Chemical Mass Production of Graphene Nanoplatelets in ∼100% Yield

Successful application of graphene is hampered by the lack of cost-effective methods for its production. Here, we demonstrate a method of mass production of graphene nanoplatelets (GNPs) by exfoliation of flake graphite in the tricomponent system made by a combination of ammonium persulfate ((NH₄)₂S₂O₈), concentrated sulfuric acid, and fuming sulfuric acid. The resulting GNPs are tens of microns in diameter and 10–35 nm in thickness. When in the liquid phase of the tricomponent media, graphite completely loses its interlayer registry. This provides a ∼100% yield of GNPs from graphite in 3–4 h at room temperature or in 10 min at 120 °C

A Combination of Two Visible-Light Responsive Photocatalysts for Achieving the Z-Scheme in the Solid State

The light reaction in natural photosynthesis is generally recognized as one of the most efficient mechanisms for converting solar energy into other energy sources. We report herein on a novel strategy for generating H2 fuel via an artificial Z-scheme mechanism by mimicking the natural photosynthesis that occurs in green plants. Designing a desirable photocatalyst by mimicking the Z-scheme mechanism leads to a conduction band that is sufficiently high to reduce protons, thus decreasing the probability of charge recombination. We combined two visible light sensitive photocatalysts, CdS and carbon-doped TiO2, with different band structures. The used of this combination, that is, CdS/Au/TiO1.96C0.04, resulted in the successful transfer of photogenerated electrons to a higher energy level in the form of the letter ‘Z’. The system produced about a 4 times higher amount of H2 under irradiation by visible light than CdS/Au/TiO2. The findings reported herein describe an innovative route to harvesting energy by mimicking natural photosynthesis, and is independent of fossil fuels

Three-Dimensional Networked Nanoporous Ta₂O_5–<i>x</i> Memory System for Ultrahigh Density Storage

Oxide-based resistive memory systems have high near-term promise for use in nonvolatile memory. Here we introduce a memory system employing a three-dimensional (3D) networked nanoporous (NP) Ta₂O_5–<i>x</i> structure and graphene for ultrahigh density storage. The devices exhibit a self-embedded highly nonlinear <i>I–V</i> switching behavior with an extremely low leakage current (on the order of pA) and good endurance. Calculations indicated that this memory architecture could be scaled up to a ∼162 Gbit crossbar array without the need for selectors or diodes normally used in crossbar arrays. In addition, we demonstrate that the voltage point for a minimum current is systematically controlled by the applied set voltage, thereby offering a broad range of switching characteristics. The potential switching mechanism is suggested based upon the transformation from Schottky to Ohmic-like contacts, and <i>vice versa</i>, depending on the movement of oxygen vacancies at the interfaces induced by the voltage polarity, and the formation of oxygen ions in the pores by the electric field

Three-Dimensional Networked Nanoporous Ta₂O_5–<i>x</i> Memory System for Ultrahigh Density Storage

Oxide-based resistive memory systems have high near-term promise for use in nonvolatile memory. Here we introduce a memory system employing a three-dimensional (3D) networked nanoporous (NP) Ta₂O_5–<i>x</i> structure and graphene for ultrahigh density storage. The devices exhibit a self-embedded highly nonlinear <i>I–V</i> switching behavior with an extremely low leakage current (on the order of pA) and good endurance. Calculations indicated that this memory architecture could be scaled up to a ∼162 Gbit crossbar array without the need for selectors or diodes normally used in crossbar arrays. In addition, we demonstrate that the voltage point for a minimum current is systematically controlled by the applied set voltage, thereby offering a broad range of switching characteristics. The potential switching mechanism is suggested based upon the transformation from Schottky to Ohmic-like contacts, and <i>vice versa</i>, depending on the movement of oxygen vacancies at the interfaces induced by the voltage polarity, and the formation of oxygen ions in the pores by the electric field

Additional file 1 of Ultrasensitive and real-time optical detection of cellular oxidative stress using graphene-covered tunable plasmonic interfaces

Additional file 1: Figure S1. Simulation of scattering spectra according to the number of graphene layers on SNP. (a) 110 nm SNP. (b) 120 nm SNP. (i) Full spectrum. (ii-iv) Plots showing shifts of λmax (ii), FWHM (iii), and scattering cross-section (σsc) (iv). Figure S2. Simulation of scattering spectra according to the number of graphene layers on GNP. (a) 55 nm GNP. (b) 60 nm GNP. (i) Full spectrum. (ii–iv) Plots showing shifts of λmax (ii), FWHM (iii), and scattering cross-section (σsc) (iv). Figure S3. Representative TEM images of the used SNPs. The average size (for n = 40) was observed to be 101.6 ± 5.0 nm (mean ± SD, nm). Scale bars represent 25 nm. Figure S4. TEM images of the used GNPs. Average size (for n = 40) was 49.5 ± 2.6 nm. Scale bars represent 25 nm. Figure S5. Scattering properties of the plasmonic GNP-graphene interface. (a) Dark-field scattering images of the graphene covered-plasmonic GNP with increasing number of graphene layers. The scale bars represent 10 µm. (b) Corresponding scattering spectra measured for the GNPs with increasing number of graphene layers. (c) Plots for the shifts in terms of λmax (i), FWHM (ii), and intensity (iii) with increasing the graphene layer on the GNP. Figure S6. Changes in photoluminescence (PL) intensities of graphene-covered NPs. (a) SNP. (b) GNP. (i) Schematic diagram, (ii) PL spectrum, and (iii) Plot for the change in PL intensity of NP at 550 nm in the presence of graphene layer. Figure S7. Fluorescence images of intracellular ROS in cells. (a) HDF, (b) NaAsO2-exposed HDF, and (c) A375P. The green fluorescence indicates intracellular ROS visualized by staining with a ROS indicating dye, 2,7-dichlorofluoroscein diacetate (DCFDA). The scale bars represent 50 µm

Atomic Rearrangement in Core–Shell Catalysts Induced by Electrochemical Activation for Favorable Oxygen Reduction in Acid Electrolytes

In Pt-based alloy structures, selective leaching out of the non-Pt metal component (known as “dealloying)” improves catalytic activity during operation due to an increase in the electrochemically active surface area. This indicates that in Pt-based alloy structures, an electrochemical stimulus induces structural change, and the non-Pt component plays an important role in determining the catalytic performance. In this study, we prepared highly active and durable Pd@Cu@Pt core–shell catalysts for an acidic oxygen reduction reaction by a facile method and elucidated the correlation between performance improvement and repetitive potential cycling beyond a simple dealloying effect. Electrochemical activation induces the formation of a localized PtCu alloy, which is strongly correlated with excellent catalytic activity and durability (mass activity after durability test: 2.6 A mg–1Pt), on the surface and subsurface via atomic rearrangement. The origin of such catalytic activity and durability is determined by synchrotron X-ray spectroscopy, electrochemical analysis, and density functional theory calculations

Carbon-Free Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions

A nanoporous Ag-embedded SnO₂ thin film was fabricated by anodic treatment of electrodeposited Ag–Sn alloy layers. The ordered nanoporous structure formed by anodization played a key role in enhancing the electrocatalytic performance of the Ag-embedded SnO₂ layer in several ways: (1) the roughness factor of the thin film is greatly increased from 23 in the compact layer to 145 in the nanoporous layer, creating additional active sites that are involved in oxygen electrochemical reactions; (2) a trace amount of Ag (∼1.7 at %, corresponding to a Ag loading of ∼3.8 μg cm^–2) embedded in the self-organized SnO₂ nanoporous matrix avoids the agglomeration of nanoparticles, which is a common problem leading to the electrocatalyst deactivation; (3) the fabricated nanoporous thin film is active without additional additives or porous carbon that is usually necessary to support and stabilize the electrocatalyst. More importantly, the Ag-embedded SnO₂ nanoporous thin film shows outstanding bifunctional oxygen electrochemical performance (oxygen reduction and evolution reactions) that is considered a promising candidate for use in metal-air batteries. The present technique has a wide range of applications for the preparation of other carbon-free electrocatalytic nanoporous films that could be useful for renewable energy production and storage applications

Three-Dimensional Networked Nanoporous Ta₂O_5–<i>x</i> Memory System for Ultrahigh Density Storage

Oxide-based resistive memory systems have high near-term promise for use in nonvolatile memory. Here we introduce a memory system employing a three-dimensional (3D) networked nanoporous (NP) Ta₂O_5–<i>x</i> structure and graphene for ultrahigh density storage. The devices exhibit a self-embedded highly nonlinear <i>I–V</i> switching behavior with an extremely low leakage current (on the order of pA) and good endurance. Calculations indicated that this memory architecture could be scaled up to a ∼162 Gbit crossbar array without the need for selectors or diodes normally used in crossbar arrays. In addition, we demonstrate that the voltage point for a minimum current is systematically controlled by the applied set voltage, thereby offering a broad range of switching characteristics. The potential switching mechanism is suggested based upon the transformation from Schottky to Ohmic-like contacts, and <i>vice versa</i>, depending on the movement of oxygen vacancies at the interfaces induced by the voltage polarity, and the formation of oxygen ions in the pores by the electric field