Synthesis of polymeric nanocomposite membranes for aqueous and non-aqueous media

Abstract

Thin film composite (TFC) membranes have long been used by many large-scale applications (i.e., water and wastewater treatment). Recently, conventional polymeric TFC membranes are facing with short longevity due to high fouling tendency and susceptibility at extreme operational conditions. On the other hand, ceramic membranes are also suffering from disadvantages like low selectivity, unreliable control over porosity and pore size which makes it difficult to achieve a reproducible final product. The aim of this project was to develop a high selective TFC membranes incorporated by functionalized TiO2 nanoparticles for aqueous and nonaqueous media applications.In order to obtain high permeable aromatic polyamide thin film nanocomposite (TFN) nanofiltration membrane, the conventional interfacial polymerization (IP) reaction was applied as the embedding media for functionalized nanoparticles. For this purpose, TFN nanofiltration membrane with appropriate structural and separation properties was developed by dispersing the aminosilanized TiO2 nanoparticles inside the diamine monomer and polymerizing the monomer in the presence of these particles. Surface-modified ceramic substrate was used to obtain high mechanical resistant composite membrane. Results from spectrometry analyses represent that the silane coupling agent called AAPTS has been successfully grafted onto the external surface of TiO2 after the chemical modification. Upon incorporation of TiO2 nanoparticles, thermal stability of nanocomposite is significantly improved in comparison with TFC membrane. Morphological investigations prove that the functionalized TiO2 nanoparticles could effectively change the surface properties and roughness of NF membranes. Performance results show that ultra-low concentration (0.005 wt%) of amine functionalized TiO2 nanoparticles improves the salt rejection as well as water flux. Flux can be further improved by the incorporation of higher percentage of the modified TiO2 into polymer membrane.In order to obtain nanofiltration membrane with high permeability and antifouling properties, TFN membrane was synthesised by dip-coating of a hydrophilized porous poly(vinylidene fluoride) (PVDF) support in different poly(vinyl alcohol) (PVA) aqueous solution. In order to improve the interfacial adhesion of nanoparticles in PVA blend, an endothermic carboxylation reaction under acidic condition was carried out on the TiO2 surface using chloroacetic acid (ClCH2COOH). Glutaraldehyde (GA) was used as a cross-linker to bond resultant PVA chains and enhances the stability of the coated PVA layer, accordingly. TiO2 nanoparticles were dispersed in PVA solution in pure and functionalized forms. Scanning electron microscopy (SEM) identified various topographies by the incorporation of TiO2 nanoparticles. Performance results showed a 40% rejection improvement of divalent salt (MgSO4) by the incorporation of 1.0 wt% surface-carboxylated TiO2 nanoparticles into PVA solution. A simultaneous 57% retention improvement was achieved for uncharged solute (PEG 2000). After PVA coating with TiO2 incorporation, the flux recovery ratio of PVDF membrane was significantly improved from 45 to 94%.In order to apply TFN membranes in non-aqueous media, a range of thin film nanocomposite solvent resistant nanofiltration membranes (SRNF) were fabricated by interfacial polymerization technique. TiO2 nanoparticles were used as inorganic fillers into polyamide chain network. TiO2 nanoparticles’ surfaces were functionalized in order to improve their compatibilization inside the polyamide matrix. For this purpose, Monoethanolamine (MEOA) and triethylenetetramine (TETA) agents were applied to aminate TiO2 nanoparticles, while thionyl chloride (TCl) was used to chlorinateation. Morphological investigations identified various topographies formed by the incorporation of TiO2 nanoparticles with different chemistry. Transport properties of membranes were evaluated by two different dyes: positively-charged Crystal Violet (CV) (408 Da) and neutral Bromothymol Blue (BTB) (624 Da). Performance results reveal that high rejection was achieved by the TFN membrane fabricated by TCl-modified TiO2 with BTB and CV rejection of 90 and 93%, respectively. These satisfactory rejection data for both charged and uncharged dyes can be attributed to formation of a dense structure after exposing the chlorinated TiO2 nanoparticles into interfacial polymerization reaction on membrane surfaces.