26 results on '"Koo, Won-Tae"'
Search Results
2. Single-Atom Pt Stabilized on One-Dimensional Nanostructure Support via Carbon Nitride/SnO2 Heterojunction Trapping.
- Author
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Shin, Hamin, Jung, Wan-Gil, Kim, Dong-Ha, Jang, Ji-Soo, Kim, Yoon Hwa, Koo, Won-Tae, Bae, Jaehyeong, Park, Chungseong, Cho, Su-Ho, Kim, Bong Joong, and Kim, Il-Doo
- Published
- 2020
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3. Hydrogen Sensors Based on MoS2 Hollow Architectures Assembled by Pickering Emulsion.
- Author
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Park, Chan Ho, Koo, Won-Tae, Lee, Young Jun, Kim, Yoon Hwa, Lee, Jiyoung, Jang, Ji-Soo, Yun, Hongseok, Kim, Il-Doo, and Kim, Bumjoon J., idkim@kaist.ac.kr
- Published
- 2020
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4. Universal Synthesis of Porous Inorganic Nanosheets via Graphene-Cellulose Templating Route.
- Author
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Jang, Ji-Soo, Cho, Seunghee, Han, Hyeuk Jin, Song, Seok-Won, Kim, Sang-Joon, Koo, Won-Tae, Kim, Dong-Ha, Jeong, Hyeonsu, Jung, Yeon Sik, and Kim, Il-Doo
- Published
- 2019
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5. Heterogeneous Metal Oxide–Graphene Thorn-Bush Single Fiber as a Freestanding Chemiresistor.
- Author
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Jang, Ji-Soo, Yu, Hayoung, Choi, Seon-Jin, Koo, Won-Tae, Lee, Jiyoung, Kim, Dong-Ha, Kang, Joon-Young, Jeong, Yong Jin, Jeong, Hyeonsu, and Kim, Il-Doo
- Published
- 2019
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6. Single-Atom Pt Stabilized on One-Dimensional Nanostructure Support via Carbon Nitride/SnO 2 Heterojunction Trapping.
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Shin H, Jung WG, Kim DH, Jang JS, Kim YH, Koo WT, Bae J, Park C, Cho SH, Kim BJ, and Kim ID
- Abstract
Catalysis with single-atom catalysts (SACs) exhibits outstanding reactivity and selectivity. However, fabrication of supports for the single atoms with structural versatility remains a challenge to be overcome, for further steps toward catalytic activity augmentation. Here, we demonstrate an effective synthetic approach for a Pt SAC stabilized on a controllable one-dimensional (1D) metal oxide nano-heterostructure support, by trapping the single atoms at heterojunctions of a carbon nitride/SnO
2 heterostructure. With the ultrahigh specific surface area (54.29 m2 g-1 ) of the nanostructure, we obtained maximized catalytic active sites, as well as further catalytic enhancement achieved with the heterojunction between carbon nitride and SnO2 . X-ray absorption fine structure analysis and HAADF-STEM analysis reveal a homogeneous atomic dispersion of Pt species between carbon nitride and SnO2 nanograins. This Pt SAC system with the 1D nano-heterostructure support exhibits high sensitivity and selectivity toward detection of formaldehyde gas among state-of-the-art gas sensors. Further ex situ TEM analysis confirms excellent thermal stability and sinter resistance of the heterojunction-immobilized Pt single atoms.- Published
- 2020
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7. Hydrogen Sensors Based on MoS 2 Hollow Architectures Assembled by Pickering Emulsion.
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Park CH, Koo WT, Lee YJ, Kim YH, Lee J, Jang JS, Yun H, Kim ID, and Kim BJ
- Abstract
For rapid hydrogen gas (H
2 ) sensing, we propose the facile synthesis of the hollow structure of Pt-decorated molybdenum disulfide (h-MoS2 /Pt) using ultrathin (mono- or few-layer) two-dimensional nanosheets. The controlled amphiphilic nature of MoS2 surface produces ultrathin MoS2 NS-covered polystyrene particles via one-step Pickering emulsification. The incorporation of Pt nanoparticles (NPs) on the MoS2 , followed by pyrolysis, generates the highly porous h-MoS2 /Pt. This hollow hybrid structure produces sufficiently permeable pathways for H2 and maximizes the active sites of MoS2 , while the Pt NPs on the hollow MoS2 induce catalytic H2 spillover during H2 sensing. The h-MoS2 /Pt-based chemiresistors show sensitive H2 sensing performances with fast sensing speed (response, 8.1 s for 1% of H2 and 2.7 s for 4%; and recovery, 16.0 s for both 1% and 4% H2 at room temperature in the air). These results mark the highest H2 sensing speed among 2D material-based H2 sensors operated at room temperature in air. Our fabrication method of h-MoS2 /Pt structure through Pickering emulsion provides a versatile platform applicable to various 2D material-based hollow structures and facilitates their use in other applications involving surface reactions.- Published
- 2020
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8. The Design and Science of Polyelemental Nanoparticles.
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Koo WT, Millstone JE, Weiss PS, and Kim ID
- Abstract
Polyelemental nanoparticles (PE NPs) containing four or more elements in a single NP have intriguing intrinsic properties compared to their single-element counterparts. The fusion of diverse elements induces synergistic effects including new physical and chemical phenomena. However, conventional methods have not offered effective strategies for the uniform creation of PE NPs with high reproducibility. Recently, with advances in nanoscience, several new methods have been developed using both thermodynamic and kinetic approaches and, often, the interplay between them. In this Perspective, we highlight recent key advances in the design of PE NPs and their underlying formation mechanisms. We discuss the potential applications of PE NPs and the outlook and future directions for this field.
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- 2020
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9. Pore-Size-Tuned Graphene Oxide Membrane as a Selective Molecular Sieving Layer: Toward Ultraselective Chemiresistors.
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Jang JS, Lee J, Koo WT, Kim DH, Cho HJ, Shin H, and Kim ID
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Conventional graphene oxide (GO)-based gas membranes, having a narrow pore-size range of less than 0.3 nm, exhibit limited gas molecular permeability because of the kinetic diameters of most volatile organic and sulfur compound (VOCs/VSCs) molecules being larger than 0.3 nm. Here, we employ GO nanosheets (NSs) with a tunable pore-size distribution as a molecular sieving layer on two-dimensional (2D) metal oxide NSs-based gas sensors, i.e., PdO-sensitized WO
3 NSs to boost selectivity toward specific gas species. The pore size, surface area, and pore density of GO NSs were simply manipulated by controlling H2 O2 concentration. In addition, the pore size-tuned GO NSs were coated on cellulose filtering paper as a free-standing nanoporous membrane. Holey GO membrane showed a highly selective H2 S permeability characteristic, exhibiting superior cross-selectivity to CH3 COCH3 (0.46 nm), C2 H5 OH (0.45 nm), and C7 H8 (0.59 nm) with larger kinetic diameters compared with H2 S (0.36 nm). Such pore-size-tuned GO nanoporous layer is scalable and robust, highlighting a great promise for designing low cost and highly efficient gas-permeable membrane for outstanding selective gas sensing platform.- Published
- 2020
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10. High-Resolution, Fast, and Shape-Conformable Hydrogen Sensor Platform: Polymer Nanofiber Yarn Coupled with Nanograined Pd@Pt.
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Kim DH, Kim SJ, Shin H, Koo WT, Jang JS, Kang JY, Jeong YJ, and Kim ID
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We report a flexible hydrogen sensing platform based on a single-strand yarn consisting of high-density electrospun nanofibers, on which nanograined Pd or Pd@Pt is coated via yarn spinning followed by sputter deposition. In general, Pd undergoes a phase transition to PdH
x (α-PdHx at [H2 ] < 1% and β-PdHx at [H2 ] > 2%), in which H atoms act as electron scattering centers, thus increasing the resistance. In our system, the sensors exhibit switchable H2 sensing behaviors, that is, (i) Δ R/ R0 > 0 at [H2 ] > 1% by the active electron scattering and (ii) Δ R/ R0 < 0 at [H2 ] < 1% derived from nanograined Pd effects. Due to high mechanical stability stemming from nanogranular morphologies of Pd, which is essential for enduring a huge volume expansion upon exposure to high-concentration H2 , we could obtain a wide concentration range (4-0.0001%) H2 detection resolution. Moreover, an ultrathin Pt overlayer coated on Pd offers an accelerated H2 detection capability based on effective gas dissociation and activation properties. Furthermore, by virtue of the core (thread)-shell (nanofiber yarn) scaffold, long cycling reliability and flexibility were achieved. This facile and low-cost yarn fabrication method offers the development of single-strand thread-type wearable chemiresistors that possess a high surface area and open porosity, facilitating gas diffusion and reaction.- Published
- 2019
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11. Pt-Functionalized PdO Nanowires for Room Temperature Hydrogen Gas Sensors.
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Cho HJ, Chen VT, Qiao S, Koo WT, Penner RM, and Kim ID
- Subjects
- Gases chemistry, Temperature, Electroplating methods, Hydrogen analysis, Nanowires chemistry, Palladium chemistry, Platinum chemistry
- Abstract
In this work, we prepared a well-aligned palladium oxide nanowire (PdO NW) array using the lithographically patterned Pd nanowire electrodeposition (LPNE) method followed by subsequent calcination at 500 °C. Sensitization with platinum (Pt) nanoparticles (NPs), which were functionalized on PdO NWs through a simple reduction process, significantly enhanced the detection capability of the Pt-loaded PdO NWs (Pt-PdO NWs) sensors toward hydrogen gas (H
2 ) at room temperature. The well-distributed Pt NPs, which are known chemical sensitizers, activated the dissociation of H2 and oxygen molecules through the spillover effect with subsequent diffusion of these products to the PdO surface, thereby transforming the entire surface of the PdO NWs into reaction sites for H2 . As a result, at a high concentration of H2 (0.2%), the Pt-PdO NWs showed an enhanced sensitivity of 62% (defined as Δ R/ Rair × 100%) compared to that (6.1%) of pristine PdO NWs. The Pt-PdO NWs exhibited a response time of 166 s, which was 2.68-fold faster than that of pristine PdO NWs (445 s). In addition, the Pt-PdO NWs responded to a very low concentration of H2 (10 ppm) with a sensitivity of 14%, unlike the pristine PdO NWs, which did not exhibit any response at that concentration. These outstanding results are mainly attributed to a homogeneous decoration of Pt NPs on the surface of well-aligned PdO NWs. In this work, we demonstrated the potential suitability of Pt-PdO NWs as a highly sensitive H2 sensing layer at room temperature.- Published
- 2018
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12. Sub-Parts-per-Million Hydrogen Sulfide Colorimetric Sensor: Lead Acetate Anchored Nanofibers toward Halitosis Diagnosis.
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Cha JH, Kim DH, Choi SJ, Koo WT, and Kim ID
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- Acrylic Resins chemistry, Breath Tests methods, Halitosis diagnosis, Humans, Limit of Detection, Nanofibers ultrastructure, Porosity, Colorimetry methods, Hydrogen Sulfide analysis, Nanofibers chemistry, Organometallic Compounds chemistry
- Abstract
Lead(II) acetate [Pb(Ac)
2 ] reacts with hydrogen sulfide to form colored brownish precipitates of lead sulfide. Thus far, in order to detect leakage of H2 S gas in industrial sectors, Pb(Ac)2 has been used as an indicator in the form of test papers with a detection limit only as low as 5 ppm. Diagnosis of halitosis by exhaled breath needs sensors able to detect down to 1 ppm of H2 S gas. In this work, high surface area and porous Pb(Ac)2 anchored nanofibers (NFs) that overcome limitations of the conventional Pb(Ac)2 -based H2 S sensor are successfully achieved. First, lead(II) acetate, which melts at 75 °C, and polyacrylonitrile (PAN) polymer are mixed and stirred in dimethylformamide (DMF) solvent at 85 °C, enabling uniform dispersion of fine liquid droplets in the electrospinning solution. During the subsequent electrospinning, Pb(Ac)2 anchored NFs are obtained, providing an ideal nanostructure with high thermal stability against particle aggregation, numerous reactions sites, and enhanced diffusion of H2 S into the three-dimensional (3D)-networked NF web. This newly obtained sensing material can detect down to 400 ppb of H2 S at a relative humidity of 90%, exhibiting high potential feasibility as a high-performance colorimetric sensor platform for diagnosis of halitosis.- Published
- 2018
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13. An Impedance-Transduced Chemiresistor with a Porous Carbon Channel for Rapid, Nonenzymatic, Glucose Sensing.
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Ogata AF, Song SW, Cho SH, Koo WT, Jang JS, Jeong YJ, Kim MH, Cheong JY, Penner RM, and Kim ID
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- Biosensing Techniques, Electrochemical Techniques, Microscopy, Electron methods, Porosity, Proof of Concept Study, Spectrum Analysis methods, Surface Properties, Tears chemistry, Blood Glucose analysis, Carbon chemistry, Electric Impedance, Glucose analysis
- Abstract
A new type of chemiresistor, the impedance-transduced chemiresistor (ITCR), is described for the rapid analysis of glucose. The ITCR exploits porous, high surface area, fluorine-doped carbon nanofibers prepared by electrospinning of fluorinated polymer nanofibers followed by pyrolysis. These nanofibers are functionalized with a boronic acid receptor and stabilized by Nafion to form the ITCR channel for glucose detection. The recognition and binding of glucose by the ITCR is detected by measuring its electrical impedance at a single frequency. The analysis frequency is selected by measuring the signal-to-noise ( S/ N) for glucose detection across 5 orders of magnitude, evaluating both the imaginary and real components of the complex impedance. On the basis of this analysis, an optimal frequency of 13 kHz is selected for glucose detection, yielding an S/ N ratio of 60-100 for [glucose] = 5 mM using the change in the total impedance, Δ Z. The resulting ITCR glucose sensor shows a rapid analysis time (<8 s), low coefficient of variation for a series of sensors (<10%), an analysis range of 50 μM to 5 mM, and excellent specificity versus fructose, ascorbic acid, and uric acid. These metrics for the ITCR are obtained using a sample size as small as 5 μL.
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- 2018
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14. Bioinspired Cocatalysts Decorated WO 3 Nanotube Toward Unparalleled Hydrogen Sulfide Chemiresistor.
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Kim DH, Jang JS, Koo WT, Choi SJ, Cho HJ, Kim MH, Kim SJ, and Kim ID
- Subjects
- Catalysis, Nanotubes, Particle Size, Surface Properties, Apoferritins chemistry, Cellulose chemistry, Hydrogen Sulfide analysis, Nanoparticles chemistry, Oxides chemistry, Tungsten chemistry
- Abstract
Herein, we incorporated dual biotemplates, i.e., cellulose nanocrystals (CNC) and apoferritin, into electrospinning solution to achieve three distinct benefits, i.e., (i) facile synthesis of a WO
3 nanotube by utilizing the self-agglomerating nature of CNC in the core of as-spun nanofibers, (ii) effective sensitization by partial phase transition from WO3 to Na2 W4 O13 induced by interaction between sodium-doped CNC and WO3 during calcination, and (iii) uniform functionalization with monodispersive apoferritin-derived Pt catalytic nanoparticles (2.22 ± 0.42 nm). Interestingly, the sensitization effect of Na2 W4 O13 on WO3 resulted in highly selective H2 S sensing characteristics against seven different interfering molecules. Furthermore, synergistic effects with a bioinspired Pt catalyst induced a remarkably enhanced H2 S response ( Rair / Rgas = 203.5), unparalleled selectivity ( Rair / Rgas < 1.3 for the interfering molecules), and rapid response (<10 s)/recovery (<30 s) time at 1 ppm of H2 S under 95% relative humidity level. This work paves the way for a new class of cosensitization routes to overcome critical shortcomings of SMO-based chemical sensors, thus providing a potential platform for diagnosis of halitosis.- Published
- 2018
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15. Bimodally Porous WO 3 Microbelts Functionalized with Pt Catalysts for Selective H 2 S Sensors.
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Kim MH, Jang JS, Koo WT, Choi SJ, Kim SJ, Kim DH, and Kim ID
- Abstract
Bimodally meso- (2-50 nm) and macroporous (>50 nm) WO
3 microbelts (MBs) functionalized with sub-3 nm Pt catalysts were fabricated via the electrospinning technique followed by subsequent calcination. Importantly, apoferritin (Apo), tea saponin and polystyrene colloid spheres (750 nm) dispersed in an electrospinning solution acted as forming agents for producing meso- and macropores on WO3 MBs during calcination. Particularly, mesopores provide not only numerous reaction sites for effective chemical reactions, but also facilitate gas diffusion into the interior of the WO3 MBs, dominated by Knudsen diffusion. The macropores further accelerate gas permeability in the interior and on the exterior of the WO3 MBs. In addition, Pt nanoparticles with mean diameters of 2.27 nm were synthesized by using biological protein cages, such as Apo, to further enhance the gas sensing performance. Bimodally porous WO3 MBs functionalized by Pt catalysts showed remarkably high hydrogen sulfide (H2 S) response ( Rair / Rgas = 61 @ 1 ppm) and superior selectivity to H2 S against other interfering gases, such as acetone (CH3 COCH3 ), ethanol (C2 H5 OH), ammonia (NH3 ), and carbon monoxide (CO). These results demonstrate a high potential for the feasibility of catalyst-loaded meso- and macroporous WO3 MBs as new sensing platforms for the possibility of real-time diagnosis of halitosis.- Published
- 2018
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16. Feasible Defect Engineering by Employing Metal Organic Framework Templates into One-Dimensional Metal Oxides for Battery Applications.
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Cheong JY, Koo WT, Kim C, Jung JW, and Kim ID
- Abstract
Facile synthesis of rationally designed nanostructured electrode materials with high reversible capacity is highly critical to meet ever-increasing demands for lithium-ion batteries. In this work, we employed defect engineering by incorporating metal organic framework (MOF) templates into one-dimensional nanostructures by simple electrospinning and subsequent calcination. The introduction of Co-based zeolite imidazole frameworks (ZIF-67) resulted in abundant oxygen vacancies, which induce not only more active sites for Li storage but also enhanced electrical conductivity. Moreover, abundant mesoporous sites are formed by the decomposition of ZIF-67, which are present both inside and outside the resultant SnO
2 -Co3 O4 nanofibers (NFs). Attributed to the creation of vacancy sites along with the synergistic effects of SnO2 and Co3 O4 , SnO2 -Co3 O4 NFs exhibit an excellent reversible capacity for 300 cycles (1287 mA h g-1 at a current density of 500 mA g-1 ) along with superior rate capabilities and improved initial Coulombic efficiency compared with pristine SnO2 NFs. This is an early report on utilizing MOF structures as the defect formation platform into one-dimensional nanostructures, which is expected to result in superior electrochemical performances required for advanced electrodes.- Published
- 2018
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17. Hierarchical Metal-Organic Framework-Assembled Membrane Filter for Efficient Removal of Particulate Matter.
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Koo WT, Jang JS, Qiao S, Hwang W, Jha G, Penner RM, and Kim ID
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Here, we propose heterogeneous nucleation-assisted hierarchical growth of metal-organic frameworks (MOFs) for efficient particulate matter (PM) removal. The assembly of two-dimensional (2D) Zn-based zeolite imidazole frameworks (2D-ZIF-L) in deionized water over a period of time produced hierarchical ZIF-L (H-ZIF-L) on hydrophilic substrates. During the assembly, the second nucleation and growth of ZIF-L occurred on the surface of the first ZIF-L, leading to the formation of flowerlike H-ZIF-L on the substrate. The flowerlike H-ZIF-L was easily synthesized on various substrates, namely, glass, polyurethane three-dimensional foam, nylon microfibers, and nonwoven fabrics. We demonstrated H-ZIF-L-assembled polypropylene microfibers as a washable membrane filter with highly efficient PM removal property (92.5 ± 0.8% for PM
2.5 and 99.5 ± 0.2% for PM10 ), low pressure drop (10.5 Pa at 25 L min-1 ), long-term stability, and superior recyclability. These outstanding particle filtering properties are mainly attributed to the unique structure of the 2D-shaped H-ZIF-L, which is tightly anchored on individual fibers comprising the membrane.- Published
- 2018
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18. Nanoscale PtO 2 Catalysts-Loaded SnO 2 Multichannel Nanofibers toward Highly Sensitive Acetone Sensor.
- Author
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Jeong YJ, Koo WT, Jang JS, Kim DH, Kim MH, and Kim ID
- Abstract
PtO
2 nanocatalysts-loaded SnO2 multichannel nanofibers (PtO2 -SnO2 MCNFs) were synthesized by single-spinneret electrospinning combined with apoferritin and two immiscible polymers, i.e., poly(vinylpyrrolidone) and polyacrylonitrile. The apoferritin, which can encapsulate nanoparticles within a small inner cavity (8 nm), was used as a catalyst loading template for an effective functionalization of the PtO2 catalysts. Taking advantage of the multichannel structure with a high porosity, effective activation of catalysts on both interior and exterior site of MCNFs was realized. As a result, under high humidity condition (95% RH), PtO2 -SnO2 MCNFs exhibited a remarkably high acetone response (Rair /Rgas = 194.15) toward 5 ppm acetone gases, superior selectivity to acetone molecules among various interfering gas species, and excellent stability during 30 cycles of response and recovery toward 1 ppm acetone gases. In this work, we first demonstrate the high suitability of multichannel semiconducting metal oxides structure functionalized by apoferritin-encapsulated catalytic nanoparticles as highly sensitive and selective gas-sensing layer.- Published
- 2018
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19. Metal-Organic Framework-Templated PdO-Co 3 O 4 Nanocubes Functionalized by SWCNTs: Improved NO 2 Reaction Kinetics on Flexible Heating Film.
- Author
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Choi SJ, Choi HJ, Koo WT, Huh D, Lee H, and Kim ID
- Abstract
Detection and control of air quality are major concerns in recent years for environmental monitoring and healthcare. In this work, we developed an integrated sensor architecture comprised of nanostructured composite sensing layers and a flexible heating substrate for portable and real-time detection of nitrogen dioxide (NO
2 ). As sensing layers, PdO-infiltrated Co3 O4 hollow nanocubes (PdO-Co3 O4 HNCs) were prepared by calcination of Pd-embedded Co-based metal-organic framework polyhedron particles. Single-walled carbon nanotubes (SWCNTs) were functionalized with PdO-Co3 O4 HNCs to control conductivity of sensing layers. As a flexible heating substrate, the Ni mesh electrode covered with a 40 nm thick Au layer (i.e., Ni(core)/Au(shell) mesh) was embedded in a colorless polyimide (cPI) film. As a result, SWCNT-functionalized PdO-Co3 O4 HNCs sensor exhibited improved NO2 detection property at 100 °C, with high sensitivity (S) of 44.11% at 20 ppm and a low detection limit of 1 ppm. The accelerated reaction and recovery kinetics toward NO2 of SWCNT-functionalized PdO-Co3 O4 HNCs were achieved by generating heat on the Ni(core)/Au(shell) mesh-embedded cPI substrate. The SWCNT-functionalized porous metal oxide sensing layers integrated on the mechanically stable Ni(core)/Au(shell) mesh heating substrate can be envisioned as an essential sensing platform for realization of low-temperature operation wearable chemical sensor.- Published
- 2017
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20. Hollow Pd-Ag Composite Nanowires for Fast Responding and Transparent Hydrogen Sensors.
- Author
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Jang JS, Qiao S, Choi SJ, Jha G, Ogata AF, Koo WT, Kim DH, Kim ID, and Penner RM
- Abstract
Pd based alloy materials with hollow nanostructures are ideal hydrogen (H
2 ) sensor building blocks because of their double-H2 sensing active sites (interior and exterior side of hollow Pd alloy) and fast response. In this work, for the first time, we report a simple fabrication process for preparing hollow Pd-Ag alloy nanowires (Pd@Ag HNWs) by using the electrodeposition of lithographically patterned silver nanowires (NWs), followed by galvanic replacement reaction (GRR) to form palladium. By controlling the GRR time of aligned Ag NWs within an aqueous Pd2+ -containing solution, the compositional transition and morphological evolution from Ag NWs to Pd@Ag HNWs simultaneously occurred, and the relative atomic ratio between Pd and Ag was controlled. Interestingly, a GRR duration of 17 h transformed Ag NWs into Pd@Ag HNWs that showed enhanced H2 response and faster sensing response time, reduced 2.5-fold, as compared with Ag NWs subjected to a shorter GRR period of 10 h. Furthermore, Pd@Ag HNWs patterned on the colorless and flexible polyimide (cPI) substrate showed highly reversible H2 sensing characteristics. To further demonstrate the potential use of Pd@Ag HNWs as sensing layers for all-transparent, wearable H2 sensing devices, we patterned the Au NWs perpendicular to Pd@Ag HNWs to form a heterogeneous grid-type metallic NW electrode which showed reversible H2 sensing properties in both bent and flat states.- Published
- 2017
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21. Accelerating Palladium Nanowire H 2 Sensors Using Engineered Nanofiltration.
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Koo WT, Qiao S, Ogata AF, Jha G, Jang JS, Chen VT, Kim ID, and Penner RM
- Abstract
The oxygen, O
2 , in air interferes with the detection of H2 by palladium (Pd)-based H2 sensors, including Pd nanowires (NWs), depressing the sensitivity and retarding the response/recovery speed in air-relative to N2 or Ar. Here, we describe the preparation of H2 sensors in which a nanofiltration layer consisting of a Zn metal-organic framework (MOF) is assembled onto Pd NWs. Polyhedron particles of Zn-based zeolite imidazole framework (ZIF-8) were synthesized on lithographically patterned Pd NWs, leading to the creation of ZIF-8/Pd NW bilayered H2 sensors. The ZIF-8 filter has many micropores (0.34 nm for gas diffusion) which allows for the predominant penetration of hydrogen molecules with a kinetic diameter of 0.289 nm, whereas relatively larger gas molecules including oxygen (0.345 nm) and nitrogen (0.364 nm) in air are effectively screened, resulting in superior hydrogen sensing properties. Very importantly, the Pd NWs filtered by ZIF-8 membrane (Pd NWs@ZIF-8) reduced the H2 response amplitude slightly (ΔR/R0 = 3.5% to 1% of H2 versus 5.9% for Pd NWs) and showed 20-fold faster recovery (7 s to 1% of H2 ) and response (10 s to 1% of H2 ) speed compared to that of pristine Pd NWs (164 s for response and 229 s for recovery to 1% of H2 ). These outstanding results, which are mainly attributed to the molecular sieving and acceleration effect of ZIF-8 covered on Pd NWs, rank highest in H2 sensing speed among room-temperature Pd-based H2 sensors.- Published
- 2017
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22. Metal Organic Framework-Templated Chemiresistor: Sensing Type Transition from P-to-N Using Hollow Metal Oxide Polyhedron via Galvanic Replacement.
- Author
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Jang JS, Koo WT, Choi SJ, and Kim ID
- Abstract
Facile synthesis of porous nanobuilding blocks with high surface area and uniform catalyst functionalization has always been regarded as an essential requirement for the development of highly sensitive and selective chemical sensors. Metal-organic frameworks (MOFs) are considered as one of the most ideal templates due to their ability to encapsulate ultrasmall catalytic nanoparticles (NPs) in microporous MOF structures in addition to easy removal of the sacrificial MOF scaffold by calcination. Here, we introduce a MOFs derived n-type SnO
2 (n-SnO2 ) sensing layer with hollow polyhedron structures, obtained from p-n transition of MOF-templated p-type Co3 O4 (p-Co3 O4 ) hollow cubes during galvanic replacement reaction (GRR). In addition, the Pd NPs encapsulated in MOF and residual Co3 O4 clusters partially remained after GRR led to uniform functionalization of efficient cocatalysts (PdO NPs and p-Co3 O4 islands) on the porous and hollow polyhedron SnO2 structures. Due to high gas accessibility through the meso- and macrosized pores in MOF-templated oxides and effective modulation of electron depletion layer assisted by the creation of numerous p-n junctions, the GRR-treated SnO2 structures exhibited 21.9-fold higher acetone response (Rair /Rgas = 22.8 @ 5 ppm acetone, 90%RH) compared to MOF-templated p-Co3 O4 hollow structures. To the best of our knowledge, the selectivity and response amplitudes reported here for the detection of acetone are superior to those MOF derived metal oxide sensing layers reported so far. Our results demonstrate that highly active MOF-derived sensing layers can be achieved via p-n semiconducting phase transition, driven by a simple and versatile GRR process combined with MOF templating route.- Published
- 2017
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23. Elaborate Manipulation for Sub-10 nm Hollow Catalyst Sensitized Heterogeneous Oxide Nanofibers for Room Temperature Chemical Sensors.
- Author
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Jang JS, Choi SJ, Koo WT, Kim SJ, Cheong JY, and Kim ID
- Abstract
Room-temperature (RT) operation sensors are constantly in increasing demand because of their low power consumption, simple operation, and long lifetime. However, critical challenges such as low sensing performance, vulnerability under highly humid state, and poor recyclability hinder their commercialization. In this work, sub-10 nm hollow, bimetallic Pt-Ag nanoparticles (NPs) were successfully formed by galvanic replacement reaction in bioinspired hollow protein templates and sensitized on the multidimensional SnO
2 -WO3 heterojunction nanofibers (HNFs). Formation of hollow, bimetallic NPs resulted in the double-side catalytic effect, rendering both surface and inner side chemical reactions. Subsequently, SnO2 -WO3 HNFs were synthesized by incorporating 2D WO3 nanosheets (NSs) with 0D SnO2 sphere by c-axis growth inhibition effect and fluid dynamics of liquid Sn during calcination. Hierarchically assembled HNFs effectively modulate surface depletion layer of 2D WO3 NSs by electron transfers from WO3 to SnO2 stemming from creation of heterojunction. Careful combination of bimetallic catalyst NPs with HNFs provided an extreme recyclability under exhaled breath (95 RH%) with outstanding H2 S sensitivity. Such sensing platform clearly distinguished between the breath of healthy people and simulated halitosis patients.- Published
- 2017
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24. Metal-Organic Framework Templated Catalysts: Dual Sensitization of PdO-ZnO Composite on Hollow SnO 2 Nanotubes for Selective Acetone Sensors.
- Author
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Koo WT, Jang JS, Choi SJ, Cho HJ, and Kim ID
- Abstract
Metal-organic framework (MOF)-derived synergistic catalysts were easily functionalized on hollow SnO
2 nanotubes (NTs) via electrospinning and subsequent calcination. Nanoscale Pd NPs (∼2 nm) loaded Zn-based zeolite imidazole framework (Pd@ZIF-8, ∼80 nm) was used as a new catalyst-loading platform for the effective functionalization of a PdO@ZnO complex catalyst onto the thin wall of one-dimensional metal oxide NTs. The well-dispersed nanoscale PdO catalysts (3-4 nm) and multiheterojunctions (PdO/ZnO and ZnO/SnO2 ) on hollow structures are essential for the development of high-performance gas sensors. As a result, the PdO@ZnO dual catalysts-loaded hollow SnO2 NTs (PdO@ZnO-SnO2 NTs) exhibited high acetone response (Rair /Rgas = 5.06 at 400 °C @ 1 ppm), superior acetone selectivity against other interfering gases, and fast response (20 s) and recovery (64 s) time under highly humid atmosphere (95% RH). In this work, the advantages of hollow SnO2 NT structures with high surface area and open porosity were clearly demonstrated by the comparison to SnO2 nanofibers (NFs). Moreover, the sensor arrays composed of SnO2 NFs, SnO2 NTs, PdO@ZnO-SnO2 NFs, and PdO@ZnO-SnO2 NTs successfully identified the patterns of the exhaled breath of normal people and simulated diabetics by using a principal component analysis.- Published
- 2017
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25. Nanoscale PdO Catalyst Functionalized Co 3 O 4 Hollow Nanocages Using MOF Templates for Selective Detection of Acetone Molecules in Exhaled Breath.
- Author
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Koo WT, Yu S, Choi SJ, Jang JS, Cheong JY, and Kim ID
- Subjects
- Catalysis, Cobalt, Gases, Metal Nanoparticles, Oxides, Palladium, Acetone chemistry
- Abstract
The increase of surface area and the functionalization of catalyst are crucial to development of high-performance semiconductor metal oxide (SMO) based chemiresistive gas sensors. Herein, nanoscale catalyst loaded Co
3 O4 hollow nanocages (HNCs) by using metal-organic framework (MOF) templates have been developed as a new sensing platform. Nanoscale Pd nanoparticles (NPs) were easily loaded on the cavity of Co based zeolite imidazole framework (ZIF-67). The porous structure of ZIF-67 can restrict the size of Pd NPs (2-3 nm) and separate Pd NPs from each other. Subsequently, the calcination of Pd loaded ZIF-67 produced the catalytic PdO NPs functionalized Co3 O4 HNCs (PdO-Co3 O4 HNCs). The ultrasmall PdO NPs (3-4 nm) are well-distributed in the wall of Co3 O4 HNCs, the unique structure of which can provide high surface area and high catalytic activity. As a result, the PdO-Co3 O4 HNCs exhibited improved acetone sensing response (Rgas /Rair = 2.51-5 ppm) compared to PdO-Co3 O4 powders (Rgas /Rair = 1.98), Co3 O4 HNCs (Rgas /Rair = 1.96), and Co3 O4 powders (Rgas /Rair = 1.45). In addition, the PdO-Co3 O4 HNCs showed high acetone selectivity against other interfering gases. Moreover, the sensor array clearly distinguished simulated exhaled breath of diabetics from healthy people's breath. These results confirmed the novel synthesis of MOF templated nanoscale catalyst loaded SMO HNCs for high performance gas sensors.- Published
- 2017
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26. Heterogeneous Sensitization of Metal-Organic Framework Driven Metal@Metal Oxide Complex Catalysts on an Oxide Nanofiber Scaffold Toward Superior Gas Sensors.
- Author
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Koo WT, Choi SJ, Kim SJ, Jang JS, Tuller HL, and Kim ID
- Abstract
We report on the heterogeneous sensitization of metal-organic framework (MOF)-driven metal-embedded metal oxide (M@MO) complex catalysts onto semiconductor metal oxide (SMO) nanofibers (NFs) via electrospinning for markedly enhanced chemical gas sensing. ZIF-8-derived Pd-loaded ZnO nanocubes (Pd@ZnO) were sensitized on both the interior and the exterior of WO
3 NFs, resulting in the formation of multiheterojunction Pd-ZnO and ZnO-WO3 interfaces. The Pd@ZnO loaded WO3 NFs were found to exhibit unparalleled toluene sensitivity (Rair /Rgas = 4.37 to 100 ppb), fast gas response speed (∼20 s) and superior cross-selectivity against other interfering gases. These results demonstrate that MOF-derived M@MO complex catalysts can be functionalized within an electrospun nanofiber scaffold, thereby creating multiheterojunctions, essential for improving catalytic sensor sensitization.- Published
- 2016
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