Chemically modulated graphene quantum dot for tuning the photoluminescence as novel sensory probe

A band gap tuning of environmental-friendly graphene quantum dot (GQD) becomes a keen interest for novel applications such as photoluminescence (PL) sensor. Here, for tuning the band gap of GQD, a hexafluorohydroxypropanyl benzene (HFHPB) group acted as a receptor of a chemical warfare agent was chemically attached on the GQD via the diazonium coupling reaction of HFHPB diazonium salt, providing new HFHPB-GQD material. With a help of the electron withdrawing HFHPB group, the energy band gap of the HFHPB-GQD was widened and its PL decay life time decreased. As designed, after addition of dimethyl methyl phosphonate (DMMP), the PL intensity of HFHPB-GQD sensor sharply increased up to approximately 200% through a hydrogen bond with DMMP. The fast response and short recovery time was proven by quartz crystal microbalance (QCM) analysis. This HFHPB-GQD sensor shows highly sensitive to DMMP in comparison with GQD sensor without HFHPB and graphene. In addition, the HFHPB-GQD sensor showed high selectivity only to the phosphonate functional group among many other analytes and also stable enough for real device applications. Thus, the tuning of the band gap of the photoluminescent GQDs may open up new promising strategies for the molecular detection of target substrates. © The Author(s) 20166511sciescopu

Low-dimensional carbon and MXene-based electrochemical capacitor electrodes

Due to their unique structure and outstanding intrinsic physical properties such as extraordinarily high electrical conductivity, large surface area, and various chemical functionalities, low-dimension-based materials exhibit great potential for application in electrochemical capacitors (ECs). The electrical properties of electrochemical capacitors are determined by the electrode materials. Because energy charge storage is a surface process, the surface properties of the electrode materials greatly influence the electrochemical performance of the cell. Recently, graphene, a single layer of sp2-bonded carbon atoms arrayed into two-dimensional carbon nanomaterial, has attracted wide interest as an electrode material for electrochemical capacitor applications due to its unique properties, including a high electrical conductivity and. large surface area. Several low-dimensional materials with. large surface areas and high conductivity such as onion-like carbons (OLCs), carbide-derived carbons (CDCs), carbon nanotubes (CNTs), graphene, metal hydroxide, transition metal dichalcogenides (TMDs), and most recently MXene, have been developed for electrochemical capacitors. Therefore, it is useful to understand the current issues of low-dimensional materials and their device applications. © 2016 IOP Publishing Ltd101111sciescopu

Impermeable flexible liquid barrier film for encapsulation of DSSC metal electrodes

Encapsulation of electronic devices such as dye-sensitized solar cells (DSSCs) is prone to degradation under normal atmospheric conditions, even with hermetic barriers on the metal electrodes. Overcoming this problem is crucial to increasing DSSC lifetimes and making them commercially viable. Herein, we report a new impermeable flexible liquid barrier film using polyvinyl alcohol (PVA) and partially reduced graphene oxide (PrGO), which dramatically enhances the lifetime of Ag metal electrodes (typically used in DSSCs) immersed in a highly acidic iodolyte solution. The Ag metal electrode encapsulated by the PVA/PrGO film survived for over 500 hrs, superior to existing barriers of glass frits, epoxy resins and polymers. The PVA/PrGO film strongly adheres to the Ag metal surface, and the resulting PVA/PrGO/Ag electrode is stable even on a curved substrate, with a sheet resistance nearly independent of curvature. These results give new insight for the design of high-performance and solution-processable flexible liquid barrier films for a wide range of applications, in particular for the encapsulation of electronic devices with liquid electrolytes1121sciescopu

Highly transparent and flexible supercapacitors using graphene-graphene quantum dots chelate

Nowadays, transparent and flexible energy storage devices are attracting a great deal of research interest due to their great potential as integrated power sources. In order to take full advantage of transparent and flexible devices, however, their power sources also need to be transparent and flexible. In the present work we fabricated new transparent and flexible micro-supercapacitors using chelated graphene and graphene quantum dots (GQDs) by a simple electrophoretic deposition (EPD) method. Through a chelate formation between graphene and GQDs with metal ions, the GQD materials were strongly adhered on an interdigitated pattern of graphene (ipG-GQDs) and its resulting porous ipG-GQDs film was used as the active material in the micro-supercapacitors. Amazingly, these supercapacitor devices showed high transparency (92.97% at 550 nm), high energy storage (9.09 μF cm-2), short relaxation time (8.55 ms), stable cycle retention (around 100% for 10,000 cycles), and high stability even under severe bending angle 45° with 10,000 cycles. © 2016 Elsevier Ltd126301sciescopu

Solar-light photocatalytic disinfection using crystalline/amorphous low energy bandgap reduced TiO2

A generation of reactive oxygen species (ROS) from TiO2 under solar light has been long sought since the ROS can disinfect organic pollutants. We found that newly developed crystalline/amorphous reduced TiO2 (rTiO2) that has low energy bandgap can effectively generate ROS under solar light and successfully remove a bloom of algae. The preparation of rTiO2 is a one-pot and mass productive solution-process reduction using lithium-ethylene diamine (Li-EDA) at room temperature. Interestingly only the rutile phase of TiO2 crystal was reduced, while the anatase phase even in case of both anatase/rutile phased TiO2 was not reduced. Only reduced TiO2 materials can generate ROS under solar light, which was confirmed by electron spin resonance. Among the three different types of Li-EDA treated TiO2 (anatase, rutile and both phased TiO2), the both phased rTiO2 showed the best performance to produce ROS. The generated ROS effectively removed the common green algae Chlamydomonas. This is the first report on algae degradation under solar light, proving the feasibility of commercially available products for disinfection.18151sciescopu

Nitrogen-Doped Partially Reduced Graphene Oxide Rewritable Nonvolatile Memory

As memory materials, two-dimensional (2D) carbon materials such as graphene oxide (GO)-based materials have attracted attention due to a variety of advantageous attributes, including their solution-processability and their potential for highly scalable device fabrication for transistor-based memory and cross-bar memory arrays. In spite of this, the use of GO-based materials has been limited, primarily due to uncontrollable oxygen functional groups. To induce the stable memory effect by ionic charges of a negatively charged carboxylic acid group of partially reduced graphene oxide (PrGO), a positively charged pyridinium N that served as a counterion to the negatively charged carboxylic acid was carefully introduced on the PrGO framework. Partially reduced N-doped graphene oxide (PrGO_DMF) in dimethylformamide (DMF) behaved as a semiconducting nonvolatile memory material. Its optical energy band gap was 1.7–2.1 eV and contained a sp² CC framework with 45–50% oxygen-functionalized carbon density and 3% doped nitrogen atoms. In particular, rewritable nonvolatile memory characteristics were dependent on the proportion of pyridinum N, and as the proportion of pyridinium N atom decreased, the PrGO_DMF film lost memory behavior. Polarization of charged PrGO_DMF containing pyridinium N and carboxylic acid under an electric field produced N-doped PrGO_DMF memory effects that followed voltage-driven rewrite-read-erase-read processes

Tunable Sub-nanopores of Graphene Flake Interlayers with Conductive Molecular Linkers for Supercapacitors

Although there are numerous reports of high performance supercapacitors with porous graphene, there are few reports to control the interlayer gap between graphene sheets with conductive molecular linkers (or molecular pillars) through a π-conjugated chemical carbon-carbon bond that can maintain high conductivity, which can explain the enhanced capacitive effect of supercapacitor mechanism about accessibility of electrolyte ions. For this, we designed molecularly gap-controlled reduced graphene oxides (rGOs) via diazotization of three different phenyl, biphenyl, and para-terphenyl bis-diazonium salts (BD1-3). The graphene interlayer sub-nanopores of rGO-BD1-3 are 0.49, 0.7, and 0.96 nm, respectively. Surprisingly, the rGO-BD2 0.7 nm gap shows the highest capacitance in 1 M TEABF4 having 0.68 nm size of cation and 6 M KOH having 0.6 nm size of hydrated cation. The maximum energy density and power density of the rGO-BD2 were 129.67 W h kg-1 and 30.3 kW kg-1, respectively, demonstrating clearly that the optimized sub-nanopore of the rGO-BDs corresponding to the electrolyte ion size resulted in the best capacitive performance. © 2016 American Chemical Society117191sciescopu

Low temperature solution synthesis of reduced two dimensional Ti3C2 MXenes with paramagnetic behaviour

MXenes - two dimensional, 2D, early transition metal, M, carbides and nitrides, X - are the latest addition to the 2D materials' world. Herein, we report on a facile low temperature solution chemical synthesis method to reduce Ti3C2Tx multilayered, ML, MXenes. Using X-ray photoelectron spectroscopy, electron spin resonance, magnetization measurements and other techniques, we concluded that immersing Ti3C2Tx MLs in the reducing agent Li-ethylenediamine (Li-EDA) - held at temperatures varying from room to 120 degrees C - reduces the 2D layers creating Ti3+ ions and oxygen vacancies. Above a temperature (T) of approximate to 10 K, the magnetic susceptibilities, , are temperature independent, implying that the resulting powders are Pauli paramagnetic. The loss of the magnetic signal upon intercalation of Li+ or EDA, together with a Curie-like increase in at T < 10 K, is consistent with that of a disordered metal that is close to a metallic to insulator transition and proves that the magnetism is associated with the 2D flakes. This result is the first evidence of any magnetism of any MXene. © The Royal Society of Chemistry 201

Catalyst-free bottom-up growth of graphene nanofeatures along with molecular templates on dielectric substrates

Synthesis of graphene nanostructures has been investigated to provide outstanding properties for various applications. Herein, we report molecular thin film-assisted growth of graphene into nanofeatures such as nanoribbons and nanoporous sheets along with a predetermined molecular orientation on dielectric substrates without metal catalysts. A Langmuir-Blodgett (LB) method was used for the formation of the molecularly patterned SiO2 substrates with ferric stearate layers, which acted as a template for the directional growth of the polypyrrole graphene precursor. The nanofeatures of the graphene were determined by the number of ferric stearate layers (e.g., nanoribbons from multiple layers and nanoporous sheets from a single layer). The graphene nanoribbons (GNRs) containing pyrrolic N enriched edges exhibited a p-type semiconducting behavior, whereas the nanoporous graphene sheets containing inhomogeneous pores and graphitic N enriched basal planes exhibited the typical electronic transport of nitrogen-doped graphene. Our approaches provide two central methods for graphene synthesis such as bottom-up and direct processes for the future development of graphene nanoelectronics. © 2016 The Royal Society of Chemistry1331sciescopu