. Fig. 3a shows the FTIR spectrum of unmodified carbon nanotubes. The appearance of peaks at 1633 is attributed to Cdouble bondC bond of carbon structure of CNTs. However, it can be seen after modification, the stronger intensity is induced because of successfully grafting of mPDA on F-MWCNTs (Fig. 3b and c), this The peak at 3445 cm 1 is attributed to the presence of hydroxyl (single bondOH) group on the unmodified MWCNTs

Conclusion

The functionalization of multi-walled carbon nanotubes (MWCNTs) was carried out by amination with 1,3-phenylenediamine (mPDA). The F-MWCNT SEM observations exhibited thicker structures compared to the pristine MWCNTs, especially at the end caps of CNTs that correspondingly increase membrane hydrophilicity. The results of FTIR revealed that the amine functional groups were formed on the surface of MWCNTs. F-MWCNTs/PES membranes were prepared by phase inversion via immersion precipitation

Acknowledgment

The authors gratefully acknowledge the financial support by the Iran National Science Foundation (INSF) (Grant No. 88002471).

References (33)

Cited by (286)

View all citing articles on Scopus
View full text