Seokhoon Ahn - Academia.edu (original) (raw)

Papers by Seokhoon Ahn

Applied Surface Science

Abstract BNNTs were functionalized by using a polymer that includes a pyridine group, which can u... more Abstract BNNTs were functionalized by using a polymer that includes a pyridine group, which can undergo dipole interactions with boron atoms in BNNTs. The functionalized BNNTs were well-dispersed in an alcohol solvent, whereas hexagonal boron nitride impurities precipitated, due presumably to stacked structures. After purification processes, acid was added to a solution that contained functionalized BNNTs to prevent pyridine-boron interactions through stronger acid-base interactions. Thus, the polymer bonded to the BNNTs was easily separated, and purified BNNTs could be obtained using a solution process.

International Journal of Molecular Sciences, 2020

Commercially available boron nitride nanotubes (BNNTs) and their purified form (pBNNTs) were disp... more Commercially available boron nitride nanotubes (BNNTs) and their purified form (pBNNTs) were dispersed in aqueous solutions with various dispersants, and their cytotoxicity and drug encapsulation capacity were monitored. Our data suggest that pBNNTs showed an average increase in dispersibility of 37.3% in aqueous solution in the presence of 10 different dispersants. In addition, 100 μg of pBNNTs induced an average decrease in cytotoxicity of 27.4% compared to same amount of BNNTs in normal cell lines. The same amount of pBNNTs can encapsulate 10.4-fold more drug (camptothecin) compared to BNNTs. These data suggest that the purification of BNNTs improves several of their properties, which can be applied to biological experiments and are thus essential in the biological application of BNNTs.

Cellulose, 2017

Cellulose hybrid fibers (CeHFs), hybridized via graphene oxide (GO) and metal ions (Ca 2?), are s... more Cellulose hybrid fibers (CeHFs), hybridized via graphene oxide (GO) and metal ions (Ca 2?), are synthesized by dry-jet wet spinning. The synthesized GO-Ca 2?-CeHFs exhibit the tensile strength and the breaking elongation of 551 ± 37.5 MPa and 5.9 ± 0.4%, respectively, while the GO/cellulose composite fibers (GO-CeFs) show the tensile strength of 403 ± 76.0 MPa and the elongation of 4.5 ± 0.5%; thus, the GO-Ca 2?-CeHFs demonstrate improved mechanical properties over GO-CeFs by 37 and 31% in terms of tensile strength and elongation, respectively. These results are attributed to the metal ions that form a good interfacial interaction between the functional groups of cellulose and GO. In addition, the tensile strength of GO-Ba 2?-CeHFs is as high as 580 ± 25 MPa, which is induced by the difference in the ionic radius. Therefore, the high mechanical properties of the synthesized cellulose-based fibers have the potential to be used as sustainable alternative to the synthetic fibers used in the industrial applications.

Journal of Materials Chemistry A, 2018

Deactivated current collector surface for reliable seawater battery.

Catalysts, 2016

Ruthenium incorporated titanium oxides (Ru x TiO 2) were prepared by a one-step hydrothermal meth... more Ruthenium incorporated titanium oxides (Ru x TiO 2) were prepared by a one-step hydrothermal method using Ti(SO 4) 2 and RuCl 3 as the precursor of Ti and Ru, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), Energy-dispersive X-ray spectroscopy (EDS) mapping, and BET were applied for the analyses of catalysts. Ruthenium atoms are well dispersed in the anatase phase of TiO 2 and the crystallite size of Ru x TiO 2 (≈17 nm) is smaller than that of pure TiO 2 (≈45 nm). In particular, we found that our homemade pure TiO 2 exhibits a strong Lewis acid property. Therefore, the cooperation of ruthenium atoms playing a role in the hydride elimination and the Lewis acid site of TiO 2 can efficiently transfer primary alcohols into corresponding aldehydes in an oxidant-free condition.

Bulletin of the Korean Chemical Society, 2014

Journal of Sol-Gel Science and Technology, 2017

This study describes a strategy to economically synthesize silica with high purity. For economica... more This study describes a strategy to economically synthesize silica with high purity. For economical synthesis, it is critical to choose proper synthetic process and raw material. Here, we have used economical sol-gel process and water glass with low cost to synthesize a silica powder, and adopted extraction process to enhance its purity. Specially, we have first examined where impurities are mainly located. Then we have considered how to enhance cleaning efficiency during extraction process for achievement of high purity. Scanning electron microscope and energy-dispersive X-ray spectroscopy analysis demonstrate that the impurities prefers to locate at the surface of silica aggregates, which indicates that large aggregates in size easily expose most of the impurities into the surface of silica whereas small sized aggregates can trap the impurities between them. Taken together with these results, we have formed large silica aggregates in size via controlling pH condition during the silica synthesis, followed by conducting Soxhlet extraction process for cleaning the impurities out. The use of this approach allows us to synthesize the silica with a purity of 99.95 wt%.

RSC Adv., 2016

We demonstrate controlled growth of vertical organic crystal nanowires on single layer graphene.

Chemical Science, 2016

We study single cluster electrical transport in a series of metal chalcogenide molecular clusters... more We study single cluster electrical transport in a series of metal chalcogenide molecular clusters using scanning tunneling microscope-based break-junction measurements.

Health care for women international, Nov 23, 2015

We examined the cultural influence on perceived body weight and the level of health practices at ... more We examined the cultural influence on perceived body weight and the level of health practices at a national and individual level. At a national level, we found that Japanese women (n = 80) overestimate body weight more than Korean (n = 82) and American (n = 63) women. At an individual level, individuals with interdependent self-construal were more prone to overestimate weight than those with independent self-construal (N = 182 American women). Based on the data, we identify that the relationship is mediated by self-criticism, and importantly, it is self-criticism rather than perceived overweight that predicts the level of health activities. Health practitioners and campaign designers across cultures are recommended to concentrate on promoting positive body esteem instead of encouraging engagement in corrective health behaviors for weight loss.

Chemical Science, 2013

We describe here the synthesis and electronic device properties of a new type of polycyclic aroma... more We describe here the synthesis and electronic device properties of a new type of polycyclic aromatic molecule, the contorted octabenzocircumbiphenyl (c-OBCB). Contorted polycyclic aromatic hydrocarbons (PAHs) are promising small active molecules for organic devices. We present two different methods to synthesize c-OBCB derivatives that allow the smooth incorporation of functional groups. The material has a highly contorted exterior with six 4-helicenes and two 5-helicenes around the exterior of the expanded core of the aromatic. With appropriate sidechains, the material is soluble in common organic solvents and forms thin films. In thin films, the tetradodecyloxy-substituted c-OBCB self-assembles to form the active layer in organic field effect transistors. It is a hole transporting organic semiconductor. In the transistors, the c-OBCB forms good contact with source and drain contacts made from graphene. The c-OBCB self-assembles into a heterojunction from solution with phenyl-C 70-butyric acid methyl ester (PC 70 BM). We observed power conversion efficiencies of $2.9 % under 100 mW cm À2 illumination at a 1 : 4 weight ratio of the c-OBCB relative to PC 70 BM. The c-OBCB is shape complementary to the ball shaped PC 70 BM.

Nano Letters, 2012

Electronic factors in molecules such as quantum interference and cross-conjugation can lead to dr... more Electronic factors in molecules such as quantum interference and cross-conjugation can lead to dramatic modulation and suppression of conductance in single-molecule junctions. Probing such effects at the singlemolecule level requires simultaneous measurements of independent junction properties, as conductance alone cannot provide conclusive evidence of junction formation for molecules with low conductivity. Here, we compare the mechanics of the conducting para-terminated 4,4′-di-(methylthio)stilbene and moderately conducting 1,2-bis(4-(methylthio)phenyl)ethane to that of insulating meta-terminated 3,3′-di(methylthio)stilbene single-molecule junctions. We simultaneously measure force and conductance across single-molecule junctions and use force signatures to obtain independent evidence of junction formation and rupture in the meta-linked crossconjugated molecule even when no clear low-bias conductance is measured. By separately quantifying conductance and mechanics, we identify the formation of atypical 3,3′-di(methylthio)stilbene molecular junctions that are mechanically stable but electronically decoupled. While theoretical studies have envisaged many plausible systems where quantum interference might be observed, our experiments provide the first direct quantitative study of the interplay between contact mechanics and the distinctively quantum mechanical nature of electronic transport in single-molecule junctions.

Langmuir, 2011

Various carboxylic acid substitution patterns on the 1,3,5-triphenylbenzene nucleus were explored... more Various carboxylic acid substitution patterns on the 1,3,5-triphenylbenzene nucleus were explored, and their influence on the symmetry of the resulting two-dimensional (2D) crystal structures was assessed. The symmetry of 1,3,5-benzenetribenzoic acid (H(3)BTB) was reduced by modifying the substitution pattern of the arene and/or adding an additional carboxylic acid. Four analogues belonging to various point groups were studied. Comparison of the monolayers of the analogues to that of H(3)BTB shows that plane group symmetry and molecular symmetry are not correlated: H(3)BTB and its analogues exhibit the same plane group p2 at the heptanoic acid/graphite interface. The 2D crystal structure of the H(3)BTB analogues is more strongly controlled by the geometry of hydrogen-bonding interactions rather than molecular symmetry. Other significant observations in this study include porosity, uncommon hydrogen-bonding motifs, and an unusually high number of inquivalent molecules (Z' = 3) present in the 2D crystal of the lowest symmetry analogue. This research demonstrates that reduction of molecular symmetry based on geometric modification of noncovalent interactions allows for control over porosity of the 2D crystals (close-packed structures to nanoporous networks) without changing the core shape of the molecule.

Langmuir, 2009

Sum frequency generation vibrational spectroscopy (SFG) has been applied to study two-dimensional... more Sum frequency generation vibrational spectroscopy (SFG) has been applied to study two-dimensional (2D) crystals formed by an isophthalic acid diester on the surface of highly oriented pyrolytic graphite, providing complementary measurements to scanning tunneling microscopy (STM) and computational modeling. SFG results indicate that both aromatic and CdO groups in the 2D crystal tilt from the surface. This study demonstrates that a combination of SFG and STM techniques can be used to gain a more complete picture of 2D crystal structure, and it is necessary to consider solvent-2D crystal interactions and dynamics in the computer models to achieve an accurate representation of interfacial structure.

Journal of the American Chemical Society, 2013

This work explores the formation of welldefined molecular p−n junctions in solution-processed sel... more This work explores the formation of welldefined molecular p−n junctions in solution-processed selfassembled heterojunction solar cells using dodecyloxysubstituted contorted hexabenzocoronene (12-c-HBC) as a donor material and phenyl-C 70-butyric acid methyl ester (PC 70 BM) as an acceptor. We find that the contorted 12-c-HBC molecules effectively assemble in solution to form a nested structure with the ball-shaped PC 70 BM. The result is a self-assembled molecular-scale p−n junction. When this welldefined p−n junction is embedded in active films, we can make efficient self-assembled solar cells with minimal amounts of donor material relative to the acceptor. The power conversion efficiency is drastically enhanced by the mode of donor and acceptor assembly within the film.

Journal of the American Chemical Society, 2013

Applied Surface Science

Abstract BNNTs were functionalized by using a polymer that includes a pyridine group, which can u... more Abstract BNNTs were functionalized by using a polymer that includes a pyridine group, which can undergo dipole interactions with boron atoms in BNNTs. The functionalized BNNTs were well-dispersed in an alcohol solvent, whereas hexagonal boron nitride impurities precipitated, due presumably to stacked structures. After purification processes, acid was added to a solution that contained functionalized BNNTs to prevent pyridine-boron interactions through stronger acid-base interactions. Thus, the polymer bonded to the BNNTs was easily separated, and purified BNNTs could be obtained using a solution process.

International Journal of Molecular Sciences, 2020

Commercially available boron nitride nanotubes (BNNTs) and their purified form (pBNNTs) were disp... more Commercially available boron nitride nanotubes (BNNTs) and their purified form (pBNNTs) were dispersed in aqueous solutions with various dispersants, and their cytotoxicity and drug encapsulation capacity were monitored. Our data suggest that pBNNTs showed an average increase in dispersibility of 37.3% in aqueous solution in the presence of 10 different dispersants. In addition, 100 μg of pBNNTs induced an average decrease in cytotoxicity of 27.4% compared to same amount of BNNTs in normal cell lines. The same amount of pBNNTs can encapsulate 10.4-fold more drug (camptothecin) compared to BNNTs. These data suggest that the purification of BNNTs improves several of their properties, which can be applied to biological experiments and are thus essential in the biological application of BNNTs.

Cellulose, 2017

Cellulose hybrid fibers (CeHFs), hybridized via graphene oxide (GO) and metal ions (Ca 2?), are s... more Cellulose hybrid fibers (CeHFs), hybridized via graphene oxide (GO) and metal ions (Ca 2?), are synthesized by dry-jet wet spinning. The synthesized GO-Ca 2?-CeHFs exhibit the tensile strength and the breaking elongation of 551 ± 37.5 MPa and 5.9 ± 0.4%, respectively, while the GO/cellulose composite fibers (GO-CeFs) show the tensile strength of 403 ± 76.0 MPa and the elongation of 4.5 ± 0.5%; thus, the GO-Ca 2?-CeHFs demonstrate improved mechanical properties over GO-CeFs by 37 and 31% in terms of tensile strength and elongation, respectively. These results are attributed to the metal ions that form a good interfacial interaction between the functional groups of cellulose and GO. In addition, the tensile strength of GO-Ba 2?-CeHFs is as high as 580 ± 25 MPa, which is induced by the difference in the ionic radius. Therefore, the high mechanical properties of the synthesized cellulose-based fibers have the potential to be used as sustainable alternative to the synthetic fibers used in the industrial applications.

Journal of Materials Chemistry A, 2018

Deactivated current collector surface for reliable seawater battery.

Catalysts, 2016

Ruthenium incorporated titanium oxides (Ru x TiO 2) were prepared by a one-step hydrothermal meth... more Ruthenium incorporated titanium oxides (Ru x TiO 2) were prepared by a one-step hydrothermal method using Ti(SO 4) 2 and RuCl 3 as the precursor of Ti and Ru, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), Energy-dispersive X-ray spectroscopy (EDS) mapping, and BET were applied for the analyses of catalysts. Ruthenium atoms are well dispersed in the anatase phase of TiO 2 and the crystallite size of Ru x TiO 2 (≈17 nm) is smaller than that of pure TiO 2 (≈45 nm). In particular, we found that our homemade pure TiO 2 exhibits a strong Lewis acid property. Therefore, the cooperation of ruthenium atoms playing a role in the hydride elimination and the Lewis acid site of TiO 2 can efficiently transfer primary alcohols into corresponding aldehydes in an oxidant-free condition.

Bulletin of the Korean Chemical Society, 2014

Journal of Sol-Gel Science and Technology, 2017

This study describes a strategy to economically synthesize silica with high purity. For economica... more This study describes a strategy to economically synthesize silica with high purity. For economical synthesis, it is critical to choose proper synthetic process and raw material. Here, we have used economical sol-gel process and water glass with low cost to synthesize a silica powder, and adopted extraction process to enhance its purity. Specially, we have first examined where impurities are mainly located. Then we have considered how to enhance cleaning efficiency during extraction process for achievement of high purity. Scanning electron microscope and energy-dispersive X-ray spectroscopy analysis demonstrate that the impurities prefers to locate at the surface of silica aggregates, which indicates that large aggregates in size easily expose most of the impurities into the surface of silica whereas small sized aggregates can trap the impurities between them. Taken together with these results, we have formed large silica aggregates in size via controlling pH condition during the silica synthesis, followed by conducting Soxhlet extraction process for cleaning the impurities out. The use of this approach allows us to synthesize the silica with a purity of 99.95 wt%.

RSC Adv., 2016

We demonstrate controlled growth of vertical organic crystal nanowires on single layer graphene.

Chemical Science, 2016

We study single cluster electrical transport in a series of metal chalcogenide molecular clusters... more We study single cluster electrical transport in a series of metal chalcogenide molecular clusters using scanning tunneling microscope-based break-junction measurements.

Health care for women international, Nov 23, 2015

We examined the cultural influence on perceived body weight and the level of health practices at ... more We examined the cultural influence on perceived body weight and the level of health practices at a national and individual level. At a national level, we found that Japanese women (n = 80) overestimate body weight more than Korean (n = 82) and American (n = 63) women. At an individual level, individuals with interdependent self-construal were more prone to overestimate weight than those with independent self-construal (N = 182 American women). Based on the data, we identify that the relationship is mediated by self-criticism, and importantly, it is self-criticism rather than perceived overweight that predicts the level of health activities. Health practitioners and campaign designers across cultures are recommended to concentrate on promoting positive body esteem instead of encouraging engagement in corrective health behaviors for weight loss.

Chemical Science, 2013

We describe here the synthesis and electronic device properties of a new type of polycyclic aroma... more We describe here the synthesis and electronic device properties of a new type of polycyclic aromatic molecule, the contorted octabenzocircumbiphenyl (c-OBCB). Contorted polycyclic aromatic hydrocarbons (PAHs) are promising small active molecules for organic devices. We present two different methods to synthesize c-OBCB derivatives that allow the smooth incorporation of functional groups. The material has a highly contorted exterior with six 4-helicenes and two 5-helicenes around the exterior of the expanded core of the aromatic. With appropriate sidechains, the material is soluble in common organic solvents and forms thin films. In thin films, the tetradodecyloxy-substituted c-OBCB self-assembles to form the active layer in organic field effect transistors. It is a hole transporting organic semiconductor. In the transistors, the c-OBCB forms good contact with source and drain contacts made from graphene. The c-OBCB self-assembles into a heterojunction from solution with phenyl-C 70-butyric acid methyl ester (PC 70 BM). We observed power conversion efficiencies of $2.9 % under 100 mW cm À2 illumination at a 1 : 4 weight ratio of the c-OBCB relative to PC 70 BM. The c-OBCB is shape complementary to the ball shaped PC 70 BM.

Nano Letters, 2012

Electronic factors in molecules such as quantum interference and cross-conjugation can lead to dr... more Electronic factors in molecules such as quantum interference and cross-conjugation can lead to dramatic modulation and suppression of conductance in single-molecule junctions. Probing such effects at the singlemolecule level requires simultaneous measurements of independent junction properties, as conductance alone cannot provide conclusive evidence of junction formation for molecules with low conductivity. Here, we compare the mechanics of the conducting para-terminated 4,4′-di-(methylthio)stilbene and moderately conducting 1,2-bis(4-(methylthio)phenyl)ethane to that of insulating meta-terminated 3,3′-di(methylthio)stilbene single-molecule junctions. We simultaneously measure force and conductance across single-molecule junctions and use force signatures to obtain independent evidence of junction formation and rupture in the meta-linked crossconjugated molecule even when no clear low-bias conductance is measured. By separately quantifying conductance and mechanics, we identify the formation of atypical 3,3′-di(methylthio)stilbene molecular junctions that are mechanically stable but electronically decoupled. While theoretical studies have envisaged many plausible systems where quantum interference might be observed, our experiments provide the first direct quantitative study of the interplay between contact mechanics and the distinctively quantum mechanical nature of electronic transport in single-molecule junctions.

Langmuir, 2011

Various carboxylic acid substitution patterns on the 1,3,5-triphenylbenzene nucleus were explored... more Various carboxylic acid substitution patterns on the 1,3,5-triphenylbenzene nucleus were explored, and their influence on the symmetry of the resulting two-dimensional (2D) crystal structures was assessed. The symmetry of 1,3,5-benzenetribenzoic acid (H(3)BTB) was reduced by modifying the substitution pattern of the arene and/or adding an additional carboxylic acid. Four analogues belonging to various point groups were studied. Comparison of the monolayers of the analogues to that of H(3)BTB shows that plane group symmetry and molecular symmetry are not correlated: H(3)BTB and its analogues exhibit the same plane group p2 at the heptanoic acid/graphite interface. The 2D crystal structure of the H(3)BTB analogues is more strongly controlled by the geometry of hydrogen-bonding interactions rather than molecular symmetry. Other significant observations in this study include porosity, uncommon hydrogen-bonding motifs, and an unusually high number of inquivalent molecules (Z' = 3) present in the 2D crystal of the lowest symmetry analogue. This research demonstrates that reduction of molecular symmetry based on geometric modification of noncovalent interactions allows for control over porosity of the 2D crystals (close-packed structures to nanoporous networks) without changing the core shape of the molecule.

Langmuir, 2009

Sum frequency generation vibrational spectroscopy (SFG) has been applied to study two-dimensional... more Sum frequency generation vibrational spectroscopy (SFG) has been applied to study two-dimensional (2D) crystals formed by an isophthalic acid diester on the surface of highly oriented pyrolytic graphite, providing complementary measurements to scanning tunneling microscopy (STM) and computational modeling. SFG results indicate that both aromatic and CdO groups in the 2D crystal tilt from the surface. This study demonstrates that a combination of SFG and STM techniques can be used to gain a more complete picture of 2D crystal structure, and it is necessary to consider solvent-2D crystal interactions and dynamics in the computer models to achieve an accurate representation of interfacial structure.

Journal of the American Chemical Society, 2013

This work explores the formation of welldefined molecular p−n junctions in solution-processed sel... more This work explores the formation of welldefined molecular p−n junctions in solution-processed selfassembled heterojunction solar cells using dodecyloxysubstituted contorted hexabenzocoronene (12-c-HBC) as a donor material and phenyl-C 70-butyric acid methyl ester (PC 70 BM) as an acceptor. We find that the contorted 12-c-HBC molecules effectively assemble in solution to form a nested structure with the ball-shaped PC 70 BM. The result is a self-assembled molecular-scale p−n junction. When this welldefined p−n junction is embedded in active films, we can make efficient self-assembled solar cells with minimal amounts of donor material relative to the acceptor. The power conversion efficiency is drastically enhanced by the mode of donor and acceptor assembly within the film.

Journal of the American Chemical Society, 2013