2D molybdenum disulphide nanosheets incorporated with single heteroatoms for the electrochemical hydrogen evolution reaction.

2D nanosheets give enhanced surface area to volume ratios in particle morphology and they can also provide defined surface sites to disperse foreign atoms. Placing atoms of catalytic interest on 2D nanosheets as Single Atom Catalysts (SAC) represents one of the novel approaches due to their unique but tunable electronic and steric characteristics. Here in this mini-review, we particularly highlight some recent and important developments on heteroatom doped MoS2 nanosheets (SAC-MoS2) as catalysts for the electrochemical hydrogen evolution reaction (HER) from water, which could lead to opening up to a flagship of important renewable technologies in future. It is shown that the nature of dopants, doping positions and the polytypes of MoS2 nanosheets are the determining factors in the overall catalytic abilities of these functionalised nanosheets. This may serve to obtain atomic models which lead to further understanding of the 'metal-support interaction' in catalysis.

Flash microwave-assisted solvothermal (FMS) synthesis of photoactive anatase sub-microspheres with hierarchical porosity.

The synthesis of nanostructured sub-microspheres of TiO2 anatase with hierarchical nano- and mesoporosity was successfully achieved by using an innovative approach that applies the principles of acidic digestion to microwave (MW) solvothermal synthesis. This process, termed flash microwave-assisted solvothermal (FMS) synthesis, facilitates the formation of spherical particles without surfactants or templating agents, exploiting the rapid reaction kinetics engendered by MW heating. Unlike many other MW-assisted solvothermal methods, the application of constant MW power leads to a rapid increase of the autogenous pressure, inducing burst-nucleation of small primary crystallites and subsequent rapid agglomeration into secondary particles, with reaction times reduced to minute-timescales. The use of non-aqueous polar solvents such as ethanol is key to the production of regular spheres with a narrow size distribution, composed of nanocrystallites. Morphology, porosity, specific surface area, phase composition, crystallite size and optical properties of the particles can be controlled via a judicious selection of physical and chemical synthesis parameters, especially precursor choice and acid concentration. The complex structure of the particles leads to surface areas of up to ca. 500 m2 g-1 with intergranular mesoporosity. The as-synthesised FMS particles show increased adsorption under dark conditions and selective de-ethylation of rhodamine B under visible light compared to a commercial photocatalyst (Degussa P25). The photodegradation mechanism hinges on the capacity of the spheres to accept electrons from the photoexcited state of molecules at the particle surface, with the large sphere surface area maximising adsorption capacity and improving the efficiency of the photocatalytic processes. The singular characteristics and properties of the particles could pave the way for further applications in water purification and optoelectronic devices.

Facile One-Pot Synthesis of Bimetallic Co/Mn-MOFs@Rice Husks, and its Carbonization for Supercapacitor Electrodes.

Novel hybrid nanomaterials comprising metal-organic framework compounds carbonised in the presence of biomass material derived from rice husk have been investigated as a new class of sustainable supercapacitor materials for electrochemical energy storage. Specifically, two synthetic routes were employed to grow Co/Mn metal-organic framework compounds in the channels of rice husks, which had been activated previously by heat treatment in air at 400 °C to produce a highly porous network. Pyrolysis of these hybrid materials under nitrogen at 700 °C for 6 h produced metal-containing phases within the nanocarbon, comprising intimate mixtures of Co, MnO and CoMn2O4. The materials thus produced are characterized in detail using a range of physical methods including XRD, electron microscopy and X-ray photoelectron spectroscopy. The synthetic pathway to the metal-organic framework compound is shown to influence significantly the physical properties of the resulting material. Electrochemical evaluation of the materials fabricated revealed that higher specific capacitances were obtained when smaller crystallite sized bimetallic Co/Mn-MOFs were grown inside the rice husks channels compared to larger crystallite sizes. This was in-part due to increased metal oxide loading into the rice husk owing to the smaller crystallite size as well as the increased pseudocapacitance exhibited by the smaller crystallite sizes and increased porosity.

Transition metal atom doping of the basal plane of MoS2 monolayer nanosheets for electrochemical hydrogen evolution.

Surface sites of extensively exposed basal planes of MoS2 monolayer nanosheets, prepared via BuLi exfoliation of MoS2, have been doped with transition metal atoms for the first time to produce 2D monolayer catalysts used for the electrochemical hydrogen evolution reaction (HER). Their HER activity is significantly higher than the corresponding thin and bulk MoS2 layers. HAADF-STEM images show direct proof that single transition metal atoms reside at the surface basal sites, which subtly modify the electro-catalytic activity of the monolayer MoS2, dependent on their electronic and stereospecific properties. It is found that these dopants play an important role in tuning the hydrogen adsorption enthalpies of the exposed surface S atoms and Mo atoms in HER. We report electrochemical testing, characterization and computational modelling and demonstrate that Co can significantly enhance the HER activity by the dominant Co-S interaction, whereas Ni substantially lowers the HER rate due to the Ni-Mo interaction at the same basal site. The two transition metal dopants show opposite doping behavior despite the fact that they are neighbors in the periodic table.

The mechanism of electrochemical reduction of hydrogen peroxide on silver nanoparticles.

The reduction of hydrogen peroxide on a silver nanoparticle modified boron doped diamond electrode in a neutral solution is shown to proceed through a CE mechanism. Hydrogen peroxide undergoes a disproportionation reaction to form oxygen (and water) on the silver surface, creating a diffusion layer of oxygen, which, at a sufficiently biased electrode, is then reduced to hydrogen peroxide. Voltammetry and a full mechanistic simulation are undertaken to confirm the mechanism, showing at short times a dependence of the reductive signal on waiting time prior to voltammetric analysis reflecting the extent of the disproportionation step which occurs prior to voltammetric analysis.

Novel Modifications to Carbon-Based Electrodes to Improve the Electrochemical Detection of Dopamine.

In this work, we describe three simple modifications to carbon electrodes that were found to improve the detection of an exemplar neurotransmitter (dopamine) in the presence of physiological interferents (ascorbic acid and/or uric acid). First, the electro-oxidation of ascorbic acid, as a pretreatment, at boron-doped diamond electrode (BDE) interfaces is studied. This treatment did suppress the detection of ascorbic acid oxidation signal, but only in a manner suitable for single-use detection of high concentrations of dopamine (i.e., > 1 µM). Second, the hydrogenation of BDE by electrochemical cathodic treatment and plasma hydrogenation was investigated. Large cathodic, applied potentials (i.e., > - 5 V) and hydrogen plasma pretreatment of BDE lead to the partial and complete oxidization of ascorbic acid before dopamine, respectively. The consequence at hydrogen-plasma treated BDE is the complete electrochemical separation of these two species without any typical catalytic reactions between the analytes. Third, the modification of glassy carbon electrodes with carbon black nanoparticles is explored. This modification enables the simultaneous detection of ascorbic acid, dopamine and uric acid, significantly enhancing the sensitivity of dopamine. Dopamine was best detected using the unconventional route of detecting 5,6-dihydroxyindole, which is made possible by use of carbon-black nanoparticles. The potential of all three studied modifications to be of electroanalytical use is highlighted throughout this work.

New Routes to Functionalize Carbon Black for Polypropylene Nanocomposites.

Methods for chemical surface functionalization for carbon black (CB) nanoparticles were studied to produce (CB)/polypropylene (PP) nanocomposites with superior electrical and thermal properties. Nanoparticle dispersion is known to directly control the extent to which nanocomposites maximize the unique attributes of their nanoscale fillers. As a result, tailored nanoparticle surface chemistry is a widely utilized method to enhance the interfacial interactions between nanoparticles and polymer matrices, assisting improved filler dispersion. In this work, a rapid chemical functionalization approach using a number of diarylcarbene derivatives, followed by the azo-coupling of substituted diazonium salts, for the covalent introduction of selected functional groups to the CB surface, is reported. Characterization of the modified CB by XPS, TGA, CHN, and ATR-IR collectively confirmed surface functionalization, estimating surface grafting densities of the order of 10(13) and 10(14) molecules/cm(2). Nanocomposites, synthesized by solvent mixing PP with pristine and modified CB, demonstrated macroscopic property changes as a result of the nanoparticle surface functionalization. Pronounced improvements were observed for PP nanocomposites prepared with a dodecyl-terminated diaryl functionalized CB, in which TEM analysis established improved nanofiller dispersion owing to the enhanced CB-PP interfacial interactions in the nanocomposite. Observed dielectric relaxation responses at 20 wt % loading and a reduced percolation threshold realized conductivities of 1.19 × 10(-4) S cm(-1) at 10 wt %, compared to 2.62 × 10(-15) S cm(-1) for pristine CB/PP nanocomposites at the same filler loading. In addition, thermal properties signify an increase in the number of nucleation sites by the raised degree of crystallinity as well as increased melting and crystallization temperatures.

Cellulose-Derived Supercapacitors from the Carbonisation of Filter Paper.

Advanced carbon materials are important for the next-generation of energy storage apparatus, such as electrochemical capacitors. Here, the physical and electrochemical properties of carbonised filter paper (FP) were investigated. FP is comprised of pure cellulose and is a standardised material. After carbonisation at temperatures ranging from 600 to 1700 °C, FP was contaminant-free, containing only carbon and some oxygenated species, and its primary fibre structure was retained (diameter ≈20-40 µm). The observed enhancement in conductivity of the carbonised FP was correlated with the carbonisation temperature. Electrochemical capacitance in the range of ≈1.8-117 F g(-1) was achieved, with FP carbonised at 1500 °C showing the best performance. This high capacitance was stable with >87 % retained after 3000 charge-discharge cycles. These results show that carbonised FP, without the addition of composite materials, exhibits good supercapacitance performance, which competes well with existing electrodes made of carbon-based materials. Furthermore, given the lower cost and renewable source, cellulose-based materials are the more eco-friendly option for energy storage applications.

Surface Modification of Boron-Doped Diamond with Microcrystalline Copper Phthalocyanine: Oxygen Reduction Catalysis.

Surface modification of boron-doped diamond (BDD) with copper phthalocyanine was achieved using a simple and convenient dropcast deposition, giving rise to a microcrystalline structure. Both unmodified and modified BDD electrodes of different surface terminations (namely hydrogen and oxygen) were compared via the electrochemical reduction of oxygen in aqueous solution. A significant lowering of the cathodic overpotential by about 500 mV was observed after modification of hydrogen-terminated (hydrophobic) diamond, while no voltammetric peak was seen on modified oxidised (hydrophilic) diamond, signifying greater interaction between copper phthalocyanine and the hydrogen-terminated BDD. Oxygen reduction was found to undergo a two-electron process on the modified hydrogen-terminated diamond, which was shown to be also active for the reduction of hydrogen peroxide. The lack of a further conversion of the peroxide was attributed to its rapid diffusion away from the triple phase boundary at which the reaction is expected to exclusively occur.

Surface Characterization and in situ Protein Adsorption Studies on Carbene-Modified Polymers.

Polystyrene thin films were functionalized using a facile two-step chemical protocol involving carbene insertion followed by azo-coupling, permitting the introduction of a range of chemical functional groups, including aniline, hexyl, amine, carboxyl, phenyl, phosphonate diester, and ethylene glycol. X-ray photoelectron spectroscopy (XPS) confirmed the success of the two-step chemical modification with a grafting density of at least 1/10th of the typical loading density (10(14)-10(15)) of a self-assembled monolayer (SAM). In situ, real-time quartz crystal microbalance with dissipation (QCM-D) studies show that the dynamics of binding of bovine serum albumin (BSA) are different at each modified surface. Mass, viscoelastic, and kinetic data were analyzed, and compared to cheminformatic descriptors (i.e., c log P, polar surface area) typically used for drug discovery. Results show that functionalities may either resist or adsorb BSA, and uniquely influence its adsorption dynamics. It is concluded that carbene-based surface modification can usefully influence BSA binding dynamics in a manner consistent with, and more robust than, traditional systems based on SAM chemistry.

Interfacial electron-shuttling processes across KolliphorEL monolayer grafted electrodes.

Covalently grafted KolliphorEL (a poly(ethylene glycol)-based transporter molecule for hydrophobic water-insoluble drugs; MW, ca. 2486; diameter, ca. 3 nm) at the surface of a glassy-carbon electrode strongly affects the rate of electron transfer for aqueous redox systems such as Fe(CN)6(3-/4-). XPS data confirm monolayer grafting after electrochemical anodization in pure KolliphorEL. On the basis of voltammetry and impedance measurements, the charge transfer process for the Fe(CN)6(3-/4-) probe molecule is completely blocked after KolliphorEL grafting and in the absence of a "guest". However, in the presence of low concentrations of suitable ferrocene derivatives as guests, mediated electron transfer across the monolayer via a shuttle mechanism is observed. The resulting amplification of the ferrocene electroanalytical signal is investigated systematically and compared for five ferrocene derivatives. The low-concentration electron shuttle efficiency decreases in the following sequence: (dimethylaminomethyl)ferrocene > n-butyl ferrocene > ferrocene dimethanol > ferroceneacetonitrile > ferroceneacetic acid.

Amplified electron transfer at poly-ethylene-glycol (PEG) grafted electrodes.

"Amplified" electron transfer is observed purely based on electron transfer kinetic effects at modified carbon surfaces. An anodic attachment methodology is employed to modify the surface of glassy carbon or boron doped diamond electrodes with poly-ethylene glycols (PEGs) for polymerisation degrees of n = 4.5 to 9.1 (PEG200 to PEG400). Voltammetry and impedance data for aqueous Fe(CN)6(3-/4-) suggest systematic PEG structure-dependent effects on the standard rate constant for heterogeneous electron transfer as a function of PEG deposition conditions and average polymer chain length. Tunnel distance coefficients are polymerisation degree dependent and estimated for shorter PEG chains, ß = 0.17 Å(-1) for aqueous Fe(CN)6(3-/4-), consistent with a diffuse water-PEG interface. In contrast, electron transfer to 1,1'-ferrocene-dimethanol (at 1 mM concentration) appears un-impeded by PEG grafts. Mediated or "amplified" electron transfer to Fe(CN)6(3-/4-) based on the 1,1'-ferrocene-dimethanol redox shuttle is observed for both oxidation and reduction with estimated bimolecular rate constants for homogeneous electron transfer of kforward = 4 × 10(5) mol dm(3) s(-1) and kbackward = 1 × 10(5) mol dm(3) s(-1). Digital simulation analysis suggests an additional resistive component within the PEG graft double layer.

Glutamate biosensors based on diamond and graphene platforms.

l-Glutamate is one of the most important neurotransmitters in the mammalian central nervous system, playing a vital role in many physiological processes and implicated in several neurological disorders, for which monitoring of dynamic levels of extracellular glutamate in the living brain tissues may contribute to medical understanding and treatments. Electrochemical sensing of glutamate has been developed recently mainly using platinum, carbon fibre and carbon nanotube electrodes. In the present work, we explore the fabrication and properties of electrochemical glutamate sensors fabricated on doped chemical vapour deposition diamond electrodes and graphene nanoplatelet structures. The sensors incorporate platinum nanoparticles to catalyse the electrooxidation of hydrogen peroxide, glutamate oxidase to oxidise glutamate, and a layer of poly-phenylenediamine to impart selectivity. The performance of the devices was compared to a similar sensor fabricated on glassy carbon. Both the diamond and the graphene sensor showed very competitive performance compared to the majority of existing electrochemical sensors. The graphene based sensor showed the best performance of the three investigated in terms of sensitivity, linear dynamic range and long term stability, whereas it was found that the diamond device showed the best limit of detection.

Hydrothermal conversion of one-photon-fluorescent poly(4-vinylpyridine) into two-photon-fluorescent carbon nanodots.

A novel two-photon-fluorescent N,O-heteroatom-rich carbon nanomaterial has been synthesized and characterized. The new carbon nanoparticles were produced by hydrothermal conversion from a one-photon-fluorescent poly(4-vinylpyridine) precursor (P4VP). The carbonized particles (cP4VP dots) with nonuniform particle diameter (ranging from sub-6 to 20 nm with some aggregates up to 200 nm) exhibit strong fluorescence properties in different solvents and have also been investigated for applications in cell culture media. The cP4VP dots retain their intrinsic fluorescence in a cellular environment and exhibit an average excited-state lifetime of 2.0 ± 0.9 ns in the cell. The cP4VP dots enter HeLa cells and do not cause significant damage to outer cell membranes. They provide one-photon or two-photon fluorescent synthetic scaffolds for imaging applications and/or drug delivery.

Shape selective plate-form Ga(2)O(3) with strong metal-support interaction to overlying Pd for hydrogenation of CO(2) to CH(3)OH.

A stronger metal-support interaction between Pd and plate-form Ga(2)O(3) nanocrystals covered with the predominant 002 surface than other Ga(2)O(3) surfaces is found, which gives higher methanol yield in catalytic CO(2) hydrogenation.

Plasma electrochemistry: development of a reference electrode material for high temperature plasma.

This report describes the development of a high temperature reference electrode material for gas phase electrochemistry investigations. The electrode is constructed by careful assessment of different metal/metal oxide materials and operational stability in flame electrolyte medium. This will enable reliable dynamic electrochemistry investigations into redox reactions at the solid/gas interface, free of any solvent defined potential window restrictions.

Shape-dependent acidity and photocatalytic activity of Nb2O5 nanocrystals with an active TT (001) surface.

Nb(2)O(5) nanorods and nanospheres were synthesized, and their photocatalytic activity for methylene blue decomposition in water compared. Nb(2)O(5) nanorods clearly displayed higher activity, despite their comparable surface area. With a shape-dependent surface acidity, hydrothermal stability, and high photoactivity, these Nb(2)O(5) nanorods are a unique and exciting nanomaterial for non-classical photocatalytic mineralization of organic compounds in water.

Enhanced TiO2 surface electrochemistry with carbonised layer-by-layer cellulose-PDDA composite films.

In this report we demonstrate a versatile (and potentially low-cost) cellulose nano-whisker-based surface carbonisation method that allows well-defined films of TiO(2) nanoparticles surface-modified with carbon to be obtained. In a layer-by-layer electrostatic deposition process based on TiO(2) nanoparticles, cellulose nano-whiskers, and poly(diallyl-dimethylammonium) or PDDA are employed to control the ratio of surface carbon to TiO(2). Characterisation based on optical, AFM, XRD, and XPS methods is reported. Electrochemical measurements suggest improved access to surface states, dopamine binding at the anatase surface, and surface redox cycling aided by the thin amorphous carbon film in mesoporous TiO(2). In future, the amorphous carbon layer method could be applied for surface processes for a wider range of semiconductor or insulator surfaces.

Permselective properties of polystyrene opal films at diamond electrode surfaces.

The permselective properties of stable opal films formed by polystyrene nanospheres on boron-doped diamond (BDD) electrodes were studied for the first time by means of electrochemical voltammetric and impedance techniques. Films formed from spheres with a diameter above 200 nm are highly porous and have little influence on electrochemical properties. In contrast, porous films formed from 50 nm spheres have a selective influence on the electrochemistry observed, providing an enhancement in the redox peak current for neutral (ferrocenemethanol, dopamine) and positively-charged redox probe mediators (Ru(NH(3))(6)(3+)) and suppressing the current due to a negatively-charged redox species Fe(CN)(6)(4-). This is because the latter is repelled from the film, whereas the former are selectively partitioned within it. Partition coefficients, film permeability and diffusion coefficients of species within the polystyrene opal layer are determined. It is shown that a Langmuir isotherm analysis for adsorption on the polystyrene sphere surface can describe successfully the incorporation of ferrocenemethanol and Ru(NH(3))(6)(3+) within the thin film, with Gibb's free energies (DeltaG(o)) of adsorption in the range of -27 to 28 kJ mol(-1). Apart from influencing the magnitude of the detected electrochemical response, it is also shown the opal film increases the resistance to electrode fouling by the reaction products formed by the oxidation of dopamine. Electrochemical impedance measurements further illustrate the effects of the polystyrene layer.

Carbon nanoparticle surface functionalisation: converting negatively charged sulfonate to positively charged sulfonamide.

The surface functionalities of commercial sulfonate-modified carbon nanoparticles (ca. 9-18 nm diameter, Emperor 2000) have been converted from negatively charged to positively charged via sulfonylchloride formation followed by reaction with amines to give suphonamides. With ethylenediamine, the resulting positively charged carbon nanoparticles exhibit water solubility (in the absence of added electrolyte), a positive zeta-potential, and the ability to assemble into insoluble porous carbon films via layer-by-layer deposition employing alternating positive and negative carbon nanoparticles. Sulfonamide-functionalised carbon nanoparticles are characterised by Raman, AFM, XPS, and voltammetric methods. Stable thin film deposits are formed on 3 mm diameter glassy carbon electrodes and cyclic voltammetry is used to characterise capacitive background currents and the adsorption of the negatively charged redox probe indigo carmine. The Langmuirian binding constant K = 4000 mol(-1)dm(3) is estimated and the number of positively charged binding sites per particle determined as a function of pH.