There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The chemistry of graphene oxide is discussed in this critical review Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references)

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The chemistry of graphene oxide

Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.

Large-scale pattern growth of graphene films for stretchable transparent electrodes

A low-temperature solution-based synthetic method was developed for the large-scale synthesis of one-dimensional nanostructures of alkali titanates. Two kinds of highly pure ribbonlike titanates were synthesized successfully in gram quantities without introducing any templates or catalysts. The structure and composition of the titanates were characterized by XRD, HRTEM, and EDX. The chemical and physical properties were preliminarily characterized, and some distinctive properties were observed.

Large-scale synthesis of sodium and potassium titanate nanobelts.

Disclosed are nanoparticles, such as carbon nanotubes or other graphitic sheet materials having extended aromatic surfaces, which are used to deliver active agents such as drugs, labels or dyes (termed for convenience a “drug”) to the interior of cells. The nanoparticles are functionalized by a hydrophilic polymer or adsorption of an amphiphilic molecule to render them stable in suspension. The drug is therefore capable of release in the cell exterior. The drug is more rapidly released at lower pH, as found e.g., in tumor cells. The drug may also be linked to a branched chain hydrophilic polymer, so that each polymer molecule carries more than one drug bound by a cleavable linker.

Supramolecular functionalization of graphitic nanoparticles for drug delivery

3D Ni–Mo electrocatalysts with well-controlled composition, dimensions and nanoporosity are fabricated using a facile and effective electrodeposition technique on Cu foam. These catalysts exhibit enhanced stability and activity for the hydrogen evolution reaction (HER). By optimizing the Ni/Mo ratio, electrodeposition current density, and reaction time, the overpotential for the HER is reduced to 10 mV. The ultrahigh activity and stability of these catalysts are the highest among non-precious-metal electrocatalysts previously reported. The optimized Ni–Mo electrocatalyst has similar overpotential and a much higher current density compared to Pt/C. The improved HER performance is attributed to the Ni/Mo ratio (4:1), the large surface area, and the in situ growth method, which provides a well-defined catalyst. These catalysts are potentially an attractive alternative to Pt in HERs, and therefore represent new technological opportunities for the development of renewable and economic hydrogen production.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/celc.201402180

A 3D Nanoporous Ni–Mo Electrocatalyst with Negligible Overpotential for Alkaline Hydrogen Evolution

Atomic composition tuning and defect engineering are effective strategies toenhance the catalytic performance of multicomponent catalysts by improvingthe synergetic effect; however, it remains challenging to dramatically tune the active sites on multicomponent materials through simultaneous defect engineeringat the atomic scale because of the similarities of the local environment. Herein,using the oxygen evolution reaction (OER) as a probe reaction, we deliberatelyintroduced base-soluble Zn(II) or Al(III) sites into NiFe layered double hydroxides(LDHs), which are one of the best OER catalysts. Then, the Zn(II) or Al(III) siteswere selectively etched to create atomic M(II)/M(III) defects, which dramaticallyenhanced the OER activity. At a current density of 20 mA·cm−2, only 200 mV overpotential was required to generate M(II) defect-rich NiFe LDHs, which is the best NiFe-based OER catalyst reported to date. Density functional theory(DFT) calculations revealed that the creation of dangling Ni–Fe sites (i.e., unsaturated coordinated Ni–Fe sites) by defect engineering of a Ni–O–Fe site at the atomic scale efficiently lowers the Gibbs free energy of the oxygen evolutionprocess. This defect engineering strategy provides new insights into catalysts atthe atomic scale and should be beneficial for the design of a variety of catalysts.

Layered double hydroxides with atomic-scale defects for superior electrocatalysis

Atomically dispersed metal-nitrogen-carbon complexes on carbon supports have drawn tremendous attention in the electrocatalysis fields. Herein, we managed the synthesis of atomically dispersed binary NixFe100-x-NC (x = 0–100) materials with tunable Ni/Fe ratios and investigated their underneath synergy effects for the enhancement of oxygen reduction (ORR) and oxygen evolution reactions (OER). EXAFS revealed the abundant presence of Ni(N3)-Fe(N3)-Cn moieties in Ni66Fe34-NC sample. XPS fine scans indicated deep synergy of dual-site Ni/Fe that favored more charge localized over Ni/Fe sites. Electrochemical measurments showed that the Ni66Fe34-NC delivered a very high ORR half-wave potential (E1/2) of 0.85 V and a low OER overpotential of 467 mV at ∼10 mA cm−2 (Ej=10). The Fe site with Ni neighboring, as suggested by DFT simulations and in-situ Raman, was the responsible site for both ORR and OER. Furthermore, the Ni66Fe34-NC-assembled Zn-air battery afforded large specific power density and extraordinary cycling stability.

Xiaoming Sun

Papers

Large-scale synthesis of sodium and potassium titanate nanobelts.

Supramolecular functionalization of graphitic nanoparticles for drug delivery

A 3D Nanoporous Ni–Mo Electrocatalyst with Negligible Overpotential for Alkaline Hydrogen Evolution

Layered double hydroxides with atomic-scale defects for superior electrocatalysis

Boosting the bifunctional oxygen electrocatalytic performance of atomically dispersed Fe site via atomic Ni neighboring