Younghun Kim

Kinetics of removal of chromium from water and electronic process wastewater by ion exchange resins: 1200H, 1500H and IRN97H

The removal of chromium from aqueous solution by an ion exchange resin is described. Ion exchange resins 1200H, 1500H and IRN97H show a remarkable increase in sorption capacity for chromium, compared to other adsorbents. The adsorption process, which is pH dependent show maximum removal of chromium in the pH range 2-6 for an initial chromium concentration of 10mg/l. The metal ion adsorption obeyed linear, Langmuir and Freundlich isotherms. The adsorption of chromium on these cation exchange resins follows first-order reversible kinetics and pseudo-first-order kinetics. The intraparticle diffusion of chromium on ion exchange resins represents the rate-limiting step. The uptake of chromium by the ion exchange resins was reversible and thus have good potential for the removal/recovery of chromium from aqueous solutions. We conclude that such ion exchange resins can be used for the efficient removal of chromium from water and wastewater.

Synthesis of functionalized porous silicas via templating method as heavy metal ion adsorbents: the introduction of surface hydrophilicity onto the surface of adsorbents

Bi-functional porous silicas, functionalized via the introduction of chelating ligands (mercaptopropyl and aminopropyl groups), were synthesized for use in the removal of heavy metal ions from aqueous solutions. Dodecylamine was used as a template, and tetraethoxysilane (TEOS) as a silica precursor. Adsorbents were synthesized via a co-condensation process using the sequential or simultaneous addition of TEOS and high concentrations of the organosilanes (3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane). The sequential addition of TEOS and organosilanes resulted in well-ordered porous silicates. The effect of the presence of functional groups on the properties of adsorbents was also examined. The results show that amino ligands increased the surface hydrophilicity of the adsorbents. In addition, the adsorbents had high loading capacities and selectivity for mercury ions in aqueous solutions.

Batch adsorptive removal of copper ions in aqueous solutions by ion exchange resins: 1200H and IRN97H

The removal of copper from aqueous solution by ion exchange resins, such as 1200H and IRN97H, is described. Effect of initial metal ion concentration, agitation time and pH on adsorption capacities of ion exchange resins was investigated in a batch mode. The adsorption process, which is pH dependent, shows maximum removal of copper in the pH range 2–7 for an initial copper concentration of 10 mg/L. The experimental data have been analyzed by using the Freundlich, Langmuir, Redlich-Peterson, Temkin and Dubinin-Radushkevich isotherm models. The batch sorption kinetics have been tested for a first-order, pseudo-first order and pseudo-second order kinetic reaction models. The rate constants of adsorption for all these kinetic models have been calculated. Results showed that the intraparticle diffusion and initial sorption into resins of Cu(II) in the ion exchange resins was the main rate limiting step. The uptake of copper by the ion exchange resins was reversible and thus has good potential for the removal/recovery of copper from aqueous solutions. We conclude that such ion exchange resins can be used for the efficient removal of copper from water and wastewater.

Preparation of Mesoporous Catalyst Supported on Silica with Finely Dispersed Ni Particles

A novel nickel catalyst supported on SBA-15 type mesoporous silica was synthesized by the grafting of N-(trimethoxysilylpropyl)ethylene diamine triacetic acid salt (EDTA) onto the surface of SBA-15 and followed by adsorption of nickel ions and calcinations (Ni-E-SBA). The catalysts prepared were characterized using XRD, TEM, TED, SAXS and N2 adsorption/desorption measurements. While nickel particles loaded on catalysts prepared by the wet impregnation method were found to be aggregated on the outer wall of the supports, nickel particles were finely dispersed on the surface of the mesopores in the Ni-E-SBA catalyst. The catalytic performances of the prepared catalysts were evaluated using the hydrodechlorination (HDC) of 1,1,2-trichloroethane (TCEa) as a model reaction. Results showed that the Ni-E-SBA catalyst had the highest activities of the catalysts examined under the given conditions.

Colorimetric detection of Co2+ ion using silver nanoparticles with spherical, plate, and rod shapes.

A highly sensitive colorimetric sensing platform for the selective trace analysis for Co(2+) ions is reported, based on glutathione (GSH)-modified silver nanoparticles (AgNP). The shape of metallic nanoparticles used in colorimetric detection, using the unique optical properties of plasmonic nanoparticles, is almost spherical. Therefore, in this work we attempted to investigate the selective detection of heavy metal ion (Co(2+)), with the shape of AgNPs (nanosphere, nanoplate, and nanorod). GSH-AgNP with spherical shape shows a high sensitivity for all of the metal ions (Ni(2+), Co(2+), Cd(2+), Pb(2+), and As(3+)) but poor selective recognition for target metal ions. Whereas, AgNPs solution containing rod-type GSH-AgNP has a special response to Co(2+), and its selective detection might be based on the cooperative effect of CTAB and GSH. Therefore, Co(2+) ion could be selectively recognized using rod-type GSH-AgNPs.

Synthesis and characterization of mesoporous alumina as a catalyst support for hydrodechlorination of 1,2-dichloropropane: Effect of catalyst preparation method

A mesoporous alumina was synthesized by a posthydrolysis method. The prepared mesoporous alumina was found to have randomly ordered pores, and retained relatively high surface area with narrow pore size distribution centered at ca. 4 nm. Nickel precursors were then supported on the mesoporous alumina by an impregnation (Ni-IMP) and vapor deposition (Ni-VD) method. Several characterizations were carried out in order to investigate physical and chemical properties of mesoporous alumina and supported Ni catalysts. TPR, XPS, and UV-DRS measurements revealed that the Ni-IMP catalyst retained much more amounts of surface nickel aluminate-like species than the Ni-VD sample. TPD experiments also showed that nickel aluminate species affected the adsorption amounts of reactant (1,2-dichloropropane). In the hydrodechlorination of 1,2-dichloropropane (DCPA), DCPA conversion over the Ni-VD catalyst was about two times higher than that over the Ni-IMP catalyst at 300 °C. It is probably due to the fact that the Ni-VD catalyst, which had low contents of nickel aluminate species compared to the Ni-IMP catalyst, exhibited higher degree of reduction than the Ni-IMP catalyst at pretreatment conditions. The difference in DCPA conversion between two catalysts was closely related to the degree of reduction of nickel species and the amounts of adsorption of DCPA onto the catalyst as well.

Preparation of Functionalized Mesostructured Silica Containing Magnetite (MSM) for the Removal of Copper Ions in Aqueous Solutions and Its Magnetic Separation

The removal of copper ions from an aqueous solution by both adsorption onto mesostructured silica containing magnetite (MSM) and magnetic separation were investigated. Magnetite (core) was used as a magnetic carrier material for magnetic separation, while amine-functionalized mesostructured silica (shell) was used as a heavy metal ion adsorbent. The pore properties, magnetic properties, and phase of the prepared materials were measured by a N2 sorptometer, a vibration sample magnetometer, and powder x-ray diffraction (XRD), respectively. After silica coating, the magnetite-core of the MSMs maintained their magnetic properties. The prepared adsorbent had a large loading capacity for Cu ions; up to 0.5 mmol of Cu per g of adsorbent. The recovery process of the metal ion loaded adsorbents by an electromagnetic force was very rapid and effective.

Rapid, reversible preparation of size-controllable silver nanoplates by chemical redox.

Citrate-stabilized silver nanoplates (AgNPs) were prepared using a seed-mediated growth method. The AgNP shape and size were controlled using potassium permanganate (KMnO(4)) as an oxidant and ascorbic acid (AA) as a reductant. Using KMnO(4), 42 nm nanoplates were changed to 22.9 nm nanodisks because of the release of silver ions. Using AA, the oxidized AgNPs were resynthesized to their initial plate form. These results are similar to those obtained using photoinduced shape control of silver nanoparticles; however, the chemical oxidation/reduction method can control the shape of AgNPs, both quantitatively and reversibly. In addition, because of redox-related visible spectral changes, solution color varies with AgNPs size. That feature may be useful in various applications.

A novel method for synthesis of a Ni/Al2o3 catalyst with a mesoporous structure using stearic acid salts

Nickel stearate was used as a chemical template and metal source for the easy-and-fast preparation of Ni/Al2O3 catalyst with a mesoporous structure. Ni-Nx and Ni-Hx were prepared using an NH4OH-treated precipitate and a HCl-treated solution as the chemical template, respectively, and these materials show only the effect of the chemical template, a regular pore size distribution. Ni-Nx with both a developed framework and textural porosity show a larger surface area and pore volume but a less irregular pore structure than Ni-Hx which shows a well-developed framework porosity. The 27Al NMR MAS analysis showed that nickel oxide supported on active alumina allows Ni2+ ions to diffuse into the surface lattice vacancies of the alumina spinel structure. Such a migration of metal ions may be limited to the first few layers of the supports, but leads to the production of hard-to-reduce metal oxide (i.e. a high metal-to-support interaction). Ni-Nx was also found to have a more dispersed nickel particle configuration than Ni-Hx after reduction.

Effect of Framework and Textural Porosities of Functionalized Mesoporous Silica on Metal Ion Adsorption Capacities

Abstract The effects of the framework and/or textural porosities and functional group densities of the functionalized HMS on the metal adsorption capacities were examined. Mercapto concentration was weakly correlated with pore size and the surface area of the supports, but was strongly dependent on the framework pore volume. In case of adsorbents with a well‐developed framework porosity, the uptake of mercury ions increased with an increase in mercapto concentration, while adsorbents with a well‐developed textural porosity show a slight increase with mercapto concentration. The characteristics of lead ions showed a similar absorption trend to that of mercury ions. The results showed that the amounts of metal ion uptake of SBA having long range 2‐D pore channels were less than those of HMS having short range interconnected 3‐D pore channels.