Showing papers in "Advanced Functional Materials in 2011"

Asymmetric Supercapacitors Based on Graphene/MnO2 and Activated Carbon Nanofiber Electrodes with High Power and Energy Density

Abstract: Asymmetric supercapacitor with high energy density has been developed successfully using graphene/MnO2 composite as positive electrode and activated carbon nanofibers (ACN) as negative electrode in a neutral aqueous Na2SO4 electrolyte. Due to the high capacitances and excellent rate performances of graphene/MnO2 and ACN, as well as the synergistic effects of the two electrodes, such asymmetric cell exhibits superior electrochemical performances. An optimized asymmetric supercapacitor can be cycled reversibly in the voltage range of 0–1.8 V, and exhibits maximum energy density of 51.1 Wh kg−1, which is much higher than that of MnO2//DWNT cell (29.1 Wh kg−1). Additionally, graphene/MnO2//ACN asymmetric supercapacitor exhibits excellent cycling durability, with 97% specific capacitance retained even after 1000 cycles. These encouraging results show great potential in developing energy storage devices with high energy and power densities for practical applications.

Electrochemical Na Insertion and Solid Electrolyte Interphase for Hard-Carbon Electrodes and Application to Na-Ion Batteries

Abstract: Recently, lithium-ion batteries have been attracting more interest for use in automotive applications. Lithium resources are confirmed to be unevenly distributed in South America, and the cost of the lithium raw materials has roughly doubled from the first practical application in 1991 to the present and is increasing due to global demand for lithium-ion accumulators. Since the electrochemical equivalent and standard potential of sodium are the most advantageous after lithium, sodium based energy storage is of great interest to realize lithium-free high energy and high voltage batteries. However, to the best of our knowledge, there have been no successful reports on electrochemical sodium insertion materials for battery applications; the major challenge is the negative electrode and its passivation. In this study, we achieve high capacity and excellent reversibility sodium-insertion performance of hard-carbon and layered NaNi0.5Mn0.5O2 electrodes in propylene carbonate electrolyte solutions. The structural change and passivation for hard-carbon are investigated to study the reversible sodium insertion. The 3-volt secondary Na-ion battery possessing environmental and cost friendliness, Na+-shuttlecock hard-carbon/NaNi0.5Mn0.5O2 cell, demonstrates steady cycling performance as next generation secondary batteries and an alternative to Li-ion batteries.

Highly Conductive PEDOT:PSS Electrode with Optimized Solvent and Thermal Post-Treatment for ITO-Free Organic Solar Cells

Abstract: Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as stand-alone electrodes for organic solar cells have been optimized using a solvent post-treatment method. The treated PEDOT:PSS films show enhanced conductivities up to 1418 S cm−1, accompanied by structural and chemical changes. The effect of the solvent treatment on PEDOT:PSS has been investigated in detail and is shown to cause a reduction of insulating PSS in the conductive polymer layer. Using these optimized electrodes, ITO-free, small molecule organic solar cells with a zinc phthalocyanine (ZnPc):fullerene C60 bulk heterojunction have been produced on glass and PET substrates. The system was further improved by pre-heating the PEDOT:PSS electrodes, which enhanced the power conversion efficiency to the values obtained for solar cells on ITO electrodes. The results show that optimized PEDOT:PSS with solvent and thermal post-treatment can be a very promising electrode material for highly efficient flexible ITO-free organic solar cells.

Nanostructured Tungsten Oxide – Properties, Synthesis, and Applications

Abstract: Metal oxides are the key ingredients for the development of many advanced functional materials and smart devices. Nanostructuring has emerged as one of the best tools to unlock their full potential. Tungsten oxides (WOx) are unique materials that have been rigorously studied for their chromism, photocatalysis, and sensing capabilities. However, they exhibit further important properties and functionalities that have received relatively little attention in the past. This Feature Article presents a general review of nanostructured WOx, their properties, methods of synthesis, and a description of how they can be used in unique ways for different applications. Tungsten oxides (WOx) are unique functional materials that can be obtained in a vast variety of nanostructured forms. This Feature Article presents a comprehensive review on the properties of WOx that goes beyond chromism and photocatalysis, for which they are usually investigated for. This is followed by a survey of their synthesis methods and implementations for different applications.

N-Doped Polypyrrole-Based Porous Carbons for CO2 Capture

Abstract: Highly porous N-doped carbons have been successfully prepared by using KOH as activating agent and polypyrrole (PPy) as carbon precursor. These materials were investigated as sorbents for CO2 capture. The activation process was carried out under severe (KOH/PPy = 4) or mild (KOH/PPy = 2) activation conditions at different temperatures in the 600–800 °C range. Mildly activated carbons have two important characteristics: i) they contain a large number of nitrogen functional groups (up to 10.1 wt% N) identified as pyridonic-N with a small proportion of pyridinic-N groups, and ii) they exhibit, in relation to the carbons prepared with KOH/PPy = 4, narrower micropore sizes. The combination of both of these properties explains the large CO2 adsorption capacities of mildly activated carbon. In particular, a very high CO2 adsorption uptake of 6.2 mmol·g−1 (0 °C) was achieved for porous carbons prepared with KOH/PPy = 2 and 600 °C (1700 m2·g−1, pore size ≈ 1 nm and 10.1 wt% N). Furthermore, we observed that these porous carbons exhibit high CO2 adsorption rates, a good selectivity for CO2-N2 separation and it can be easily regenerated.

Polyester Materials with Superwetting Silicone Nanofilaments for Oil/Water Separation and Selective Oil Absorption

Abstract: Superhydrophobic and superoleophilic polyester materials are successfully prepared by one-step growth of silicone nanofilaments onto the textile via chemical vapor deposition of trichloromethylsilane. The successful growth of silicone nanofilaments is confirmed with scanning electron microscopy, energy-dispersive X-ray analysis, and investigation of the wetting behavior of water on the textile. Even microfibers deeply imbedded inside a woven material could be coated very well with the nanofilaments. The coated textile is water repellant and could only be wetted by liquids of low surface tension. The applications of the coated textile as a membrane for oil/water separation and as a bag for selective oil absorption from water are studied in detail. Owing to the superwetting properties and flexibility of the coated textile, excellent reusability, oil/water separation efficiency, and selective oil absorption capacity are observed, which make it very promising material, e.g., for practical oil absorption.

Battery Performance and Photocatalytic Activity of Mesoporous Anatase TiO 2 Nanospheres/Graphene Composites by Template-Free Self-Assembly

Abstract: [Li, Na; Liu, Gang; Zhen, Chao; Li, Feng; Zhang, Lili; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Li, N (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua RD, Shenyang 110016, Peoples R China;fli@imr.ac.cn cheng@imr.ac.cn

Carbide‐Derived Carbons – From Porous Networks to Nanotubes and Graphene

Abstract: Carbide-derived carbons (CDCs) are a large family of carbon materials derived from carbide precursors that are transformed into pure carbon via physical (e.g., thermal decomposition) or chemical (e.g., halogenation) processes. Structurally, CDC ranges from amorphous carbon to graphite, carbon nanotubes or graphene. For halogenated carbides, a high level of control over the resulting amorphous porous carbon structure is possible by changing the synthesis conditions and carbide precursor. The large number of resulting carbon structures and their tunability enables a wide range of applications, from tribological coatings for ceramics, or selective sorbents, to gas and electrical energy storage. In particular, the application of CDC in supercapacitors has recently attracted much attention. This review paper summarizes key aspects of CDC synthesis, properties, and applications. It is shown that the CDC structure and properties are sensitive to changes of the synthesis parameters. Understanding of processing–structure–properties relationships facilitates tuning of the carbon material to the requirements of a certain application.

Organic D-A-π-A Solar Cell Sensitizers with Improved Stability and Spectral Response

Abstract: A novel concept “D-A-π-A” organic sensitizer instead of traditional D-π-A ones is proposed. Remarkably, the incorporated low bandgap, strong electron-withdrawing unit of benzothiadiazole shows several favorable characteristics in the areas of light-harvesting and efficiency: i) optimized energy levels, resulting in a large responsive range of wavelengths into NIR region; ii) a very small blue-shift in the absorption peak on thin TiO2 films with respect to that in solution; iii) an improvement in the electron distribution of the donor unit to distinctly increase the photo-stability of synthetic intermediates and final sensitizers. The stability and spectral response of indoline dye-based DSSCs are improved by the strong electron-withdrawing benzothiadizole unit in the conjugation bridge. The incident-photon-conversion efficiency of WS-2 reaches nearly 850 nm with a power conversion efficiency as high as 8.7% in liquid electrolyte and 6.6% in ionic-liquid electrolyte.

V2O5 Nanowires with an Intrinsic Peroxidase-Like Activity

Abstract: V2O5 nanowires exhibit an intrinsic catalytic activity towards classical peroxidase substrates such as 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 3,3,5,5,-tetramethylbenzdine (TMB) in the presence of H2O2. These V2O5 nanowires show an optimum reactivity at a pH of 4.0 and the catalytic activity is dependent on the concentration. The Michaelis-Menten kinetics of the ABTS oxidation over these nanowires reveals a behavior similar to that of their natural vanadium-dependent haloperoxidase (V-HPO) counterparts. The V2O5 nanowires mediate the oxidation of ABTS in the presence of H2O2 with a turnover frequency (k(cat)) of 2.5 x 10(3) s(-1). The K-M values of the V2O5 nanowires for ABTS oxidation (0.4 mu M) and for H2O2 (2.9 mu M) at a pH of 4.0 are significantly smaller than those reported for horseradish peroxidases (HRP) and V-HPO indicating a higher affinity of the substrates for the V2O5 nanowire surface. Based on the kinetic parameters and similarity with vanadium-based complexes a mechanism is proposed where an intermediate metastable peroxo complex is formed as the first catalytic step. The nanostructured vanadium-based material can be re-used up to 10 times and retains its catalytic activity in a wide range of organic solvents (up to 90%) making it a promising mimic of peroxidase catalysts.

Sustained Lithium-Storage Performance of Hierarchical, Nanoporous Anatase TiO2 at High Rates: Emphasis on Interfacial Storage Phenomena

Abstract: A hierarchical, nanoporous TiO2 structure is successfully prepared by a simple in situ hydrolysis method. Used as an anode material, it achieves a sustained high lithium storage performance especially at high charge/discharge rates due to its substantially high surface area. The material shows two different major storage modes: a) bulk insertion, and b) pseudo-capacitive interfacial storage, which is responsible for 64% of the total capacity. In order to kinetically emphasize the interfacial storage even further, we cycle the material directly at high rates, giving 302 mA h g−1 and 200 mA h g−1 of fully reversible discharge capacity at charge/discharge rates of 1 C and 5 C with very high cycle stability. We propose an overall view on the different Li insertion mechanisms of the high-surface-area nanoporous TiO2 and emphasize the importance of interfacial storage for electrode applications in Li-ion batteries.

Highly Luminescent Organosilane‐Functionalized Carbon Dots

Abstract: The first use of an organosilane as a coordinating solvent to synthesize highly luminescent (quantum yield = 47%) amorphous carbon dots (CDs) in one minute is reported. The CDs, which benefit from surface methoxysilyl groups, have a diameter of ~0.9 nm and can easily be fabricated into pure CD fluorescent films or monoliths simply by heating them at 80 oC for 24 h. Moreover, the non-water-stable CDs can be further transformed into water-soluble CDs/silica particles, which are biocompatible with and nontoxic to the selected cell lines in our preliminary evaluation. The proposed novel synthetic route is believed to provide an alternative synthesis route and should inspire more research into the origin and applications of CDs, as well as delivering CD-based materials.

Nanograssed Micropyramidal Architectures for Continuous Dropwise Condensation

Abstract: Engineering the dropwise condensation of water on surfaces is critical in a wide range of applications from thermal management (e.g. heat pipes, chip cooling etc.) to water harvesting technologies. Surfaces that enable both effi cient droplet nucleation and droplet self-removal (i.e. droplet departure) are essential to accomplish successful dropwise condensation. However it is extremely challenging to design such surfaces. This is because droplet nucleation requires a wettable surface while droplet departure necessitates a super-hydrophobic surface. Here we report that these confl icting requirements can be satisfi ed using a hierarchical (multiscale) nanograssed micropyramid architecture that yield a gobal superhydrophobicity as well as locally wettable nucleation sites, allowing for ˜65% increase in the drop number density and ˜450% increase in the drop self-removal volume as compared to a superhydrophobic surface with nanostructures alone. Further we fi that synergistic co-operation between the hierarchical structures contributes directly to a continuous process of nucleation, coalescence, departure, and re-nucleation enabling sustained dropwise condensation over prolonged periods. Exploiting such multiscale coupling effects can open up novel and exciting vistas in surface engineering leading to optimal condensation surfaces for high performance electronics cooling and water condenser systems.

High Thermoelectric Performance in PbTe Due to Large Nanoscale Ag2Te Precipitates and La Doping

Abstract: Thermoelectrics are being rapidly developed for waste heat recovery applications, particularly in automobiles, to reduce carbon emissions. PbTe-based materials with small ( 1.5 at 775 K.

Electrochemically Induced High Capacity Displacement Reaction of PEO/MoS2/Graphene Nanocomposites with Lithium

Abstract: MoS2/PEO/graphene composite is successfully prepared and the discharge mechanism of MoS2 as an anode material for Li-ion batteries has been investigated systematically in this work The simultaneous formation of Li2S and Mo at deep discharge depth has been shown for the first time The deposition of Mo metal with Li residing on the defects after the first discharge increases the intrinsic electronic conductivity of the electrode leading to a superior cycling stability for over 185 cycles After the first discharge the amorphous Mo matrix allows a large amount of Li+ ions to repeatedly deposit and being oxidized during cycling while the transition between Li2S and S contribute to the capacity above 20 V The interactions between as-formed Mo and S prevents the dissolution of the intermediate polysulfide thus providing clues to immobilize the soluble species in a Li-S battery Excellent rate performances are achieved in this MoS2/PEO/graphene composite indicating a fast diffusion path of Li+ ions existing not only in the bulk material but also in the interface between the electrode and the electrolyte

One‐Step Electrochemical Synthesis of Graphene/Polyaniline Composite Film and Its Applications

Abstract: This work describes a new one-step large-scale electrochemical synthesis of graphene/polyaniline (PANI) composite films using graphite oxide (GO) and aniline as the starting materials. The size of the film could be controlled by the area of indium tin oxide (ITO). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible absorption spectrum (UV–vis) results demonstrated that the graphene/PANI composite film was successfully synthesized. The obtained graphene/PANI composite film showed large specific area, high conductivity, good biocompatibility, and fast redox properties and had perfect layered and encapsulated structures. Electrochemical experiments indicated that the composite film had high performances and could be widely used in applied electrochemical fields. As a model, horseradish peroxidase (HRP) was entrapped onto the film-modified glassy carbon electrode (GCE) and used to construct a biosensor. The immobilized HRP showed a pair of well-defined redox peaks and high catalytic activity for the reduction of H2O2. Furthermore, the graphene/PANI composite film could be directly used as the supercapacitor electrode. The supercapacitor showed a high specific capacitance of 640 F g−1 with a retention life of 90% after 1000 charge/discharge cycles.

Epitaxial Growth of Branched α-Fe2O3/SnO2 Nano-Heterostructures with Improved Lithium-Ion Battery Performance

Abstract: We report the synthesis of a novel branched nano-heterostructure composed of SnO 2 nanowire stem and α -Fe 2 O 3 nanorod branches by combining a vapour transport deposition and a facile hydrothermal method. The epitaxial relationship between the branch and stem is investigated by high resolution transmission electron microscopy (HRTEM). The SnO 2 nanowire is determined to grow along the [101] direction, enclosed by four side surfaces. The results indicate that distinct crystallographic planes of SnO 2 stem can induce different preferential growth directions of secondary nanorod branches, leading to six-fold symmetry rather than four-fold symmetry. Moreover, as a proof-of-concept demonstration of the function, such α -Fe 2 O 3 /SnO 2 composite material is used as a lithium-ion batteries (LIBs) anode material. Low initial irreversible loss and high reversible capacity are demonstrated, in comparison to both single components. The synergetic effect exerted by SnO 2 and α -Fe 2 O 3 as well as the unique branched structure are probably responsible for the enhanced performance.

Water‐Soluble Poly(N‐isopropylacrylamide)–Graphene Sheets Synthesized via Click Chemistry for Drug Delivery

Abstract: Covalently functionalized graphene sheets are prepared by grafting a well-defined thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) via click chemistry. The PNIPAM-grafted graphene sheets (PNIPAM-GS) consist of about 50% polymer, which endows the sheets with a good solubility and stability in physiological solutions. The PNIPAM-GS exhibits a hydrophilic to hydrophobic phase transition at 33 °C, which is relatively lower than that of a PNIPAM homopolymer because of the interaction between graphene sheets and grafted PNIPAM. Moreover, through π–π stacking and hydrophobic interaction between PNIPAM-GS and an aromatic drug, the PNIPAM-GS is able to load a water-insoluble anticancer drug, camptothecin (CPT), with a superior loading capacity of 15.6 wt-% (0.185 g CPT per g PNIPAM-GS). The in vitro drug release behavior of the PNIPAM-GS-CPT complex is examined both in water and PBS at 37 °C. More importantly, the PNIPAM-GS does not exhibit a practical toxicity and the PNIPAM-GS-CPT complex shows a high potency of killing cancer cells in vitro. The PNIPAM-GS is demonstrated to be an effective vehicle for anticancer drug delivery.

Organic Resistive Memory Devices: Performance Enhancement, Integration, and Advanced Architectures

Abstract: In recent years, organic resistive memory devices in which active organic materials possess at least two stable resistance states have been extensively investigated for their promising memory potential From the perspective of device fabrication, their advantages include simple device structures, low fabrication costs, and printability Furthermore, their exceptional electrical performances such as a nondestructive reading process, nonvolatility, a high ON/OFF ratio, and a fast switching speed meet the requirements for viable memory technologies Full understanding of the underlying physics behind the interesting phenomena is still challenging However, many studies have provided useful insights into scientific and technical issues surrounding organic resistive memory This Feature Article begins with a summary on general characteristics of the materials, device structures, and switching mechanisms used in organic resistive devices Strategies for performance enhancement, integration, and advanced architectures in these devices are also presented, which may open a way toward practically applicable organic memory devices

ph-Dependent Synthesis of Pepsin-Mediated Gold Nanoclusters with Blue Green and Red Fluorescent Emission

Abstract: This report demonstrates the first pH-dependent synthesis of pepsin-mediated gold nanoclusters (AuNCs) with blue-, green-, and red-fluorescent emission from Au5 (Au8), Au13, and Au25, respectively Pepsin is a gastric aspartic proteinase (molecular weight, 34 550 g/mol) that plays an integral role in the digestive process of vertebrates It was found that the pH of the reaction solution was critical in determining the size of Au NCs (ie, the number of gold atoms of AuNCs) Interestingly, enzyme function of pepsin contributes to the formation of these AuNCs The photo-stability of the Au25 (or Au13) NCs is much higher than that of Au5NCs (ie, Au25 ∼ Au13 > > Au5) The pepsin-mediated Au25NCs were also found to be useful as fluorescent sensors for the detection of Pb2+ ions by enhanced fluorescence and the detection of Hg2+ ions by fluorescence quenching Although the detailed formation mechanisms of these AuNCs require further analysis, the synthetic route using proteinase demonstrated here is promising for preparing new types of fluorescent metal nanoclusters for application in catalysis, optics, biological labeling, and sensing

Well-Ordered Large-Pore Mesoporous Anatase TiO2 with Remarkably High Thermal Stability and Improved Crystallinity: Preparation, Characterization, and Photocatalytic Performance

Abstract: Thermally-stable, ordered mesoporous anatase TiO2 with large pore size and high crystallinity has been successfully synthesized through an evaporation-induced self-assembly technique, combined with encircling ethylenediamine (EN) protectors to maintain the liquid crystal mesophase structure of TiO2 primary particles, followed by calcination at higher temperature. The structures of the prepared mesoporous TiO2 are characterized in detail by small-angle and wide-angle X-ray diffraction, Raman spectra, N2 adsorption/desorption isotherms, and transmission electron microscopy. Experimental results indicate that the well-ordered mesoporous structure could be maintained up to 700 °C (M700) and also possesses large pore size (10 nm), high specific BET surface area (122 m2 g−1), and high total pore volumes (0.20 cm3 g−1), which is attributed to encircling EN protectors for maintaining the mesoporous framework against collapsing, inhibiting undesirable grain growth and phase transformation during the calcination process. A possible formation mechanism for the highly stable large-pore mesoporous anatase TiO2 is also proposed here, which could be further confirmed by TG/FT-IR in site analysis and X-ray photoelectron spectroscopy. The obtained mesoporous TiO2 of M700 exhibit better photocatalytic activity than that of Degussa P25 TiO2 for degradation of highly toxic 2,4-dichlorophenol under UV irradiation. This enhancement is attributed to the well-ordered large-pore mesoporous structure, which facilitates mass transport, the large surface area offering more active sites, and high crystallinity that favors the separation of photogenerated electron-hole pairs, confirmed by surface photovoltage spectra.

Fe3O4 Nanoparticles Confined in Mesocellular Carbon Foam for High Performance Anode Materials for Lithium‐Ion Batteries

Abstract: Fe 3 O 4 nanocrystals confi ned in mesocellular carbon foam (MSU-F-C) are synthesized by a “ host‐guest ” approach and tested as an anode material for lithium-ion batteries (LIBs). Briefl y, an iron oxide precursor, Fe(NO 3 ) 3 · 9H 2 O, is impregnated in MSU-F-C having uniform cellular pores ∼ 30 nm in diameter, followed by heat-treatment at 400 ° C for 4 h under Ar. Magnetite Fe 3 O 4 nanocrystals with sizes between 13‐27 nm are then successfully fabricated inside the pores of the MSU-F-C, as confi rmed by transmission electron microscopy (TEM), dark-fi eld scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and nitrogen sorption isotherms. The presence of the carbon most likely allows for reduction of some of the Fe 3 + ions to Fe 2 + ions via a carbothermoreduction process. A Fe 3 O 4 /MSU-F-C nanocomposite with 45 wt% Fe 3 O 4 exhibited a fi rst charge capacity of 1007 mA h g − 1 (Li + extraction) at 0.1 A g − 1 ( ∼ 0.1 C rate) with 111% capacity retention at the 150 th cycle, and retained 37% capacity at 7 A g − 1 ( ∼ 7 C rate). Because the three dimensionally interconnected open pores are larger than the average nanosized Fe 3 O 4 particles, the large volume expansion of Fe 3 O 4 upon Li-insertion is easily accommodated inside the pores, resulting in excellent electrochemical performance as a LIB anode. Furthermore, when an ultrathin Al 2 O 3 layer ( < 4 A) was deposited on the composite anode using atomic layer deposition (ALD), the durability, rate capability and undesirable side reactions are signifi cantly improved.

Bioinspired Tunable Lens with Muscle-Like Electroactive Elastomers

Abstract: Optical lenses with tunable focus are needed in several fields of application, such as consumer electronics, medical diagnostics and optical communications. To address this need, lenses made of smart materials able to respond to mechanical, magnetic, optical, thermal, chemical, electrical or electrochemical stimuli are intensively studied. Here, we report on an electrically tunable lens made of dielectric elastomers, an emerging class of “artificial muscle” materials for actuation. The optical device is inspired by the architecture of the crystalline lens and ciliary muscle of the human eye. It consists of a fluid-filled elastomeric lens integrated with an annular elastomeric actuator working as an artificial muscle. Upon electrical activation, the artificial muscle deforms the lens, so that a relative variation of focal length comparable to that of the human lens is demonstrated. The device combined optical performance with compact size, low weight, fast and silent operation, shock tolerance, no overheating, low power consumption, and possibility of implementation with inexpensive off-the-shelf elastomers. Results show that combing bioinspired design with the unique properties of dielectric elastomers as artificial muscle transducers has the potential to open new perspectives on tunable optics.

Simultaneous Reduction and Surface Functionalization of Graphene Oxide by Mussel‐Inspired Chemistry

Abstract: This study presents a method of simultaneous reduction and surface functionalization of graphene oxide by a one-step poly(norepinephrine) functionalization. The pH-induced aqueous functionalization of graphene oxide by poly(norepinephrine), a catecholamine polymer inspired by the robust adhesion of marine mussels, chemically reduced and functionalized graphene oxide. Moreover, the polymerized norepinephrine (pNor) layer provided multifunctionality on the reduced graphene oxide that includes surface-initiated polymerization and spontaneous metallic nanoparticle formation. This facile surface modifi cation strategy can be a useful platform for graphene-based nano-composites.

Spontaneous Formation of Liquid Crystals in Ultralarge Graphene Oxide Dispersions

Abstract: A novel process is developed to synthesize graphene oxide sheets with an ultralarge size based on a solution-phase method involving pre-exfoliation of graphite flakes. Spontaneous formation of lyotropic nematic liquid crystals is identified upon the addition of the ultralarge graphene oxide sheets in water above a critical concentration of about 0.1 wt%. It is the lowest filler content ever reported for the formation of liquid crystals from any colloid, arising mainly from the ultrahigh aspect ratio of the graphene oxide sheets of over 30 000. It is proposed that the self-assembled brick-like graphene oxide nanostructure can be applied in many areas, such as energy-storage devices and nanocomposites with a high degree of orientation.

Functional Porous Polymers by Emulsion Templating: Recent Advances

Abstract: Porous materials are currently of great scientific as well as technological interest. A strategy that is increasingly employed to prepare highly porous and well defined macroporous polymers is emulsion templating, whereby the droplets of a high internal phase emulsion are used to create pores in a solid material by curing or polymerization of the emulsion continuous phase. This Feature Article covers recent work in this area, focusing on: the preparation of such materials from new precursors and via novel approaches; the chemical modification of existing materials; and the application of the resulting porous structures in diverse areas of science and technology.

Open-Ended, N-Doped Carbon Nanotube-Graphene Hybrid Nanostructures as High-Performance Catalyst Support

Abstract: A hierarchical N-doped carbon nanotube-graphene hybrid nanostructure (NCNT-GHN), in which the graphene layers are distributed inside the CNT inner cavities, was designed to efficiently support noble metal (e.g., PtRu) nanoparticles. Well-dispersed PtRu nanoparticles with diameters of 2–4 nm were immobilized onto these NCNT-GHN supports by a low-temperature chemical reduction method without any pretreatment. Compared to conventional CNTs and commercial catalysts. a much better catalytic performance was achieved by a synergistic effect of the hierarchical structure (graphene-CNT hybrid) and electronic modulation (N-doping) during the methanol electrooxidation reaction. Improved single-cell performances with long-term stability are also demonstrated using NCNT-GHN as catalyst support.

Origin of the Ultra‐nonlinear Switching Kinetics in Oxide‐Based Resistive Switches

Abstract: Experimental pulse length–pulse voltage studies of SrTiO3 memristive cells are reported, which reveal nonlinearities in the switching kinetics of more than nine orders of magnitude. The results are interpreted using an electrothermal 2D finite element model. The nonlinearity arises from a temperature increase in a few-nanometer-thick disc-shaped region at the Ti electrode and a corresponding exponential increase in oxygen-vacancy mobility. The model fully reproduces the experimental data and it provides essential design rules for optimizing the cell concept of nanoionic resistive memories. The model is generic in nature: it is applicable to all those oxides which become n-conducting upon chemical reduction and which show significant ion conductivity at elevated temperatures.

Optimal Size of Nanoparticles for Magnetic Hyperthermia: A Combined Theoretical and Experimental Study

Abstract: Progresses in the prediction and optimization of the heating of magnetic nanoparticles in an alternative magnetic field are highly desirable for their application in magnetic hyperthermia. Here a model system consisting of metallic iron nanoparticles with a size ranging from 5.5 to 28 nm is extensively studied. Different regimes as a function of the nanoparticles size are evidenced: single-domain superparamagnetic, single-domain ferromagnetic and multi-domain. Ferromagnetic single-domain nanoparticles are the best candidates and display the highest specific losses reported in the literature so far (11.2±1 mJ g-1). Measurements are analysed using state-of-the-art analytical formula and numerical simulations of hysteresis loops. Several features expected theoretically are observed for the first time experimentally: i) the correlation between the nanoparticle diameter and their coercive field ii) the correlation between the amplitude of the coercive field and the losses iii) the variation of the optimal size with the amplitude the magnetic field. None of these features are predicted by the linear response theory-generally used to interpret hyperthermia experiments-but are a natural Submitted to 2 2 consequence of theories deriving from the Stoner-Wohlfarth model; they also appear clearly in numerical simulations. These results open the path to a more accurate description, prediction and analysis of magnetic hyperthermia.

The Role of NiO Doping in Reducing the Impact of Humidity on the Performance of SnO2-Based Gas Sensors: Synthesis Strategies, and Phenomenological and Spectroscopic Studies

Abstract: The humidity dependence of the gas-sensing characteristics in SnO2-based sensors, one of the greatest obstacles in gas-sensor applications, is reduced to a negligible level by NiO doping. In a dry atmosphere, undoped hierarchical SnO2 nanostructures prepared by the self-assembly of crystalline nanosheets show a high CO response and a rapid response speed. However, the gas response, response/recovery speeds, and resistance in air are deteriorated or changed significantly in a humid atmosphere. When hierarchical SnO2 nanostructures are doped with 0.64–1.27 wt% NiO, all of the gas-sensing characteristics remain similar, even after changing the atmosphere from a dry to wet one. According to diffuse-reflectance Fourier transform IR measurements, it is found that the most of the water-driven species are predominantly absorbed not by the SnO2 but by the NiO, and thus the electrochemical interaction between the humidity and the SnO2 sensor surface is totally blocked. NiO-doped hierarchical SnO2 sensors exhibit an exceptionally fast response speed (1.6 s), a fast recovery speed (2.8 s) and a superior gas response (Ra/Rg = 2.8 at 50 ppm CO (Ra: resistance in air, Rg: resistance in gas)) even in a 25% r.h. atmosphere. The doping of hierarchical SnO2 nanostructures with NiO is a very-promising approach to reduce the dependence of the gas-sensing characteristics on humidity without sacrificing the high gas response, the ultrafast response and the ultrafast recovery.