Simple Additive-Free Method to Manganese Monoxide Mesocrystals and Their Template Application for the Synthesis of Carbon and Graphitic Hollow Octahedrons

Mesocrystals are of great importance owing to their novel hierarchical microstructures and potential applications. In the present work, a simple additive-free method has been developed for the controllable synthesis of manganese monoxide (MnO) mesocrystals, in which cheap manganese acetate (Mn­(Ac)₂) and ethanol were used as raw materials without involving any other expensive additives such as surfactants, polyelectrolyte, or polymers. The particle size of the resulting MnO mesocrystals is tunable in the range 400–1500 nm by simply altering the concentration of Mn­(Ac)₂ in ethanol. The percentage yield of the octahedral MnO mesocrystals is about 38 wt % with respect to the starting Mn­(Ac)₂. The selective adsorption of oligomers, which was resulted from the polymerization of ethanol, acted as an important role for the mesocrystal formation. A mechanism involving the oriented aggregation of MnO nanoparticle subunits and the subsequent ripening process was proposed. Moreover, for the first time, the as-synthesized MnO mesocrystals were employed as a novel template to fabricate functional materials with an octahedral morphology including MnO@C core/shells, carbon, and graphitic hollow octahedrons. This method shows the importance of mesocrystals not only for the field of material research but also for the application in functional materials synthesis

Teflon: A Decisive Additive in Directly Fabricating Hierarchical Porous Carbon with Network Structure from Natural Leaf

Hierarchically porous carbons are of increasing importance due to their special physicochemical properties. The state-of-the-art approaches for synthesizing hierarchical porous carbon with network structure normally suffer from specific chemistries, rigid reaction conditions, high cost, and multiple tedious steps that limit their large scale production. Herein, we present an interesting insight into the important role of Teflon additive in fabrication of hierarchical porous carbon derived from biomass and, thus, use natural Indicalamus leaves for the first time to successfully synthesize hierarchical porous carbon with a three-dimensional morphology of interconnected nanoparticle units by using a facile and post-treatment-free carbonization technique. It is surprisingly found that the addition of Teflon not only reduces the synthesis procedure by combining post-removal of silica and carbonization in a single step but also plays a decisive role in generating the hierarchical carbonaceous network structure with a specific surface area as high as 1609 m²/g without any extra activation procedures. Benefiting from the combination of well-developed porosity and valuable hierarchical porous morphology, this type of hierarchical porous carbon has demonstrated attractive liquid-phase adsorption properties toward organic molecules

Facile Synthesis of Highly Porous Carbon from Rice Husk

Highly porous carbon materials have attracted great interest for a wide range of important applications. Many examples for their synthesis exist, but these synthetic processes can be quite complex and also very time-consuming. There is still a major challenge to develop a facile yet versatile conceptual approach to produce them. Here, we present an efficient, activation-free, post-treatment-free strategy for the synthesis of highly porous carbon by a simple carbonization of a mixture of rice husk and polytetrafluoroethylene (PTFE) powder. PTFE employed here can <i>in situ</i> generate HF to etch out natural silica during the carbonization treatment of rice husk. This strategy not only reduces the synthesis procedure by combining carbonization and post-removal of silica into a single step but also eliminates completely the usage of hazardous HF or corrosive NaOH or KOH. The as-synthesized carbon materials exhibit a BET surface area as high as 2051 m²/g without any activation treatment, which is about 20 times enhanced in porosity compared to that of the traditional carbon material from rice husk. With the combination of the high porosity and the valuable hierarchical porous structure, the as-prepared porous carbon materials serve well as electrodes for supercapacitive energy storage, including a large capacitance of 317 F/g, good rate performance, and high capacitances per surface area. These findings could provide a new avenue for the facile production of high-performance porous carbon materials with promising applications in various areas

Facile Synthesis of Three-Dimensional Heteroatom-Doped and Hierarchical Egg-Box-Like Carbons Derived from Moringa oleifera Branches for High-Performance Supercapacitors

In this paper, we demonstrate that Moringa oleifera branches, a renewable biomass waste with abundant protein content, can be employed as novel precursor to synthesize three-dimensional heteroatom-doped and hierarchical egg-box-like carbons (HEBLCs) by a facile room-temperature pretreatment and direct pyrolysis process. The as-prepared HEBLCs possess unique egg-box-like frameworks, high surface area, and interconnected porosity as well as the doping of heteroatoms (oxygen and nitrogen), endowing its excellent electrochemical performances (superior capacity, high rate capability, and outstanding cycling stability). Therefore, the resultant HEBLC manifests a maximum specific capacitance of 355 F g^–1 at current density of 0.5 A g^–1 and remarkable rate performance. Moreover, 95% of capacitance retention of HEBLCs can be also achieved after 20 000 charge–discharge cycles at an extremely high current density (20 A g^–1), indicating a prominent cycling stability. Furthermore, the as-assembled HEBLC//HEBLC symmetric supercapacitor displays a superior energy density of 20 Wh kg^–1 in aqueous electrolyte and remarkable capacitance retention (95.6%) after 10 000 charge–discharge cycles. This work provides an environmentally friendly and reliable method to produce higher-valued carbon nanomaterials from renewable biomass wastes for energy storage applications