Hongsik Yoon

Extraction of Salinity Gradient Energy using a Hybrid Capacitive-mixing System

Salinity-gradient energy (SGE) is a renewable energy source available wherever two solutions with different salinity mix. Capacitive-mixing (Capmix) is a technology that directly extracts the SG potential through the movements of ions in high- and low-concentration solutions. However, the energy-harvesting performance of Capmix needs further improvement. Herein, a hybrid Capmix that consists of a battery and capacitive electrodes is proposed. In this system, sodium ions and anions are captured/released by the metal oxide and carbon electrodes, respectively. The hybrid Capmix extracted an energy density that was approximately three times higher (130 J m-2 ) and exhibited a notable power output (97 mW m-2 ) compared to the previous Capmix using ion-exchange membranes. Furthermore, the hybrid system operated successfully with real river water and seawater. These results suggest that the hybrid Capmix could be a viable option to harvest energy from salinity gradients.

Influence of the sublayer structure of thin-film composite reverse osmosis membranes on the overall water flux

We found that a support layer of a reverse osmosis (RO) membrane could have a significant effect on the membrane filtration efficiency. To be specific, we determined that the pressure drop occurring in the support layer during the RO operation can increase such that it affects the overall water flux, as a dense sponge-like structure and closed finger-like structure become predominant in the support layer. This considerable resistance was assumed to occur while more water passes through tortuous and segmented regions after being evenly discharged from the active layer. This hypothesis was supported by the estimated pressure drop using the Ergun equation and the tortuosity obtained from a forward osmosis test conducted to better reflect the influence of the sponge-like region. We attempted to factor in all of the parameters used in the Ergun equation in order to determine the main cause of the high pressure drop, and the tortuosity was found to be dominant. An interesting finding was that the tortuosity of the support layer can also significantly influence the overall water flux, even during the RO process. Moreover, the above phenomenon can become much more obvious when the active layer is highly permeable, suggesting that the support layer must be considered alongside the active layer when developing thin-film composite membranes with a highly permeable active layer. Overall, we concluded that the concentration of the polymer solution should be less than 20 wt% to ensure the best performance when preparing a support layer for brackish-water RO membranes.

Corrigendum: Extraction of Salinity-Gradient Energy by a Hybrid Capacitive-Mixing System

Figure 5 Change in the energy and power density production of the hybrid Capmix on varying the applied current from 1 to 4 mA with a total charge of 0.24 C; correct secondary y-axis. The authors and the editorial office apologize for this oversight and for any inconvenience caused. J. Lee, H. Yoon, J. Lee, T. Kim, J. Yoon* Extraction of Salinity-Gradient Energy by a Hybrid Capacitive-Mixing System ChemSusChem 2017, 10, 1600–1606 DOI: 10.1002/cssc.201601656

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.