Preparation and Lithium-Ion Capacitance Performance of Nitrogen and Sulfur Co-Doped Carbon Nanosheets with Limited Space via the Vermiculite Template Method

Nitrogen and sulfur co-doped graphene-like carbon nanosheets (CNSs) with a two-dimensional structure are prepared by using methylene blue as a carbon source and expanded vermiculite as a template. After static negative pressure adsorption, high-temperature calcination, and etching in a vacuum oven, they are embedded in the limited space of the vermiculite template. The addition of an appropriate number of mixed elements can improve the performance of a battery. Via scanning electron microscopy, it is found that the prepared nitrogen-sulfur-co-doped carbon nanosheets exhibit a thin yarn shape. The XPS results show that there are four elements of C, N, O, and S in the carbon materials (CNS-600, CNS-700, CNS-800, CNS-900) prepared at different temperatures, and the N atom content shows a gradually decreasing trend. It is mainly doped into a graphene-like network in four ways (graphite nitrogen, pyridine nitrogen, pyrrole nitrogen, and pyridine nitrogen oxide), while the S element shows an increasing trend, mainly in the form of thiophene S and sulfur, which is covalently linked to oxygen. The results show that CNS-700 has a discharge-specific capacity of 460 mAh/g at a current density of 0.1 A/g, and it can still maintain a specific capacity of 200 mAh/g at a current density of 2 A/g. The assembled lithium-ion capacitor has excellent energy density and power density, with a maximum power density of 20,000 W/kg.

Bottom-up Synthesis of Nanosheets at Various Interfaces

Nanostructured materials with high aspect ratios have been widely studied for their unique properties. In particular, nanosheets have safety, dispersibility, and nanosized effects, and nanosheets with exceptionally small thicknesses exhibit unique properties. For non-exfoliable materials, the bottom-up nanosheet growth using various interfaces as templates have been investigated. This review article presents the synthesis of nanosheets at the interfaces and layered structure; it explains the features of each interface type, its advantages, and its uniqueness. The interfaces work as templates for nanosheet synthesis. We can easily use the liquid-liquid and gas-liquid interfaces as the templates; however, the thickness of nanosheets usually becomes thick because it allows materials to grow in thickness. The solid-gas and solid-liquid interfaces can prevent nanosheets from growing in thickness. However, the removal of template solids is required after the synthesis. The layered structures of various materials provide two-dimensional reaction fields between the layers. These methods have high versatility, and the nanosheets synthesized by these methods are thin. Finally, this review examines the key challenges and opportunities associated with scalable nanosheet synthesis methods for industrial production.

Bitumen and asphaltene derived nanoporous carbon and nickel oxide/carbon composites for supercapacitor electrodes

Asphaltenes from bitumen are abundant resource to be transformed into carbon as promising supercapacitor electrodes, while there is a lack of understanding the impact from different fractions of bitumen and asphaltenes, as well as the presence of transition metals. Here, nanoporous carbon was synthesized from bitumen, hexane-insoluble asphaltenes and N,N-dimethylformamide (DMF)-fractionated asphaltenes by using Mg(OH)₂ nanoplates as the template with in-situ KOH activation, and used as an supercapacitor electrode material. All of the carbon exhibited large surface area (1500-2200 m² g^-1) with a distribution of micro and mesopores except for that derived from the DMF-soluble asphaltenes. The pyrolysis of asphaltenes resulted in the formation of nickel oxide/carbon composite (NiO/C), which demonstrated high capacitance of 380 F g^-1 at 1 A g^-1 discharge current resulting from the pseudocapacitance of NiO and the electrochemical double layer capacitance of the carbon. The NiO/C composite obtained from the DMF-insoluble portion had low NiO content which led to lower capacitance. Meanwhile, the specific capacitance of NiO/C composite from the DMF-soluble part was lower than the unfractionated asphaltene due to the higher NiO content resulting in lower conductivity. Therefore asphaltenes derived from nickel-rich crude bitumen is suitable for the synthesis of nanoporous NiO/C composite material with high capacitance.

Simplified synthesis of silver nanoparticles on graphene oxide and their applications in electrocatalysis

In this work the possibility of synthesizing in situ silver nanoparticles (AgNPs) on graphene oxide (GO) surfaces without commonly used additional reducing or alkalizing agents or increased temperature was investigated. Using diverse microscopic (atomic force microscopy, transmission electron microscopy) and spectroscopic methods, it was proved that very small AgNPs were formed on GO by simple incubation for 2 h in a mixture of GO dispersion and AgNO₃. The prepared nanomaterial (GO_Ag) was also assessed using electrochemical methods, and it exhibited electrochemical behavior similar to the GO_Ag nanomaterial prepared with a help of citric acid as a reducing agent. Furthermore, it was found that (i) the electrochemical reduction of the GO_Ag on the electrode surface decreased the voltammetric response even though this step increased the surface conductivity and (ii) GO_Ag can be employed for the sensing of chlorides with a detection limit of 79 μM and a linear range of up to 10 mM. It could also provide an electrochemical response toward the chloroacetanilide herbicide metazachlor. Hence, the reducing capabilities of GO were proved to be applicable for in situ synthesis of metal nanoparticles with the highest possible simplification, and the as-prepared nanomaterials could be employed for fabrication of different electrochemical sensors.

Facile synthesis of hollow hierarchical Ni@C nanocomposites with well-dispersed high-loading Ni nanoparticles embedded in carbon for reduction of 4-nitrophenol

Hollow hierarchical Ni@C nanocomposites with highly dispersed Ni nanoparticles (NPs) embedded in well-graphitized carbon matrix have been synthesized by solid-state pyrolysis of simple, well-defined organic–inorganic layered nickel hydroxide. The integration of highly dispersed Ni NPs, high Ni NPs content (up to ∼88.01 wt%), well-graphitized carbon as well as strong Ni/carbon interaction in the Ni@C make them display excellent catalytic activity and stable magnetic recyclability toward the reduction of 4-nitrophenol by NaBH₄.

Hollow hierarchical Ni@C nanocomposites with highly dispersed Ni nanoparticles (NPs) embedded in well-graphitized carbon matrix have been synthesized by solid-state pyrolysis of simple, well-defined organic–inorganic layered nickel hydroxide.