Elsevier

Desalination

Volume 322, 1 August 2013, Pages 69-75
Desalination

Antifouling and performance enhancement of polysulfone ultrafiltration membranes using CaCO3 nanoparticles

https://doi.org/10.1016/j.desal.2013.04.031Get rights and content

Highlights

  • CaCO3 nanoparticles were synthesized.

  • Psf/PEG/CaCO3 hybrid membrane was prepared by phase inversion.

  • The added CaCO3 nanoparticles enhanced the hydrophilicity.

  • Prepared membrane exhibits greater hydrophilicity, permeation and antifouling property.

Abstract

Calcium carbonate nanoparticles were synthesized from calcium nitrate via chemical precipitation method. The nanoparticles were characterized using scanning electron microscope (SEM), Attenuated total reflectance infra red (ATR-IR) spectrum and by X-ray diffraction (XRD). These nanoparticles were used as additive for polysulfone (PSf) ultrafiltration membrane along with polyethylene glycol (PEG) as pore forming agent. The PSf hybrid membranes were characterized by ATR-IR, XRD, and SEM studies. ATR-IR and XRD results indicated the successful incorporation of the nanoparticles in the membranes. Cross sectional images of the membranes along with the elemental mapping of calcium on the membrane surface were assessed using SEM. Hydrophilicity of the membranes was evaluated in terms of contact angle measurements. The permeability of the membranes was determined by measuring the pure water flux (PWF). Membranes were also subjected to antifouling studies using bovine serum albumin (BSA) as the standard protein for rejection. The membranes showed better permeability and antifouling property with the increased addition of CaCO3 nanoparticles.

Graphical abstract

The present research is an attempt to develop hybrid PSf ultrafiltration membranes using CaCO3 nanoparticles as additives. The work indicates that, CaCO3 incorporated PSf membranes showed enhanced hydrophilicity, permeation and antifouling properties.

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Introduction

Membrane separation processes are widely in use particularly in the field of water treatment [1]. The performance of a membrane separation process depends on the membrane characteristics such as, hydrophilicity, porous structure, antifouling property and chemical resistance of the feed solution [2], [3]. Among the various polymers in use today for ultrafiltration (UF), polysulfone (PSf) is a remarkable one because of its good chemical stability, film forming nature and desirable mechanical properties. The main shortcoming of this polymer is its hydrophobic nature which in turn makes it more susceptible to fouling [4]. Various methodologies have been developed in the past in order to increase its hydrophilic character such as, chemical surface treatment and the addition of hydrophilic additives [5], [6], [7]. The additives in the casting solution affect the morphology and performance of the prepared membrane. Among them, PEG is known to promote the pore formation in the polymeric membranes and thus enhance the permeation properties and also helps in better dispersion of other additives in the membrane [8], [9]. However excess dosage of PEG will adversely affect membrane rejection and strength [10], [11].

Nanoparticle incorporated membranes have become a new domain of interest in membrane technology. Researchers have previously investigated organic polymeric membranes incorporated with various inorganic nanoparticles and obtained better performance membranes [12], [13], [14]. With regard to PSf membranes, incorporation of silver nanoparticles and titanium oxide nanoparticles are the most common in the field of water treatment [15]. Aluminum oxide, zirconium oxide and nanosilica are some of the other incorporations that have also shown to enhance membrane characteristics [16], [17]. Improving hydrophilicity by incorporation of hydrophilic nanoparticles indicates better prospects with regard to hydrophobic PSf.

Calcium carbonate nanoparticles (CCNP) are the largest commercially produced nanoparticles due to their widespread use in rubber, plastics, paints, paper, medicine and food products [18]. Moreover they are easier for synthesis and comparatively cheaper than other nanoparticles. Calcium carbonate is hydrophilic and researchers have been working on their surface modifications to develop hydrophobic CCNPs in order to facilitate compatibility with polymer matrices [19], [20]. To the best of our knowledge, so far there are no any reports on CCNPs in the membrane technology. On the contrary, these naturally hydrophilic particles can be directly brought to use in membrane technology to enhance hydrophilicity. Calcium carbonate is almost insoluble in water which can be presumed from its low solubility 0.014 g L 1 at 25 °C. Surface atoms of CCNPs tend to get hydroxylated to form Ca–OH groups in water; this can result in a considerable increase in hydrophilicity [21]. Moreover the calcium carbonate addition in some polymer composites has shown improvement in mechanical properties especially tensile strength [22], [23]. Also these nanoparticles have been reported to possess antibacterial properties [24]. In the present study, at first CCNPs were synthesized via reported procedure in the literature [25]. Then, these nanoparticles were incorporated in different compositions to prepare PSf/PEG/CCNP hybrid membranes (PEG was used as a pore former). The effect of CCNPs on the properties of PSf UF membranes was evaluated using of SEM, XRD, FT-IR, PWF and hydrophilicity studies. Further the membranes were subjected to antifouling studies using bovine serum albumin (BSA) as the standard protein for rejection.

Section snippets

Materials

Polysulfone (PSf) with molecular weight 35,000 Da, polyethylene glycol (PEG) with molecular weight 600 Da and Bradford reagent were purchased from Sigma-Aldrich Co, Bangalore, India. 1-Methyl-2-pyrrolidone (NMP), sodium carbonate (Na2CO3), sodium hydroxide (NaOH) and calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) were purchased from Merck, India Ltd. BSA was purchased from Central Drug House (CDH), New Delhi, India.

Preparation of calcium carbonate nanoparticles (CCNP)

The CaCO3 nanoparticles were synthesized using the reported procedure in the

Characterization of CaCO3 nanoparticles

SEM image of the synthesized CCNPs is shown in Fig. 1. The synthesized CCNPs showed an average size of about 400 nm × 150 nm × 50 nm. The ATR-IR spectrum of the nanoparticles is given in Fig. 2(b), the absorption peaks at around 1094 cm 1 indicates the presence of aragonite while the absorption peak of 706.2 cm 1 showed the calcite formed [29]. Peaks at 867.6 cm 1 and 1391.2 cm 1 are the combined peaks for polymorphs and the broad peak about 3405.8 cm 1 corresponds to the presence of moisture [30]. It

Conclusions

The synthesized CCNPs showed an average size of about 400 nm × 150 nm × 50 nm. CCNP incorporated PSF/PEG membranes were successfully synthesized as confirmed from XRD and ATR-IR. The incorporated nanoparticles uniformly distributed within the polymer matrix which can be seen from the X-ray elemental mapping. All the membranes are found to have an asymmetric structure as seen from SEM images. Increased membrane hydrophilicity was observed with increasing concentration of nanoparticles as seen from

Acknowledgments

The authors would like to thank the Defense Research Development Organization (DRDO), Government of India for their financial support. They also thank Prof K. Narayana Prabhu, Head, Metallurgical and Materials Department of NITK Surathkal, India for providing SEM and contact angle measurement facility.

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