Dr Jangmee Lee

Heteroatom doped nanomaterials are reported to be excellent electrodes for energy storage and conversion applications. However, the introduction of these heteroatoms in materials such as carbon nitride is quite challenging owing to the poor thermodynamic stability of these atoms in the carbon matrix. In this report, we demonstrate the single-step approach for the preparation of highly ordered nanoporous carbon oxynitride (O-MCN) materials with tailored pore sizes by employing carbohydrazide as a single C, N, O precursor using nano-templating approach. Experimental characterization of the O-MCN confirms oxygen doping in C-N framework. Density functional theory (DFT) calculations demonstrate that the O-MCN optimized with AB type bilayer structure can adsorb nine Li ions per unit cell with mild Li-ion binding energy value of 5.16 eV. The synthesized O-MCN materials are firstly applied in Li-ion batteries as anode materials. The optimized O-MCN displays 2.5 times higher reversible capacity than that of non-porous g-C3N4 with remarkable stability in the long run in the Li-ion battery.

In this investigation, a hybrid of metal sulfide and carbon nitride (CN) is synthesized by in-situ chemical conversion between metallic species and a single precursor of carbon, nitrogen and sulfur elements through a strong p-d conjugation approach. It is observed that the local chemical alteration in the vicinity of N atom in the CN template triggers the formation of a highly p-conjugated CN system and efficient p-d hybridization at heterointerface. This is accelerated by partial substitution of the Fe atom for Mn ions in the MnS phase which significantly enhances the battery performance, delivering 2031 mA h g-1 after 500 cycles with inverse capacity growth. Via systematic in-depth characterizations, it is found that the gradual increase of Li-ion diffusion coefficients and charge transfer kinetics for repeated cycling is ascribed to the highly dispersed and uniform particles that are confined within the CN template through a strong p-d hybridization.

In the published paper, the affiliations of Eui-Ho Hwang and Woo-Bin Jin were wrongly designated, and the corrected version is shown below. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

The composite formation with a conductive metal sulfide domain can provide an effective methodology to improve the Na-ion electrode functionality of metal oxide. The heat treatment of TiO2(B) under CS2 flow yields an intimately coupled TiO2(B)-TiS2 nanocomposite with intervened TiS2 domain, since the reaction between metal oxide and CS2 leads to the formation of metal sulfide and CO2. The negligible change in lattice parameters and significant enhancement of visible light absorption upon the reaction with CS2 underscore the formation of conductive metal sulfide domains. The resulting TiO2(B)-TiS2 nanocomposites deliver greater discharge capacities with better rate characteristics for electrochemical sodiation-desodiation process than does the pristine TiO2(B). The 23Na magic angle spinning nuclear magnetic resonance analysis clearly demonstrates that the electrode activities of the present nanocomposites rely on the capacitive storage of Na+ ions, and the TiS2 domains in TiO2(B)-TiS2 nanocomposites play a role as mediators for Na+ ions to and from TiO2(B) domains. According to the electrochemical impedance spectroscopy, the reaction with CS2 leads to the significant enhancement of charge transfer kinetics, which is responsible for the accompanying improvement in electrode performance. The present study provides clear evidence for the usefulness in composite formation between the semiconducting metal oxide and metal sulfide in exploring new efficient NIB electrode materials.

Efficient inorganic nanosheet-based electrode materials can be synthesized by the calcination of exfoliated Ti5NbO14 nanosheets under C2H2 flow. While the calcination in Ar atmosphere causes a phase transformation from layered Ti5NbO14 to TiO2 and Nb2O5, employing C2H2 atmosphere leads to the maintenance of the original layered structure of Ti5NbO14 upon the heat-treatment, which is attributable to the stabilization of layered lattice by surface passivation by deposited carbon layer. The resulting carbon@titanoniobate materials show mesoporous house-of-cards-type stacking structure of 2D nanosheets. This carbon@titanoniobate material delivers large discharge capacity of ~320¿mA¿h¿g-1 with excellent cyclability and rate performance, which is much superior to that of carbon-free homologue. The present study clearly demonstrates that the heat-treatment under C2H2 flow provides a simple and effective route to high-performance inorganic nanosheet-based electrode materials.

A novel efficient and safe methodology to sanitize algae in natural water without secondary pollution is developed by fabricating floating graphene-inorganic hybrid films. Two kinds of floating freestanding hybrid films of layered titanate-graphene with efficient algae-killing functionality are fabricated by vacuum-assisted filtration of mixed colloidal suspensions of reduced graphene oxide (rG-O) nanosheets and exfoliated layered titanate nanosheets. Both the titanate nanosheets with lepidocrocite- and trititanate-type structures form homogeneous colloidal mixtures and hybrid freestanding films with rG-O nanosheets. The incorporation of a layered titanate nanosheet enhances the algae-killing activity of the graphene freestanding film, highlighting the beneficial role of photocatalytically-active titanate nanosheet. In comparison to the trititanate nanosheet, the lepidocrocite-type titanate nanosheet is more effective as a building block for enhancing the algae-killing activity of graphene film and for forming a novel nanoblade structure on the surface of the graphene film. The observed high sterilization functionality of the present layered titanate-graphene hybrid films is attributable to both the formation of the novel sharp nanoblade structure and the photocatalytic activity of layered titanate. The present result underscores that hybridization between graphene and photocatalytically-active inorganic nanosheets can provide a powerful way to explore pollution-free recoverable matrix efficient for removing harmful microorganisms in natural water.

Mesoporous hybrid network of reduced graphene oxide (rG-O) and layered MnO<inf>2</inf> nanosheets could act as an efficient immobilization matrix for improving the electrochemical activity of layered double hydroxide (LDH). The control of MnO<inf>2</inf>/rG-O ratio is crucial in optimizing the porous structure and electrical conductivity of the resulting hybrid structure. The immobilization of Co-Al-LDH on hybrid MnO<inf>2</inf>/rG-O network is more effective in enhancing its electrode activity compared with that of on pure rG-O network. The Co-Al-LDH-rG-O-MnO<inf>2</inf> nanohybrid deliveres a greater specific capacitance than does MnO<inf>2</inf>-free Co-Al-LDH-rG-O nanohybrid. The beneficial effect of MnO<inf>2</inf> incorporation on the electrode performance of nanohybrid is more prominent for higher current density and faster scan rate, underscoring the significant enhancement of the electron transport of Co-Al-LDH-rG-O. This is supported by electrochemical impedance spectroscopy. The present study clearly demonstrates the usefulness of the porously assembled hybrid network of graphene and metal oxide nanosheets as an effective platform for exploring efficient LDH-based functional materials.

The 2D nanosheets of layered inorganic solids prepared by soft-chemical exfoliation reaction can be used as effective building blocks for hybridization with inorganic, organic, bio-, and polymer molecules/nanostructures. In comparison with graphene nanosheets, the 2D inorganic nanosheets boast much higher tunability in their chemical composition and physicochemical properties, leading to the creation of unexpected novel functionalities upon hybridization. Despite such unique and intriguing advantages of inorganic nanosheets, there are still only limited numbers of studies regarding the inorganic nanosheet-based hybrid materials. This Feature Article focuses on fundamental aspects of diverse synthetic strategies of the 2D nanosheet-based nanohybrids such as electrostatically derived reassembling, layer-by-layer deposition, crystal growth on the surface sites of nanosheets, and so on. Also, diverse functionalities of these 2D nanohybrid materials are discussed with an emphasis on the energy and environmental applications such as Li-ion batteries, supercapacitors, photocatalysts, fuel cells, and greenhouse gas capture. A prospect for the exploration of novel inorganic 2D nanosheet-based functional materials is provided along with new strategies to optimize the functionality of 2D inorganic nanosheets and their nanohybrids. © 2014 American Chemical Society.

Hybridization with exfoliated two-dimensional (2D) nanosheets provides a very effective and powerful way not only to control the physicochemical properties of hybridized species but also to explore nanocomposites with novel functionalities. Deliberate coupling between the hybridized species is critically important in maximizing the effect of hybridization on the physicochemical properties and functionality of hybridized components. The very small thickness and extremely large surface of exfoliated 2D nanosheets render these materials ideal candidates for achieving a strong coupling with diverse guest species. This Perspective focuses on the unique characteristics of exfoliated 2D nanosheets as building blocks for designing hybrid materials. Several intriguing examples of strong interaction between exfoliated 2D nanosheets and hybridized species are summarized with an emphasis on the effective control of electronic, optical, structural, and morphological characteristics. An outlook on the future research directions is provided along with new strategies to maximize the coupling in the 2D nanosheet-based hybrid materials.

Mesoporous nanocomposites of Pt-reduced graphene oxide (RGO)-layered titanate are synthesized by the reaction of a mixture of exfoliated layered titanate nanosheets, graphene oxide nanosheets, and H<inf>2</inf>PtCl <inf>6</inf> with NaBH<inf>4</inf> to investigate the effect of layered metal oxide nanosheets on the electrocatalyst performance of Pt-RGO nanocomposites. The obtained ternary nanocomposites are composed of a porous stacking assembly of layered titanate/RGO nanosheets with well-dispersed Pt nanocrystals whose particle size becomes smaller with the increase of titanate content. The incorporation of layered titanate nanosheets into the Pt-RGO nanocomposite induces a marked increase of surface area through the frustration of a strong p-p interaction between RGO nanosheets by the intervention of titanate nanosheets. In addition, the incorporation of layered titanate nanosheets gives rise to a remarkable improvement of electrocatalytic activity for oxygen reduction reaction (ORR). Of prime importance is that the present nanocomposites show a more positive onset potential for ORR than commercial Pt/carbon catalysts, underscoring a powerful role of titanate nanosheets in optimizing the electrocatalyst performance of Pt-RGO nanocomposites. This is the first report showing the usefulness of metal oxide nanosheets as an effective additive for enhancing the electrocatalyst performance of platinum nanoparticles. The observed enhancement of electrocatalytic activity upon the addition of titanate nanosheets is attributable to the decrease of Pt crystal size, the increase of surface area, and the increase of surface hydrophilicity. The present findings clearly demonstrate that the incorporation of layered titanate nanosheets is quite effective in improving the electrocatalytic functionality of Pt-RGO nanocomposites. © The Royal Society of Chemistry 2013.

Homogeneously mixed colloidal suspensions of reduced graphene oxide, or RGO, and layered manganate nanosheets have been synthesized by a simple addition of the exfoliated colloid of RGO into that of layered MnO 2. The obtained mixed colloidal suspensions with the RGO/MnO 2 ratio of =0.3 show good colloidal stability without any phase separation and a negatively charged state with a zeta (¿) potential of -30 to -40 mV. The flocculation of these mixed colloidal suspensions with lithium cations yields porous nanocomposites of Li/RGO-layered MnO 2 with high electrochemical activity and a markedly expanded surface area of around 70-100 m 2 g -1. Relative to the Li/RGO and Li/layered MnO 2 nanocomposites (¿116 and ¿167 F g -1), the obtained Li/RGO-layered MnO 2 nanocomposites deliver a larger capacitance of approximately 210 F g -1 with good cyclability of around 95-97 % up to the 1000th cycle, thus indicating the positive effect of hybridization on the electrode performances of RGO and lithium manganate. Also, an electrophoretic deposition of the mixed colloidal suspensions makes it possible to easily fabricate uniform hybrid films composed of graphene and manganese oxide. The obtained films show a distinct electrochemical activity and a homogeneous distribution of RGO and MnO 2. The present experimental findings clearly demonstrate that the utilization of the mixed colloidal suspensions as precursors provides a facile and universal methodology to synthesize various types of graphene/metal oxide hybrid materials. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Strongly coupled nanocomposites of layered titanate and reduced graphene oxide (RGO) are synthesized by electrostatically derived self-assembly between negatively charged RGO nanosheets and positively charged TiO 2 nanosols, which is then followed by a phase transition of the anatase TiO 2 component into layered titanate. The resulting nanocomposite consists of thin 2D nanoplates of lepidocrocite-type layered titanate immobilized on the surface of RGO nanosheets. The composite formation with RGO nanosheets is effective not only in promoting the phase transition of anatase TiO 2 nanosols, but also in improving the thermal stability of the layered titanate, indicating the role of RGO nanosheets as an agent for directing and stabilizing layered structures. The layered-titanate-RGO nanocomposites exhibit remarkably expanded surface area with the formation of micropores and mesopores. The composite formation with RGO nanosheets gives rise to the disappearance of the reflectance edge of layered titanate in the diffuse reflectance UV-vis spectra, indicating a strong electronic coupling between the RGO and layered titanate. The strong electronic correlation between the two components is further evidenced by the visible-light-induced generation of photocurrents after the hybridization with RGO. The layered-titanate-RGO nanocomposite shows a higher activity for the photodegradation of organic molecules than uncomposited layered titanate, underscoring the usefulness of graphene hybridization in improving the photocatalyst performance of layered titanate. The experimental findings presented here clearly demonstrate that the self-assembly of metal oxide nanoparticles with RGO 2D nanosheets is quite effective not only in synthesizing porous metal-oxide-graphene nanocomposites with improved photo-induced functionality, but also in achieving strong electronic coupling between RGO and metal oxides. Strongly coupled nanocomposites of layered titanate and reduced graphene oxide (RGO) are synthesized by self-assembly involving RGO nanosheets and TiO 2 nanosols and the following phase transformation of titania. A strong electronic coupling between the two nanospecies remarkably enhances visible light absorption. The hybridization with RGO improves the photocatalytic activity of the layered titanate for the visible-induced generation of photocurrent and the photodegradation of organic molecules. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.