Won Kil Choi

Synthesis and characterization of polyamide/polyester thin-film nanocomposite membranes achieved by functionalized TiO2 nanoparticles for water vapor separation

In this study, we report the synthesis of thin film nanocomposite (TFN) membranes by interfacial polymerization (IP) on porous polysulfone (PSf) hollow fiber membrane supports. We also investigate the synthesis of carboxylated TiO2 (C-TiO2) and hydroxylated TiO2 (H-TiO2) nanoparticles using a simple technique and evaluate the performance of the TFN membranes incorporated with these nanoparticles for water vapor separation. Comparative studies were carried out on membranes with and without the incorporation of nanoparticles (TFN and TFC) for water vapor separation. Aqueous 3,5-diaminobenzoic acid (DABA)/nanoparticles mixture solutions and organic trimesoyl chloride (TMC) were used in the IP process. The reaction between these two monomer solutions at the interfaces of PSf hollow fiber substrates resulted in the formation of the TFN membranes. Functionalized TiO2 nanoparticles (TiO2NPs) with a size of about 60 nm were used for the fabrication of the TFN hollow fiber membranes. These TFN membranes were characterized using different modern techniques and evaluated in comparison with the tidy TFC membranes. Their performances were evaluated based on the water vapor permeability and selectivity. Experimental results indicate that the carboxylated TiO2 nanoparticle (C-TiO2NPs) incorporated membrane shows improved performance compared to other membranes. By changing the nanoparticles, better hydrophilicity was obtained; the contact angle was decreased from 90° (PSf) to 46° (TFN) and the water vapor permeance was increased from 780 GPU (TFC) to 1131 GPU (TFN) with high selectivity being maintained (from 115 to 548) when the C-TiO2NPs content was 0.05 (wt%).

Highly selective thin film composite hollow fiber membranes for mixed vapor/gas separation

In the present study, thin film composite membranes have been prepared using an interfacial polymerization method. First, we coated a polydopamine (PDA) layer using different concentrations of PDA solution on polyethersulfone (PES) hollow fiber supports. After the PDA coating layer, thin film composite (TFC) membranes were prepared with 3,5-diaminobenzoic acid (3,5-DABA) as an aqueous phase monomer and trimesoyl chloride (TMC) as an organic phase monomer to synthesize a hydrophilic polyamide layer. This prepared selective layer is considered desirable to fabricate hydrophilic TFC membranes for water vapor/N2 separation. The TFC membranes by interfacial polymerization were confirmed and discussed using the accumulated results of characterization. Hollow fiber membranes (HFM) surface modification with PDA before TFC coatings was proposed to modestly and effectively enhance the membrane selectivity. The newly prepared TFC hollow fiber membranes acquired reasonably excellent selectivity and superior permeation fluxes. As a result, membrane sample MS4 coated with 2.0 wt% PDA and TFC prepared using 0.5 wt% of 3,5-DABA with 0.2 wt% of TMC and 60 s of reaction time showed the best permeance and selectivity as 3185 GPU and 195, respectively, compared with other TFC membranes prepared with different PDA concentrations. Overall, the membranes showed good performance in the entire range of operating conditions investigated.

Synthesis of cross-linked amides and esters as thin film composite membrane materials yields permeable and selective material for water vapor/gas separation

In this work, 3,5-diaminobenzoic acid (BA) was selected to synthesize polyamide as a selective layer because it is considered desirable to fabricate hydrophilic thin film composite (TFC) membranes for water vapor separation. Cross-linked chains of TFC membranes by interfacial polymerization were suggested, confirmed and discussed by using the compiled results of characterization, such as ATR-FTIR, XPS, FE-SEM, BET surface area, TGA and water contact angle. As a result, the BA-1-10 membrane (1.0 wt% of BA, 0.2 wt% of TMC and 10 min of reaction time) showed the best permeance and separation factor as 2160 GPU and 23, respectively, compared with other TFC membranes prepared under different conditions. It was shown that with a higher concentration of BA containing carboxylic acid a faster diffusion, greater reactivity and the formation of hydrophobic esters are possible. Moreover, the acyl chloride group (–COCl) of TMC was hydrolyzed to COOH and improved the hydrophilicity for a better sorption of water vapor. However, the hydrophobic esters were generated on a selective layer due to the excessive reaction time over 10 min. It was found that the reaction time should be the same as the immersion time of the aqueous monomer to give adequate high performances.

Preparation, modification and characterization of polymeric hollow fiber membranes for pressure-retarded osmosis

The present study evaluated the performance of polymeric hollow fiber membranes in the pressure-retarded osmosis (PRO) process for power generation. This study systematically investigated ways to develop a high flux and high power density. The polyethersulfone (PES) membrane support was modified by coating with polydopamine (PDA). After polydopamine coating, the effect of an additive during interfacial polymerization to make a thin film composite (TFC) layer on the polydopamine-coated layer was studied. At the time of interfacial polymerization, we added tributyl phosphate (TBP) as an additive in the organic monomer solution to increase the water flux and power density. The modified membranes were then well characterized by ATR-FTIR, SEM, AFM, TEM, porometry, and contact angle analysis; their performance in salt rejection, water permeability, and power density was evaluated. The relationship between the performance of the TBP additive and the physicochemical properties of the polyamide layers, that is, the free volume, surface roughness and hydrophilicity, seemed very high. The experimental results indicate that the addition of TBP additives changes the retention properties of the composite membrane; a certain concentration of TBP additives retained in the membrane increases the membrane water flux along with power density.