Sunhee Kim’s research while affiliated with University of Pittsburgh and other places

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Publications (10)


Direct Spectroscopic Observation of the Role of Humidity in Surface Diffusion through an Ionic Adsorbent Powder. The Behavior of Adsorbed Pyridine on Nanocrystalline MgO
  • Article

January 2009

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21 Reads

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18 Citations

The Journal of Physical Chemistry C

Xiaoye Wang

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Sunhee Kim

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Corneliu Buda

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[...]

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Jr. John T. Yates

The influence of water vapor on the surface diffusion behavior of pyridine adsorbed on powdered MgO surfaces has been studied by Fourier transform IR (FTIR) absorption spectroscopy. It has been found that the introduction of water vapor significantly increases the pyridine surface diffusion coefficient. FTIR spectra showed that water vapor converted Lewis acid Mg2+ sites to Brønsted Mg−OH sites. These measurements also detected the change in surface bonding of pyridine to the two types of sites. The activation energy for escape of chemisorbed pyridine into a mobile precursor state is lower for pyridine bound to Mg−OH sites than for binding to Mg2+ sites, causing the hydroxylated MgO to exhibit a higher diffusivity than that found for dry MgO containing no surface hydroxyl groups. This effect was confirmed by DFT calculations of the binding energy of pyridine to MgO(100) sites and to defect sites on MgO(100), where hydroxylation decreases the binding energy by 30 kJ mol−1 on each type of site.


IR Spectroscopic Measurement of Diffusion Kinetics of Chemisorbed Pyridine through Nanocrystalline MgO Particles. The Involvement of Surface Defect Sites in Slow Diffusion

January 2009

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16 Reads

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21 Citations

The Journal of Physical Chemistry C

The molecular transport of pyridine through nanosized MgO particles has been investigated by Fourier transform IR spectroscopy. Two regimes of chemisorbed pyridine diffusion are observed. A fast diffusion process is associated with pyridine bound to nondefective smooth MgO(100) facets which exhibit an activation energy barrier of 35.7 kJ mol−1 for escape into a mobile precursor. The slow pyridine diffusion process occurs from defect sites, where the activation energy of escape to the mobile precursor is measured to be 64.6 kJ mol−1. The escape barriers controlling pyridine diffusion through MgO powders are similar to the calculated adsorption energy on MgO(100) and to the calculated adsorption energies on various defect sites on MgO(100) having lower Mg2+ coordination numbers than those on MgO(100) facets.


Infrared Spectroscopic Study of ClCN Adsorption on Clean and Triethylenediamine-Precovered γ-Al2O3

November 2007

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34 Reads

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13 Citations

The Journal of Physical Chemistry C

The effect of triethylenediamine (TEDA) (also named 1,4-diazabicyclo [2.2.2]octane, DABCO) on the adsorption of ClCN on a γ-Al2O3 absorbent has been investigated. Both Fourier transform infrared (FTIR) and theoretical studies indicate that no direct interaction between amine groups of TEDA and ClCN molecules takes place. Instead, we found that TEDA competes with ClCN for active surface sites on γ-Al2O3. In addition, the adsorption behavior of cyanogen chloride (ClCN) on a clean γ-Al2O3 surface has been studied. The sequence of the thermally activated processes of diffusion, adsorption, desorption, and decomposition of ClCN molecules on the clean γ-Al2O3 surface following icelike ClCN layer formation at lower temperature was observed. One of the decomposition products, Al−NCO, was assigned by using an Al−18OH labeled surface for reaction with ClCN. In addition, Al−CN and Al2−OCN species were also detected upon ClCN decomposition. Good correlation of the calculated vibrational frequencies for the adsorbed species with experimental data is found.


IR Spectroscopic Observation of Molecular Transport through Pt@CoO Yolk−Shell Nanostructures

September 2007

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32 Reads

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74 Citations

Journal of the American Chemical Society

FTIR spectroscopy has been used to monitor the transport of CO to the Pt cores of Pt@CoO nanoparticles forming CO/Pt species. It was found that external Pt sites are not present on the outer surfaces of the approximately 10 nm diameter nanostructures and that CO transports to Pt adsorption sites by an activated surface diffusion process through the CoO shells surrounding approximately 2 nm diameter Pt cores. The CO transport process is not due to gas-phase transport below 300 K. The weakly bound adsorbed CO/CoO species responsible for transport was directly observed at approximately 2147 cm(-1) during transport through the CoO shells.


Infrared Spectroscopic Study of the Adsorption of HCN by γ-Al 2 O 3 : Competition with Triethylenediamine for Adsorption Sites

April 2007

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55 Reads

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27 Citations

The Journal of Physical Chemistry C

The adsorption and vibrational properties of chemisorbed HCN on Lewis acid sites, Lewis base sites, and Brønsted Al-OH acid sites on a partially hydroxylated [gamma]-Al2O3 surface have been obtained by a combination of FTIR and density functional theory studies. The vibrational modes from the molecular and dissociative adsorption of HCN were assigned by using deuterium and 13C-labeled D13CN molecules at 170 K. In addition, [eta]2(C, N)-HCN bonding is also found from the [nu](CdN) vibrational spectra. Good correlation of the calculated vibrational frequencies for the adsorbed species with experimental data is found. The effect of triethylenediamine (TEDA) (also called 1, 4-diazabicyclo [2.2.2]octane, DABCO) on the adsorption of hydrogen cyanide (HCN) on the high area [gamma]-Al2O3 surface has been investigated using transmission FTIR spectroscopy. During HCN adsorption on TEDA-functionalized surfaces, there is no spectral change or emerging feature in either the TEDA or HCN spectral regions, indicating that no direct interaction occurs between these two molecules. Instead, we found that TEDA competes with HCN for the active sites on [gamma]-Al2O3. The observed [nu](C [identical with] N) mode on a TEDA-precovered surface is due to the HCN adsorption on Lewis base sites (Al-O-Al) which are less affected by TEDA preadsorption.


Spectroscopic Measurement of Diffusion Kinetics through Subnanometer and Larger Al 2 O 3 Particles by a New Method: The Interaction of 2-Chloroethylethyl Sulfide with γ-Al 2 O 3

June 2006

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8 Reads

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12 Citations

The Journal of Physical Chemistry B

A new method to study the diffusion properties of molecules into porous materials using transmission IR spectroscopy is employed. A measurement of the diffusion of the 2-chloroethylethyl sulfide (2-CEES) molecule into two types of gamma-Al2O3 powder is performed, showing that the diffusion rate into subnanometer crystallite particle size gamma-Al2O3 powders (subnano-Al2O3) is higher than that into the larger crystallite particle size powder. It is shown that a surface diffusion mechanism can be used to model the diffusion process giving good agreement with the experimental results, where Dsubnano-Al2O3 is approximately 5 times larger than Dmultinano-Al2O3 at 170 K for the 2-CEES molecule.


Perturbation of Adsorbed CO by Amine Derivatives Coadsorbed on the γ-Al 2 O 3 Surface: FTIR and First Principles Studies

April 2006

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16 Reads

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16 Citations

The Journal of Physical Chemistry B

The coadsorption of CO and triethylenediamine (TEDA) (also called 1,4-diazabicyclo[2.2.2]octane, DABCO) on a high-area gamma-Al2O3 surface has been investigated with use of transmission FTIR spectroscopy. It has been found that TEDA binds more strongly to both Lewis acid sites and to Brønsted Al-OH sites than does CO. Competition experiments indicate that TEDA displaces CO to less strong binding sites. Evidence for weak CO...TEDA interactions is found in which small nu(CO) redshifts are produced. Comparison between different amines such as triethylenemonoamine (TEMA) (also called 1-azabicyclo[2.2.2]octane, ABCO), trimethylamine (TMA), and ammonia indicates that the nu(CO) redshift increases with increasing amine polarizability, indicating that the redshift is mainly due to dipole image damping effects on the CO oscillator frequency. The direct bonding between the exposed N lone pair electrons of the TEDA molecule and CO does not occur. First principles theoretical studies have characterized the bonding of CO with gamma-Al2O3 Lewis acid sites of various types as well as TEDA bonding to both Lewis acid sites and to Al-OH groups. The theoretical studies also indicate that strong bonding of adsorbed CO with TEDA molecules does not occur, and that the observed decrease in the binding energy of CO when coadsorbed with TEDA on gamma-Al2O3 is expected.


Adsorption of Triethylenediamine on Al 2 O 3 -III: Bonding to Lewis Acid Al 3+ Sites

May 2005

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13 Reads

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15 Citations

The Journal of Physical Chemistry B

The adsorption of triethylenediamine (TEDA) on Lewis acid (Al(3+)) sites of the highly dehydroxylated Al(2)O(3) surface has been observed by FT-IR spectroscopy. This was done by monitoring the competitive adsorption of TEDA and CO on the Al(3+) sites. A stoichiometric replacement of Al(3+)-CO species was observed as Al(3+)-TEDA surface species were formed.


The Adsorption of Triethylenediamine on Al 2 O 3 -I: A Vibrational Spectroscopic and Desorption Kinetic Study of Surface Bonding

April 2005

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14 Reads

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18 Citations

The Journal of Physical Chemistry B

The adsorption of triethylenediamine (TEDA) at 300 K is observed to occur via hydrogen bonding to isolated Al-OH groups on the surface of partially dehydroxylated high area gamma-Al(2)O(3) powder. This form of bonding results in +0.3 to +0.4% blue shifts in the CH(2) scissor modes at 1455 cm(-1) and a -0.4% red shift in the CN skeletal mode at 1060 cm(-1), compared to the gas-phase frequencies. Other modes are red shifted less than 0.1%. The isolated OH modes are red shifted by -200 to -1000 cm(-1) due to the strong hydrogen bonding association of Al-OH groups with an N atom in TEDA. Thermal desorption of adsorbed TEDA from the surface occurs in the range 300-700 K. Mass spectral and infrared studies indicate that the decomposition of TEDA occurs on Al(2)O(3) above 725 K, and that C-H bonds are broken, forming adsorbed species with N-H bonds which are stable to 1000 K or above. In contrast to adsorption at 300 K, adsorption of TEDA at 85 K results in the formation of a condensed ice of TEDA, which covers the outer surface of the porous Al(2)O(3) and which does not interact with Al-OH groups inside the porous powder due to immobility.


The Adsorption of Triethylenediamine on Al 2 O 3 -II: Hydrogen Bonding to Al−OH Groups

April 2005

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15 Reads

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15 Citations

The Journal of Physical Chemistry B

The hydrogen bonding of the triethylenediamine (TEDA) molecule to isolated Al-OH groups on partially dehydroxylated high area gamma-Al(2)O(3) powder has been studied using transmission IR spectroscopy. It has been found that TEDA adsorbs both singly and as multiple species to single Al-OH groups in clearly separable equilibrium stages of adsorption at 300 K. The reversible adsorption of a single TEDA molecule to Al-OH fits the Langmuir adsorption isotherm well, and the enthalpy of adsorption is found to be -15.6 +/- 0.5 kJ mol(-1) in the range of fractional coverage of 0.5-0.6. Red shifts of the Al-OH frequency from approximately -200 cm(-1) to approximately -1000 cm(-1) are observed as a result of -OH bonding to the N lone pair in the TEDA molecule.

Citations (9)


... It is within this region of five stellar radii where SiO + aluminum (Al 2 O 3 ) dust grain surface reactions can occur, while the AlO + silicon (SiC) dust grain surface reaction is more likely further from the stellar surface. Such surface reaction processes have been investigated for similar aluminum-bearing molecules (AlCO and AlCN), demonstrating the feasibility of the proposed mechanism (Casarin et al. 2000;Kim et al. 2007;Van de Sande et al. 2019). Further out, near the outer CSE, high-energy ionizing radiation would increase the likelihood of an ion-neutral collision, such as Al + + SiO, a binary collision between an ion and a neutral molecule in which the ion induces a dipole moment in the neutral molecule, increasing the longrange attractive forces. ...

Reference:

Spectroscopic Properties of the Astrochemical Molecules [Al, O, Si] x (x = 0, +1)
Infrared Spectroscopic Study of the Adsorption of HCN by γ-Al 2 O 3 : Competition with Triethylenediamine for Adsorption Sites
  • Citing Article
  • April 2007

The Journal of Physical Chemistry C

... In the most common neutralization technologies use is made of mixtures that consist of nanoparticles of such metal oxides as MgO, CaO, ZnO, SrO, TiO 2 , Al 2 O 3 , CuO, Fe 2 O 3 with grain diameters ranging from a few nanometers to several dozen micrometers . The nanocrystalline MgO with grains of a 4 µm diameter and a specific surface exceeding 500 m 2 /g is characterized by a particularly large surface and activity [14][15][16][17][18]30,34]. Reducing the size of nanocrystallites causes a significant increase in the share of surface atoms, including those occupying edge and corner places, particularly as their network defects comprise the active sites of the oxide neutralizer [34]. ...

Direct Spectroscopic Observation of the Role of Humidity in Surface Diffusion through an Ionic Adsorbent Powder. The Behavior of Adsorbed Pyridine on Nanocrystalline MgO
  • Citing Article
  • January 2009

The Journal of Physical Chemistry C

... The increase of Knudsen diffusion into porous media at the onset of desorption has been demonstrated experimentally (Ballinger et al. 1989). Outward diffusion of an adsorbate through MgO powders with nanosized interparticle voids showed both a fast and a slow diffusion channel, suggestive of bonding on two types of sites, and thermal desorption followed a symmetric TPD curve unlike a first-order curve (Kim et al. 2009, their Figure 4). We suggest that these experimental results are similar to our findings that desorption from a powder is slower than an exponential decay of the adsorbate reservoir even for well-defined sites. ...

IR Spectroscopic Measurement of Diffusion Kinetics of Chemisorbed Pyridine through Nanocrystalline MgO Particles. The Involvement of Surface Defect Sites in Slow Diffusion
  • Citing Article
  • January 2009

The Journal of Physical Chemistry C

... The VFs of γ-SiC slightly varied whereas the VFs of gas molecules suffer significant variation due to deformation through adsorption ( Table 2). The values in the parenthesis represent the VFs of isolated gas molecules which satisfies previous reports [41][42][43][44][45] . The decrease in stretching VFs of the gas molecules represents an increase in bond lengths and vice versa which verifies Table 1 ...

Infrared Spectroscopic Study of ClCN Adsorption on Clean and Triethylenediamine-Precovered γ-Al2O3
  • Citing Article
  • November 2007

The Journal of Physical Chemistry C

... 38 In the presence of HA and FA, the amount of surface hydroxyl groups increased aer the PSMPs adsorption of As(III), more so in the presence of HA as compared to FA because the molecular weight, structural complexity, and number of oxygencontaining functional groups are higher on HA. 39 Aer adsorption, the FTIR band associated with hydroxyl group vibrations was red-shied to a lower energy, indicating that the energy required for the vibration of the hydroxyl group is less and the group is less stable. 40 Thus, considering that the adsorption of metal ions is related to the chemical functions of oxygen on the adsorbent, 41 we speculate that As(III) may interact with the surface -OH of PSMPs. ...

Perturbation of Adsorbed CO by Amine Derivatives Coadsorbed on the γ-Al 2 O 3 Surface: FTIR and First Principles Studies
  • Citing Article
  • April 2006

The Journal of Physical Chemistry B

... With the goal of evaluating the transport dynamics of CWAs in Zr-based MOFs, our research efforts began by developing a method for monitoring molecular transport under pristine conditions. Our approach, adapted from Kim et al., 46 utilized in situ infrared (IR) spectroscopy operating under ultrahigh vacuum (UHV) conditions to monitor changes that occur during exposure, diffusion, and desorption of the analytes of interest within porous materials, specifically Zr-based MOFs. 30,46−48 Initial diffusion studies were performed on UiO-66 with a series of linear and aromatic hydrocarbons to validate the method. ...

Spectroscopic Measurement of Diffusion Kinetics through Subnanometer and Larger Al 2 O 3 Particles by a New Method: The Interaction of 2-Chloroethylethyl Sulfide with γ-Al 2 O 3
  • Citing Article
  • June 2006

The Journal of Physical Chemistry B

... As for the reason why Metal/Al 2 O 3 was selected as the co-milling regent of MCT of HCB, many previous studies demonstrated its effectiveness in the organic pollutants treatment from their excellent adsorption and chemical composition properties [48][49][50][51][52]. HCB was selected as the model pollutant due to its universality, typical symmetry and polysubstitution. ...

The Adsorption of Triethylenediamine on Al 2 O 3 -II: Hydrogen Bonding to Al−OH Groups
  • Citing Article
  • April 2005

The Journal of Physical Chemistry B

... Apart from above mentioned multifunctional materials, Al 2 O 3 , as a catalyst and/or catalyst support used in organic pollutants elimination has been endowed heightened interests owing to its large surface and pore volume (Li et al., 2010;Lu et al., 2017). In addition, among multiple kinds of Al 2 O 3 crystalline forms, g-Al 2 O 3 , attributed to its specific defective spinel structure, processes large amounts of surface-adsorbed oxygen species, Brønsted and Lewis acid sites (Kim et al., 2005;Liu et al., 2017c;Lu et al., 2017). Given that, Lu et al. (2017) successfully synthesized micro/nano-g-Al 2 O 3 rod-like fibers to perform the gaseous degradation of 1chloronaphthalene (CN-1), and the proposed mechanism is shown in Fig. S1. ...

Adsorption of Triethylenediamine on Al 2 O 3 -III: Bonding to Lewis Acid Al 3+ Sites
  • Citing Article
  • May 2005

The Journal of Physical Chemistry B

... For instance, Pt@CoO yolk@shell CNHSs were found to exhibit the typical catalytic activity of Pt for the hydrogenation of ethylene. Dedicated experiments revealed that, because of their small sizes, the molecular reactants and byproducts could approach the surface of the buried Pt core by permeating through the porous CoO shell [189,193]. Encouraged by the success of prototypical biological assays, in which FePt@CoS 2 and Co@Au yolk@shell CNHSs were proven to act as effective killers for cancer cells [165] and as carriers for gene delivery [187], respectively, FePt@Fe 3 O 4 yolk@shell CNHSs were assessed for their potential as MRI contrast agents and as anticancer drugs [188]. ...

IR Spectroscopic Observation of Molecular Transport through Pt@CoO Yolk−Shell Nanostructures
  • Citing Article
  • September 2007

Journal of the American Chemical Society