Separation of reactive dyes from textile effluent by hydrolyzed polyacrylonitrile hollow fiber ultrafiltration quantifying the transport of multicomponent species through charged membrane pores

Abstract

A hydrolyzed polyacrylonitrile (PAN) based ultrafiltration grade hollow fiber membrane using sodium hydroxide having high surface potential was developed in this work. Efficacy of this membrane was demonstrated in treatment of textile effluent. Scanning electron microscopy (SEM) clearly showed that hydrolysis of PAN fibers (HPAN) made them dense. Fourier transform infrared (FTIR) spectra clearly indicated the functional groups confirming the hydrolysis of PAN matrix. The molecular weight cut-off of the HPAN fibers was reduced to 5 kDa from 20 kDa of untreated PAN lowering the average pore radius from 3.6 to 1.8 nm. A decline in the water contact angle of HPAN to 54° from 78° indicated the formation of a more hydrophilic membrane. The surface zeta potential of the hollow fiber was lowered to −12 mV from −2 mV imparting the negative potential on the membrane promoting charge-charge interaction between membrane pore and charged species during filtration. The surface roughness of the membrane was reduced almost by one order of magnitude after hydrolysis indicating its antifouling characteristics. The transport of the dyes and the electrolyte through the membrane pores was analyzed using Donnan steric pore model (DSPM) for a multicomponent system applicable for low cut off ultrafiltration. Contribution of various transport mechanisms, i.e., diffusion, convection and electro-migration was quantified. Thus, the novelty of this work includes (i) development of low cut off ultrafiltration grade hollow fibers; (ii) their application in treatment of real life effluent containing four reactive dyes; (iii) development of multicomponent pore transport model using DSPM.