Long-range selective transport of anions and cations in graphene oxide membranes, causing selective crystallization on the macroscale

Monoatomic nanosheets can form 2-dimensional channels with tunable chemical properties, for ion storage and filtering applications. Here, we demonstrate transport of K+, Na+, and Li+ cations and F- and Cl- anions on the centimeter scale in graphene oxide membranes (GOMs), triggered by an electric bias. Besides ion transport, the GOM channels foster also the aggregation of the selected ions in salt crystals, whose composition is not the same as that of the pristine salt present in solution, highlighting the difference between the chemical environment in the 2D channels and in bulk solutions

Electrical release of dopamine and levodopa mediated by amphiphilic \u3b2-cyclodextrins immobilized on polycrystalline gold

Vesicles of cationic amphiphilic \u3b2-cyclodextrins have been immobilized on polycrystalline gold by exploiting the chemical affinity between their amino groups and Au atoms. The presence of cyclodextrins has been widely investigated by means of AFM, XPS, kelvin probe and electrochemical measurements. This multi-functional coating confers distinct electrochemical features such as pH-dependent behavior and partial/total blocking properties towards electro-active species. The host-guest properties of \u3b2-cyclodextrins have been successfully exploited in order to trap drugs, like dopamine and levodopa. The further release of these drugs was successfully achieved by providing specific electrical stimuli. This proof-of-concept led us to fabricate an electronic device (i.e. an organic transistor) capable of dispensing both dopamine and levodopa in aqueous solution

Allylic and Allenylic Dearomatization of Indoles promoted by Graphene Oxide via Covalent Grafting Activation Mode

The site‐selective allylative and allenylative dearomatization of indoles with alcohols is performed under carbocatalytic regime in the presence of graphene oxide (GO, 10 wt% loading) as the promoter. Metal‐free conditions, absence of stoichiometric additive, environmentally friendly conditions (H2O/CH3CN, 55 \ub0C, 6 h), broad substrate scope (33 examples, yield up to 92%) and excellent site‐ and stereoselectivity characterize the present methodology. Moreover, a covalent activation model exerted by GO functionalities was corroborated by spectroscopic, experimental and computational evidences. Recovering and regeneration of the GO catalyst via simple acidic treatment was also documented

A robust, modular approach to produce graphene-MO X multilayer foams as electrodes for Li-ion batteries

Major breakthroughs in batteries would require the development of new composite electrode materials, with a precisely controlled nanoscale architecture. However, composites used for energy storage are typically a disordered bulk mixture of different materials, or simple coatings of one material onto another. We demonstrate here a new technique to create complex hierarchical electrodes made of multilayers of vertically aligned nanowalls of hematite (Fe 2 O 3 ) alternated with horizontal spacers of reduced graphene oxide (RGO), all deposited on a 3D, conductive graphene foam. The RGO nanosheets act as porous spacers, current collectors and protection against delamination of the hematite. The multilayer composite, formed by up to 7 different layers, can be used with no further processing as an anode in Li-ion batteries, with a specific capacity of up to 1175 μA h cm -2 and a capacity retention of 84% after 1000 cycles. Our coating strategy gives improved cyclability and rate capacity compared to conventional bulk materials. Our production method is ideally suited to assemble an arbitrary number of organic-inorganic materials in an arbitrary number of layers

Systematic study of the correlation between surface chemistry, conductivity and electrocatalytic properties of graphene oxide nanosheets

A main advantage of graphene oxide (GO) over other materials is the high tunability of its surface functional groups and of its electric conductivity. However, the complex chemical composition of GO renders difficult to unravel the correlation between structural and electric properties. Here, we use a combination of electron spectroscopy and electrochemistry to correlate the surface chemistry of GO to its electrical conductivity and electrocatalytic properties with respect to two molecules of high biological interest: β-nicotinamide adenine dinucleotide (NADH) and vitamin C. We demonstrate that the electrocatalytic properties of the material are due to hydroxyl, carbonyl and carboxyl groups residues that, even if already present on pristine GO, become electroactive only upon GO reduction. The results of this study demonstrate the advantages in the use of GO in amperometric biosensing and in enzymatic biofuel cells: it allows the oxidation of the target molecules at low potential values, with a sensitivity >15 times higher with respect to standard, carbon-based electrode materials. Finally, we demonstrate that the right amount of chemical groups to achieve such high performance can be obtained also by direct electrochemical exfoliation of bulk graphite, without passing through GO production, thus rendering this approach suitable for cheap, large-scale applications

A robust, modular approach to produce graphene\u2013MOx multilayer foams as electrodes for Li-ion batteries

Major breakthroughs in batteries would require the development of new composite electrode materials, with a precisely controlled nanoscale architecture. However, composites used for energy storage are typically a disordered bulk mixture of different materials, or simple coatings of one material onto another. We demonstrate here a new technique to create complex hierarchical electrodes made of multilayers of vertically aligned nanowalls of hematite (Fe2O3) alternated with horizontal spacers of reduced graphene oxide (RGO), all deposited on a 3D, conductive graphene foam. The RGO nanosheets act as porous spacers, current collectors and protection against delamination of the hematite. The multilayer composite, formed by up to 7 different layers, can be used with no further processing as an anode in Li-ion batteries, with a specific capacity of up to 1175 \u3bcA h cm 122 and a capacity retention of 84% after 1000 cycles. Our coating strategy gives improved cyclability and rate capacity compared to conventional bulk materials. Our production method is ideally suited to assemble an arbitrary number of organic\u2013inorganic materials in an arbitrary number of layers

Ultrafast Charge Carrier Dynamics in Vanadium-Modified TiO2 Thin Films and Its Relation to Their Photoelectrocatalytic Efficiency for Water Splitting

Light absorption and charge transport in oxide semiconductors can be tuned by the introduction, during deposition, of a small quantity of foreign elements, leading to the improvement of the photoelectrocatalytic performance. In this work, both unmodified and vanadium-modified TiO2 thin films deposited by radio-frequency magnetron sputtering are investigated as photoanodes for photoelectrochemical water splitting. Following a structural characterization by X-ray diffraction, atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, photoelectrocatalysis is discussed based on ultrafast transient absorbance spectroscopy measurements. In particular, three different pump wavelengths from UV to the visible range are used (300, 390, and 530 nm) in order to cover the relevant photoactive spectral range of modified TiO2. Incident photon-to-current conversion efficiency spectra show that incorporation of vanadium in TiO2 extends water splitting in the visible range up to approximate to 530 nm, a significant improvement compared to unmodified TiO2 that is active only in the UV range less than or similar to 390 nm. However, transient absorbance spectroscopy clearly reveals that vanadium accelerates electron-hole recombination upon UV irradiation, resulting in a lower photon-to-current conversion efficiency in the UV spectral range with respect to unmodified TiO2. The new photoelectrocatalytic activity in the visible range is attributed to a V-induced introduction of intragap levels at approximate to 2.2 eV below the bottom of the conduction band. This is confirmed by long-living transient signals due to electrons photoexcited into the conduction band after visible light (530 nm) pulses. The remaining holes migrate to the semiconductor-electrolyte interface where they are captured by long-lived traps and eventually promote water oxidation under visible light

Controllable Coating Graphene Oxide and Silanes on Cu Particles as Dual Protection for Anticorrosion

Although two-dimensional nanosheets like graphene could be ideal atomic coatings to prevent corrosion, it is\ua0still controversial whether they are actually effective due to the\ua0presence of parasitic effects such as galvanic corrosion. Here, we\ua0reported a reduced graphene oxide (RGO) coating strategy to\ua0protect sintered Cu metal powders from corrosion by addressing\ua0the common galvanic corrosion issue of graphene. A layer of silane\ua0molecules, namely, (3-aminopropyl)triethoxysilane (APTES), is\ua0deposited between the surface of Cu particles and the graphene oxide (GO), acting as a primer to enhance adhesion and as an\ua0insulating interlayer to prevent the direct contact of the Cu with conductive RGO, mitigating the galvanic corrosion. Due to this\ua0core−shell coating, the RGO uniformly distributes in the Cu matrix after sintering, avoiding aggregation of RGO, which takes place\ua0in conventional GO-Cu composites. The dual coating of GO and silane results in bulk samples with improved anticorrosion\ua0properties, as demonstrated by galvanostatic polarization tests using Tafel analysis. Our development not only provides an efficient\ua0synthesis method to controllably coat GO on the surface of Cu but also suggests an alternative strategy to avoid the galvanic\ua0corrosion effect of graphene to improve the anticorrosion performance of metal

Graphene oxide–polysulfone filters for tap water purification, obtained by fast microwave oven treatment

The availability of clean, pure water is a major challenge for the future of our society. 2-Dimensional nanosheets of GO seem promising as nanoporous adsorbent or filters for water purification; however, their processing in macroscopic filters is challenging, and their cost\ua0vs.\ua0standard polymer filters is too high. Here, we describe a novel approach to combine graphene oxide (GO) sheets with commercial polysulfone (PSU) membranes for improved removal of organic contaminants from water. The adsorption physics of contaminants on the PSU-GO composite follows Langmuir and Brunauer–Emmett–Teller (BET) models, with partial swelling and intercalation of molecules in between the GO layers. Such a mechanism, well-known in layered clays, has not been reported previously for graphene or GO. Our approach requires minimal amounts of GO, deposited directly on the surface of the polymer, followed by stabilization using microwaves or heat. The purification efficiency of the PSU-GO composites is significantly improved\ua0vs.\ua0benchmark commercial PSU, as demonstrated by the removal of two model contaminants, rhodamine B and ofloxacin. The excellent stability of the composite is confirmed by extensive (100 hours) filtration tests in commercial water cartridges

Glycerol to lactic acid conversion by NHC-stabilized iridium nanoparticles

Hydrogen reduction of an Ir(I) complex featured by a bulky N-heterocyclic carbene (NHC) ligand in dichloromethane gave small-sized (1.8 nm) Ir nanoparticles (NPs) decorated with NHC ligands (IrNHC). 1,4-Dioxane solutions of the latter particles were successfully applied to convert glycerol into lactic acid in the presence of NaOH (i.e. 1 mol equivalent with respect to glycerol). IrNHC showed an atom-related TOF value of almost 104 h−1, an almost exclusive formation of liquid reaction products, a high selectivity for lactic acid (93.0%) and a complete recyclability in air atmosphere. Attempts to synthesize analogous NHC-stabilized Ir NPs on a high surface area carbon support (CK) by reducing the same Ir(I) precursor, supported onto CK, prior to the hydrogen reduction in water, gave almost naked CK-supported Ir NPs (1.4 nm). Their catalytic activity tested for the same reaction in water as reaction medium, exhibited much lower catalytic activity (4 7 103 h−1), a lower percentage of liquid reaction products (i.e. 27.0% of the converted glycerol) and a lower selectivity for lactic acid compared to IrNHC