Jaemoon Jun

Fabrication of amorphous carbon-coated NiO nanofibers for electrochemical capacitor applications

Amorphous carbon-coated nickel oxide nanofibers (NiC NFs) were fabricated using vapor deposition polymerization (VDP) on electrospun nickel oxide nanofibers (NiO NFs), followed by carbonization. To decorate the surface with amorphous carbon, the NiO NF starting materials were prepared by electrospinning a PVP solution containing a nickel oxide precursor (NiAc2·4H2O) and calcining the electrospun NFs. Then, polypyrrole (PPy)-coated NiO nanofibers (NiP NFs) were fabricated as intermediate materials using the pyrrole monomer in the VDP method. Finally, carbonization of the NiP NFs converted the PPy into amorphous carbon and thereby formed the NiC NFs. According to X-ray diffraction (XRD) and Barrett–Joyner–Halenda (BJH) analyses, the NiO structure was maintained during the PPy coating and heat treatment processes. Furthermore, a new pore structure was formed with each fabrication step. The NiC NFs were used as electrochemical capacitors (ECs) with 1 M KOH as the electrolyte. The electrochemical results show that NiC NFs with a thin coating (NiC_L) had a higher specific capacitance (288 F g−1 at 0.3 A g−1) and longer cycle stabilization (89% capacitance maintained after 3000 cycles) than pristine NiO NFs (221 F g−1 at 0.3 A g−1; 56% capacitance maintained after 3000 cycles). Herein, the synthetic methodology is an effective route to obtain hybrid core (inorganic)–shell (organic) nanostructures for electrochemical applications.

Wireless Hydrogen Smart Sensor Based on Pt/Graphene-Immobilized Radio-Frequency Identification Tag

Hydrogen, a clean-burning fuel, is of key importance to various industrial applications, including fuel cells and the aerospace and automotive industries. However, hydrogen gas is odorless, colorless, and highly flammable; thus, appropriate safety protocol implementation and monitoring are essential. Highly sensitive hydrogen-gas leak detection and surveillance systems are needed; additionally, the ability to monitor large areas (e.g., cities) via wireless networks is becoming increasingly important. In this report, we introduce a radio frequency identification (RFID)-based wireless smart-sensor system, composed of a Pt-decorated reduced graphene oxide (Pt_rGO)-immobilized RFID sensor tag and an RFID-reader antenna-connected network analyzer to detect hydrogen gas. The Pt_rGOs, produced using a simple chemical reduction process, were immobilized on an antenna pattern in the sensor tag through spin coating. The resulting Pt_rGO-based RFID sensor tag exhibited a high sensitivity to hydrogen gas at unprecedentedly low concentrations (1 ppm), with wireless communication between the sensor tag and RFID-reader antenna. The wireless sensor tag demonstrated flexibility and a long lifetime due to the strong immobilization of Pt_rGOs on the substrate and battery-independent operation during hydrogen sensing, respectively.

Flower-like Palladium Nanoclusters Decorated Graphene Electrodes for Ultrasensitive and Flexible Hydrogen Gas Sensing

Flower-like palladium nanoclusters (FPNCs) are electrodeposited onto graphene electrode that are prepared by chemical vapor deposition (CVD). The CVD graphene layer is transferred onto a poly(ethylene naphthalate) (PEN) film to provide a mechanical stability and flexibility. The surface of the CVD graphene is functionalized with diaminonaphthalene (DAN) to form flower shapes. Palladium nanoparticles act as templates to mediate the formation of FPNCs, which increase in size with reaction time. The population of FPNCs can be controlled by adjusting the DAN concentration as functionalization solution. These FPNCs_CG electrodes are sensitive to hydrogen gas at room temperature. The sensitivity and response time as a function of the FPNCs population are investigated, resulted in improved performance with increasing population. Furthermore, the minimum detectable level (MDL) of hydrogen is 0.1 ppm, which is at least 2 orders of magnitude lower than that of chemical sensors based on other Pd-based hybrid materials.

Multidimensional polypyrrole/iron oxyhydroxide hybrid nanoparticles for chemical nerve gas agent sensing application.

Multidimensional FeOOH nanoneedle-decorated hybrid polypyrrole nanoparticles (PFFs) were fabricated using dual-nozzle electrospray and heat stirring process. To decorate metal oxide nanoneedles on the polypyrrole (PPy) surface, metal oxide particle-decorated PPys (E_PPy) were fabricated as starting materials. The E_PPy particles were prepared by dual-nozzle electrospray because ferric ions (Fe(3+)) dispersed on the surface reacted with hydroxide (OH(-)) ions in the collector solution without aggregation of each particles. Multidimensional hybrid PFFs with maximized surface area were then formed by heat stirring reaction in the aqueous metal precursor contained solutions. The decoration morphology of the metal oxide nanoneedles could be controlled by precursor concentration in the aqueous solution. These multidimensional hybrid PPFs were applied to nerve gas agent (DMMP) chemical sensor at room temperature with excellent sensitivity. The minimum detectable level (MDL) of PFFs was as low as 0.1 ppb, which is higher than that for a chemical sensor based on hybrid materials. This is because the metal oxide nanoneedles increase surface area and affinity to DMMP vapor.

Aptamer-Functionalized Hybrid Carbon Nanofiber FET-Type Electrode for a Highly Sensitive and Selective Platelet-Derived Growth Factor Biosensor

Precise selectivity and rapid responses to target biomolecules are important in the development of biosensors. In particular, highly sensitive and selective biosensors have been used in clinical treatment to detect factors such as cancer oncoproteins and endocrine disruptors. Herein, highly sensitive liquid electrolyte field-effect transistor (FET) system biosensors were fabricated to detect platelet-derived growth factor (PDGF) using a PDGF-B binding aptamer conjugated with carboxylic polypyrrole-coated metal oxide-decorated carbon nanofibers (CPMCNFs) as the signal transducer. First, CPMCNFs were fabricated using vapor deposition polymerization (VDP) of the carboxylic pryrrole monomer (CPy) on metal oxide-decorated carbon nanofiber (MCNF) surfaces with no treatment for carbon surface functionalization. Furthermore, a 3 nm thick uniformly coated carboxylic polypyrrole (CPPy) layer was formed without aggregation. The CPMCNFs were integrated with the PDGF-B binding aptamer and immobilized on the interdigitated array substrate by covalent anchoring to produce a FET-type biosensor transducer. The PDGF-B binding aptamer conjugated CPMCNF (CPB-Apt) FET sensor was highly sensitive (5 fM) and extremely selective for isoforms of PDGFs. Additionally, the CPB-Apt FET sensor could be reused over a few weeks.

Fe3O4/Carbon Hybrid Nanoparticle Electrodes for High-Capacity Electrochemical Capacitors

Fe3O4/carbon hybrid nanoparticles (FeCHNPs) were fabricated using dual-nozzle electrospraying, vapor deposition polymerization (VDP), and carbonization. FeOOH nanoneedles decorated with polypyrrole (PPy) nanoparticles (FePNPs) were fabricated by electrospraying pristine PPy mixed with FeCl3 solution, followed by heating stirring reaction. A PPy coating was then formed on the FeOOH nanoneedles through a VDP process. FeCHNPs were produced through carbonization of PPy and FeOOH phase transitions. These hybrid carbon nanoparticles (NPs) were used to build electrodes of electrochemical capacitors. The specific capacitance of the FeCHNPs was 455 F g(-1), which is larger than that of pristine PPy NPs (105 F g(-1)) or other hybrid PPy NPs. Furthermore, the FeCHNP-based capacitors exhibited better cycle stability during charge-discharge cycling than other hybrid NP capacitors. This is because the carbon layer on the Fe3 O4 surface formed a protective coating, preventing damage to the electrode materials during the charge-discharge processes. This fabrication technique is an effective approach for forming stable carbon/metal oxide nanostructures for energy storage applications.

Ultrasensitive Bisphenol A Field-Effect Transistor Sensor Using an Aptamer-Modified Multichannel Carbon Nanofiber Transducer

Bisphenol A (BPA) is a known endocrine-disrupting compound (EDC) that has a structure similar to that of the hormone estrogen. Even low concentrations of BPA are able to bind estrogen receptors, thereby inducing severe diseases such as reproductive disorders, chronic diseases, and various types of cancer. Despite such serious effects, the use of BPA remains widespread. Therefore, monitoring of both dietary and nondietary exposure to BPA is important for human healthcare. Herein, we present a field-effect transistor (FET) sensor using aptamer-modified multichannel carbon nanofibers (MCNFs) to detect BPA. The MCNFs are fabricated via single-nozzle electrospinning of two immiscible polymer solutions followed by thermal treatment in an inert atmosphere. The MCNFs are then oxidized using a solution of HNO3 and H2SO4 to introduce carboxyl groups on the surface of the fibers. The carboxyl-functionalized MCNFs (CMCNFs) are immobilized on an amine-functionalized electrode substrate by forming a covalent bond, and amine-functionalized BPA-binding aptamers are modified in the same manner on the CMCNFs. The resulting FET sensors exhibit a high sensitivity, as well as specificity toward BPA at an unprecedentedly low concentration of 1 fM. Furthermore, these sensors are stable and could be reused for repeated assays.

Sulfur‐Immobilized, Activated Porous Carbon Nanotube Composite Based Cathodes for Lithium–Sulfur Batteries

Activated highly porous carbon nanotubes are synthesized with a facile dual-nozzle co-electrospinning and a redox process to apply the framework of a sulfur-immobilized composite as a high-performance cathode in lithium-sulfur batteries.

A metal-oxide nanofiber-decorated three-dimensional graphene hybrid nanostructured flexible electrode for high-capacity electrochemical capacitors

Carbonized polypyrrole-coated SnO2/Co3O4 nanofiber-decorated three-dimensional graphene (CPSC-3rGO) was fabricated using single-nozzle co-electrospinning, freeze-drying, and thermal reduction. Polypyrrole-coated SnO2/Co3O4 nanofibers (PSCNFs) were fabricated using vapor deposition polymerization (VDP) of SnO2/Co3O4 nanofibers. The PSCNFs were then mixed with an aqueous graphene oxide (GO) solution and freeze dried to form a PSCNF-decorated 3D GO (CPSC-3GO) structure. The CPSC-3rGO was produced via thermal reduction to form a hybrid nanomaterial for use as the electrodes of electrochemical capacitors (ECs). The specific capacitance of the CPSC-3rGO was 446 F g−1, which is larger than that of the other 3D nanomaterials investigated (the specific capacitance of PSCNFs was 270 F g−1, that of PSC-3GO was 285 F g−1, and that of 3D rGO was 150 F g−1). In addition, ECs with two symmetrical CPSC-3rGO electrodes were fabricated from two layers of CPSC-3rGO separated by a polymer electrolyte gel and encapsulated in polyethylene terephthalate (PET) membranes. These devices exhibited excellent electrical performance, which was preserved following repeated mechanical deformation.

Multidimensional MnO2 nanohair-decorated hybrid multichannel carbon nanofiber as an electrode material for high-performance supercapacitors.

One-dimensional (1D)-structured nanomaterials represent one of the most attractive candidates for energy-storage systems due to their contribution to design simplicity, fast charge-transportation network, and their allowance for more accessible ion diffusion. In particular, 1D-structured nanomaterials with a highly complex inner-pore configuration enhance functionality by taking advantage of both the hollow and 1D structures. In this study, we report a MnO2 nanohair-decorated, hybrid multichannel carbon nanofiber (Mn_MCNF) fabricated via single-nozzle co-electrospinning of two immiscible polymer solutions, followed by carbonization and redox reactions. With improved ion accessibility, the optimized Mn_MCNF sample (Mn_MCNF_60 corresponding to a reaction duration time of 60 min for optimal MnO2 nanohair growth) exhibited a high specific capacitance of 855 F g(-1) and excellent cycling performance with ∼87.3% capacitance retention over 5000 cycles.