- Title
- Development of a thin-film nanocomposite membrane with improved properties for increasing performance in nanofiltration processes
- Creator
- Zarei, Mohammad Mehdi
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The use of thin-film nanocomposite (TFN) membranes in water/waste treatment plants for the removal of heavy metals has increased in the last few decades. TFN membranes utilise nanotechnology combined with thin-film composite (TFC) technology to improve separation performance. Nanoparticles (NPs) can be introduced into the polyamide (PA) layer of a TFC membrane to modify the membrane structure, which results in improvements in its physicochemical properties, such as hydrophilicity and selectivity. The chemical interaction between inorganic NPs and organic (polymer/monomer) membranes, NP dispersibility, and their compatibility with polymers and monomers requires particular consideration to achieve successful membrane fabrication. In addition, the fabrication technique, optimisation of the polymer/NP concentration, modification of NPs and selection of an appropriate support layer are necessary to improve the separation efficiency. In the present study, a new superhydrophilic TFN membrane for nanofiltration of water with a tuneable permeation and rejection of heavy metal salts (e.g. copper ions) was fabricated through interfacial polymerisation (IP) of a PA layer on a nanocomposite polyphenylsulfone (PPSU). Amine-modified silica nanoparticles (A-MSNPs) were used in the PA layer of a TFC membrane using conventional and vacuum filtration (VF) techniques to achieve a high-performance membrane separation. First, the hydrophilic and positively charged A-MSNPs were synthesised using a novel one-pot process with tetraethoxysilane (TEOS) as the silica precursor and polyethyleneimine (PEI) as the polyamine catalyst. Then, a series of neat and blended PPSU membranes were successfully fabricated and incorporated with the modified silica NPs. The prepared membranes were analysed via several characterisation techniques such as water contact angle, water permeability and scanning electron microscopy, and their separation performance was evaluated through a cross-flow filtration set-up. Finally, the membrane with the highest water flux and copper rejection was selected as the base for the fabrication of thin-film membranes. In the next stage, TFC and TFN membranes were fabricated using the prepared nanocomposite PPSU membrane as the support layer for a PA layer. Trimesoyl chloride (TMC) with m-phenylenediamine (MPD) were polymerised to prepare the thin PA layer on top of the support layer to control the n-TFC membrane. Different concentrations of the hydrophilic A-MSNP were loaded into the PA layer of the n-TFC membrane. Next, the structure and physical properties of the n-TFC membrane were compared with the prepared TFN membranes. Lastly, the desalination performance of all fabricated membranes was examined and compared using water flux, copper rejection and fouling evaluation. In the last stage of the study, a novel superhydrophilic TFN membrane was incorporated with MSNPs and PEI-TMC into the PA layer. TFNPEI-SiO2 and TFNVF membranes were fabricated through conventional and VF interfacial polymerisation, respectively. The generation of robust covalent bonds between the PEI and the PA layer led to improved compatibility of the A-MSNPs and the PA layer and resulted in the enhancement of the physicochemical properties of the TFN membrane. Gaining fundamental knowledge of polymeric membranes with respect to their morphology, structure and chemistry is crucial for improving their performance. Thus, the synthesised membranes were characterised using high-resolution techniques at the micro/nano scales to provide an insight into the chemical and interfacial interaction between the polymer and PA layer of the prepared thin-film membranes. Characterisation techniques, such as attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD), dynamic light scattering (DLS), zeta potential, water contact angle (WCA), and thermogravimetric analysis (TGA) were employed to analyse the structure of nanocomposite and thin-film membranes. The desalination performance of the fabricated membranes was also evaluated using the nanofiltration (NF) set-up for water flux, salt, metal ions and dye rejection. In addition, the antifouling properties of the prepared membranes were examined with a feed containing bovine serum albumin (BSA) as a common foulant. The obtained result showed that the PPSU membrane surface significantly improved in presence of the hydrophilic A-MSNPs in terms of water flux and copper removal. The neat PPSU membrane presented water flux at 44.0 ± 1.2 L/(m2h) with 80% copper rejection. The modified nanocomposite PPSU/PEI-SiO2, TFNPEI-SiO2 and TFNVF membranes exhibited water flux and copper removal at 44.0 ± 1.2 L/(m2h), 33.4 ± 0.8 and 37.0 ± 0.9 L/(m2h) with the copper rejection of 83.4 ± 1.3%, 97.5± 1.4% and 98.0 ± 1.4% respectively. The divalent cations Cu2+ is a good candidate to investigate positively charged membranes. Mechanism of the copper rejection can be explained by the Donnan Exclusion theory (charge-charge repulsion). Also, the mechanism of PEI-Cu2+ demonstrates binding of lone-pair nitrogen atoms and Cu2+ ions based on the acid and base Lewis theory, which shows a better understanding of the applied PEI in the A-MSNP/membrane. The efficacy of the novel membranes to remove model organic and biological contaminants was also evaluated. Dye removal of the prepared n-TFCPEI, TFNPEI/SiO2 and TFNVF membranes was evaluated using an aqueous solution of Congo red dye (MW = 700 Da) at constant transmembrane pressure of 400 kPa. Dye removal rates are observed at 94.3 ± 0.9%, 98.0 ± 1.3% and 98.8 ± 1.8% for n-TFCPEI, TFNPEI/SiO2 and TFNVF, respectively. The performance of the fabricated membranes and their long-term stability against bovine serum albumin (BSA) fouling was evaluated using flux recovery ratio (FRR) measurements. The flux recovery ratio increases from 70.2% for the n-TFCPEI to 82.1% for TFNPEI/SiO2 and 86.5% for TFNVF. This research project has attempted to advance in-principle knowledge about the polyamide layer in modified nanocomposite fabrication. It has also investigated the basic processes that prevail in water/waste treatment and used reactive nanomaterials to progress the development of TFN membranes.
- Subject
- thin-film nanocomposite (TFN) membranes; membrane fabrication; hydrophilic membrane; amine-modified silica nanoparticles
- Identifier
- http://hdl.handle.net/1959.13/1509680
- Identifier
- uon:56280
- Rights
- Copyright 2023 Mohammad Mehdi Zarei
- Language
- eng
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