Dual Ni/Co-hemin metal-organic framework-PrGO for high-performance asymmetric hybrid supercapacitor

In this study, we conducted direct synthesis of a dual metal-organic framework (Ni/Co-Hemin MOF) on phosphorous-doped reduced graphene oxide (PrGO) to serve as an active material in high-performance asymmetrical supercapacitors. The nanocomposite was utilized as an active material in supercapacitors, exhibiting a noteworthy specific capacitance of 963 C g^-1 at 1.0 A g^-1, along with a high rate capability of 68.3% upon increasing the current density by 20 times, and superior cycling stability. Our comprehensive characterization and control experiments indicated that the improved performance can be attributed to the combined effect of the dual MOF and the presence of phosphorous, influencing the battery-type supercapacitor behavior of GO. Additionally, we fabricated an asymmetric hybrid supercapacitor (AHSC) using Ni/Co-Hemin/PrGO/Nickel foam (NF) and activated carbon (AC)/NF. This AHSC demonstrated a specific capacitance of 281 C g^-1 at 1.0 A g^-1, an operating voltage of 1.80 V, an impressive energy density of 70.3 Wh kg^-1 at a high power density of 0.9 kW kg^-1. Notably, three AHSC devices connected in series successfully powered a clock for approximately 42 min. These findings highlight the potential application of Hemin-based MOFs in advanced supercapacitor systems.

Supercritical Fluid-Facilitated Exfoliation and Processing of 2D Materials

Since the first intercalation of layered silicates by using supercritical CO2 as a processing medium, considerable efforts have been dedicated to intercalating and exfoliating layered two-dimensional (2D) materials in various supercritical fluids (SCFs) to yield single- and few-layer nanosheets. Here, recent work in this area is highlighted. Motivating factors for enhancing exfoliation efficiency and product quality in SCFs, mechanisms for exfoliation and dispersion in SCFs, as well as general metrics applied to assess quality and processability of exfoliated 2D materials are critically discussed. Further, advances in formation and application of 2D material-based composites with assistance from SCFs are presented. These discussions address chemical transformations accompanying SCF processing such as doping, covalent surface modification, and heterostructure formation. Promising features, challenges, and routes to expanding SCF processing techniques are described.

Preparation of a magnetic multiwalled carbon nanotube@polydopamine/zeolitic imidazolate framework-8 composite for magnetic solid-phase extraction of triazole fungicides from environmental water samples

A novel magnetic zinc-based zeolitic imidazolate framework (MMP/ZIF-8) has been prepared using a magnetic multiwalled carbon nanotube@polydopamine nanocomposite as the magnetic core and support. It was then used as an adsorbent for magnetic solid-phase extraction of triazole fungicides from environmental water samples. Successful synthesis of MMP/ZIF-8 was confirmed by material characterization, and the results showed that the synthetic composite has a high Brunauer-Emmett-Teller surface area (141.56 m2 g-1), large total pore volume (0.636 mL g-1), and high superparamagnetism with a saturation magnetization of 44.1 emu g-1. To evaluate the extraction performance of MMP/ZIF-8, the main parameters that affect the extraction efficiency were optimized. Under the optimal conditions, the developed method shows good linearity (R 2 ≥ 0.9915) in the concentration range 1-400 μg L-1. Low limits of detection (0.08-0.27 μg L-1, signal/noise = 3 : 1) and good precision (intraday relative standard deviation ≤ 7.73%, interday relative standard deviation ≤ 9.65%) are also achieved. The developed method was applied for analysis of triazole fungicides in environmental water samples.

Supercritical diethylamine facilitated loading of ultrafine Ru particles on few-layer graphene for solvent-free hydrogenation of levulinic acid to γ-valerolactone

We demonstrate a facile and versatile method to grow Ru particles uniformly on pristine few-layer graphene (FLG) in supercritical diethylamine. In particular, a large number of Ru subnanometer clusters less than 1.0 nm were observed. The particle size can be tuned by manipulating the loading content of Ru and controlling the reaction temperature. The resulting Ru/FLG showed remarkably high activity, selectivity, and reusability towards the hydrogenation of levulinic acid to γ-valerolactone. This method is flexible, and can be extended to the synthesis of a variety of other ultrafine metal particles supported on FLG.

Demonstrating the steady performance of iron oxide composites over 2000 cycles at fast charge-rates for Li-ion batteries

The feasibility of using iron oxides as negative electrode materials for safe high-power Li-ion batteries is demonstrated by the carbon-coated FeOx/CNT composite synthesized by controlled pyrolysis of ferrocene, which delivered a specific capacity retention of 84% (445 mA h g(-1)) after 2000 cycles at 2000 mA g(-1) (4C).

Enhancement of Electrochemical Performance by the Oxygen Vacancies in Hematite as Anode Material for Lithium-Ion Batteries

The application of hematite in lithium-ion batteries (LIBs) has been severely limited because of its poor cycling stability and rate performance. To solve this problem, hematite nanoparticles with oxygen vacancies have been rationally designed by a facile sol-gel method and a sequential carbon-thermic reduction process. Thanks to the existence of oxygen vacancies, the electrochemical performance of the as-obtained hematite nanoparticles is greatly enhancing. When used as the anode material in LIBs, it can deliver a reversible capacity of 1252 mAh g^-1 at 2 C after 400 cycles. Meanwhile, the as-obtained hematite nanoparticles also exhibit excellent rate performance as compared to its counterparts. This method not only provides a new approach for the development of hematite with enhanced electrochemical performance but also sheds new light on the synthesis of other kinds of metal oxides with oxygen vacancies.

Facile, general and template-free construction of monodisperse yolk–shell metal@carbon nanospheres

A versatile, general and template-free strategy for the construction of well-defined yolk–shell metal@carbon nanostructures is described.

In-depth mesocrystal formation analysis of microwave-assisted synthesis of LiMnPO4 nanostructures in organic solution

Formation of LiMnPO₄ mesocrystals via self-assembled subunits employing microwave-assisted synthesis in rac-1-phenylethanol.

Dodecylamine-derived thin carbon-coated single Fe3O4 nanocrystals for advanced lithium ion batteries

Thin carbon-coated single Fe₃O₄ nanocomposite were synthesized by a solvothermal process using dodecylamine. The composite structure can accommodate the large volume change of Fe₃O₄ and thus enabled excellent electrochemical performance.

Controlled Formation of Metal@Al₂O₃ Yolk-Shell Nanostructures with Improved Thermal Stability

Yolk-shell structured nanomaterials have shown interesting potential in different areas due to their unique structural configurations. A successful construction of such a hybrid structure relies not only on the preparation of the core materials, but also on the capability to manipulate the outside wall. Typically, for Al2O3, it has been a tough issue in preparing it into a uniform nanoshell, making the use of Al2O3-based yolk-shell structures a challenging but long-awaited task. Here, in benefit of our success in the controlled formation of Al2O3 nanoshell, we demonstrated that yolk-shell structures with metal confined inside a hollow Al2O3 nanosphere could be successfully achieved. Different metals including Au, Pt, Pd have been demonstrated, forming a typical core@void@shell structure. We showed that the key parameters of the yolk-shell structure such as the shell thickness and the cavity size could be readily tuned. Due to the protection of a surrounding Al2O3 shell, the thermal stability of the interior metal nanoparticles could be substantially improved, resulting in promising performance for the catalytic CO oxidation as revealed by our preliminary test on Au@Al2O3.

Ethanol Gas Detection Using a Yolk-Shell (Core-Shell) α-Fe2O3 Nanospheres as Sensing Material

Three-dimensional (3D) nanostructures of α-Fe2O3 materials, including both hollow sphere-shaped and yolk-shell (core-shell)-shaped, have been successfully synthesized via an environmentally friendly hydrothermal approach. By expertly adjusting the reaction time, the solid, hollow, and yolk-shell shaped α-Fe2O3 can be selectively synthesized. Yolk-shell α-Fe2O3 nanospheres display outer diameters of 350 nm, and the interstitial hollow spaces layer is intimately sandwiched between the inner and outer shell of α-Fe2O3 nanostructures. The possible growth mechanism of the yolk-shell nanostructure is proposed. The results showed that the well-defined bilayer interface effectively enhanced the sensing performance of the α-Fe2O3 nanostructures (i.e., yolk-shell α-Fe2O3@α-Fe2O3), owing predominantly to the unique nanostructure, thus facilitated the transport rate and augmented the adsorption quantity of the target gas molecule under gas detection.