Polyvinyl alcohol/polyethersulfone thin-film nanocomposite membranes with carbon nanomaterials incorporated in substrate for water treatment

A new class of thin-film nanocomposite (TFN) nanofiltration (NF) membrane was synthesized successfully by incorporation of carbon nanomaterials (oxidized multi-walled carbon nanotube (O-MWCNT) and graphene oxide (GO)) into polyethersulfone (PES) substrate via phase inversion method, substrate surface coating with polyvinyl alcohol (PVA) and then cross-linking with glutaraldehyde (GA). For better comparison, thin-film composite (TFC) membranes (without carbon nanomaterials incorporation into PES substrate) were also synthesized and the optimum concentrations of PVA and GA solutions were obtained. The fabricated TFC and TFN (TFN/OMWCNTs and TFN/GO) membranes were characterized by SEM, AFM, ATR-IR spectroscopy and contact angle measurements. It was found that incorporation of O-MWCNTs and GO into the PES substrate results in more elongated finger-like pores and larger macrovoids in the substrate and also reduced thickness of the thin skin layer and roughness of the membrane surface. The optimum TFC membrane showed pure water flux of about 13.2 LMH and Na2SO4 rejection of 84 % at 4 bar, while the TFN/O-MWCNTs and TFN/GO membranes showed 54 % and 35 % improvement in water permeability, respectively, without immolating Na2SO4 rejection. The rejection sequence was obtained as R (Na2SO4) > R (MgSO4) > R (NaCl) that confirms the membranes surface has negatively charge.