Chemically Modified Graphene Nanosheets for Highly Efficient Energy Storage and Conversion Systems

NanochemistryDue to the resource exhaustion and environmental issues, the increasing energy demands have stimulated intense research on alternative energy storage and conversion systems with high efficiency, low cost, and environmental benignity. Graphene, two-dimensional sp2-hybridized carbon structure, has recently attracted enormous interest for promising electrode materials due to its superior properties such as high electrical conductivity, large surface area, and chemical and mechanical stability. Chemical exfoliation method has been the most popular protocols to achieving stable suspensions in various solvents. This approach is a very efficient and scalable; however, it unavoidably introduces the surface defects, which hamper the conductivity of the resulting graphene sheets. Nevertheless, chemically exfoliated graphene nanosheet provides an ideal single-atom-thick substrate for growth of functional nanomaterials to render them electrochemically active and electrically conductive properties due to many oxygen functional groups on the surface of graphene nanosheets. In addition, it can readily adding the other groups to graphene oxide nanosheets using various chemical reactions that provides for either covalent or non-covalent attachment to the resulting chemically modified graphenes. Such approaches, which add functionality to groups that are already present on the graphene oxide, render graphene oxide a more versatile precursor for a wide range of applications. In this study, we synthesized diverse graphene-based nanocomposites by chemical functionalization and demonstrated for energy storage and conversion systems with enhanced electrochemical performance.ope

Physical Activity Recognition based on Rotated Acceleration Data using Orientation Filter

The purpose of the study was to examine the accuracy of physical activity (PA) classification algorithms using a rotational analysis

Spatial Clustering based Meteorological Fields Construction for Regional Vulnerability Assessment

Chemical accidents have affected the social-environmental system. For the regional vulnerability assessment, which is the baseline work to assess the impact on the environment, a meteorological field is needed to determine how chemicals from multiple adjacent companies are propagated. In this study, we present the method of meteorological field based on the spatial cluster which is the main component of vulnerability assessment on regional chemical accident scenario. To integrate spatially dense chemical companies into a cluster, we adopt spatial clustering algorithms. Experiment result shows that DBSCAN-based approach reduces 80.5% total area of the meteorological field against brute-force algorithm, and shows good performance on the average of the overlap ratio, and utility ratio for clustering results

Covalent functionalization based heteroatom doped graphene nanosheet as a metal-free electrocatalyst for oxygen reduction reaction

Oxygen reduction reaction (ORR) is an important reaction in energy conversion systems such as fuel cells and metal-air batteries. Carbon nanomaterials doped with heteroatoms are highly attractive materials for use as electrocatalysts by virtue of their excellent electrocatalytic activity, high conductivity, and large surface area. This study reports the synthesis of highly efficient electrocatalysts based on heteroatom-doped graphene nanosheets prepared through covalent functionalization using various small organic molecules and a subsequent thermal treatment. A series of nitrogen-doped reduced graphene oxide (NRGOn) nanosheets exhibited varying degrees and configurations of nitrogen atoms within the graphitic framework depending on the type of precursors used. On the basis of the rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) experiments, NRGO3, with a high degree of pyridinic-N content, displayed the desired one-step, quasi-four-electron transfer pathway during ORR, similar to commercial Pt/C. We also demonstrated the potential of covalent functionalization of sulfur and boron-doped graphene nanosheets.close4

Mussel-inspired nitrogen-doped graphene nanosheet supported manganese oxide nanowires as highly efficient electrocatalysts for oxygen reduction reaction

Electrocatalysts for oxygen reduction reaction (ORR) play a vital role in determining the performance of fuel cells and metal-air batteries. Carbon nanomaterials doped with heteroatoms are highly attractive by virtue of their excellent electrocatalytic activity, high conductivity and large surface area. This study reports the synthesis of a highly efficient electrocatalyst based on nitrogen-doped (N-doped) graphene nanosheets (NG) using mussel-inspired dopamine as a nitrogen source. Dopamine undergoes oxidative polymerization that can functionalize the surface of graphene and also introduces nitrogen atoms onto the graphene nanosheets upon pyrolysis. N-doping not only leads to improved catalytic activity, but it also provides anchoring sites for the growth of electroactive amorphous manganese oxide nanowires on the graphene nanosheets (NG/MnOx). On the basis of a Koutecky-Levich plot, it is found that the hybrid NG/MnOx catalyst exhibits excellent catalytic activity with a direct four-electron pathway in ORR. Furthermore, the hybrid electrocatalyst possesses superior stability and gives a low yield of peroxide compared to commercial Pt/C catalysts. This suggests that the unique combination of an N-doped graphene support and amorphous MnOx nanowires can synergistically improve the catalytic activity for ORR.close1

Ionic liquid modified graphene nanosheets anchoring manganese oxide nanoparticles as efficient electrocatalysts for Zn-air batteries

Ionic liquid (IL) modified reduced graphene oxide (rGO-IL) nanosheets anchoring manganese oxide (Mn3O4) are synthesized via a facile solution-based growth mechanism and applied to a Zn-air battery as an effective electrocatalyst for the oxygen reduction reaction (ORR). In this study, the IL moiety in these composites increases not only the conductivity of the system, but also the electrocatalytic activity compared to pristine rGO, together with the synergic effect of facilitating the ORR with the intrinsic catalytic activity of Mn3O4. Based on the Koutecky-Levich plot, we suggest that the ORR pathway of these composites is tunable with the relative amount of Mn3O4 nanoparticles supported onto the graphene sheets; for example, the ORR mechanism of the system with a lower Mn3O4 (19.2%) nanoparticle content is similar to a Pt/C electrode, i.e., a one-step, quasi-4-electron transfer, unlike that with a higher Mn3O4 (52.5%) content, which undergoes a classical two-step, 2-electron pathway. We also demonstrate the potential of these hybrid rGO-IL/Mn3O4 nanoparticles as efficient catalysts for the ORR in the Zn-air battery with a maximum peak power density of 120 mW cm(-2); a higher performance than that from commercial cathode catalysts.close584

Versatile double hydrophilic block copolymer: dual role as synthetic nanoreactor and ionic and electronic conduction layer for ruthenium oxide nanoparticle supercapacitors

The facile synthetic approach to ruthenium oxide nanoparticles using double hydrophilic block copolymers (DHBCs) and their application toward the supercapacitor are presented. Nanostructured hydrous ruthenium oxide (RuO2) nanoparticles are synthesized using a double hydrophilic block copolymer of poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA) as a template, forming a micelle upon addition of the ruthenium precursor, which then transformed into RuO2 nanoparticles of controlled dimension with reducing agents. The synthesized hydrous RuO2 center dot xH(2)O nanoparticles are very stable for several months without any noticeable aggregates. Furthermore, we have demonstrated their utility in application as supercapacitors. Through annealing at 400 degrees C, we found that the crystallinity of RuO2 nanoparticles increases considerably with a simultaneous transformation of the surrounding double hydrophilic block copolymer into ionic and electronic conducting buffer layers atop RuO2 nanoparticles, which contribute to the significant enhancement of the overall specific capacitance from 106 to 962 F g(-1) at 10 mV s(-1). The RuO2 nanoparticles annealed at 400 degrees C also exhibit a superior retention of capacitance over 1000 cycles at very high charge-discharge rates at 20 A g(-1). We envision that the double hydrophilic block copolymer will provide a facile and general tool in creating functional nanostructures with controlled dimensions that are useful for various applications.close9

Facile synthesis of hybrid graphene and carbon nanotubes as a metal-free electrocatalyst with active dual interfaces for efficient oxygen reduction reaction

We report metal-free electrocatalysts to enhance utilization of dissolved and gaseous oxygen during oxygen reduction reaction (ORR). Proper balance between hydrophobicity and hydrophilicity is achieved using reduced graphene oxide (rGO) and polyelectrolyte functionalized multiwalled carbon nanotubes (pMWNTs). In this unique architecture, both two- and three-phase reactions in ORR can be maximized with a quasi-four-electron pathway.close6

Drug delivery by a self-assembled DNA tetrahedron for overcoming drug resistance in breast cancer cells

A DNA tetrahedron is employed for efficient delivery of doxorubicin into drug-resistant breast cancer cells. The drug delivered with the DNA nanoconstruct is considerably cytotoxic, whereas free doxorubicin is virtually non-cytotoxic for the drug-resistant cells. Thus, the DNA tetrahedron, made of the inherently natural and biocompatible material, can be a good candidate for the drug carrier to overcome MDR in cancer cells.close11