General template-free strategy for fabricating mesoporous two-dimensional mixed oxide nanosheetsviaself-deconstruction/reconstruction of monodispersed metal glycerate nanospheres

Kaneti, Yusuf Valentino,Salunkhe, Rahul R.,Wulan Septiani, Ni Luh,Young, Christine,Jiang, Xuchuan,He, Yan-Bing,Kang, Yong-Mook,Sugahara, Yoshiyuki,Yamauchi, Yusuke The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.14

<P>In this work, we propose a general template-free strategy for fabricating two-dimensional mesoporous mixed oxide nanosheets, such as metal cobaltites (MCo2O4, M = Ni, Zn) through the self-deconstruction/reconstruction of highly uniform Co-based metal glycerate nanospheres into 2D Co-based metal glycerate/hydroxide nanosheets, induced by the so-called “water treatment” process at room temperature followed by their calcination in air at 260 °C. The proposed ‘self-deconstruction/reconstruction’ strategy is highly advantageous as the resulting 2D metal cobaltite nanosheets possess very high surface areas (150-200 m<SUP>2</SUP>g<SUP>−1</SUP>) and mesoporous features with narrow pore size distribution. In addition, our proposed method also enables the crystallization temperature to achieve pure metal cobaltite phase from the precursor phase to be lowered by 50 °C. Using the 2D mesoporous NiCo2O4nanosheets as a representative sample, we found that they exhibit 6-20 times higher specific capacitance and greatly enhanced capacitance retention compared to the NiCo2O4nanospheres achieved through the direct calcination of the Ni-Co glycerate nanospheres. This highlights another advantage of the proposed strategy for enhancing the electrochemical performance of the mixed oxide products for supercapacitor applications. Furthermore, the asymmetric supercapacitor (ASC) assembled using the 2D NiCo2O4nanosheets//graphene oxide (GO) exhibits a maximum energy density of 38.53 W h kg<SUP>−1</SUP>, while also showing a high capacitance retention of 91% after 2000 cycles at 5 A g<SUP>−1</SUP>. It is expected that the proposed general method may be extended to other transition metal elements for creating 2D mixed oxide nanosheets with enhanced surface areas and improved electrochemical performance.</P>

Hybrid nanoarchitecturing of hierarchical zinc oxide wool-ball-like nanostructures with multi-walled carbon nanotubes for achieving sensitive and selective detection of sulfur dioxide

Septiani, Ni Luh Wulan,Kaneti, Yusuf Valentino,Yuliarto, Brian,Nugraha, Brian,Dipojono, Hermawan Kresno,Takei, Toshiaki,You, Jungmok,Yamauchi, Yusuke Elsevier 2018 Sensors and actuators. B Chemical Vol.261 No.-

<P><B>Abstract</B></P> <P>This work reports a facile glycerol-assisted solvothermal method for synthesizing hierarchical three-dimensional (3D) wool-ball-like zinc oxide (ZnO) nanostructures and their subsequent modifications with multi-walled carbon nanotubes (MWCNTs) as modifiers for achieving sensitive and selective detection of toxic sulfur dioxide (SO<SUB>2</SUB>) gas. Structurally, the as-synthesized 3D wool-ball-like ZnO is assembled of two-dimensional (2D) plate-like structures, which themselves are arranged by numerous small nanoparticles. Furthermore, in this work we observed an interesting new phenomenon in which when a high concentration of MWCNTs is introduced, many small nanorods grew on the surface of the plate-like structures which assemble the 3D wool-ball-like ZnO nanostructures. When evaluated for SO<SUB>2</SUB> detection, the ZnO/MWCNTs (10:1) composite (ZnO:MWCNTs = 10:1) shows a high response of 220.8 to 70 ppm of SO<SUB>2</SUB> gas (approximately three times higher than the response of pure wool-ball-like ZnO) at an optimum operating temperature of 300 °C. Additionally, the composite also displays good stability and selectivity to SO<SUB>2</SUB> with the response to 50 ppm of SO<SUB>2</SUB> being 7–14 times higher than the responses to other tested gases at a similar concentration. The excellent sensing performance of the wool-ball-like ZnO/MWCNTs (10:1) composite is mainly attributed to: (i) the formation of <I>p</I>-<I>n</I> heterojunctions at the ZnO/MWCNTs interfaces, which greatly enhance the resistance changes upon exposure to SO<SUB>2</SUB> gas and (ii) the increased amount of adsorption sites for O<SUB>2</SUB> and SO<SUB>2</SUB> gas molecules owing to the larger surface area of the composite and defects sites generated by the functionalization process of MWCNTs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hierarchical 3D wool-ball-like ZnO nanostructures were synthesized via a solvothermal method. </LI> <LI> 3D wool-ball like ZnO/MWCNT composites with different ratios (3:1, 5:1, and 10:1) were prepared. </LI> <LI> The 3D wool-ball like ZnO/MWCNT composite showed high response and good selectivity to SO<SUB>2</SUB> gas. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Gold nanoparticles supported on mesoporous iron oxide for enhanced CO oxidation reaction

Tanaka, Shunsuke,Lin, Jianjian,Kaneti, Yusuf Valentino,Yusa, Shin-ichi,Jikihara, Yohei,Nakayama, Tsuruo,Zakaria, Mohamed Barakat,Alshehri, Abdulmohsen Ali,You, Jungmok,Hossain, Md. Shahriar A.,Yamauch The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.10

<P>Herein, we report the synthesis of gold (Au)-loaded mesoporous iron oxide (Fe2O3) as a catalyst for both CO and NH3 oxidation. The mesoporous Fe2O3 is firstly prepared using polymeric micelles made of an asymmetric triblock copolymer poly(styrene-<I>b</I>-acrylic acid-<I>b</I>-ethylene glycol) (PS-<I>b</I>-PAA-<I>b</I>-PEG). Owing to its unique porous structure and large surface area (87.0 m<SUP>2</SUP> g<SUP>−1</SUP>), the as-prepared mesoporous Fe2O3 can be loaded with a considerably higher amount of Au nanoparticles (Au NPs) (7.9 wt%) compared to the commercial Fe2O3 powder (0.8 wt%). Following the Au loading, the mesoporous Fe2O3 structure is still well-retained and Au NPs with varying sizes of 3-10 nm are dispersed throughout the mesoporous support. When evaluated for CO oxidation, the Au-loaded mesoporous Fe2O3 catalyst shows up to 20% higher CO conversion efficiency compared to the commercial Au/Fe2O3 catalyst, especially at lower temperatures (25-150 °C), suggesting the promising potential of this catalyst for low-temperature CO oxidation. Furthermore, the Au-loaded mesoporous Fe2O3 catalyst also displays a higher catalytic activity for NH3 oxidation with a respectable conversion efficiency of 37.4% compared to the commercial Au/Fe2O3 catalyst (15.6%) at 200 °C. The significant enhancement in the catalytic performance of the Au-loaded mesoporous Fe2O3 catalyst for both CO and NH3 oxidation may be attributed to the improved dispersion of the Au NPs and enhanced diffusivity of the reactant molecules due to the presence of mesopores and a higher oxygen activation rate contributed by the increased number of active sites, respectively.</P>

A Glucose-Assisted Hydrothermal Reaction for Directly Transforming Metal-Organic Frameworks into Hollow Carbonaceous Materials

Wang, Jie,Luo, Xiliang,Young, Christine,Kim, Jeonghun,Kaneti, Yusuf Valentino,You, Jungmok,Kang, Yong-Mook,Yamauchi, Yusuke,Wu, Kevin C.-W. American Chemical Society 2018 Chemistry of materials Vol.30 No.13

<P>Hollow micro-/nanostructures with controllable shape, size, and composition are an intriguing class of porous materials with a promising potential for various applications. Metal-organic frameworks (MOFs) have been attractive as promising precursors for preparing carbon materials with various kinds of nanoartchitectures owing to the rich variety in their composition, morphology, and structure. Herein, we report a glucose-assisted hydrothermal method for directly transforming MOFs into hollow carbonaceous materials. During the hydrothermal reaction, the MOF particles (zeolitic imidazolate frameworks-8, ZIF-8) are decomposed, which is induced by the acid generated from the hydrolysis of glucose. At the same time, the species released from the decomposed MOF continuously diffuse out and react with the glucose-derived polymers, resulting in the formation of hollow Zn-containing carbonaceous composites. Following calcination at 900 °C and 500 °C under a nitrogen atmosphere, hollow carbon and zinc oxide/carbon (ZnO/C) materials can be obtained, respectively. The obtained ZnO/C materials with hollow interiors exhibit more active sites, which are supported by their superior electrochemical performance for supercapacitor applications. The proposed method in this work provides a pathway for synthesizing a variety of multicompositional inorganic hollow structures from MOFs, which would facilitate their potential use in practical applications.</P> [FIG OMISSION]</BR>

Advanced Functional Carbons and Their Hybrid Nanoarchitectures towards Supercapacitor Applications

Young, C.,Park, T.,Yi, J. W.,Kim, J.,Hossain, M. S.,Kaneti, Y. V.,Yamauchi, Y. WILEY-VCH 2018 CHEM SUS CHEM Vol.11 No.20

Boosting capacitive performance of manganese oxide nanorods by decorating with three-dimensional crushed graphene

Reaz Akter Hossain,Saha Shimul,Roy Chanchal Kumar,Wahab Md Abdul,Will Geoffrey,Amin Mohammed A.,Yamauchi Yusuke,Liu Shude,Kaneti Yusuf Valentino,Hossain Md. Shahriar,Firoz Shakhawat H. 나노기술연구협의회 2022 Nano Convergence Vol.9 No.10

This work reports the rational design of MnOx nanorods on 3D crushed reduced graphene oxide (MnOx/C-rGO) by chemical reduction of Ni-incorporated graphene oxide (GO) followed by chemical etching to remove Ni. The resulting MnOx/C-rGO composite synergistically integrates the electronic properties and geometry structure of MnOx and 3D C-rGO. As a result, MnOx/C-rGO shows a significantly higher specific capacitance (Csp) of 863 F g−1 than MnOx/2D graphene sheets (MnOx/S-rGO) (373 F g−1) and MnOx (200 F g−1) at a current density of 0.2 A g−1. Furthermore, when assembled into symmetric supercapacitors, the MnOx/C-rGO-based device delivers a higher Csp (288 F g−1) than MnOx/S-rGO-based device (75 F g−1) at a current density of 0.3 A g−1. The superior capacitive performance of the MnOx/C-rGO-based symmetric device is attributed to the enlarged accessible surface, reduced lamellar stacking of graphene, and improved ionic transport provided by the 3D architecture of MnOx/C-rGO. In addition, the MnOx/C-rGO-based device exhibits an energy density of 23 Wh kg−1 at a power density of 113 Wkg−1, and long-term cycling stability, demonstrating its promising potential for practical application.