Poly (vinylidene fluoride)/Polyaniline/MWCNT Nanocomposite Ultrafiltration Membrane for natural organic matter removal

Abstract:The objective of this work was to improve the permeability and the rejection properties of poly (vinylidene fluoride) PVDF ultrafiltration(UF) membrane using multi-wall carbon nanotubes(MWCNTs)/ polyaniline (PANI)... [ view full abstract ]

Abstract:The objective of this work was to improve the permeability and the rejection properties of poly (vinylidene fluoride) PVDF ultrafiltration(UF) membrane using multi-wall carbon nanotubes(MWCNTs)/ polyaniline (PANI) composite prepared by phase inversion through in situ polymerization method of PANI, for removal of natural organic matter (NOM) in water.
1. Introduction:PVDF is a promising UF membrane material due to its excellent properties such as high mechanical strength, high thermal stability and chemical resistance to organic solvents[1]. However, its hydrophobicity is considered to be the main drawback that reduces water flux and increases fouling[2]. Modification of the membrane surface by addition of nanoparticles like CNTs increases the membrane hydrophilicity with enhanced specific surface area, chemical stability and ease of functionalization[3]; this improves the permeability and antifouling properties of membranes.
2. Membrane preparation: MWCNT was dispersed in DMF solvent by ultrasonication first, then aniline hydrochloride and ammonium persulphate (APS) were added to the mixture which was stirred for 72 hrs at room temperature to synthesize the MWCNT/PANI nanocomposite by in-situ polymerization.Fixed amount of PVDF was added and stirred at 60 0C for 24 hr. The casting solution was degassed and cast on a glass plate. The cast film was immersed into a pure water bath to achieve in situ polymerization of aniline with different percentage amounts of MWCNT ranging from 0.25wt.% to 2wt.% in PVDF casting solutions.
4. Results and Discussion:The measurements of permeability, NOM rejection, contact angle, porosity, tensile strength, zeta potential and scanning electron microscopy (SEM) were performed. The resultant membrane (of PANI/1.5%MWCNT) showed the highest permeability (1320 LMH/bar) with a 35-fold of permeability improvement in comparison to pristine PVDF membrane; furthermore, the filtration test showed 78% rejection for Suwannee River Humic acid (HA). This significant improvement is due to the inclusion of MWCNT/PANI complex in the PVDF matrix, which increased hydrophilicity and formed more porous areas with well-developed finger like smaller pores under the top layer connected to the larger pores in the underneath layer see Fig.1. Moreover, the MWCNT/PANI increased the adsorption capacity of the membrane by the interaction of the negative NOM and the positively charged membrane surface.