Shunsuke Tanaka

Fabrication of an MOF-derived heteroatom-doped Co/CoO/carbon hybrid with superior sodium storage performance for sodium-ion batteries

Metal–organic frameworks (MOFs) have gained significant attention as precursors for the fabrication of porous hybrid materials due to their highly controllable composition, structure and pore size. However, at present, MOF-derived materials have rarely been investigated as anode materials for sodium-ion batteries. In this work, we report the fabrication of a Ni-doped Co/CoO/N-doped carbon (NC) hybrid using bimetallic Ni–Co-ZIF as the starting precursor. The resulting Ni-doped Co/CoO/NC hybrid is highly microporous with a high specific surface area of 552 m2 g−1. When employed as an anode material for sodium-ion batteries, the Ni-doped Co/CoO/NC hybrid exhibited both good rate performance with a high discharge capacity of 218 mA h g−1 at a high current density of 500 mA g−1 and good cycling stability, as a high discharge capacity of 218.7 mA h g−1 can be retained after 100 cycles at 500 mA g−1, corresponding to a high capacity retention of 87.5%. The excellent electrochemical performance of the Ni-doped Co/CoO/NC hybrid for SIBs may be attributed to the synergistic effects of various factors, including: (i) the presence of a carbon matrix which provides protection against aggregation and pulverization during sodiation/desodiation; (ii) the highly microporous nature along with the presence of a few mesopores which facilitates better insertion/de-insertion of Na+ ions; (iii) the Ni-doping which introduces defect sites into the atomic structure of CoO via partial substitution, thus enhancing the conductivity of the cobalt oxide (CoO) component and hence, the overall hybrid material, and (iv) the N-doping which promotes a faster migration speed of sodium ions (Na+) across the carbon layer by creating defect sites, thereby improving the conductivity of the carbon frameworks in the hybrid material.

Prussian blue derived iron oxide nanoparticles wrapped in graphene oxide sheets for electrochemical supercapacitors

Hybrid materials have shown promising potential for energy storage applications, such as supercapacitors due to the combined properties or advantages of two (or more) individual constituents. In this work, we report the fabrication of a new composite which combines graphene oxide (GO) sheets with Prussian blue (PB) nanoparticles, which act as a precursor for iron oxide (IO). The GO/PB composite precursors with different GOu2006:u2006PB ratios can be successfully converted into nanoporous GO/IO hybrid composites through a thermal treatment in air at 400 °C. In the resulting GO/IO composites, the GO sheets are efficiently spaced due to the insertion of IO layers. Interestingly, the GO/IO hybrid (GOu2006:u2006PB ratio = 25u2006:u200675) exhibits a higher surface area of 120 m2 g−1 compared to pure GO (34.9 m2 g−1) and IO (93.1 m2 g−1) samples. When employed as a supercapacitor electrode, the GO/IO hybrid (prepared from GOu2006:u2006PB = 75u2006:u200625) showed a higher specific capacitance of 91 F g−1 at a scan rate of 20 mV s−1, compared to pure GO (81 F g−1) and pure IO (47 F g−1). The enhanced electrochemical performance of the GO/IO hybrid electrode may be attributed to the insertion of IO nanoparticles in between the GO layers which creates a well-spaced electrical transportation path for electrolytes and ions, whilst also enabling easy access for the electrolytes to the whole electrode surface. Furthermore, the presence of GO in the GO/IO hybrid composite helps to lower the resistivity of IO and increase the specific capacitance value of the hybrid, as a result of the improved conductivity.

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

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-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG). Owing to its unique porous structure and large surface area (87.0 m2 g-1), 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.

Porous nanozymes: the peroxidase-mimetic activity of mesoporous iron oxide for the colorimetric and electrochemical detection of global DNA methylation

Nanomaterials (nanozymes) with peroxidase-mimetic activity have been widely used in biosensing platforms as low-cost, relatively stable and prevailing alternatives to natural enzymes. Herein, we report on the synthesis and application of the peroxidase-mimetic activity of mesoporous iron oxide (MIO) for the detection of global DNA methylation in colorectal cancer cell lines. The target DNA was extracted and denatured to get ssDNA followed by direct adsorption onto the surface of a bare screen-printed gold electrode (SPGE). A 5-methylcytosine antibody (5mC) functionalized nanomaterial (MIO-5mC) was then used to recognise the methylcytosine groups present on the SPGE. The MIO-5mC conjugates catalyse the TMB solution in the presence of hydrogen peroxide to give the colorimetric (i.e., naked-eye observation) and electrochemical detection of DNA methylation. The assay could successfully detect as low as 10% difference in the global DNA methylation level in synthetic samples and cell lines with good reproducibility and specificity (%RSD = <5%, for n = 3). This strategy avoids the use of natural enzyme horseradish peroxidase (HRP), traditional PCR based amplification and bisulfite treatment steps that are generally used in many conventional DNA methylation assays. We envisage that our assay could be a low-cost platform with great potential for genome-wide DNA methylation analysis in point-of-care applications.

Room temperature carbon monoxide oxidation based on two-dimensional gold-loaded mesoporous iron oxide nanoflakes

In this work, we fabricate a highly effective catalyst for carbon monoxide oxidation based on gold-loaded mesoporous maghemite nanoflakes which exhibit nearly 100% CO conversion and a very high specific activity of 8.41 molCO gAu-1 h-1 at room temperature. Such excellent catalytic activity is promoted by the synergistic cooperation of their high surface area, large pore volume, and mesoporous structure.