Hye-Jin Hong

Degradation of trichloroethylene (TCE) by nanoscale zero-valent iron (nZVI) immobilized in alginate bead.

Nowadays, many researchers have studied the environmental application of the nanoscale zero-valent iron (nZVI) and several field applications for the groundwater remediation have been reported. Still, there are many concerns on the fate and transport of the nZVI and the corresponding risks. To avoid such concerns, it was investigated to immobilize nZVI in a support and then it was applied to degrade trichloroethylene (TCE). The nZVI and palladium-doped nZVI (Fe(0)- and Fe/Pd-alginate) were immobilized in the alginate bead where ferric and barium ions are used as the cross-linking cations of the bead. According to TEM (transmission electron microscopy), the size of the immobilized ZVI was as small as a few nanometers. From the surface analysis of the Fe/Pd-alginate, it is found that the immobilized nZVI has the core-shell structure. The core is composed of single crystal Fe(0), while most of irons on the surface are oxidized to Fe(3+). When 50 g/L of Fe/Pd-alginate (3.7 g Fe/L) was introduced to the aqueous solution, >99.8% of TCE was removed and the release of metal from the support was <3% of the loaded iron. The removal of TCE by Fe/Pd-alginate followed pseudo-first-order kinetics. The observed pseudo-first-order reaction constant (k(obs)) of Fe/Pd-alginate was 6.11 h(-1) and the mass normalized rate constant (k(m)) was 1.6 L h(-1) g(-1). The k(m) is the same order of magnitude with that of iron nanoparticles. In conclusion, it is considered that Fe/Pd-alginate can be used efficiently in the treatment of chlorinated solvent.

Preparation and Evaluation of Fe-Al Binary Oxide for Arsenic Removal: Comparative Study with Single Metal Oxides

In this study, Fe-Al binary oxide was synthesized and evaluated for arsenic removal. Due to its large surface area, Fe-Al mixed oxide shows four times higher As(V) and As(III) adsorption capacity than conventional iron oxide. For a comparative study, single metal oxides such as iron oxide and aluminum oxide are also synthesized. The physical and chemical characteristics of the prepared adsorbents are analyzed by SEM, XRD, and BET analyzer. Through the adsorption isotherm and pH effect experiments, it is discovered that Fe-Al binary oxide shows excellent arsenic adsorption capacity compared with single metal oxides.

Biosorption of chromium (Cr(III)/Cr(VI)) on the residual microalga Nannochloris oculata after lipid extraction for biodiesel production.

In order to increase the economic feasibility of biodiesel production from microalgae, the residual biomass after biodiesel production can be utilized as biosorbent for heavy metal removal. In this study, biosorption of chromium by residual Nannochloris oculata after lipid extraction was investigated. Increased surface area of N. oculata was observed after lipid extraction. Cr(III) removal increased as the pH increased from 2 to 6, while Cr(VI) removal was highest at pH 2 and it decreased with the increase in pH. Cr(VI) was reduced to Cr(III) in the presence of biomass under acidic conditions; X-ray photoelectron spectroscopy revealed that the converted Cr(III) was bound to the biomass. Chromium removal was significantly enhanced at high chromium concentrations, which indicates that surface reactions may occur at high chromium/biomass ratios. FTIR study indicated that phosphate and carboxyl functional groups of the biomass were mainly responsible for chromium binding.

Removal of anionic contaminants by surfactant modified powdered activated carbon (SM-PAC) combined with ultrafiltration

A variety of inorganic contaminants may form toxic oxyanions in aqueous systems which pose significant hazard to human health and the ecosystem. In order to remove the oxyanions from aqueous stream effectively, surfactant-modified powdered activated carbon (SM-PAC) combined with ultrafiltration (UF) was proposed in this study. As the cationic surfactant, cetylpyridinium chloride (CPC), adsorbs on the surface of PAC, the zeta potential of PAC increases to +40 mV. Oxyanions such as chromate, ferricyanide and arsenate bind on SM-PAC by electrostatic interaction, then the contaminants bound with SM-PAC can be separated by UF membrane. 0.3 mM of chromate and ferricyanide are removed completely with 4.0 g/L of SM-PAC. In case of arsenate, the removal efficiency was lower than chromate and ferricyanide. It is considered that the competition occurs among anionic pollutants on the limited binding sites of SM-PAC and lower valence of arsenate results in the lower removal efficiency. High permeate flux is maintained during filtration. The spent SM-PAC was regenerated by the concentrated Cl(-) solutions. NaCl solution whose molar Cl(-) concentration is 1.4 times higher than the contaminants bound on SM-PAC was optimal for the regeneration. Regenerated SM-PAC exhibited similar adsorption capacity to fresh SM-PAC. SM-PAC combined with UF can effectively remove anionic contaminants. Moreover, the simple and efficient regeneration process is proposed.

Arsenic Removal Behavior by Fe-Al Binary Oxide: Thermodynamic and Kinetic Study

In this study, thermodynamic and kinetic behaviors of As(V) and As(III) adsorption on Fe-Al binary oxide were investigated. Adsorptions of both As(V) and As(III) on Fe-Al binary oxide were exothermic reactions (ΔH0 < 0) and occurred spontaneously (ΔG0 < 0). Because of strong electrostatic interaction between the As(V) anion and the positive Fe-Al binary oxide, As(V) was adsorbed rapidly and the adsorption rate was controlled by chemical adsorption. On the other hand, As(III) exists in a nonionic form, because of which it was not adsorbed through strong attractive forces. Therefore, the adsorption rate of As(III) was controlled by a combination of diffusion processes and chemical sorption.

Kinetic study for phenol degradation by ZVI-assisted Fenton reaction and related iron corrosion investigated by X-ray absorption spectroscopy.

In this study, we investigated phenol degradation via zero-valent iron (ZVI)-assisted Fenton reaction through kinetic and spectroscopic analysis. In batch experiments, 100 mg/L of phenol was completely degraded, and 75% of TOC was removed within 3 min under an optimal hydrogen peroxide (H2O2) concentration (50 mM) via the Fenton reaction. In the absence of H2O2, oxygen (O2) was dissolved into the solution and produced H2O2, which resulted in phenol degradation. However, phenol removal efficiency was not very high compared to external H2O2 input. The Fenton reaction rapidly occurred at the surface of ZVI, and then phenol mobility from the solution to the ZVI surface was the rate determining step of the whole reaction. The pseudo-second order adsorption kinetic model well describes phenol removal, and its rate increased according to the H2O2 concentration. X-ray absorption spectroscopic analysis revealed that iron oxide (Fe-O bonding) was formed on ZVI with [H2O2] > 50 mM. A high concentration of H2O2 led to rapid degradation of phenol and caused corrosion on the ZVI surface, indicating that Fe(2+) ions were rapidly oxidized to Fe(3+) ions due to the Fenton reaction and that Fe(3+) was precipitated as iron oxide on the ZVI surface. However, ZVI did not show corroded characteristics in the absence of H2O2 due to the insufficient ZVI-assisted Fenton reaction and oxidation of Fe(2+) to Fe(3+).

Removal of Bromate (BrO− 3) from Water using Cationic Surfactant-Modified Powdered Activated Carbon (SM-PAC)

Bromate ( ) is the harmful element that could be produced from disinfection of drinking water. In this study, surfactant-modified powdered activated carbon(SM-PAC) was synthesized and used for the removal of bromate ( ) from water. Three cationic surfactants, cetylpyridinium chloride (CPC), hexadecyltrimethyl-ammonium chloride (CTAC), and hexadecyltrimethyl-ammonium bromide (CTAB) were used for modification. The effect of operation parameters, pH, and contact time were obtained. Moreover, adsorption mechanisms on SM-PACs were discussed. Compared with untreated activated carbon, CTAC modified SM-PAC exhibited 3 times higher adsorption capacity. These results indicated that SM-PAC removed effectively and rapidly from water without producing harmful byproducts.

Preparation of Low-Cost Adsorbents from Paper Industry Wastes and their Pb(II) Removal Behavior in Water

In this study, we prepare low-cost adsorbents from paper industry waste (newspaper (NP) and white paper (WP) waste) through a simple drying process and used them for Pb(II) removal. Characteristics, maximum Pb(II) removal capacities of prepared adsorbents, and Pb(II) removal mechanisms are investigated. The maximum amounts of adsorbed Pb(II) on NP and WP derived from the Langmuir isotherm are 42.4 and 18.5 mg·g−1, respectively. This value is similar or more effective than commercial and other low-cost Pb(II) sorbents. It indicates that low-cost adsorbents prepared from paper industry waste have high potential as inexpensive and effective heavy metal adsorbents.

Carboxymethlyated cellulose nanofibrils(CMCNFs) embedded in polyurethane foam as a modular adsorbent of heavy metal ions

Polyurethane (PU) foam was utilized as an efficient and durable template to immobilize surface-functionalized nanocellulose, carboxymethylated cellulose nanofibrils (CMCNFs), to address some of the challenges for the application of nanocellulose to industrial water purification, such as its agglomeration, difficulties in separation from effluent, and regeneration. The composite foams exhibited well dispersed CMCNFs in PU matrices with open pore structure; the hydrogen bonds result in the enhancement of mechanical strength, which is another requirement of ideal adsorbents for wastewater treatment. The composite foams show high adsorption capacity and the potential for recyclability. The combination of optimal surface modification of nanocellulose with isolation and immobilization in durable PU foam achieved an efficient and cost-competitive bio-sorbent for heavy metal ions.

Removal of Anionic and Cationic Dyes from Water by Fe-Al Binary Oxide

Al was incorporated in iron oxide to enhance dye removal capacity (Fe-Al binary oxide). Oxides with different Fe:Al ratios (10:0, 9:1, 7:3, 5:5, 3:7, 1:9, and 0:10) were synthesized and applied for removal of organic dyes. Increase of incorporated Al expanded effective surface area that could contact with dye. The highest dye removal efficiency was achieved by 5:5 and 3:7 Fe:Al ratio. The effects of operation parameters such as solution pH, initial dye, and H2O2 concentration on removal of Acid blue 25 were investigated. Fe-Al binary oxide could be repeatedly used for dye removal without the regeneration process.