Research Interests

In Smart Hybrid Materials Lab, we are interested in hybrid mesoporous structures for energy related devices such as energy generation (solar cells) and energy storage (supercapacitors) as well as hybrid membrane filters for water and air purification. We are also interested in nano-materials such as graphene for bullet proof composite materials.

Nanoporous structures of metal oxide

• Nanoporous structures are necessary materials not only for filtration and transparent electrode, but also for energy related applications such as solar cells and supercapacitors. However, it is not easy to control pore size and distribution.
• In our laboratory, we are attempting to prepare mesoporous ZnO and MnO2 for solar cells and supercapacitor application, respectively, via sol-gel process in combination with chemical bath deposition.
• For hybrid solar cells, conjugated polymers are infiltrated into the porous structures of ZnO, in which metal oxide works as electron transport path, while the polymer is providing path for holes. Due to the high electron transport rate, high efficiency is expected.
• Similarly, mesoporous structure of MnO2 is also being prepared by sol-gel process in combination with chemical bath deposition application since it is known to be the best materials for supercapacitor up to date.
• For this application, high surface area as well as high conductivity are prime requirements for maximum charges density. Thus, we are attempting to control the porosity of this. In addition, we also attempt to enhance specific capacitance by incorporating inorganic and organic materials.

Nanoporous carbon and cellulose filter membrane

• Due to environmental pollution or natural contamination of water, purification of these became critical concern for high quality of life.
• For purification, membrane filters have been utilized and studied intensively recently, and among the materials, activated carbons from charcoal and fibers are widely utilized.
• However, these materials are small and thus it is not easy to handle and moreover, it may be inhaled while being used by people.
• Thus, in our laboratory, we are attempting to prepare disc-type carbon membrane with polymeric materials (which we cannot disclose at this moment), via carbonization and followed by activation.

• In addition, we are also attempting to prepare disc type membrane filters with bacterial cellulose (BC) which is produced by bacteria and thus it is environmentally friendly materials
• BC membrane filters can be functionalized by chemical modification or by activation process to enhance absorption capability.
• Current our objectives are 1) how to strengthen BC so it can be stable in water and thus can be used for water purification, 2) how to introduce functional groups to BC for better absorption of target materials, and 3) how to get mass production of BC membrane to lower cost.

Inexpensive graphene via surface only oxidation and sonication exfoliation

• Ever since preparation of graphene via so-called “scotch-tape method”, followed by receiving Nobel Prize, it has received extensive attention due to very wide application, owing to excellent properties, including electronic devices, transparent electrodes and bullet proof composites for soldiers.
• Thus, one of prime concerns is preparing inexpensive graphene, which can be achieved by chemical oxidation methods in which graphites are oxidized and one by one layer is being displaced due to increased hydrophilicity via oxidation, introducing hydrophilic functional groups.
• However, this approach generates highly oxidized graphene, or graphene oxide, and thus these have to be reduced for applications mentioned above, using very toxic chemicals.
• Thus, we are attempting to prepare inexpensive graphene from graphite by surface only oxidation, followed by sulfonic acid grafting and sonication exfoliation, which does not require reduction process.
• We have been successful to prepare true graphene, but yield is still low. Thus, an attempt is being made to increase yield, while the prepared graphenes are being tested for supercapacitor and bullet proof composites.

Large size few-layer-graphene via mild oxidation and milstone exfoliation

• Ever since graphene was prepared via so-called “scotch-tape method”, it has received great attention due to its excellent properties and thus possible application wide area, including electronic devices, filtration, transparent electrodes and bullet proof composites.
• However, this method provided very low yield despite excellent property, leading to development of other methods, such as chemical oxidation in which graphites are oxidized and then exfoliated via sonication, in general
• This provided graphene oxide not graphene, and yield is directly related to degree of oxidation; higher the degree of oxidation, higher the yield, but poorer the property due to broken sp2 carbon bonds.
• Of course, these bonds can be restored by reduction but complete restoration is impossible unless there was very mild oxidation. Thus, it is necessary to have mild oxidation to get good property, but this is at the expense of low yield and poor dispersion in water.
• Thus, we employed sulfonic acid grafting and then sonication exfoliation to give high hydrophilicity and high yield after mild oxidation to minimize destruction of sp2 carbon bonds to keep good property. This generated high quality few-layer-graphene (FLG) with high hydrophilicity with no reduction process (RSC Advances, 7, 35717 (2017)).
• However, it generated small size FLG due to sonication, we introduced millstone exfoliation, providing large size FLG comparted to that by sonication method (Nanoscale Research Letters, 13, 186 (2018)).
• Currently, we are working on graphene hydrogel with graphene oxide from mild oxidation

Monolithic porous carbon structures with hierarchical porosity

• Porous carbon materials have been widely utilized for filtration of water and air and recently for electrode materials for energy storage devices (battery and supercapacitor) due to their high porosity and excellent adsorption.
• Traditional porous carbon materials are particulate (activated carbon) and thus they are not easy to handle or apply, which is big problem for energy storages, requiring binders. Besides, their conductivity is also relatively low for electrode materials for energy storages.
• Thus, in our laboratory, like other researchers, we attempted to prepare monolithic porous carbon materials from resorcinol-formaldehyde via base-catalyzed condensation reaction, which was introduced by Pekala.
• Of course, there have been a great amount of research, but only a few studies reported successful preparation of monolithic porous carbons with inter-connected pore structure and possibly hierarchical porosity. But, they were by very complicated process; multi-step process with template and/or other additives making the carbon expensive.
• Thus, we have attempted one-step, template-free process, which was published recently (RSC Advances, 8, 21326 (2018)), while the second manuscript is being prepared based on not only one-step and template-free but also catalyst-free process.
• Currently, we are working on monolithic porous carbon with graphene oxide to enhance electrical properties, while is from mild oxidation.

Shear thickening polymer mixture for liquid armor

• The first bullet proof vest was made in Chosun dynasty with cotton fabric and later silk.
• Since then, there has been a great amount of research on personal armor devices such as bullet proof vest and helmet, leading to large progress but still not so good due to high stiffness and heavy weight
• To solve the former problem, shear thickening fluids have been widely studied to replace hard composite plates. One example is polyethylene oxide with nano-sized silica with, being called “liquid armor
• However, due to low bp of polyethylene oxide, it evaporated slowly and thus loosing bullet proof property. Thus, a number of polymers as well as oligomers are being studied currently.
• In this laboratory, we are working on a number of low Tg polymer with silica particles and hoping to report new formulation for liquid armor soon.