Multifunctional Graphene Sheets Embedded in Silicone Encapsulant for Superior Performance of Light-Emitting Diodes

Graphene nanosheets with uniform shape are successfully incorporated into a silicone encapsulant of a light-emitting diode (LED) using a solvent-exchange approach which is a facile and straightforward method. The graphene nanosheets embedded in the silicone encapsulant have a multifunctional role which improves the performance of light-emitting diodes. The presence of graphene gives rise to effective heat dissipation, improvement of protection ability from external stimuli, such as moisture and hazardous gas, and enhancement of mechanical properties such as elastic modulus and fracture toughness. Consequently, the LEDs composed of a graphene-embedded silicone encapsulant exhibit long-term stability without loss of luminous efficiency by addition of relatively small amounts of graphene. This novel strategy offers a feasible candidate for their practical or industrial applications

Hexagonal β‑NaYF₄:Yb³⁺, Er³⁺ Nanoprism-Incorporated Upconverting Layer in Perovskite Solar Cells for Near-Infrared Sunlight Harvesting

Hexagonal β-NaYF₄:Yb³⁺, Er³⁺ nanoprisms, successfully prepared using a hydrothermal method, were incorporated into CH₃NH₃PbI₃ perovskite solar cells (PSCs) as an upconverting mesoporous layer. Due to their near-infrared (NIR) sunlight harvesting, the PSCs based on the upconverting mesoporous layer exhibited a power conversion efficiency of 16.0%, an increase of 13.7% compared with conventional TiO₂ nanoparticle-based PSCs (14.1%). This result suggests that the hexagonal β-NaYF₄:Yb³⁺, Er³⁺ nanoprisms expand the absorption range of the PSC via upconversion photoluminescence, leading to an enhancement of the photocurrent

Poly(vinylidene fluoride)/NH₂‑Treated Graphene Nanodot/Reduced Graphene Oxide Nanocomposites with Enhanced Dielectric Performance for Ultrahigh Energy Density Capacitor

This work describes a ternary nanocomposite system, composed of poly­(vinylidene fluoride) (PVDF), NH₂-treated graphene nanodots (GNDs), and reduced graphene oxides (RGOs), for use in high energy density capacitor. When the RGO sheets were added to PVDF matrix, the β-phase content of PVDF became higher than that of the pristine PVDF. The surface-treatment of GNDs with an ethylenediamine can promote the hydrogen bonding interactions between the GNDs and PVDF, which promote the formation of β-phase PVDF. This finding could be extended to combine the advantages of both RGO and NH₂-treated GND for developing an effective and reliable means of preparing PVDF/NH₂-treated GND/RGO nanocomposite. Relatively small amounts of NH₂-treated GND/RGO cofillers (10 vol %) could make a great impact on the α → β phase transformation, dielectric, and ferroelectric properties of the ternary nanocomposite. The resulting PVDF/NH₂-treated GND/RGO nanocomposite exhibited higher dielectric constant (ε′ ≈ 60.6) and larger energy density (<i>U</i>_e ≈ 14.1 J cm^–3) compared with the pristine PVDF (ε′ ≈ 11.6 and <i>U</i>_e ≈ 1.8 J cm^–3)

Enhanced Electrochemical Performance of Highly Porous Supercapacitor Electrodes Based on Solution Processed Polyaniline Thin Films

Enhancement to the electrochemical performance of supercapacitor electrodes were realized by incorporating highly porous conductive polymer films prepared with solution-processed polyaniline. The resultant nanostructures contained characteristic pores measuring 30–150 nm. Such electrodes generated from a solution of polyaniline-camphorsulfonic acid (PANI/CSA) exhibited higher porosity and electro-catalytic activity than those generated from conventional PANI nanomaterials. These improvements were attributed to faster ion diffusion at the PANI electrode/electrolyte interface. The highest specific capacitance observed for a supercapacitor fabricated with a porous PANI electrode obtained was 361 F g^–1 at 0.25 A g^–1, which is more than twice that of an equivalent electrode made with pristine PANI. Furthermore, supercapacitors made with highly porous PANI electrodes exhibited high electrochemical stability and rate performances

Dual-Functional CeO₂:Eu³⁺ Nanocrystals for Performance-Enhanced Dye-Sensitized Solar Cells

Single-crystalline, octahedral CeO₂:Eu³⁺ nanocrystals, successfully prepared using a simple hydrothermal method, were investigated to determine their photovoltaic properties in an effort to enhance the light-harvesting efficiency of dye-sensitized solar cells (DSSCs). The size of the CeO₂:Eu³⁺ nanocrystals (300–400 nm), as well as their mirrorlike facets, significantly improved the diffuse reflectance of visible light. Excitation of the CeO₂:Eu³⁺ nanocrystal with 330 nm ultraviolet light was re-emitted via downconversion photoluminescence (PL) from 570 to 672 nm, corresponding to the ⁵D₀ → ⁷F_J transition in the Eu³⁺ ions. Downconversion PL was dominant at 590 nm and had a maximum intensity for 1 mol % Eu³⁺. The CeO₂:Eu³⁺ nanocrystal-based DSSCs exhibited a power conversion efficiency of 8.36%, an increase of 14%, compared with conventional TiO₂ nanoparticle-based DSSCs, because of the strong light-scattering and downconversion PL of the CeO₂:Eu³⁺ nanocrystals

Fabrication of Au@Ag Core/Shell Nanoparticles Decorated TiO₂ Hollow Structure for Efficient Light-Harvesting in Dye-Sensitized Solar Cells

Improving the light-harvesting properties of photoanodes is promising way to enhance the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). We synthesized Au@Ag core/shell nanoparticles decorated TiO₂ hollow nanoparticles (Au@Ag/TiO₂ HNPs) via sol–gel reaction and chemical deposition. The Au@Ag/TiO₂ HNPs exhibited multifunctions from Au@Ag core/shell NPs (Au@Ag CSNPs) and TiO₂ hollow nanoparticles (TiO₂ HNPs). These Au@Ag CSNPs exhibited strong and broadened localized surface plasmon resonance (LSPR), together with a large specific surface area of 129 m² g^–1, light scattering effect, and facile oxidation–reduction reaction of electrolyte from TiO₂ HNPs, which resulted in enhancement of the light harvesting. The optimum PCE of η = 9.7% was achieved for the DSSCs using photoanode materials based on TiO₂ HNPs containing Au@Ag/TiO₂ HNPs (0.2 wt % Au@Ag CSNPs with respect to TiO₂ HNPs), which outperformed by 24% enhancement that of conventional photoanodes formed using P25 (η = 7.8%)

Graphene Size Control via a Mechanochemical Method and Electroresponsive Properties

Highly dispersible graphene oxide (GO) sheets of uniform submicrometer size were successfully fabricated from pristine graphite using a simple mechanochemical process. The GO flake morphology was transformed into a spherical form, and the density was decreased slightly via the ball-milling process. Ball-milled GO can be used as an electrorheological (ER) material because of its small particle size, low conductivity, and outstanding dispersibility in silicone oil. We found that the 2-h ball-milled GO-based ER fluid had the best ER performance (shear stress of 78.5 Pa and 630% ER efficiency), which was double that of the nonmilled GO-based ER fluid. The response time to form a fibrillar structure along the applied electric field direction and the recovery time to the starting level decreased with increasing ball-milling time. Additionally, the retarded settling velocity of isolated GO sheets and the electrostatic repulsion between oxygen functional groups on the GO sheets combined to improve the antisedimentation property. The ability to control the size of graphene sheets is a great opportunity to advance graphene commercialization in a high-quality, scalable production setting

Fabrication of SiO₂/TiO₂ Double-Shelled Hollow Nanospheres with Controllable Size via Sol–Gel Reaction and Sonication-Mediated Etching

Size-controllable double-shell SiO₂/TiO₂ hollow nanoparticles (DS HNPs) were fabricated using a simple sol–gel reaction and sonication-mediated etching. The size of the DS HNPs was controlled using SiO₂ core templates of various sizes. Moreover, monodisperse DS HNPs were produced on a large scale (10 g per 1 batch) using the sol–gel method. The surface area and porosity of intrashell and inner-cavity pores were measured by Brunauer–Emmett–Teller analysis. As a result, 240 nm DS HNPs (240 DS HNPs) exhibited the highest surface area of 497 m² g^–1 and a high porosity. Additionally, DS HNPs showed excellent light-scattering ability as a scattering layer in dye-sensitized solar cells due to their structural properties, such as a composite, double-shell, hollow structure, as well as intrashell and inner cavity pores. The DSSCs incorporating 240 DS HNPs demonstrated an 18.3% enhanced power conversion efficiency (PCE) compared to TiO₂ nanoparticles

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 (<i>e.g.</i>, cities) <i>via</i> 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

Fluorescent Polymer Nanoparticle for Selective Sensing of Intracellular Hydrogen Peroxide

Fluorescent boronate-modified polyacrylonitrile (BPAN) nanoparticles of 50 nm diameter were fabricated for use as a selective H₂O₂ sensor. The fluorescence intensity changed and an emission peak shifted when BPAN nanoparticles selectively interacted with H₂O₂, relative to other reactive oxygen species (ROS). The BPAN nanoparticles undergo photoinduced electron transfer (PET) between a Schiff base moiety and boronate, which enhances the fluorescence and makes the nanoparticles suitable for selective ROS recognition. We demonstrate the use of these nanoparticles as a detector of endogenous H₂O₂ produced in living cells. The representative features of the fluorescent BPAN nanoparticles that make them particularly attractive for H₂O₂ and ROS detection are the following: they are easily synthesized as PET sensors; they exhibit a characteristic emission peak and peak shift that distinguishes reaction with H₂O₂ from other ROS; and compared to organic compounds, the sensing moiety on BPAN polymer nanoparticles is more thermally stable and has superior mechanical properties, enabling their use in various biomedical applications