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Baek, Youngbin,Freeman, Benny D.,Zydney, Andrew L.,Yoon, Jeyong American Chemical Society 2017 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.56 No.19
<P>Polydopamine (PDA) is widely used to modify the membrane surface to increase the hydrophilicity with the goal of producing a low fouling membrane. However, current methods of PDA modification require alkali conditions and relatively long reaction times. Herein, we introduced the use of UV irradiation during the PDA modification of the membrane surface. The effects of UV irradiation on the characteristics of the synthesized PDA and the performance of the resulting membrane were evaluated. The PDA was rapidly synthesized in DI water, providing a significant increase in hydrophilicity and a reduction in surface roughness of the polyamide reverse osmosis (RO) membranes. The PDA-modified RO membranes exhibited excellent antifouling behavior upon exposure to alginate while maintaining good water permeability and salt rejection. The use of UV allowed the PDA modification to be conducted in DI water in less than 30 min, a significant improvement compared to current methods.</P>
Baek, Youngbin,Seo, Dong Kyun,Choi, Jong Ho,Lee, Byeongho,Kim, Yong Hyup,Park, Seung Min,Jung, Jungwoo,Lee, Sangho,Yoon, Jeyong Taylor Francis 2016 Desalination and Water Treatment Vol.57 No.58
<P>Carbon nanotube (CNT) membranes are considered as next-generation membranes for desalination. Among the various types of CNT membranes, vertically aligned (VA) CNT membranes provide rapid water transport. However, when the water permeability of VA CNT membranes are compared with those of the commercial membrane, the VA CNT membranes only showed slightly higher water permeability due to their low pore densities. Additionally, the applicability of VA CNT membranes for desalination has been limited due to their larger pore sizes. Herein, we improved VA CNT membranes in terms of the desalination potential, flux enhancement, and scale-up. For the desalination potential, graphene oxide (GO) or polyamide (PA) were coated on a VA CNT membrane as a selective layer, which showed approximately 40-65% NaCl rejection, respectively. A pretreatment polyelectrolyte coating for a GO-coated VA CNT membrane increased the water permeability by approximately 50%. For the flux enhancement, the water permeability of a VA CNT membrane was nearly doubled when the VA CNT forest was mechanically densified by half. Finally, an enlarged VA CNT forest (2 x 2 cm(2)), sequential VA CNT forests (1 x 1 cm(2)) in a large cast, and an assembly of the VA CNT membrane were suggested as scale-up approaches.</P>
Microtube Light-Emitting Diode Arrays with Metal Cores
Tchoe, Youngbin,Lee, Chul-Ho,Park, Jun Beom,Baek, Hyeonjun,Chung, Kunook,Jo, Janghyun,Kim, Miyoung,Yi, Gyu-Chul American Chemical Society 2016 ACS NANO Vol.10 No.3
<P>We report the fabrication and characteristics of vertical microtube light-emitting diode (LED) arrays with a metal core inside the devices. To make the LEDs, gallium nitride (GaN)/indium gallium nitride (InxGa1-xN)/zinc oxide (ZnO) coaxial microtube LED arrays were grown on an n-GaN/c-aluminum oxide (Al2O3) substrate. The micro tube LED arrays were then lifted-off the substrate by wet chemical etching of the sacrificial ZnO microtubes and the silicon dioxide (SiO2) layer. The chemically lifted-off LED layer was then transferred upside-down on other supporting substrates. To create the metal cores, titanium/gold and indium tin oxide were deposited on the inner shells of the microtubes, forming n-type electrodes inside the metal-cored LEDs. The characteristics of the resulting devices were determined by measuring electroluminescence and current voltage characteristic curves. To gain insights into the current spreading characteristics of the devices and understand how to make them more efficient, we modeled them computationally.</P>