Jeonghun Kim

Noninvasive photodetachment of stem cells on tunable conductive polymer nano thin films: selective harvesting and preserved differentiation capacity.

Viable mesenchymal stem cells (MSCs) were efficiently and selectively harvested by near-infrared (NIR) light using the photothermal effect of a conductive polymer nano thin film. The poly(3,4-ethylenedioxy thiophene) (PEDOT)-coated cell culture surfaces were prepared via a simple and fast solution-casting polymerization (SCP) technique. The absorption of PEDOT thin films in the NIR region was effectively triggered cell harvesting upon exposure to an NIR source. By controlling the NIR absorption of the PEDOT film through electrochemical doping or growing PEDOT with different thin film thickness from 70 to 300 nm, the proliferation and harvesting of MSCs on the PEDOT surface were controlled quantitatively. This light-induced cell detachment method based on PEDOT films provides the temporal and spatial control of cell harvesting, as well as cell patterning. The harvested stem cells were found to be alive and well proliferated despite the use of temperature increase by NIR. More importantly, the harvested MSCs by this method preserved their intrinsic characteristics as well as multilineage differentiation capacities. This PEDOT surfaces could be used for repetitive culture and detachment of MSCs or for efficient selection or depletion of a specific subset from heterogeneous population during culture of various tissue-derived cells because there were no photodegradation and photobreakage in the PEDOT films by NIR exposure.

Template-Free Fabrication of Mesoporous Alumina Nanospheres Using Post-Synthesis Water-Ethanol Treatment of Monodispersed Aluminium Glycerate Nanospheres for Molybdenum Adsorption

This work reports the template-free fabrication of mesoporous Al2 O3 nanospheres with greatly enhanced textural characteristics through a newly developed post-synthesis water-ethanol treatment of aluminium glycerate nanospheres followed by high temperature calcination. The proposed water-ethanol treatment is highly advantageous as the resulting mesoporous Al2 O3 nanospheres exhibit 2-4 times higher surface area (up to 251 m2 g-1 ), narrower pore size distribution, and significantly lower crystallization temperature than those obtained without any post-synthesis treatment. To demonstrate the generality of the proposed strategy, a nearly identical post-synthesis water treatment method is successfully used to prepare mesoporous monometallic (e.g., manganese oxide (MnO2 )) and bimetallic oxide (e.g., CuCo2 O4 and MnCo2 O4 ) nanospheres assembled of nanosheets or nanoplates with highly enhanced textural characteristics from the corresponding monometallic and bimetallic glycerate nanospheres, respectively. When evaluated as molybdenum (Mo) adsorbents for potential use in molybdenum-99/technetium-99m (99 Mo/99m Tc) generators, the treated mesoporous Al2 O3 nanospheres display higher molybdenum adsorption performance than non-treated Al2 O3 nanospheres and commercial Al2 O3 , thereby suggesting the effectiveness of the proposed strategy for improving the functional performance of oxide materials. It is expected that the proposed method can be utilized to prepare other mesoporous metal oxides with enhanced textural characteristics and functional performance.

Significant Effect of Pore Sizes on Energy Storage in Nanoporous Carbon Supercapacitors

Mesoporous carbon can be synthesized with good control of surface area, pore-size distribution, and porous architecture. Although the relationship between porosity and supercapacitor performance is well known, there are no thorough reports that compare the performance of numerous types of carbon samples side by side. In this manuscript, we describe the performance of 13 porous carbon samples in supercapacitor devices. We suggest that there is a critical pore size at which guest molecules can pass through the pores effectively. In this context, the specific surface area (SSA) and pore-size distribution (PSD) are used to show the point at which the pore size crosses the threshold of critical size. These measurements provide a guide for the development of new kinds of carbon materials for supercapacitor devices.

Electrochemical Deposition: An Advanced Approach for Templated Synthesis of Nanoporous Metal Architectures

Well-constructed porous materials take an essential role in a wide range of applications, including energy conversion and storage systems, electrocatalysis, photocatalysis, and sensing. Although the tailored design of various nanoarchitectures has made substantial progress, simpler preparation methods are compelled to meet large-scale production requirements. Recently, advanced electrochemical deposition techniques have had a significant impact in terms of precise control upon the nanoporous architecture (i.e., pore size, surface area, pore structure, etc.), enabling access to a wide range of compositions. In this Account, we showcase the uniqueness of electrochemical deposition techniques, detail their implementation toward the synthesis of novel nanoporous metals, and finally outline the future research directions. Nanoporous metallic structures are attractive in that they can provide high surface area and large pore volume, easing mass transport of reactants and providing high accessibility to catalytically active metal surface. The great merit of the electrochemical deposition approach does not only lie in its versatility, being applicable to a wide range of compositions, but also in the nanoscale precision it affords when it comes to crystal growth control, which cannot be easily achieved by other bottom-up or top-down approaches. In this Account, we describe the significant progress made in the field of nanoporous metal designed through electrochemical deposition approaches using hard templates (i.e., porous silica, 3D templates of polymer and silica colloids) and soft templates (i.e., lyotropic liquid crystals, polymeric micelles). In addition, we will point out how it accounts for precise control over the crystal growth and describe the unique physical and chemical properties emerging from these novel materials. Up to date, our group has reported the synthesis of several nanoporous metals and alloys (e.g., Cu, Ru, Rh, Pd, Pt, Au, and their corresponding alloys) under various conditions through electrochemical deposition, while investigating their various potential applications. The orientation of the channel structure, the composition, and the nanoporosity can be easily controlled by selecting the appropriate surfactants or block copolymers. The inherent properties of the final product, such as framework crystallinity, catalytic activity, and resistance to oxidation, are depending on both the composition and pore structure, which in turn require suitable electrochemical conditions. This Account is divided into three main sections: (i) a history of electrochemical deposition using hard and soft templates, (ii) a description of the important mechanisms involved in the preparation of nanoporous materials, and (iii) a conclusion and future perspectives. We believe that this Account will promote a deeper understanding of the synthesis of nanoporous metals using electrochemical deposition methods, thus enabling new pathways to control nanoporous architectures and optimize their performance toward promising applications such as catalysis, energy storage, sensors, and so forth.

Facile synthesis of palladium-nanoparticle-embedded N-doped carbon fibers for electrochemical sensing

In recent years, there have been many studies on metal/carbon hybrid materials for electrochemical applications. However, reducing the metal content in catalysts is still a challenge. Here, a facile synthesis of palladium (Pd) nanoparticle-embedded N-doped carbon fibers (Pd/N-C) through electropolymerization and reduction methods is demonstrated. The as-prepared Pd/N-C contains only 1.5u2005wtu2009% Pd. Under optimal conditions, bisphenolu2005A is detected by using amperometry in two dynamic ranges from 0.1 to 10u2005μm and from 10 to 200u2005μm, and the obtained correlation coefficients are close to 0.9836 and 0.9987, respectively. The detection limit (DL) for bisphenolu2005A is determined to be 29.44 (±0.77)u2005nm.

Electrochemical Synthesis of Mesoporous Au–Cu Alloy Films with Vertically Oriented Mesochannels Using Block Copolymer Micelles

We synthesized Au-Cu bimetallic alloy films with a controlled mesoporous architecture through electrochemical deposition using an electrolyte solution containing spherical polymeric micelles. The composition of the alloy films can be easily controlled by tuning the ratio between the Au and Cu species present in the electrolyte solution. At low Cu content, cage-type mesopores are formed, reflecting the parent micellar template. Surprisingly, upon increasing the Cu content, the cage-type mesopores fuse to form vertically aligned one-dimensional mesochannels. The vertical alignment of these mesopores is favorable for enhanced mass and ion transfer within the channels due to low diffusion resistance. The atomic distribution of Au and Cu is uniform over the entire film and free of any phase segregation. The as-synthesized mesoporous Au-Cu films exhibit excellent performance as a nonenzymatic glucose sensor with high sensitivity and selectivity, and the current response is linear over a wide range of concentrations. This work identifies the properties responsible for the promising performance of such mesoporous alloy films for the clinical diagnosis of diabetes. This micelle-assisted electrodeposition approach has a high degree of flexibility and can be simply extended from monometallic compounds to a multimetallic system, enabling the fabrication of various mesoporous alloy films suitable for different applications.

Mesoporous Manganese Phosphonate Nanorods as a Prospective Anode for Lithium-Ion Batteries

Mesoporous materials can serve as well-performed electrode candidates for lithium-ion batteries (LIBs). Mesoporous manganese phosphonate (MnP) nanorods are composed of an interconnected network of pores that have high infiltration capacity for electrolyte and less tortuous transport pathways for lithium/electron charge carriers. The mesoporous architecture should also help alleviate stress from volume variation upon lithium intercalation/deintercalation cycles. We used MnP as an LIB anode and observed an initial reversible capacity of 420 mA h g-1 and a modest Coulombic efficiency of 68.7% at a relatively high current density of 144 mA g-1. The reversible capacity stabilizes at 253 mA h g-1 after 100 repetitive cycles, while most of the time, the Coulombic efficiency remains around 100%. The results show that, as a prospective LIB anode, the mesoporous MnP can achieve desirable capacity with decent durability and rate capability.

Antibacterial poly (3,4-ethylenedioxythiophene):poly(styrene-sulfonate)/agarose nanocomposite hydrogels with thermo-processability and self-healing

Recently, Near-infrared (NIR)-induced photothermal killing of pathogenic bacteria has received considerable attention due to the increase in antibiotic resistant bacteria. In this paper, we report a simple aqueous solution-based strategy to construct an effective photothermal nanocomposite composed of poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and agarose with thermo-processability, light triggered self-healing, and excellent antibacterial activity. Our experiments revealed that PEDOT:PSS/agarose was easily coated on both a 2D glass substrate and 3D cotton structure. Additionally, PEDOT:PSS/agarose can be designed into free-standing objects of diverse shape as well as restored through an NIR light-induced self-healing effect after damage. Taking advantage of strong NIR light absorption, PEDOT:PSS/agarose exhibited a sharp temperature increase of 24.5u2009°C during NIR exposure for 100u2009s. More importantly, we demonstrated that the temperature increase on PEDOT:PSS/agarose via photothermal conversion resulted in the rapid and effective killing of nearly 100% of the pathogenic bacteria within 2u2009min of NIR irradiation.

Micelle-Assisted Strategy for the Direct Synthesis of Large-Sized Mesoporous Platinum Catalysts by Vapor Infiltration of a Reducing Agent

Stable polymeric micelles have been demonstrated to serve as suitable templates for creating mesoporous metals. Herein, we report the utilization of a core-shell-corona type triblock copolymer of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) and H2PtCl6·H2O to synthesize large-sized mesoporous Pt particles. After formation of micelles with metal ions, the reduction process has been carried out by vapor infiltration of a reducing agent, 4-(Dimethylamino)benzaldehyde. Following the removal of the pore-directing agent under the optimized temperature, mesoporous Pt particles with an average pore size of 15 nm and surface area of 12.6 m2·g−1 are achieved. More importantly, the resulting mesoporous Pt particles exhibit superior electrocatalytic activity compared to commercially available Pt black.

Mesoporous Metallic Iridium Nanosheets

Two-dimensional (2D) metals are an emerging class of nanostructures that have attracted enormous research interest due to their unusual electronic and thermal transport properties. Adding mesopores in the plane of ultrathin 2D metals is the next big step in manipulating these structures because increasing their surface area improves the utilization of the material and the availability of active sites. Here, we report a novel synthetic strategy to prepare an unprecedented type of 2D mesoporous metallic iridium (Ir) nanosheet. Mesoporous Ir nanosheets can be synthesized with close-packed assemblies of diblock copolymer (poly-(ethylene oxide)- b-polystyrene, PEO- b-PS) micelles aligned in the 2D plane of the nanosheets. This novel synthetic route opens a new dimension of control in the synthesis of 2D metals, enabling new kinds of mesoporous architectures with abundant catalytically active sites. Because of their unique structural features, the mesoporous metallic Ir nanosheets exhibit a high electrocatalytic activity toward the oxygen evolution reaction (OER) in acidic solution as compared to commercially available catalysts.