Ho Seok Park

Phase-Controlled Iron Oxide Nanobox Deposited on Hierarchically Structured Graphene Networks for Lithium Ion Storage and Photocatalysis.

The phase control, hierarchical architecturing and hybridization of iron oxide is important for achieving multifunctional capability for many practical applications. Herein, hierarchically structured reduced graphene oxide (hrGO)/α-Fe2O3 and γ-Fe3O4 nanobox hybrids (hrGO/α-Fe and hrGO/γ-Fe NBhs) are synthesized via a one-pot, hydrothermal process and their functionality controlled by the crystalline phases is adapted for energy storage and photocatalysis. The three-dimensionally (3D) macroporous structure of hrGO/α-Fe NBhs is constructed, while α-Fe2O3 nanoboxes (NBs) in a proximate contact with the hrGO surface are simultaneously grown during a hydrothermal treatment. The discrete α-Fe2O3 NBs are uniformly distributed on the surface of the hrGO/α-Fe and confined in the 3D architecture, thereby inhibiting the restacking of rGO. After the subsequent phase transition into γ-Fe3O4, the hierarchical structure and the uniform distribution of NBs are preserved. Despite lower initial capacity, the hrGO/α-Fe NBhs show better rate and cyclic performances than those of commercial rGO/α-Fe due to the uniform distribution of discrete α-Fe2O3 NBs and electronic conductivity, macroporosity, and buffering effect of the hrGO for lithium ion battery anodes. Moreover, the catalytic activity and kinetics of hrGO/γ-Fe NBhs are enhanced for photo-Fenton reaction because of the uniform distribution of discrete γ-Fe3O4 NBs on the 3D hierarchical architecture.

Self-healable mussel-mimetic nanocomposite hydrogel based on catechol-containing polyaspartamide and graphene oxide.

Stimuli-responsive and self-healing materials have a wide range of potential uses, and some significant research has focused on cross-linking of hydrogel materials by means of reversible coordination bonding. The resulting materials, however, tend to have poor mechanical properties with pronounced weakness and brittleness. In this work, we present a novel mussel-inspired graphene oxide(GO)-containing hydrogel based on modified polyaspartamide with γ-amino butyric acid (GABA), 3.4-dihydroxyphenethylamine (DOPA), and ethanolamine (EA), termed PolyAspAm(GABA/DOPA/EA). Here both GO nanosheets and boric acid (H3BO3) act as cross-linkers, interacting with polar functional groups of the PolyAspAm(GABA/DOPA/EA). Compared to PolyAspAm(GABA/DOPA/EA)/B(3+) gel without GO, the same containing 5wt% of GO yielded a 10-fold increase in both the storage and loss moduli, as well as 134% and 104% increases in the tensile and compressive strengths, respectively. In addition, the GO-containing polyaspartamide hydrogel exhibited rapid and autonomous self-healing property. Two types of bonding, boron-catechol coordination and strong hydrogen bonding interactions between PolyAspAm side chains and GO nanosheets, would impart the enhanced mechanical strength and good reversible gelation behavior upon pH stimulation to the hydrogel, making this biocompatible hydrogel a promising soft matter for biomedical applications.

The confinement of SnO2 nanocrystals into 3D RGO architectures for improved rate and cyclic performance of LIB anode

In this study, we demonstrate the synthesis of a composite with SnO2 nanoparticles anchored on three-dimensional (3D) reduced graphene oxide (RGO) as an anode for Li ion batteries (LIBs). SnO2 nanoparticles were uniformly deposited on the surface of RGO sheets and the resulting RGO–SnO2 architecture had an interconnected hierarchical structure. This hierarchical RGO–SnO2 architecture exhibited outstanding electrochemical performance with a high reversible capacity of 810 mAh g−1 at 0.1 A g−1 and a high rate capacity of 210 mAh g−1 at 2 A g−1. Moreover, this architecture achieves 99% capacity retention even after 150 cycles at 0.1 A g−1. The improved performance of the RGO–SnO2 architecture is attributed to the uniform dispersion of SnO2 nanoparticles and the 3D macroporous continuity, which afford a highly accessible area, easy ion accessibility, a short ion diffusion length, and rapid mass and charge transport. The composite described here is practically useful in the development of high-energy-density anode materials for LIBs.

Sorption behavior of slightly reduced, three-dimensionally macroporous graphene oxides for physical loading of oils and organic solvents

High pollutant-loading capacities (up to 319 times its own weight) are achieved by three-dimensional (3D) macroporous, slightly reduced graphene oxide (srGO) sorbents, which are prepared through ice-templating and consecutive thermal reduction. The reduction of the srGO is readily controlled by heating time under a mild condition (at 1 10–2 Torr and 200°C). The saturated sorption capacity of the hydrophilic srGO sorbent (thermally reduced for 1 h) could not be improved further even though the samples were reduced for 10 h to achieve the hydrophobic surface. The large meso- and macroporosity of the srGO sorbent, which is achieved by removing the residual water and the hydroxyl groups, is crucial for achieving the enhanced capacity. In particular, a systematic study on absorption parameters indicates that the open porosity of the 3D srGO sorbents significantly contributes to the physical loading of oils and organic solvents on the hydrophilic surface. Therefore, this study provides insight into the absorption behavior of highly macroporous graphene-based macrostructures and hence paves the way to development of promising next-generation sorbents for removal of oils and organic solvent pollutants.

Ultralight and compressible mussel-inspired dopamine-conjugated poly(aspartic acid)/Fe3+-multifunctionalized graphene aerogel

The reduced graphene oxide (rGO) aerogels are particularly attractive owing to their ultralight-weight, high surface area and interconnected macroporosity for energy storage applications. However, pure rGO aerogels are generally weak and brittle to limit their practical applications. To overcome this drawback, a small amount of synthetic dopamine-conjugated poly(aspartic acid) was mixed with graphene oxide to fabricate ultralight rGO aerogels with high porosity and mechanical integrity via hydrothermal reactions at 80xa0°C and freeze-drying process. In addition, the Fe3+ ionic species was chosen for an additional cross-linker to further strengthen the ultralight poly(aspartic acid/dopamine) functionalized rGO aerogel, abbreviation for PAAD/rGO, through the coordination bonding between Fe3+ and carboxylic acid or catechol groups of both polymer and rGO sheets at pH 9 (PAAD/rGO-Fe❾). The hybrid electrodes of PAAD/rGO-Fe❾ showed the reversible transformation of the Fe3+ tris-catecholate complexes into mono-catecholate promoting Quinone (Q)-hydroquinone (QH2) in 1.0xa0molxa0L−1 H2SO4 electrolyte, thus delivering a high specific capacitance of 276.4xa0Fxa0g−1 at 0.5xa0Axa0g−1 and capacitance retention of 88.2% after 5000 cycles. Moreover, this compressible aerogel provided high strength with 150xa0kPa without noticeable structural fracture after 80% compression and repeated deformation processes suggesting applications in energy storage and absorption.