R. Jamshidi Gohari

Novel polyethersulfone (PES)/hydrous manganese dioxide (HMO) mixed matrix membranes with improved anti-fouling properties for oily wastewater treatment process

In this work, hydrophilic hydrous manganese dioxide (HMO) nanoparticles were synthesized and used as the inorganic filler for the preparation of mixed matrix membranes (MMMs). The aim of adding HMO nanoparticles into the polyethersulfone (PES) membrane matrix is to improve membrane hydrophilicity and anti-fouling resistance against oil deposition and/or adsorption. The resulting membranes were characterized by SEM, AFM, FTIR, contact angle measurements and ultrafiltration (UF) of synthetic oily wastewater. Experimental results showed that the hydrophilicity of the PES/HMO membrane was significantly improved to a low value of contact angle (16.4°) by HMO loading, which as a consequence led to a promising pure water permeability (573.2 L m−2 h−1 bar−1). In comparison, the pristine PES membrane only demonstrated 69.5° and 39 L m−2 h−1 bar−1, respectively. Furthermore, the PES/HMO membrane exhibited an excellent oil rejection (almost 100%) and a promising water flux recovery (75.4%) when it was used to treat a synthetic oily solution containing 1000 ppm oil. The promising anti-fouling properties of the PES/HMO membrane could be attributed to the presence of hydrophilic –OH groups on the membrane surface resulting from HMO addition, making this membrane less susceptible to fouling when challenged with oil-in-water emulsions.

A practical approach to synthesize polyamide thin film nanocomposite (TFN) membranes with improved separation properties for water/wastewater treatment

Thin film nanocomposite (TFN) membranes containing 0.05 or 0.10 w/v% surface-functionalized titanate nanotubes (TNTs) in a polyamide selective layer were synthesized via interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC) monomers. Nanomaterials were dispersed into the monomer solution using two different approaches. In the first one, the functionalized TNTs were dispersed into the amine aqueous solution, while in the second approach the same nanomaterials were dispersed in TMC organic solution. The TFN membranes were characterized and compared with a control thin film composite (TFC) membrane to investigate the effect of nanofiller loadings and the fabrication approach on membrane properties. Results showed that introducing nanofillers into the organic phase was more effective to synthesize a TFN membrane of greater separation performance as the use of a rubber roller to remove aqueous solution from the substrate surface could cause the loss of a significant amount of nanofillers, which further affected the polyamide layer integrity. It was also found that the incorporation of a high nanofiller loading tended to interfere with interfacial polymerization and weaken the bonds between monomer blocks, resulting in poor polyamide–nanotube integrity. Compared to the TFC membrane, the TFN membrane made of 2% PIP and 0.15% TMC with 0.5% nanofiller incorporation could achieve greater water flux (7.5 vs. 5.4 L m−2 h−1 bar−1) and Na2SO4 rejection (96.4% vs. 86%) while exhibiting higher resistance against fouling by protein and dye.

Control of Membrane Surface Roughness and Pattern Wave Length by Changing the Nonsolvent (Water) Influx Rate

The control of surface roughness of polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PS) and cellulose (CE) membranes was attempted by changing the rate of nonsolvent influx in the phase inversion process. PVDF and CE were chosen to represent membranes of high hydrophobicity and hydrophilicity, respectively, while PES and PS were chosen to represent membranes of intermediate hydrophobicity/-philicity. The concentration of sodium chloride (NaCl) in the aqueous coagulation medium was increased from 0 to 1.9 mol/L to decrease the rate of nonsolvent (water) influx in the solvent/nonsolvent exchange process. As well, the effect of polymer concentration and solvent on the surface roughness was investigated with respect to PVDF and PES. It was observed that the membrane surface roughness increased and decreased, respectively, for the hydrophobic PVDF and hydrophilic CE membrane as the rate of nonsolvent influx was decreased. For the PES and PS membranes of intermediate hydrophilic/-philicity, no significant roughness change was observed. The surface roughness tended to increase as the solution viscosity decreased. It was also observed that the pattern wave length of the hydrophobic membrane did not change significantly while that of the hydrophilic membrane increased significantly as the solvent influx rate was reduced. This trend is predictable by considering the shrinking or swelling of the cast polymer solution during the solvent/nonsolvent exchange process.