• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.339-339
• /
• 2010

The metallic nanoparticles (Pt, Au, Ag. Cu, etc.) supported on ceria-titania mixed oxide exhibit a high catalytic activity for the water gas shift reaction ($H_2O\;+\;CO\;{\leftrightarrow}\;H_2\;+\;CO_2$) and the CO oxidation ($O_2\;+\;2CO\;{\leftrightarrow}\;2CO_2$). It has been speculated that the high catalytic activity is related to the easy exchange of the oxidation states of ceria ($Ce^{3+}$ and $Ce^{4+}$) on titania, but very little is known about the ceria titanium interaction, the growth mode of metal on ceria titania complex, and the reaction mechanism. In this work, the growth of $CeO_x$ and Au/$CeO_x$ on rutile $TiO_2$(110) have been investigated by Scanning Tunneling Microscopy (STM), Photoelectron Spectroscopy (PES), and DFT calculation. In the $CeO_x/TiO_2$(110) systems, the titania substrate imposes on the ceria nanoparticles non-typical coordination modes, favoring a $Ce^{3+}$ oxidation state and enhancing their chemical activity. The deposition of metal on a $CeO_x/TiO_2$(110) substrate generates much smaller nanoparticles with an extremely high activity. We proposed a mechanism that there is a strong coupling of the chemical properties of the admetal and the mixed-metal oxide: The adsorption and dissociation of water probably take place on the oxide, CO adsorbs on the admetal nanoparticles, and all subsequent reaction steps occur at the oxide-admetal interface.

• Applied Biological Chemistry
• /
• v.41 no.1
• /
• pp.89-94
• /
• 1998

Various Mn-oxides can oxidize Cr(III) to Cr(VI). Behaviors of chromium species in the oxidation system, especially on the oxide surface, are expected to control the reaction. During Cr(III) oxidation by birnessite and pyrolusite, Cr species in the reaction system were determined to elucidate their effects on the oxidation. Capacities of Cr oxidation of the two Mn-oxides were quite different. Solution pH and initial Cr(III) concentration also had significant effects on the Cr(III) oxidation by Mn-oxides. Chromium oxidation by pyrolusite was less than 5% of the oxidation by birnessite. The high crystallinity of pyrolusite could be one of the reasons and the difficulty of Cr (III) diffusion to the positive pyrolusite surface and Cr(VI) and Cr(III) adsorption seems to be other controlling factors. At pH 3, adsorption or precipitation of Cr species on the surface of birnessite were not found. Small amount of Cr(VI) adsorption was found on the surface of pyrolusite, but arty Cr precipitation on the oxide surface was not found. Therefore Cr(III) oxidation at pH 3 seems to be controlled mainly by the characteristics of Mn-oxides. Chromiun oxidation by Mn-oxides is thermodynamically more favorable at higher solution pH. However as solution pH increased Cr oxidation by birnessite was significantly inhibited. For Cr oxidation by pyrolusite, as pH increased the oxidation increased, but as Cr(III) addition increased the reaction was inhibited. Under these conditions some unidentified fraction of Cr species was found and this fraction is considered to be Cr(III) precipitation an the oxide surface. Chromium(III) precipitation on the oxide surface seems to play an important role in limiting Cr(III) oxidation by armoring the reaction surface on Mn-oxides as well as lowering Cr(III) concentration available for the oxidation reaction.

• Applied Chemistry for Engineering
• /
• v.7 no.6
• /
• pp.1192-1203
• /
• 1996

$Al_2O_3-TiO_2$ composite oxide adsorbents which could be applied in high-temperature water were prepared by hydrolysis of aluminum and titanium alkoxide. The prepared adsorbents were calcined at $600{\sim}1400^{\circ}C$ and in order to investigate the various properties - the transition of crystals, thermal properties, and specific surface area, X-ray diffractometry, thermal analysis, FT-IR, SEM and BET method were employed. And the $Co^{2+}$ adsorption characteristics of these adsorbents in high-temperature water were investigated by batch adsorption experiment in a stirred autoclave. Since the adsorption of $Co^{2+}$ on the $Al_2O_3-TiO_2$ adsorbents was irreversible endothermic in the temperature range of $150{\sim}250^{\circ}C$, the standard enthalpy changes of 26, 43, and 80 mol% of $TiO_2$ on $Al_2O_3$ were in the range of $16.5{\sim}26.0kJ{\cdot}mol^{-1}$. The adsorbent of 26 mol% of $TiO_2$ on $Al_2O_3$ which was calcined at $600^{\circ}C$ for 2 hours showed the adsorption amount of $0.1674meq{\cdot}g^{-1}$ in the high temperature water at $250^{\circ}C$.

• Environmental Engineering Research
• /
• v.14 no.1
• /
• pp.41-47
• /
• 2009

Column experiments were performed in this study to investigate humic acid adhesion to iron oxide-coated sand (ICS) under different experimental conditions including influent humic acid concentration, flow rate, solution pH, and ionic strength/composition. Breakthrough curves of humic acid were obtained by monitoring effluents, and then column capacity for humic acid adsorption ($C_cap$), total adsorption percent (R), and mass of humic acid adsorbed per unit mass of filter media ($q_a$) were quantified from these curves. Results showed that humic acid adhesion was about seven times higher in ICS than in quartz sand at given experimental conditions. This indicates that humic acid removal can be enhanced through the surface charge modification of quartz sand with iron oxide coating. The adhesion of humic acid in ICS was influenced by influent humic acid concentration. $C_cap$ and $q_a$ increased while R decreased with increasing influent humic acid concentration in ICS column. However, the influence of flow rate was not eminent in our experimental conditions. The humic acid adhesion was enhanced with increasing salt concentration of solution. $C_cap$, $q_a$ and R increased in ICS column with increasing salt concentration. On the adhesion of humic acid, the impact of CaCl2 was greater than that of NaCl. Also, the humic acid adhesion to ICS decreased with increasing solution pH. $C_cap$, $q_a$ and R decreased with increasing solution pH. This study demonstrates that humic acid concentration, salt concentration/composition, and solution pH should be controlled carefully in order to improve the ICS column performance for humic acid removal from water.

• Korean Journal of Materials Research
• /
• v.30 no.5
• /
• pp.267-271
• /
• 2020

Cerium oxide (ceria, CeO₂) is one of the most wide-spread oxide supporting materials for the precious metal nanoparticle class of heterogeneous catalysts. Because ceria can store and release oxygen ions, it is an essential catalytic component for various oxidation reactions such as CO oxidation (2CO + O₂ 2CO₂). Moreover, reduced ceria is known to be reactive for water activation, which is a critical step for activation of water-gas shift reaction (CO + H₂O → H₂ + CO₂). Here, we apply van der Waals-corrected density functional theory (DFT) calculations combined with U correction to study the mechanism of water chemisorption on CeO₂(111) surfaces. A stoichiometric CeO₂(111) and a defected CeO₂(111) surface showed different water adsorption chemistry, suggesting that defected CeO₂ surfaces with oxygen vacancies are responsible for water binding and activation. An appropriate level of water-ceria chemisorption energy is deduced by vdW-corrected non-local correlation coupled with the optB86b exchange functional, whereas the conventional PBE functional describes weaker water-ceria interactions, which are insufficient to stabilize (chemisorb) water on the ceria surfaces.

• Nuclear Engineering and Technology
• /
• v.50 no.3
• /
• pp.416-424
• /
• 2018

Microstructure of oxide formed on Zr-Nb-Sn tube sample was intensively examined by scanning transmission electron microscopy after exposure to simulated primary water chemistry conditions of various concentrations of Zn (0 or 30 ppb) and dissolved hydrogen ($H_2$) (30 or 50 cc/kg) for various durations without applying desirable heat flux. Microstructural analysis indicated that there was no noticeable change in the microstructure of the oxide corresponding to water chemistry changes within the test duration of 100 days (pretransition stage) and no significant difference in the overall thickness of the oxide layer. Equiaxed grains with nano-size pores along the grain boundaries and microcracks were dominant near the water/oxide interface, regardless of water chemistry conditions. As the metal/oxide interface was approached, the number of pores tended to decrease. However, there was no significant effect of $H_2$ concentration between 30 cc/kg and 50 cc/kg on the corrosion of the oxide after free immersion in water at $360^{\circ}C$. The adsorption of Zn on the cladding surface was observed by X-ray photoelectron spectroscopy and detected as ZnO on the outer oxide surface. From the perspective of $OH^-$ ion diffusion and porosity formation, the absence of noticeable effects was discussed further.

• Carbon letters
• /
• v.24
• /
• pp.82-89
• /
• 2017

In this study, composite PAN-based ACNFs embedded with MgO and $MnO_2$ were prepared by the electrospinning method. The resultant pristine ACNFs, ACNF/MgO and $ACNF/MnO_2$ were characterized in terms of their morphological changes, SSA, crystallinity and functional group with FESEM-EDX, the BET method, XRD and FTIR analysis, respectively. Results from this study showed that the SSA of the ACNF/MgO composite ($1893m^2g^{-1}$) is significantly higher than that of the pristine ACNFs and $ACNF/MnO_2$ which is 478 and $430m^2g^{-1}$, respectively. FTIR analysis showed peaks of 476 and $547cm^{-1}$, indicating the presence of MgO and $MnO_2$, respectively. The FESEM micrographs analysis showed a smooth but coarser structure in all the ACNFs. Meanwhile, the ACNF/MgO has the smallest fiber diameter ($314.38{\pm}62.42nm$) compared to other ACNFs. The presence of MgO and $MnO_2$ inside the ACNFs was also confirmed with EDX analysis as well as XRD. The adsorption capacities of each ACNF toward $CH_4$ were tested with the volumetric adsorption method in which the ACNF/MgO exhibited the highest $CH_4$ adsorption up to $2.39mmol\;g^{-1}$. Meanwhile, all the ACNF samples followed the pseudo-second order kinetic model with a $R^2$ up to 0.9996.

• Journal of Korean Society on Water Environment
• /
• v.22 no.6
• /
• pp.991-995
• /
• 2006

The layered double hydroxide with the insertion of chloride ions (LDH-Cl), which was synthesized by the co-precipitation method, was applied to investigate the fundamental aspects of the absorptive agent for phosphate removal from wastewater. The adsorption capacity was best described by the Langmuir-FreundIich isotherm, and the estimated isotherm parameters indicate that the LDH-CI capacity for the phosphate removal is much higher than that observed using a natural adsorbent material such iron oxide tailing. The kinetic experiment also showed that the LDH-Cl adsorption reaction rapidly at the adsorptive rate of 0.55 mg-P/g-LDH/min, implying that this adsorbent can be of use in the full-scale applications. The pH had a minimal effect on the LDH adsorption capacity in the range of 5 to 11, although the capacity dropped at the low pHs because of the change in LDH surface properties. Furthermore, other anions such as $Cl^-$ and $NO_3{^-}$ commonly found in the wastewater streams insignificantly affected the phosphate removal efficiencies, while $HCO_3{^-}$ ions had a negative effect on the LDH adsorption capacity due to its high selectivity. The phosphate removal experiment using the actual secondary effluent from a wastewater treatment plant showed the similar decrease in adsorption capacity, indicating that the bicarbonate ions in the wastewater were competing with phosphate for the adsorptive site in the surface of the LDH-Cl. Overall, the synthetic adsorbent material, LDH-Cl, can be a feasible alternative over other conventional chemical agents, since the LDH-Cl exhibits the high phosphate removal capacity with the low sensitivity to other environmental conditions.

• Applied Chemistry for Engineering
• /
• v.33 no.6
• /
• pp.630-635
• /
• 2022

Copper(II) oxide (CuO), electroless plated on a nitrogen-containing carbon sponge prepared by a melamine sponge thermal treatment, was developed as a nitric oxide (NO) gas sensor that operates without a wafer. The CuO content on the surface of the carbon sponge increased as the plating time increased, but the content of nitrogen known to induce NO gas adsorption decreased. The untreated carbon sponge showed a maximum resistance change (5.0%) at 18 min. On the other hand, the CuO plated sample (CuO30s-CS) showed a maximum resistance change of 18.3% in 8 min. It is considered that the improvement of the NO gas sensing capability was caused by the increase in hole carriers of the carbon sponge and improved movement of electrons due to CuO. However, the NO gas detection resistance of the CuO electroless plated carbon sponge for 60 s decreased to 1.9%. It is considered that the surface of the carbon sponge was completely plated with CuO, resulting in a decrease in the NO gas adsorption capacity and resistance change. Thus, CuO-plated carbon sponge can be used as an effective NO gas sensor because it has fast and excellent resistance change properties, but CuO should not be completely plated on the surface of the carbon sponge.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.1B
• /
• pp.149-152
• /
• 2008

The reaction between iron oxide and ferrous iron is known to be the adsorption of ferrous iron onto the oxide surfaces that produces Fe(II)-Fe(III) (hydr)oxides and ferrous oxide oxidized to ferric ion which is the reducing agent of the target compounds. In our investigations on DS/S using ferrous modified steel slag, the results did not follow the trends. FeO and Fe(II), the major component of steel slag, were used to investigate the degradation of TCE. Degradation did not take place for the first and suddenly degraded after awhile. Degradation of TCE in this system was unexpected because Fe(II)-Fe(III) (hydr)oxides could not be produced in absence of ferric oxide. In this study, the characteristics of FeO/Fe(II) system as a reducing agent were observed through the degradation of TCE, measuring byproducts of TCE and the concentration of Fe(II) and Fe(III). Adsorption of ferrous ion on FeO was observed and the generation of byproducts of TCE showed the degradation of TCE by reduction in the system is obvious. However it did not correspond with the typical reducing mechanisms. Future research on this system needs to be continued to find out whether new species are generated or any unknown mineral oxides are produced in the system that acted in the degradation of TCE.