Adsorption of Cadmium (II) ions from aqueous solutions using Poly(amidoamine)/ multi-walled carbon nanotubes doped Poly(vinylidene fluoride-co-hexafluoropropene) composite membrane

Composite membranes consisting of Poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) blended with functionalised multi-walled carbon nanotubes (MWCNTs) and poly-amidoamine (PAMAM) were prepared using a phase inversion technique for adsorptive elimination of Cd (II) ions from contaminated water samples. Upon the addition of PAMAM-MWCNTs on PVDF-HFP, a stable, microporous structure with enhanced surface area and hydrophilic composite membranes were obtained; as confirmed by Focused Ion Beam Scanning electron microscopy (FIB-SEM), Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) analysis and contact angle measurements. The pH, adsorption isotherm, thermodynamic parameters and reusability of the composite membranes were investigated in batch experiments. The maximum adsorption capacity of 1 wt.% PAMAM-MWCNTs/PVDF-HFP composite membrane calculated by Langmuir model was 167 mg/g at 25 oC and pH 6.5. All composite membranes demonstrated that the Cd(II) ions adsorption conformed to Freundlich model (R2 = 0.999), which suggests that the adsorption process is multilayer. In addition, the thermodynamic parameters indicated that the adsorption process is spontaneous and endothermic in nature. The adsorption capacity of 1 wt.% PAMAM-MWCNTs/PVDF-HFP composite membrane remained above 90% after four reusability cycles, as confirmed by Inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis. The 1 wt.% PAMAM-MWCNTs/PVDF-HFP composite membrane exhibited higher selectivity coefficients towards Cd(II) in Cu(II), Zn(II) and Ni(II) binary metal solutions.