Chang-Mao Hung

Fe3O4 Magnetic Nanoparticles: Characterization and Performance Exemplified by the Degradation of Methylene Blue in the Presence of Persulfate

Abstract In this study, the oxidation of methylene blue (MB) over iron oxide magnetic nanoparticles (Fe3O4), which effectively activates persulfate anions (S2O82−) to form sulfate free radicals (SO4−•), was explored. In addition, the effect of the initial pH, sodium persulfate (Na2S2O8, PS) concentration, and Fe3O4 content on the decolorization of MB was investigated. The results revealed that the decolorization rate increased when the persulfate concentration increased from 0.03 to 0.12 g/L and the Fe3O4 content from 0.1 to 0.8 g/L. Therefore, the Fe3O4 nanoparticles enhanced the decolorization of MB. The catalyst was analyzed using cyclic voltammetry (CV), three-dimensional excitation-emission fluorescence matrix (EEFM) spectroscopy, and zeta potential measurements. The CV spectra indicated that a reversible redox reaction may explain the high catalytic activity of the catalyst. EEFM was used to evaluate the yield of a fresh Fe3O4 catalyst, and two peaks were observed at EX/EM wavelengths of 230/300 nm and 270/300 nm. Furthermore, the structure and surface morphology of the catalyst were characterized using X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM)-energy dispersive spectroscopy (EDS), respectively. The XRD result confirmed the existence of Fe3O4 in the catalyst. ESEM was used to determine the Fe3O4 particle size, indicating a high degree of nanoparticle dispersion.

Platinum particles supported on mesoporous carbons: fabrication and electrocatalytic performance in methanol-tolerant oxygen-reduction reactions

In this report, we describe the preparation and electrochemical characterization of a Pt electrocatalyst, which was synthesized from hexachloroplatinic acid, using the incipient wetness impregnation method. This carbon mesoporous materials (Pt-CMMs) electrocatalyst was used for catalyzing the oxidation of methanol and its oxygen-reduction reaction. The electrocatalytic oxidation of methanol was studied using linear-sweep voltammograms (LSV), polarization and chronoamperometric measurements. Phase characterizations and morphological analyses were performed using 3D excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption measurements, and X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM) techniques; the ESEM system was equipped with an energy-dispersive spectrometer (EDS). The oxidation capacity measured using a LSV might explain the high activity exhibited by the Pt-CMM electrocatalysts in methanol-tolerant oxygen reduction, and the results demonstrated that the potential and current density of the main reaction peak of the Pt-CMMs electrocatalyst changed during the reaction. Moreover, EEFM spectroscopy and XRD were determined to be appropriate and effective methods for characterizing Pt clusters that enhance their intrinsic emission from Pt-CMMs electrocatalysts in electrocatalytic-treatment systems. Furthermore, the ESEM-EDS results showed that fresh Pt nanoparticles were highly dispersed on CMMs and featured a 20 nm diameter and a narrow particle-size distribution.

Synthesis of magnetic biochar from bamboo biomass to activate persulfate for the removal of polycyclic aromatic hydrocarbons in marine sediments

This study developed a new and cost-effective method for the remediation of marine sediments contaminated with PAHs. Fe3O4 particles were synthesized as the active component, supported on bamboo biochar (BB) to form a composite catalyst (Fe3O4-BB). The effects of critical parameters, including the initial pH, sodium persulfate (PS) concentration, and dose of catalyst were investigated. The concentration of high-molecular-weight PAHs in sediments was much higher than that of low-molecular-weight PAHs; pyrene was an especially prominent marker of PAH contamination in sediments. Fe3O4-BB/PS exhibited a substantial improvement in PAH degradation efficiency (degradation rate: Fe3O4-BB/PS, 86%; PS, 14%) at a PS concentration of 1.7×10-5M, catalyst concentration of 3.33g/L, and pH of 3.0. The results of this study demonstrate that possible activation mechanisms include Fe2+-Fe3+ redox coupling and electron shuttling that mediates electron transfer of the BB oxygen functional groups, promoting the generation of SO4- in the Fe3O4-BB/PS system.

Removal of Polycyclic Aromatic Hydrocarbons from Sediments using Chemical Oxidation Processes

Abstract The presence of polycyclic aromatic hydrocarbons (PAHs) in sediments is a major concern of risks associated with the aquatic ecosystems through bioaccumulation in food chains. To minimize the ecological risks due to contaminated sediments, processes that can degrade the sorbed PAHs are urgently needed. The present study aims at assessing the treatment efficiency of several chemical oxidation processes using potassium permanganate (KMnO4), sodium persulfate (Na2S2O8), conventional Fenton, and modified Fenton. Efforts were focused on identifying the most effective liquid oxidant to obtain the maximum acceptable concentration for a total of 16 PAH compounds (1000 ng/g) and on assessing the optimal reactant doses. The concentration of PAHs in the untreated sediment was around 4226 ng/g (2-ring at 273 ng/g, 3-ring at 1285 ng/g, 4-ring at 1508 ng/g, 5-ring at 789 ng/g, and 6-ring at 369 ng/g) and 76% of degradation was required to meet the remediation goals. The removal efficiency was 5.3-72.8%, 10.7-39.1%, 0-30.9% and 31.5-68.3% by KMnO4, Na2S2O8, conventional Fenton and modified Fenton, respectively. Results demonstrated a medium reduction of a mixture of 16 PAHs in sediments; only in case of using KMnO4 that showed the highest removal efficiency (72.8%) using a considerably large amount of oxidizer. Modified Fenton showed remarkable improvement in removal efficiency compared with the conventional Fenton method. Sodium citrate resulted in the maximum contaminant removal through H2O2 activation at near neutral pH environment. Sodium pyrophosphate and sodium oxalate at higher dosages could cause negative effect on the removal efficiency. In general, the degradation of PAHs in slurry system was limited, which could be attributed to the availability and reactivity of PAHs and physical-chemical composition of the sediment.

Evaluating the leachable metals in Kaohsiung Harbor sediment using the toxicity characteristic leaching procedure (TCLP)

AbstractThe toxicity characteristic leaching procedure (TCLP) method was used to analyze the contaminants in the sediment materials of Kaohsiung Harbor as to evaluate the pollution potential associated with the Kaohsiung Harbor. A total of 80 sediment samples were collected at 20 locations and characterized for water content, organic matter (OM), total nitrogen (TN), total phosphorus (TP), and total grease (TG) as well as the leachable and total metals. The results indicated that the leachable metal concentrations were below the low detectable levels for mercury (Hg), lead (Pb), cadmium (Cd), chromium (Cr), and silver (Ag), between 0.005 and 0.281 mg/L, 0.07 and 24.0 mg/L, and 0.013 and 0.221 mg/L for Cu, Zn, and Ni, respectively. The leachable metal concentration at the river mouth vicinity was higher than that at other locations indicating that upstream industrial and domestic wastewater discharges were the main pollutant sources. Results of correlation studies revealed that the OM concentration in the ...

Material characterization and electrochemical performance of copper-based rare earth composite oxide electrodes for use in ammonia electrocatalytic oxidation

AbstractThe process of electrochemical oxidation (ECO) of ammonia (NH3) is becoming an increasingly important issue in environmental electrochemistry and has various prospective applications. A copper-based rare earth electrode material was synthesized by co-precipitation of a mixture that included copper, lanthanum, and cerium nitrate salts, and this material was applied in a typical electrocatalytic reaction, such as NH3-ECO, for fuel cell applications. In this study, the ability to oxidize ammonium for ECO while immersed in a 0.5 M H2SO4 solution was evaluated using a cyclic voltammetry (CV) technique. The changes in the properties of the electrocatalytic materials were analyzed using UV–vis absorption spectra, fluorescence spectroscopy (FS), and environmental scanning electron microscopy, revealing that the activity of the copper-based rare earth electrode materials utilized a high potential scan rate. The maximum current density was reached when the NH3-ECO voltage was −0.1 V. The reversible redox ab...

Magnetic Nanoparticles and Their Heterogeneous Persulfate Oxidation Organic Compound Applications

Nano–zero–valent iron (nZVI), Fe0, has been successfully used to transform and degrade contaminants in soils and water. Additionally, it has been used as a catalyst to heterogeneously activate persulfate (Na2S2O8, PS) for the treatment of various contaminants. The nZVI–PS oxidation system has received increasing attention because of its successful use in the treatment of sediments contaminated with recalcitrant organic compounds; treated sediments have improved considerably to meet remediation goals, such as the remediation goal for polycyclic aromatic hydrocarbons (PAHs). The presence of PAHs in sediments is a major concern because of the risks posed to aquatic ecosystems through bioaccumulation in food chains. To minimize ecological risks posed by contaminated sediments, it is imperative to develop processes that can degrade the sorbed PAHs. Efforts have been focused on identifying the most effective PS oxidant for obtaining the maximum acceptable PAH compound concentration. Moreover, the oxidation of PAHs in sediments by PS along with the simultaneous activation of the PS by nZVI, which is a source of catalytic ferrous iron, has been investigated. The determination and quantification of PAHs in sediment samples were performed using gas chromatography coupled to mass spectrometry (GC-MS). An adequate amount of PS must be present because it is the source of sulfate radicals, which are responsible for the degradation of PAHs. Results have indicated that the addition of a larger amount of nZVI to a PS-slurry system can enhance the PS oxidation process, suggesting that nZVI assists PS in the ex-situ treatment of PAH-contaminated sediments. Thus, nZVI-assisted PS is a promising choice for organic compound treatment for environmental remediation. This paper presents a study on magnetic nanoparticles and the heterogeneous PS oxidation of the nanoparticles and organic compounds (PAH-contaminated sediment), conducted in our laboratory.

Synthesis of Platinum Particles Supported on Microporous Carbons for an Electrocatalysis Study of Ammonia and Cytotoxicity

Abstract This study investigated the electrocatalytic oxidation (ECO) behavior of ammonia (NH3) over a Pt XC-72 electrocatalytic material immersed in a 0.5-M H2SO4 solution using a linear sweep voltaimnogram (LSV) technique. The Pt/XC-72 electrode was synthesized by impregnating XC-72 microporous carbon black with H2PtCl6 to improve its capability for the ECO of NH3. The experimental data indicate that a high ECO activity was achieved during the catalytic oxidation over the Pt XC-72 electrocatalytic material when using a high potential sweep rate; the maximum current density achieved for the NH3 oxidation was 0.3 mA at a voltage of 0.5 V. This LSV oxidation ability may explain the significant activity of the catalyst in an acidic environment. The catalyst structure was characterized by polarization curves. UV-Vis spectroscopy, excitation-emission fluorescent matrix (EEFM) spectroscopy and environmental scanning electron microscopy (ESEM). EEFM was applied to evaluate the fresh catalyst yields for the fluorescence plots generated at 250 nm and 270 nm. The ESEM images of the catalyst show Pt nanoparticles with uniformly dispersed on the XC-72 carbon black surface with size ranging from 10 to 30 nm account for the higher electrocatalytic performances. In addition, the Pt/XC-72 composite- induced cytotoxicity in the MRC-5 human lung cell line was tested, and the percentage cell survival was determined by 3-(4,5-diniethylthiazol-2-yl)-5-(3-carboxyniethoxyphenyl)-2-(4-sulfophenyl)-2H-tetra-zohuni (MTS) analysis in vitro. No apparent cytotoxicity was observed when the human lung cells were exposed to the Pt/XC- 72 composite.

Catalytic Performance and Characterization of Copper-based Rare Earth Composite Materials for Selective Catalytic Oxidation Reaction with Simulated Synthetic Ammonia Stream

Abstract Renewable energy and fuels typically contain nitrogen compounds, which convert to ammonia (NH3) during gasification. Hence, copper-based rare earth composite metal materials were tested for their activity in the selective catalytic oxidation (SCO) of NH3 with O2 in simulated biomass gasification stream. This study addresses the oxidation behavior of NH3 at temperatures between 423 and 723 K by SCO over a Cu-La-Ce composite catalyst that was prepared by coprecipitating copper nitrate, lanthanum nitrate and cerium nitrate at a molar ratio of 6:2:2 and a calcination temperature of 773 K. The catalysts were characterized using cyclic voltammetry (CV), UV-Vis absorption spectra, dynamic light-scattering (DLS), zeta potential, excitationemission fluorescent matrix (EEFM) spectroscopy, X-ray powder diffraction (XRD) and environmental scanning electron microscopy with an energy dispersive X-ray spectrometer (ESEM-EDX). In this report, approximately 98% of the NH3 was decreased by catalytic oxidation over the Cu-La-Ce composite catalyst. The synergetic interaction between the three metal components played an important role in the elevated activity of the NH3 catalytic oxidation. In addition, N2 was the primary product of this NH3-SCO process. The CV reversible redox ability may explain the significant activity of the catalysts. The UV-Vis absorption spectra observations indicate that the Cu2+-O2- species with a peak absorbance value at 230 nm accounted for the higher catalytic performance. The X-ray powder diffraction approach confirmed that copper (II), lanthanum (III) and cerium (IV) oxide active sites were formed on the Cu-La-Ce composite catalyst.