Muk-Fung Yuen

Nickel–Cobalt Diselenide 3D Mesoporous Nanosheet Networks Supported on Ni Foam: An All‐pH Highly Efficient Integrated Electrocatalyst for Hydrogen Evolution

Novel 3D Ni1-x Cox Se2 mesoporous nanosheet networks with tunable stoichiometry are successfully synthesized on Ni foam (Ni1-x Cox Se2 MNSN/NF with x ranging from 0 to 0.35). The collective effects of special morphological design and electronic structure engineering enable the integrated electrocatalyst to have very high activity for hydrogen evolution reaction (HER) and excellent stability in a wide pH range. Ni0.89 Co0.11 Se2 MNSN/NF is revealed to exhibit an overpotential (η10 ) of 85 mV at -10 mA cm-2 in alkaline medium (pH 14) and η10 of 52 mV in acidic solution (pH 0), which are the best among all selenide-based electrocatalysts reported thus far. In particular, it is shown for the first time that the catalyst can work efficiently in neutral solution (pH 7) with a record η10 of 82 mV for all noble metal-free electrocatalysts ever reported. Based on theoretical calculations, it is further verified that the advanced all-pH HER activity of Ni0.89 Co0.11 Se2 is originated from the enhanced adsorption of both H+ and H2 O induced by the substitutional doping of cobalt at an optimal level. It is believed that the present work provides a valuable route for the design and synthesis of inexpensive and efficient all-pH HER electrocatalysts.

Advances for the colorimetric detection of Hg2+ in aqueous solution

Exposure to mercury ions, even at very low levels, is known to cause a wide variety of diseases in the brain, kidney, and central nervous system, which is an increasing serious problem for human beings and the environment. Accordingly, great efforts have been devoted to the development of colorimetric sensors, which can selectively and conveniently detect Hg2+. In this feature article, to present the readers a better understanding of the specific methods and their mechanisms, we will highlight colorimetric sensors according to their receptors into several categories, including organic dye-based sensors, complex based sensors, polymer based sensors, and nanoparticles based sensors, which are mentioned in the literature and our own work during the recent years.

Fe1−xS/C nanocomposites from sugarcane waste-derived microporous carbon for high-performance lithium ion batteries

We report a novel strategy to collect microporous carbon from disposable sugarcane waste for lithium ion battery (LIB) applications. First boiled in water and ethanol and then calcined, the sugarcane waste successfully transforms into microporous carbon, delivering a specific capacity of 311 mA h g −1 at 0.33C as a LIB anode material. For improved LIB performance, pyrrhotite-5T Fe 1−x S nanoparticles were uniformly dispersed and robustly attached to the scaffold of the microporous carbon using a novel sulfurization method. A remarkably ultrahigh capacity of 1185 mA h g −1 (well beyond the theoretical value by 576 mA h g −1 ) was achieved after 200 charging/discharging cycles at a current density of 100 mA g −1 , suggesting desirable synergetic effects between Fe 1−x S and microporous carbon which lead to a shortened lithium ion transportation path, enhanced conductivity and effective prevention of polysulfide dissolution. Our approach opens a convenient route for mass-producing sustainable, superior LIB electrodes from natural wastes that can substitute commercial graphite.

Plasma-assisted growth and nitrogen doping of graphene films

Microwave plasmas were employed to synthesize single- or double-layer graphene sheets on copper foils using a solid carbon source, polymethylmetacrylate. The utilization of reactive plasmas enables the graphene growth at reduced temperatures as compared to conventional thermal chemical vapor deposition processes. The effects of substrate temperature on graphene quality were studied based on Raman analysis, and a reduction of defects at elevated temperature was observed. Moreover, a facile approach to incorporate nitrogen into graphene by plasma treatment in a nitrogen/hydrogen gas mixture was demonstrated, and most of the nitrogen atoms were verified to be pyridinelike in carbon network.

Bactericidal activity of biomimetic diamond nanocone surfaces

The formation of biofilms on implant surfaces and the subsequent development of medical device-associated infections are difficult to resolve and can cause considerable morbidity to the patient. Over the past decade, there has been growing recognition that physical cues, such as surface topography, can regulate biological responses and possess bactericidal activity. In this study, diamond nanocone-patterned surfaces, representing biomimetic analogs of the naturally bactericidal cicada fly wing, were fabricated using microwave plasma chemical vapor deposition, followed by bias-assisted reactive ion etching. Two structurally distinct nanocone surfaces were produced, characterized, and the bactericidal ability examined. The sharp diamond nanocone features were found to have bactericidal capabilities with the surface possessing the more varying cone dimension, nonuniform array, and decreased density, showing enhanced bactericidal ability over the more uniform, highly dense nanocone surface. Future research will focus on using the fabrication process to tailor surface nanotopographies on clinically relevant materials that promote both effective killing of a broader range of microorganisms and the desired mammalian cell response. This study serves to introduce a technology that may launch a new and innovative direction in the design of biomaterials with capacity to reduce the risk of medical device-associated infections.

Electrical properties and electronic structure of Si-implanted hexagonal boron nitride films

Si ion implantation with a set of ion energies and ion doses was carried out to dope hexagonal boron nitride (hBN) thin films synthesized by radio-frequency magnetron sputtering. Hall effect measurements revealed n-type conduction with a low resistivity of 0.5 Ω cm at room temperature, corresponding to an electron concentration of 2.0 × 1019 cm−3 and a mobility of 0.6 cm2/V s. Temperature-dependent resistivity measurements in a wide temperature range from 50 to 800 K demonstrated two shallow donor levels in the hBN band gap induced by Si doping, which was in consistence with the theoretical calculation by density function theory.

Mesoporous C-coated SnOx nanosheets on copper foil as flexible and binder-free anodes for superior sodium-ion batteries

Carbon-coated binder-free flexible porous SnOx nanosheets (SnO/SnO2 heterogeneous structure) were fabricated and tested as anode materials for Na-ion batteries (NIBs). The novel free-standing and binder-free porous C@SnOx nanosheets were first self-assembled on a Cu substrate via a facile, low-cost anodization method followed by the carbonization treatment. Instrumental analyses show that the porous C@SnOx nanosheets exhibit a remarkably large surface area of 221 m2 g−1, delivering a reversible discharge capacity of 510 mA h g−1 after 100 cycles at 100 mA g−1, demonstrating great potential for Na+ storage applications. The superior electrochemical performance is ascribed to the unique hierarchical porous architecture which greatly facilitates electrolyte penetration and ion transportation with the carbon coating further increasing the electrode conductivity and alleviating strains generated by volume change upon Na+ ion insertion/extraction.

Fabrication of arrays of high-aspect-ratio diamond nanoneedles via maskless ECR-assisted microwave plasma etching

Arrays of high-aspect-ratio diamond nanoneedles display great potential in high-throughput and efficient delivery of drugs and biological molecules to a variety of cells including neurons. In this paper, we introduce a simple technique to fabricate arrays of large-area high-aspect-ratio diamond nanoneedles using an ECR-assisted microwave plasma etching process. To manufacture such structures, a nanodiamond film was deposited on a substrate followed by etching in hydrogen and argon plasma. The feature of the fabricated nanoneedle arrays depends on not only the etching parameters but also the conductivity of the pristine film and substrate. On a silicon substrate, the diamond nanoneedles show a vertical side wall profile with a height of 4–8 μm and a diameter of 70 nm to 1 μm at an optimum bias voltage (−230 V) and pressure (5.8–6.3 mTorr). The aspect ratios can be as high as ~50. On the insulating SiO2/Si wafer substrate, high-aspect-ratio nanoneedles can also be obtained and, attractively, are able to be easily delaminated from the substrate without damaging the nanoneedle structure. To understand the growth mechanism, we studied the etching profiles of the nanostructures over the etching duration. It was found that, when thick nanodiamond films are etched in the plasma on a Mo substrate holder, Mo and β-Mo2C nanoparticles can be self-generated and distribute on the diamond film surface. Such self-masking effects result in the formation of diamond nanoneedle arrays by reactive ion etching without the necessity of any artificial etching mask. This simple and high-throughput fabrication technique for diamond nanoneedle arrays paves the way to their application in intracellular delivery and nano-biotechnology.

Water-enabled crystallization of mesoporous SnO2 as a binder-free electrode for enhanced sodium storage

Water-enabled crystallization of amorphous anodic SnO2 is reported. After low-temperature water soaking for a short period of time (e.g., 60 °C for 2 h), mesoporous rutile SnO2 with a remarkably increased surface area is achieved (nearly 2-fold that of the as-anodized SnO2 and 3.3 times that of SnO2 annealed at high temperature). Closer examination reveals that the water-crystallized SnO2 possesses a hierarchical nanostructure that features 1D nanochannels (e.g., ∼30 nm in diameter) and thin channel walls (e.g., 20 nm thick) that are comprised of tiny nanoparticles (e.g., ∼4 nm big). The water-crystallized SnO2 directly grown on the copper foil can be directly applied as a novel type of binder-free electrode for sodium-ion storage, delivering a high reversible capacity of 514 mA h g−1 after 100 cycles at a current rate of 0.1C.