Kwang-Sun Ryu

Reductive removal of 2,4-dinitrotoluene and 2,4-dichlorophenol with zero-valent iron-included biochar

In order to remediate organic contaminants in natural waters and soils, a novel zero-valent iron [Fe(0)]-included biochar was synthesized via slow pyrolysis. 2,4-Dinitrotoluene (DNT) and 2,4-dichlorophenol (DCP) were removed in water via sorption to the Fe(0)-included biochar. Compared to sorption control without Fe(0), the sorbed DNT and DCP were further transformed to reduction products by Fe(0)-included biochar. Compared to the reduction control with Fe(0), the presence of biochar promoted the reductive transformation of DNT and DCP. Increasing the pyrolysis temperature resulted in enhancing the removal of DNT and DCP, suggesting that the aromaticity of biochar may be responsible for the removal. The yields of the reduction products also indicated that unlike the direct reduction by Fe(0), different reduction pathways existed in the reduction of DNT and DCP with Fe(0)-included biochar. The results suggest that Fe(0)-included biochar is a viable option to immobilize and transform redox-sensitive organic contaminants in natural environments.

Effects of graphene on MoO2-MoS2 composite as anode material for lithium-ion batteries

The electrochemical properties of MoO2-MoS2/graphene electrode were compared with those of MoO2-MoS2, bulk MoS2, and graphene electrode. MoO2-MoS2 composite was prepared by a hydrothermal reaction of molybdenum (VI) oxide with sodium sulfide. MoO2-MoS2/graphene composite was obtained by the mechanical mixing of prepared MoO2-MoS2 composite with graphene. MoO2-MoS2/graphene and graphene electrodes exhibited good cycling stability, while MoO2-MoS2 and bulk MoS2 electrodes showed a decrease of capacity during cycling. Especially, the MoO2-MoS2/graphene composite anode showed a high discharge capacity (974xa0mAh/g) after 20th cycle and superior high-rate capability. Such excellent reversible capability and cycle performance may be attributed to the good combination of MoO2, MoS2, and graphene.

Recovery and electrochemical performance in lithium secondary batteries of biochar derived from rice straw

Renewable biomass has attracted great attention for the production of biooil, biogas, and biochar, a carbon residual applicable for carbon sequestration and environmental remediation. Rice straw is one of the most common biomasses among agricultural wastes in South Korea. As part of our advanced and environmentally friendly research, we applied biochar derived from rice straw as the anode material for lithium-ion batteries (LIBs). Porous carbons with a high surface area were prepared from rice straw. Such porous carbons have exhibited particularly large reversible capacity and hence proven to be a candidate anode material for high-rate and high-capacity LIBs. Rice straw-derived biochars were synthesized at four different temperatures: 400, 550, 700, and 900xa0°C. The surface was modified by using HCl and H2O2 on the 550xa0°C biochar in order to increase the surface area. The resulting biochar was characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The surface area was measured by Brunauer–Emmett–Teller (BET) method. The electrochemical characterizations were investigated by galvanostatic charge–discharge (CD) curves, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). All samples exhibited reversible capacities of below 200xa0mAhxa0g−1. The surface-modified biochars exhibited improved cycle performance. Surface modification using HClxa0showed better cycle performance than H2O2. However, the capacities of the treated 550xa0°C biochar were similar to those of non-surface-modified biochar.

Conducting polymer actuator based on chemically deposited polypyrrole and polyurethane-based solid polymer electrolyte working in air

Conducting polymers (CPs), such as polypyrrole, polythiophene, and polyaniline, are unique in that they have switchable properties due to their two or more mechanically stable oxidation states. Thus, their films or coatings can be easily switched by the application of a small voltage and current to change their volume during electrochemical redox processes. In particular, polypyrrole (PPy) has been studied most extensively because of its high electrical conductivity and good environmental stability under ambient conditions. In this work, we have studied a new CP actuator, fully polymeric, assembled with two PPy film electrodes and a solid polymer electrolyte (SPE), polyurethane/Mg(ClO4)2. Polyurethanes (PUs) were synthesized from 4,4-diphenylmethane diisocyanate (MDI), 1,4-butanediol (1,4-BD) and three types of polyol: poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and PPG-block-PEG-block-PPG (PPG-co-PEG). The chemical polymerization of PPy by immersion in Py monomer aqueous solution and oxidant aqueous solution is an adequate method to prepare PU/PPy composite film as an actuator. To find the proper thickness of the PPy coating layer for actuation, we measured the displacements of the actuators according to the thickness of the PPy coating layer. The displacement of all actuators is discussed in connection with the properties of the SPE and PPy. All the results obtained in this work show the feasibility of electrochemomechanical devices based on PPy and SPE film being able to work in air.

Synthesis and control of the shell thickness of polyaniline and polypyrrole half hollow spheres using the polystyrene cores

Polyaniline (Pani) and polypyrrole (Ppy) half hollow spheres with different shell thicknesses were successfully synthesized by three steps process using polystyrene (PS) as the core. The PS core was synthesized by emulsion polymerization. Aniline and pyrrole monomers were polymerized on the surface of the PS core. The shells of Pani and Ppy were fabricated by adding different amounts of aniline and pyrrole monomers. PS cores were dissolved and removed from the core shell structure by solvent extraction. The thicknesses of the Pani and Ppy half hollow spheres were observed by FE-SEM and FE-TEM. The chemical structures of the Pani and Ppy half hollow spheres were characterized by FT-IR spectroscopy and UV-Vis spectroscopy. The shell thicknesses of the Pani half hollow spheres were 30.2, 38.0, 42.2, 48.2, and 52.4 nm, while the shell thicknesses of the Ppy half hollow spheres were 16.0, 22.0, 27.0, and 34.0 nm. The shell thicknesses of Pani and Ppy half hollow spheres linearly increased as the amount of themonomer increased. Therefore, the shell thickness of the Pani and Ppy half hollow spheres can be controlled in these ranges.

Structure and dye-sensitized solar cell application of TiO2 nanotube arrays fabricated by the anodic oxidation method

Well-ordered TiO2 nanotube arrays were fabricated by the potentiostatic anodic oxidation method using pure Ti foil as a working electrode and ethylene glycol solution as an electrolyte with the small addition of NH4F and H2O. The influence of anodization temperature and time on the morphology and formation of TiO2 nanotube arrays was examined. The TiO2 nanotube arrays were applied as a photoelectrode to dye-sensitized solar cells. Regardless of anodizing temperature and time, the average diameter and wall thickness of TiO2 nanotube arrays show a similar value, whereas the length increases with decreasing reaction temperature. The conversion efficiency is very low, which is due to a morphology breaking of the TiO2 nanotube arrays in the manufacturing process of a photoelectrode.

Electrochemical properties of Li–Fe–S ternary metal sulfide (lithium iron sulfide) synthesized via the molten salt method

Li–Fe–S ternary metal sulfide (lithium iron sulfide) powder was synthesized by the molten salt method. The physical and electrochemical properties of synthesized lithium iron sulfide were also investigated. From the results of XRD analysis, the chemical composition of synthesized lithium iron sulfide powder was Li1.7Fe1.17S2 with a hexagonal crystal structure. The Li/Li1.7Fe1.17S2 cell showed a first charge capacity of 153 mAh g−1-Li1.7Fe1.17S2, corresponding to 48% of theoretical capacity. To understand the charge/discharge reaction behaviors of the Li/Li1.7Fe1.17S2 cell, Li/FeS2,Li/Fe and Li/AB cells were tested. From these results, the charge/discharge mechanism of the Li/Li1.7Fe1.17S2 cell was suggested.

The application of catalyst-recovered SnO2 as an anode material for lithium secondary batteries.

We studied the electrochemical characteristics of tin dioxide (SnO2) recovered from waste catalyst material which had been previously used in a polymer synthesis reaction. In order to improve the electrochemical performance of the SnO2 anode electrode, we synthesized a nanocomposite of recovered SnO2 and commercial iron oxide (Fe2O3) (weight ratio 95:5) using a solid state method. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analyses revealed an additional iron oxide phase within a porous nanocomposite architecture. The electrochemical characterizations were based on galvanostatic charge–discharge (CD) curves, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). In the first discharge, the capacity of the SnO2–Fe2O3 nanocomposite was 1700xa0mAhxa0g−1, but was reduced to about 1200xa0mAhxa0g−1 in the second discharge. Thereafter, a discharge capacity of about 1000xa0mAhxa0g−1was maintained up to the 20th cycle. The SnO2–Fe2O3 nanocomposite showed better reversible capacities and rate capabilities than either the recovered SnO2 or commercial Fe2O3 nanoparticle samples.

The influence of the cations of salts on the electrochemical stability of a solid polymer electrolyte based on segmented poly(ether urethane)

Solid polymer electrolytes (SPEs) based on segmented poly(ether urethane) (SPEU) and lithium perchlorate or magnesium perchlorate (LiClO4 or Mg(ClO4)2) were prepared. By analyzing the Fourier-transform infrared (FT-IR) spectrum of the SPE, it was confirmed that the interaction of the magnesium ion with the oxygen of the polyether chain was stronger than that of the lithium ion. The highest ionic conductivities of 1.5×10−5 and 4.5×10−6 S cm−1 were obtained at room temperature for the SPEs containing LiClO4 and Mg(ClO4)2, respectively. The results of linear sweep voltammetry (LSV) show that an SPE consisting of SPEU and magnesium salt has good electrochemical stability up to the working voltage of 1.9 V at [O]/[Mg2+]=50.

Comparison of electrochemical performance for zinc anode via various electrolytes and conducting agents in Zn-air secondary batteries

Zn-air batteries have many advantages as energy devices but they show a poor charge-discharge cycle performance. Therefore, this study examined the effects of various types of electrolytes and conducting agents and changed the additive contents to optimize the electrochemical performance of Zn-air secondary batteries. Electrolytes, such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) solutions, and conducting agents, such as super-p, denka black, acetylene black, and ketjen black, were used to increase the electric conductivity. The electrochemical performance of the zinc anode was evaluated from charge-discharge capacities and cycle efficiency. When the capacity was compared according to each electrolyte from one to ten cycles, in contrast, the zinc anode in 6xa0M KOH showed a higher discharge capacity in the first cycle. Therefore, zinc anode was composed in the 6-M KOH electrolyte and conducting agents were added. The zinc anode included conducting agents with a higher cycle capacity than those without conducting agents, and super-p had a higher first discharge capacity than the others. Therefore, the zinc anode with super-p of 4% shows the highest performance using 6xa0M KOH in Zn-air secondary batteries.