Graphene with Covalently Grafted Amino Acid as a Route Toward Eco-Friendly and Sustainable Supercapacitors.

Eco-friendly, electrochemically active electrode materials based on covalent graphene derivatives offer enormous potential for energy storage applications. However, covalent grafting of functional groups onto the graphene surface is challenging due to its low reactivity. Here, fluorographene chemistry was employed to graft an arginine moiety via its guanidine group homogeneously on both sides of graphene. By tuning the reaction conditions and adding a non-toxic pore-forming agent, an optimum degree of functionalization and hierarchical porosity was achieved in the material. This tripled the specific surface area and yielded a high capacitance value of approximately 390 F g-1 at a current density of 0.25 A g-1 . The applicability of the electrode material was investigated under typical operating conditions by testing an assembled supercapacitor device for up to 30000 charging/discharging cycles, revealing capacitance retention of 82.3 %. This work enables the preparation of graphene derivatives with covalently grafted amino acids for technologically important applications, such as supercapacitor-based energy storage.

Hierarchical Porous Graphene-Iron Carbide Hybrid Derived From Functionalized Graphene-Based Metal-Organic Gel as Efficient Electrochemical Dopamine Sensor.

A metal-organic gel (MOG) similar in constitution to MIL-100 (Fe) but containing a lower connectivity ligand (5-aminoisophthalate) was integrated with an isophthalate functionalized graphene (IG). The IG acted as a structure-directing templating agent, which also induced conductivity of the material. The MOG@IG was pyrolyzed at 600°C to obtain MGH-600, a hybrid of Fe/Fe3C/FeOx enveloped by graphene. MGH-600 shows a hierarchical pore structure, with micropores of 1.1 nm and a mesopore distribution between 2 and 6 nm, and Brunauer-Emmett-Teller surface area amounts to 216 m2/g. Furthermore, the MGH-600 composite displays magnetic properties, with bulk saturation magnetization value of 130 emu/g at room temperature. The material coated on glassy carbon electrode can distinguish between molecules with the same oxidation potential, such as dopamine in presence of ascorbic acid and revealed a satisfactory limit of detection and limit of quantification (4.39 × 10-7 and 1.33 × 10-6 M, respectively) for the neurotransmitter dopamine.

Chemical Tuning of Specific Capacitance in Functionalized Fluorographene.

Owing to its high surface area and excellent conductivity, graphene is considered an efficient electrode material for supercapacitors. However, its restacking in electrolytes hampers its broader utilization in this field. Covalent graphene functionalization is a promising strategy for providing more efficient electrode materials. The chemistry of fluorographene is particularly attractive as it allows scalable chemical production of useful graphene derivatives. Nevertheless, the influence of chemical composition on the capacitance of graphene derivatives is a largely unexplored field in nanomaterials science, limiting further development of efficient graphene-based electrode materials. In the present study, we obtained well-defined graphene derivatives differing in chemical composition but with similar morphologies by controlling the reaction time of 5-aminoisophthalic acid with fluorographene. The gravimetric specific capacitance ranged from 271 to 391 F g-1 (in 1 M Na2SO4), with the maximum value achieved by a delicate balance between the amount of covalently grafted functional groups and density of the sp2 carbon network governing the conductivity of the material. Molecular dynamics simulations showed that covalent grafting of functional groups with charged and ionophilic/hydrophilic character significantly enhanced the ionic concentration and hydration due to favorable electrostatic interactions among the charged centers and ions/water molecules. Therefore, conductive and hydrophilic graphitic surfaces are important features of graphene-based supercapacitor electrode materials. These findings provide important insights into the role of chemical composition on capacitance and pave the way toward designing more efficient graphene-based supercapacitor electrode materials.

Recycling of typical supercapacitor materials.

A simple, facile and low-cost method for recycling of supercapacitor materials is proposed. This process aims to recover some fundamental components of a used supercapacitor, namely the electrolyte salt tetraethyl ammonium tetrafluoroborate (TEABF4) dissolved in an aprotic organic solvent such as acetonitrile (ACN), the carbonaceous material (activated charcoal, carbon nanotubes) purified, the current collector (aluminium foil) and the separator (paper) for further utilization. The method includes mechanical shredding of the supercapacitor in order to reduce its size, and separation of aluminium foil and paper from the carbonaceous resources containing TEABF4 by sieving. The extraction of TEABF4 from the carbonaceous material was based on its solubility in water and subsequent separation through filtering and distillation. A cyclic voltammetry curve of the recycled carbonaceous material revealed supercapacitor behaviour allowing a potential reutilization. Furthermore, as BF4(-) stemming from TEABF4 can be slowly hydrolysed in an aqueous environment, thus releasing F(-) anions, which are hazardous, we went on to their gradual trapping with calcium acetate and conversion to non-hazardous CaF2.

Poly(ethylene oxide)-b-poly(propylene oxide) amphiphilic block copolymer-mediated growth of silver nanoparticles and their antibacterial behavior.

Silver nanoparticles were grown in self-assembled amphiphilic poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) triblock copolymers in selective solvents. Ternary systems of block copolymer, water, and p-xylene were used, forming a dispersion of water droplets in oil (reverse micellar) as well as binary water/block copolymer solutions. Besides its stabilizing affect, the role of the copolymer as a reducing agent for the metal salt precursors was examined. It was found that block copolymer-enabled reduction, carried out mainly by the PEO blocks, could take place only under particular conditions mostly related to the metal precursor, the block copolymer concentration, and the self-assembled micellar configuration. The effect of the triblock copolymers on growth and stabilization of gold nanoparticles was also examined. The antibacterial effect of the silver nanoparticles was investigated against Escherichia coli cells, and their performance was evaluated through a series of parametrization experiments, including the effect of the metal concentration, stability, activity over time, and dosage, while particular emphasis was given on the role of ions versus nanoparticles on the antibacterial performance.

Catalytic NOx removal by single-wall carbon nanotube-supported Rh nanoparticles.

Single-wall carbon nanotubes functionalized with polyethylene glycol and doped with Rh nanoparticles were prepared and tested as catalyst for NO(x) reduction. Gravimetric adsorption studies were employed to elucidate the mechanism of NO adsorption on the active surface sites and to determine the onset of the desorption of oxygen. These studies provided information about the reaction kinetics and the lifetime of the catalyst, as well as the NO scission onset temperature and abatement rate, thus making possible to predict the conversion and define the optimum reaction conditions for efficient NO removal. Catalytic experiments were performed under different operating conditions and feed compositions, such as under rich operation, in presence of oxygen, and in presence of reducing CO and hydrocarbons. The developed nanostructured catalyst exhibits enhanced activity at lower temperatures in comparison to that reported for other Rh-based catalytic systems, while data about feed composition effects and carbon support depletion provided operating conditions that suppress N(2)O formation and extent the catalyst lifetime.

Magnetic carbon nanotubes with particle-free surfaces and high drug loading capacity.

Open-ended, multi-wall carbon nanotubes (CNTs) with magnetic nanoparticles encapsulated within their graphitic walls (magCNTs) were fabricated by a combined action of templated growth and a ferrofluid catalyst/carbon precursor, and tested as drug hosts. The hybrid nanotubes are stable under extreme pH conditions due to particle protection provided by the graphitic shell. The magCNTs are promising for high capacity drug loading given that the magnetic functionalization did not block any of the active sites available for drug attachment, either from the CNT internal void or on the internal and external surfaces. This is in contrast to typical approaches of loading CNTs with particles that proceed through surface attachment or capillary filling of the tube interior. Additionally, the CNTs exhibit enhanced hydrophilic character, as shown by water adsorption measurements, which make them suitable for biological applications. The morphological and structural characteristics of the hybrid CNTs are evaluated in conjunction to their magnetic properties and ability for drug loading (diaminophenothiazine). The fact that the magnetic functionality is provided from 'inside the walls' can allow for multimode functionalization of the graphitic surfaces and makes the magCNTs promising for targeted therapeutic applications.