Choonsoo Kim

The effect of electrode material on the generation of oxidants and microbial inactivation in the electrochemical disinfection processes.

Electrochemical disinfection has gained increasing attention as an alternative for conventional drinking water treatment due to its high effectiveness and environmental compatibility. The most common method of electrochemical disinfection is the use of electro-generated oxidants, such as active chlorine and reactive oxygen species, as disinfectants. This study examined the role of electrode material on the generation of oxidants, and elucidated the different reaction pathways for generating individual oxidants by employing boron-doped diamond (BDD), Ti/RuO(2), Ti/IrO(2), Ti/Pt-IrO(2), and Pt as anode materials. The efficiency of ()OH production, as determined by para-chlorobenzoic acid (pCBA) degradation, was in the order of BDD>>Ti/RuO(2) approximately Pt. No significant production of ()OH was observed at Ti/IrO(2) and Ti/Pt-IrO(2). The ()OH was found to play a key role in O(3) generation at BDD, but not at the other electrodes. The production of active chlorine was in the order of Ti/IrO(2)>Ti/RuO(2)>Ti/Pt-IrO(2)>BDD>Pt. The large difference in this order from that of ROS was attributed to the difference in the electrocatalytic activity of each electrode material toward the production of active chlorine, as evidenced by linear sweep voltammetry (LSV) measurements. In addition, the characteristics of microbial inactivation as a function of electrode material were examined under the presence of an inert electrolyte, using Escherichia coli as an indicator microorganism.

Hybrid capacitive deionization to enhance the desalination performance of capacitive techniques

Based on a porous carbon electrode, capacitive deionization (CDI) is a promising desalination technology in which ions are harvested and stored in an electrical double layer. However, the ion removal capacity of CDI systems is not sufficient for desalting high-concentration saline water. Here, we report a novel desalination technique referred to as “hybrid capacitive deionization (HCDI)”, which combines CDI with a battery system. HCDI consists of a sodium manganese oxide (Na4Mn9O18) electrode, an anion exchange membrane, and a porous carbon electrode. In this system, sodium ions are captured by the chemical reaction in the Na4Mn9O18 electrode, whereas chloride ions are adsorbed on the surface of the activated carbon electrode during the desalination process. HCDI exhibited more than double the ion removal sorption capacity (31.2 mg g−1) than a typical CDI system (13.5 mg g−1). Moreover, it was found that the system has a rapid ion removal rate and excellent stability in an aqueous sodium chloride solution. These results thus suggest that the HCDI system could be a feasible method for desalting a highly concentrated sodium chloride solution in capacitive techniques.

Capacitive and Oxidant Generating Properties of Black-Colored TiO2 Nanotube Array Fabricated by Electrochemical Self-Doping

Recently, black-colored TiO2 NTA (denoted as black TiO2 NTA) fabricated by self-doping of TiO2 NTA with the amorphous phase led to significant success as a visible-light-active photocatalyst. This enhanced photocatalytic activity is largely attributed to a higher charge carrier density as an effect of electrochemical self-doping resulting in a higher optical absorbance and lower transport resistance. Nevertheless, the potential of black TiO2 NTA for other electrochemical applications, such as a supercapacitor and an oxidant-generating anode, has not been fully investigated. Here, we report the capacitive and oxidant generating properties of black TiO2 NTA. The black TiO2 NTA exhibited significantly a high value for areal capacitance with a good rate capability and novel electrocatalytic activity in generating (•)OHs and Cl2 compared to pristine TiO2 NTA with the anatase phase. This study suggests that the black TiO2 NTA be applied as a supercapacitor and an oxidant generating anode.

Facile detection of photogenerated reactive oxygen species in TiO2 nanoparticles suspension using colorimetric probe-assisted spectrometric method.

This present study reports that reactive oxygen species (ROS), which mainly consist of hydroxyl (OH) and superoxide (O2(-)) radicals generated by the photocatalysis of TiO2 nanoparticles (TiO2 NPs) in suspension, can be quantitatively measured by the colorimetric probe-assisted spectrometric method without any interference by the TiO2 NPs. The interference effect of the TiO2 NPs with UV-vis spectroscopy was excluded by the selective separation of p-nitrosodimethylaniline (RNO) and tetrazolium salt (XTT) (probe compounds for OH and O2(-), respectively) from the TiO2 NPs in the suspension by centrifugation at a specified ionic strength adjusted with phosphate buffer (KH2PO4/NaOH, PB) solution. This colorimetric probe-assisted spectrometric method was also successfully applied to measure the steady-state production of photogenerated ROS in a TiO2 NPs suspension.

Electrochemical softening using capacitive deionization (CDI) with zeolite modified carbon electrode (ZMCE)

AbstractDivalent ions such as calcium and magnesium ions are thought to cause hardness in water inducing scale problems in the pipelines of boilers and heat exchangers. Thus, water softening has gained wide interest in water treatment technology. Although zeolite particles have been widely used as a material for the removal of divalent ions, its low ion-exchange efficiency based on diffusion-dependent process has limited their applications in water softening. Herein, we report effective electrochemical softening using zeolite with capacitive deionization (CDI), which is a desalination technology with electrochemical ad/desorption in an electric double layer. The carbon electrode with zeolite (denoted as a zeolite modified carbon electrode (ZMCE)) was prepared by the slurry and pasting method with zeolite particles and carbon black. ZMCE exhibited a significantly enhanced efficiency in the removal of divalent ions in softening using the CDI process compared to the normal softening process based on diffusio...

Organic-inorganic hybrid membrane with anodized aluminum oxide support layer for improving membrane performance in forward osmosis

aSchool of Chemical and Biological Engineering, College of Engineering, Institute of Chemical Process, Seoul National University (SNU), Gwanak-gu, Daehak-dong, Seoul 151-742, Korea, Tel. +82-2-880-8941; Fax: +82-2-876-8911; email: jeyong@snu.ac.kr bSchool of Chemical and Biological Engineering, College of Engineering, Institute of Chemical Process, Asian Institute for Energy, Environment & Sustainability (AIEES), Seoul National University (SNU), Gwanak-gu, Daehak-dong, Seoul 151-742, Korea

Evaluation of thin-film nanocomposite RO membranes using TiO2 nanotubes and TiO2 nanoparticles: a comparative study

AbstractThin-film nanocomposite (TFN) reverse osmosis (RO) membranes have gained attention due to their enhanced membrane performances in permeate flux and salt rejection. The structural shape of nanocomposites, such as particles and nanotubes, has been thought to have critical roles in improving their performances. However, the effects of the structural properties on membrane performance have yet to be verified. Herein, we reported the structural effects of nanocomposites on the performance of TFN RO membranes fabricated with TiO2 nanotubes (TNT) and TiO2 nanoparticles (TNP). The TFN RO membranes containing TNT or TNP exhibited similar high hydrophilicities and enhanced water permeability compared with a conventional RO membrane. In terms of membrane performance, the TNT TFN RO membranes had better water permeability than the TNP TFN RO membranes. Compared with non-porous TNP, 80-nm diameter nanochannels of TNT provided additional enhanced water permeability by serving as water transport passageways.