Hosik Park

Characterization of natural organic matter treated by iron oxide nanoparticle incorporated ceramic membrane-ozonation process.

In this study, changes in the physical and structural properties of natural organic matter (NOM) were observed during hybrid ceramic membrane processes that combined ozonation with ultrafiltration ceramic membrane (CM) or with a reactive ceramic membrane (RM), namely, an iron oxide nanoparticles (IONs) incorporated-CM. NOM from feed water and NOM from permeate treated with hybrid ceramic membrane processes were analyzed by employing several NOM characterization techniques. Specific ultraviolet absorbance (SUVA), high-performance size exclusion chromatography (HPSEC) and fractionation analyses showed that the hybrid ceramic membrane process effectively removed and transformed relatively high contents of aromatic, high molecular weight and hydrophobic NOM fractions. Fourier transform infrared spectroscopy (FTIR) and 3-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy revealed that this process caused a significant decrease of the aromaticity of humic-like structures and an increase in electron withdrawing groups. The highest removal efficiency (46%) of hydroxyl radical probe compound (i.e., para-Chlorobenzoic acid (pCBA)) in RM-ozonation process compared with that in CM without ozonation process (8%) revealed the hydroxyl radical formation by the surface-catalyzed reaction between ozone and IONs on the surface of RM. In addition, experimental results on flux decline showed that fouling of RM-ozonation process (15%) was reduced compared with that of CM without ozonation process (30%). These results indicated that the RM-ozonation process enhanced the destruction of NOM and reduced the fouling by generating hydroxyl radicals from the catalytic ozonation in the RM-ozonation process.

Alginate fouling reduction of functionalized carbon nanotube blended cellulose acetate membrane in forward osmosis.

Functionalized multi-walled carbon nanotube blended cellulose acetate (fCNT-CA) membranes were synthesized for forward osmosis (FO) through phase inversion. The membranes were characterized through SEM, FTIR, and water contact angle measurement. AFM was utilized to investigate alginate fouling mechanism on the membrane. It reveals that the fCNT contributes to advance alginate fouling resistance in FO (57% less normalized water flux decline for 1% fCNT-CA membrane was observed than that for bare CA membrane), due to enhanced electrostatic repulsion between the membrane and the alginate foulant. Furthermore, it was found that the fCNT-CA membranes became more hydrophilic due to carboxylic groups in functionalized carbon nanotube, resulting in approximately 50% higher water-permeated flux than bare CA membrane. This study presents not only the fabrication of fCNT-CA membrane and its application to FO, but also the quantification of the beneficial role of fCNT with respect to alginate fouling in FO.

Efficacy of CNT-bound polyelectrolyte membrane by spray-assisted layer-by-layer (LbL) technique on water purification

This study demonstrates the properties of surface-modified polyethersulfone (PES) composite ultrafiltration (UF) membranes prepared by a spray-assisted layer-by-layer (LbL) technique. The coating layers on the PES substrate consist of polyelectrolyte multilayers (PEMs) with and without functionalized multiwall carbon nanotubes (f-MWCNTs) as the blending additive. The composite membrane acquired a negative surface charge and the hydrophilicity of the membrane increased after adding hydrophilic f-MWCNTs. The pure water permeation tests revealed that the water flux was dependent on the f-MWCNTs/polyelectrolyte weight ratio and the number of PEMs. The prepared membrane showed slower flux reduction and lower fouling ratio (Rt) by humic acid (HA) filtration tests. Moreover, the flux recovery ratio (FRR) after deionized (DI) water flushing was improved significantly (up to 81%) compared with the PES substrate (46%), which indicated the enhancement of anti-fouling properties. The current work presents a facile way to modify the commercial membrane surface with tuned water flux and enhanced anti-fouling properties.

Improved antifouling performance of polyethersulfone (PES) membrane via surface modification by CNTs bound polyelectrolyte multilayers

In this study, commercial polyethersulfone (PES) membranes were surface-modified by the deposition of functionalized carbon nanotubes (f-CNTs) bound polyelectrolyte multilayers (PEMs) through spray-assisted layer-by-layer (LbL) technique. To investigate the anti-organic fouling properties of fabricated membranes, two representative organic foulants, bovine serum albumin (BSA) and sodium alginate (SA), were selected. Single and binary organic feed solutions in the presence or absence of calcium ions were tested in cross-flow ultrafiltration apparatus. In addition, to examine the membrane resistance to bacteria fouling, the prepared membranes were immersed into Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) suspension for 4 hours and the adhesion of bacteria cells were observed by scanning electron microscope (SEM). The fouling and antifouling mechanisms were proposed according to the specific scenarios in this study. It was found that the enhancement of hydrophilicity and surface charge of the PES membrane mitigated organic/bio-fouling under all circumstances; the fouling and antifouling of membranes were governed by a complex interplay of interactions between foulants and membrane. Among various interactions, hydration forces and electrostatic repulsion presumably contributed significantly for reducing the adhesion of foulants. The flux of fouled membranes could be restored by the simple flushing of DI water without any chemical treatment.

Invited paper: Composition-dependent electrical properties of ternary AgxSb1−xTey thin films synthesized by cationic exchange reaction

Ternary silver antimony telluride (AgxSb1−xTey) thin films with tailored compositions were synthesized by a cationic exchange reaction of thermally evaporated antimony telluride thin films, as a simple and costeffective approach. The composition of AgxSb1−xTey thin films was controlled by the reaction time. Temperaturedependent electrical properties of the AgxSb1−xTey thin films demonstrated phase transition behavior from 323 K to 343 K. The composition-dependent thermoelectric properties (i.e., electrical resistivity (ρ), Seebeck coefficient (S) and power factor (S2ρ)) of the as-deposited Sb54Te46, the transformed AgxSb1−xTey and the annealed AgxSb1−xTey thin films were investigated as a function of temperature.

Investigation of the performance behavior of a forward osmosis membrane system using various feed spacer materials fabricated by 3D printing technique

Recently, feed spacer research for improving the performance of a membrane module has adopted three-dimensional (3D) printing technology. This study aims to improve the performance of membrane feed spacers by using various materials and incorporating 3D printing. The samples were fabricated after modeling with 3D computer-aided design (CAD) software to investigate the mechanical strength, water flux, reverse solute flux, and fouling performances. This research was performed using acrylonitrile butadiene styrene (ABS), polypropylene (PP), and natural polylactic acid (PLA) as printing material, and the spacer model was produced using a diamond-shaped feed spacer, with a commercially available product as a reference. The 3D printed samples were initially compared in terms of size and precision with the 3D CAD model, and deviations were observed between the products and the CAD model. Then, the spacers were tested in terms of mechanical strength, water flux, reverse solute flux, and fouling (alginate-based waste water was used as a model foulant). Although there was not much difference among the samples regarding the water flux, better performances than the commercial product were obtained for reverse solute flux and fouling resistance. When comparing the prominent performance of natural PLA with the commercial product, PLA was found to have approximately 10% less fouling (based on foulant volume per unit area and root mean square roughness values), although it showed similar water flux. Thus, another approach has been introduced for using bio-degradable materials for membrane spacers.