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In order to undertake preparation of the membranes, resin particles were dried in an oven at 30 °C for 48 h and then pulverized into fine particles in a ball mill and sieved to the desired mesh size. The ion exchange resin with desired particles size (–325 +400 mesh) was used in membrane fabrication. The preparation proceeded by dissolving the polymer binder into THF solvent (polymer binder (PVC): solvent (THF)) (w/v), (1: 20)) in a glass reactor equipped with a mechanical stirrer for more than 5 h. This was followed by dispersing a specific quantity of ground resin particle ((resin particle: polymer binder) (w/w), (1:1)) as functional groups agents and clay nanoparticles (S1: 0.0, S2: 0.5, S3: 1.0, S4: 2.0 and S5: 4.0%wt) as additive in polymeric solution, respectively. The mixture was mixed vigorously at room temperature to obtain uniform particle distribution in polymeric solution. In addition, for better dispersion of particles and breaking up their aggregates, the polymeric solution was sonicated for 1 h using ultrasonic instrument. Excessive homogeneity and uniform distribution of particles (resin, additive) in the membrane matrix provide superior conducting regions for the membranes and generate easy flow channels for counter-ions transportation. The presence of more conducting region on the membrane surface can also strengthen the intensity of the uniform electrical field around the membrane and decreases the polarization phenomenon (Kang et al. 2003). Furthermore, uniform distribution of particles in polymeric solution increases the viscosity of solution and reduces the evaporation rate of solvent. This improves the polymer chain's conformation with particle surfaces and improves the membrane selectivity (Powell & Qiao 2006). Then, the mixing process was repeated for another 30 min by the mechanical stirrer. The mixture was then cast onto a clean and dry glass plate at 25 °C. The membranes were dried at ambient temperature and immersed in distilled water. In the final stage, membranes were pretreated by immersing in NaCl solution. The membrane thickness was measured by a digital caliper device around 60–70 μm. A summary of the membrane preparation procedure is given in Table 1.

Table 1

Flow sheet of membrane preparation procedure

The procedure for IEM preparation
Step 1 Resin particles drying (at 30 °C for 48 h) 
Step 2 Resin particles pulverizing (–325 +400 mesh) 
Step 3 Polymer dissolving into solvent (for 5 h) 
Step 4 Resin particles and additive dispersing in polymeric solution 
Step 5 Sonication of polymeric solution (for 1 h) 
Step 6 Mixing of polymeric solution (for another 30 min) 
Step 7 Casting (at 25 °C) 
Step 8 Film drying (at 25 °C for 30 min) and immersing in water 
Step 9 Membranes pretreatment by HCl and NaCl solutions 
The procedure for IEM preparation
Step 1 Resin particles drying (at 30 °C for 48 h) 
Step 2 Resin particles pulverizing (–325 +400 mesh) 
Step 3 Polymer dissolving into solvent (for 5 h) 
Step 4 Resin particles and additive dispersing in polymeric solution 
Step 5 Sonication of polymeric solution (for 1 h) 
Step 6 Mixing of polymeric solution (for another 30 min) 
Step 7 Casting (at 25 °C) 
Step 8 Film drying (at 25 °C for 30 min) and immersing in water 
Step 9 Membranes pretreatment by HCl and NaCl solutions 

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