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"Lee, Sunggyu"
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Electron-mediated control of nanoporosity for targeted molecular separation in carbon membranes
Carbon molecular sieve (CMS) membranes are considered game-changers to overcome the challenges that conventional polymeric membranes face. However, CMS membranes also confront a challenge in successfully separating extremely similar-sized molecules. In this article, high-precision tuning of the microstructure of CMS membranes is proposed by controlled electron irradiation for the separation of molecules with size differences less than 0.05 nm. Fitting CMS membranes for targeted molecular separation can be accomplished by irradiation dosage control, resulting in highly-efficient C
2
H
4/
C
2
H
6
separation for low dosages (∼250kGy, with selectivity ∼14) and ultra-selective H
2
/CO
2
separation for high dosages (1000∼2000kGy with selectivity ∼80).The electron irradiated CMS also exhibits highly stabilized permeability and selectivity for long-term operation than the pristine CMS, which suffers from significant performance degradation due to physical aging. This study successfully demonstrates electron irradiation as a possible way to construct “designer” nanoporous carbon membranes out of the standard components mostly confined to pyrolysis conditions.
Controlled molecular separation by membranes requires 2D materials with precise structures to achieve the desired selectivity. Here authors demonstrate precise selectivity tuning in carbon membranes using electron irradiation.
Journal Article
Multi-matrix contamination by cyclic and linear siloxanes in a highly industrialized estuarine environment of Korea: source identification, seasonal variation, and bioaccumulation potential
Cyclic and linear siloxanes are widely used in personal care, industrial, and consumer products. To better understand their fate and ecological risks in estuarine environments, this study investigated spatial distribution, seasonal variations, and the bioaccumulation potential of siloxanes in surface water, sediment, and in benthic organisms in an industrialized bay of Korea. Cyclic siloxanes exhibited higher concentrations than linear siloxanes across multiple environmental matrices, indicating their predominance and persistence. Water and sediment had distinct spatial distributions of siloxanes, which were influenced by local sources and hydrodynamic conditions. Industrial activities and power plant effluents were identified as major contributors to siloxane contamination in the coastal environment. Overall, the concentration of siloxanes in surface water was highest in winter. In particular, cyclic siloxanes showed a greater sensitivity to seasonal variation than linear siloxanes, with concentrations fluctuating significantly across sampling periods. The spatial distribution of siloxanes in sediment was strongly associated with organic carbon. Benthic invertebrates exhibited a strong potential for bioaccumulation of D5 and L9, with the highest bioaccumulation factors and biota-sediment accumulation factors among the detected compounds. These findings highlight the need for continued monitoring and management of siloxane contamination in industrialized estuarine environments.
Journal Article
Distribution of Polychlorinated Naphthalenes in Sediment From Industrialized Coastal Waters of Korea With the Optimized Cleanup and GC-MS/MS Methods
Limited studies have been conducted on polychlorinated naphthalenes (PCNs) in the coastal environment worldwide. In this study, analytical methods were optimized for 18 PCN congeners in sediment using a multi-layer silica gel column and a gas chromatograph coupled to tandem mass spectrometry (GC-MS/MS). The optimized analytical methods of PCNs were employed for sediment samples from heavily industrialized bays of Korea to assess the occurrence, contamination, potential sources, and ecotoxicological concerns. PCNs were detected in all sediment samples, indicating ubiquitous contamination in industrialized coastal regions of Korea. Total concentrations and toxic equivalents (TEQs) of PCNs ranged from 0.99 to 21,500 (mean: 568) pg/g dry weight and from 1.72 × 10 –5 to 18.8 (mean: 0.52) pg TEQ/g dry weight, respectively, which were within the ranges reported by other studies. A clear decreasing gradient was observed for the sedimentary PCNs from inner to outer parts of the bays, streams, and rivers. This result indicates that industrial activities are primary sources of PCNs. The highest PCN concentrations were observed in sediment close to non-ferrous and petrochemical industries, indicating potential sources. CNs 73 and 52 were predominant congeners of PCNs in all sediment samples. Diagnostic ratios and non-parametric multidimensional scaling analysis showed that the potential primary sources of PCNs are thermal-related emissions and the use of PCB technical mixtures. Although a few sediment samples exceeded the sediment quality guidelines of TEQs, the cumulative risks by dioxin-like contaminants may be caused for almost all coastal zones surveyed. This is the first report on PCNs in sediment from Korean coastal waters.
Journal Article
Polybrominated Diphenyl Ethers in Maternal Serum, Breast Milk, Umbilical Cord Serum, and House Dust in a South Korean Birth Panel of Mother-Neonate Pairs
Polybrominated diphenyl ethers (PBDEs) have been used as flame retardants. Although many reports have indicated an association between exposure to PBDEs and developmental neurotoxicity, the relative contributions of different sources of dust PBDE congeners to the levels in various tissues of mother–baby pairs is not well understood. The aims of this study were thus to measure the quantitative relationship between the level of PBDEs in house dust and tissues of mother-neonate pairs, and to investigate the chemical sources of the PBDEs. Forty-one mother-neonate pairs were recruited and provided samples of maternal serum (n = 29), umbilical cord serum (n = 25), breast milk (n = 50), and house dust (n = 41), where PBDEs were determined with high-resolution gas chromatography coupled with high-resolution mass spectrometry. While deca- (e.g., BDE 209, detected 100%), nona- (BDE 206/207, 95.1%), octa- (BDE 183, 100%), penta- (BDE 99/153, 100%, 98%) and tetra-BDEs (BDE 47, 100%) were detected abundantly in dust, penta- (BDE 99, 76%, 92%) and tetra-BDEs (BDE 47, 84%, 98%) were detected abundantly in umbilical cord serum and breast milk, respectively; tetra-BDEs (BDE 47, 86%) were detected more often relative to other congeners in maternal serum. Spearman’s pairwise comparison showed that the levels of BDE 47 (ρ = 0.52, p < 0.001) and −99 (ρ = 0.64, p < 0.01) in umbilical cord serum were associated with BDE 209 levels in dust; BDE 47 in maternal serum also showed correlation with BDE 99 in cord serum (ρ = 0.48, p < 0.01) but there was no significant correlation between maternal BDE 47 and dust BDE 209. On the other hand, a comparison of the distribution among congeners suggested probable associations of BDE 47 in maternal serum, breast milk, and umbilical cord serum with BDE 209 in dust; and of BDE 99 in maternal and umbilical cord serum, breast milk, and dust with BDE 209 in dust. Although further studies are needed, a radar chart-based distributional comparison among congeners supported associations between BDE 47 or −99 in human tissues and BDE 209 in dust.
Journal Article
Spatial and temporal trends in polychlorinated naphthalenes in sediment from Ulsan and Onsan Bays of Korea: Potential sources and ecotoxicological concerns
Few studies have been conducted on spatial and temporal trends in polychlorinated naphthalenes (PCNs) in coastal environments. Here, we describe 18 PCN congeners found in surface and dated sediment samples collected from highly industrialized bays of Korea. Measurable levels of PCN congeners were detected in all sediment samples, suggesting concurrent and historical contamination. The highest PCN concentrations were observed in sediment from rivers, streams, and the inner portions of the bays, which are surrounded by industrial complexes and commercial harbors. CNs 73, 66/67, and 52 were dominant in surface and dated sediment samples. Congener patterns and diagnostic ratios revealed that PCN contamination is originated from combustion processes and the use of polychlorinated biphenyl (PCB) technical mixtures. PCN concentrations in dated sediment increased from the 1980s to the mid-2000s and then decreased to 2015. Although the toxic equivalent (TEQ) levels of PCNs in our study did not exceed sediment quality guidelines proposed by international authorities, the cumulative risks from the TEQ concentrations of polychlorinated dibenzo-p-dioxins, furans, PCBs, and PCNs can be expected for benthic organisms.
Journal Article
Polystyrene-graft-acrylic acid as compatibilizer of polystyrene/nylon 6,6 blends
Preliminary investigations to study the feasibility of using polystyrene grafted with acrylic acid to blend polystyrene (PS) and nylon 6,6 (N66) have been done. The graft copolymer (PS‐g‐AA) was synthesized by reacting polystyrene with acrylic acid in the presence of a free radical initiator using the solid phase graft copolymerization technique. Binary blends of N66/PS and N66/PS‐g‐AA were synthesized by melt mixing. The formation of a (PS‐g‐AA)‐co‐N66 copolymer during the blend preparation has been desired. The blend morphologies were observed by scanning electron microscopy (SEM). Significant reductions in the domain sizes of the dispersed minor phase were observed when PS‐g‐AA instead of PS was incorporated into the blend. The tensile properties of the blends were investigated. The belnds containing PS‐g‐AA were found to be stiffer (higher modulus) and stronger (higher tensile strength) as compared to the blends containing PS. These results are due to the better miscibility and adhesion between nylon 6,6 and the graft copolymer. The results of the rheological measurement of these blends further supports the above result and also indicates an increase in the molecular weight distribution (MWD) of the blend when polystyrene was replaced by the graft copolymer. This increase in the MWD of the compatibilized blend can be attributed to above assumed copolymer formation between the graft copolymer and nylon 6,6 due to the reaction between the carbonyl group of the acrylic acid and the amide and the terminal amine groups of nylon 6,6.
Journal Article
Grafting of poly(vinyl chloride) and polypropylene with styrene in a supercritical CO2 solvent medium: Synthesis and characterization
Graft copolymerization of styrene onto poly(vinyl chloride) (PVC) and polypropylene (PP) was carried out in a supercritical CO2 medium using AIBN as a free radical initiator. The supercritical CO2 medium served as a reaction medium in addition to being a solvent for the styrene monomer and the free radical initiator. The reaction temperature and pressure were kept above the critical points of the solvent‐monomer mixture to form a homogeneous single‐phase medium. The resulting graft copolymers were characterized using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR) techniques. The weight percent of grafting was determined using IR absorbance ratio technique. TGA results showed that the thermal stabilily of grafted copolymer of PVC was better than that of PVC, while grafted copolymer of PP had poorer thermal stability than PP. DSC results showed that glass transition temperatures (Tg's) of the grafted copolymers were higher than those of the starting polymers PVC and PP. The presence of polystyrene attached to the backbone polymer was confirmed by 1H NMR and 13C NMR analyses.
Journal Article
Supercritical fluid process for the synthesis of maleated poly(vinylidene fluoride)
Poly(vinylidene fluoride) was grafted with maleic anhydride monomer via a free‐radical mechanism in supercritical carbon dioxide medium. The free‐radical initiator chosen for this study was benzoyl peroxide. The structure of the resultant copolymer pendant groups was determined by 1H NMR spectroscopy to consist of individual succinyl anhydride functional groups. The degree of functionalization (graft level) was obtained by FTIR spectroscopy through the correlation of absorbance bands using standard samples. The FTIR analysis indicated increased graft level with monomer loading, reaction temperature, and treatment time; however, initiator loading and reaction temperature showed more‐complex behavior. Graft levels increased at moderate benzoyl peroxide initiator loadings (5.0 wt%) and decreased at the highest initiator loadings (10.0 wt%). POLYM. ENG. SCI., 45:631–639, 2005. © 2005 Society of Plastics Engineers
Journal Article
Removal of ungrafted monomer from polypropylene-graft-maleic anhydride via supercritical carbon dioxide extraction
The removal of spent initiator, excess initiator and unbound monomer from newly synthesized polypropylene‐graft‐maleic anhydride (PP‐g‐MA) has typically been carried out using Soxhlet extraction. Standard solvents used in the Soxhlet process are xylene, toluene, acetone or methanol. These chemicals are not only hazardous to some degree, but also lead to undesirable maleic anhydride (MA) ring opening. This paper establishes that supercritical carbon dioxide (scCO2) extraction of residuals prevents anhydride ring opening and eliminates the need for post‐extraction vacuum‐drying of the copolymer product. An added benefit of this innovative process is that environmentally friendly carbon dioxide (CO2) is used in place of harmful solvents. The successful extraction of the residuals is established by thermogravimetric analysis (TGA), whereas FTIR spectroscopy is used to compare the anhydride content of Soxhlet‐extracted PP‐g‐MA to that of scCO2‐extracted copolymer. Polym. Eng. Sci. 44:1636–1641, 2004. © 2004 Society of Plastics Engineers.
Journal Article