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Optimizing electrode materials performance and improving the energy density of supercapacitors is a hot research topic. The complex hollow sphere structure material, as a supercapacitor electrode m...

Supercapacitors made by wood scraps are low cost, ecofriendly and accessible. However, there are some problems, such as a small specific surface area and low specific capacitance. How to obtain a high-performance supercapacitor by effectively increasing the specific surface area without affecting the conductivity is still a challenge. In this paper, carbon nanotubes (CNTs) were first synthesized on the inner wall of tracheids in wood carbon slices, which have complete structures and do not require any conductive additives and binder. Nanonickel particles as catalysts were uploaded on the inner wall of each tracheid for growing the CNTs, which can increase the specific surface area from 365.5 to 537.9 m2 g−1, while improving the electrochemical performance to 215.3 F g−1 or 76.5 F cm−3. The energy density of the all-solid-state supercapacitor is 39.8 Wh kg−1, and 96.2% of the capacitance could still be retained after 10,000 charging/discharging cycles. This capacitance value is approximately five times as high as that of activated wood carbon and is equal to or higher than that of supercapacitors based on wood carbon slices with pseudocapacitance materials. CNTs will greatly promote the application of wood scraps as valuable commodities.

Metal-organic frameworks (MOFs) derived carbon based nanocatalysts have been widely used in the environmental field due to high porosity, rich structural diversity/adjustability, and controllable chemical compositions. However, a suitable carrier is very necessary for solving the issues of aggregation and recovery of nanoparticles. Here, waste biomass of sawdust with low cost, abundant resource and special lumen structure, has been used as scalable carrier for Co-MOFs (ZIF-67). Due to the coordination of Co ions with abundant oxygen-containing functional groups of wood, ZIF-67 could be uniformly grown in situ on the surface of poplar sawdust with tracheid skeleton, and a magnetic catalyst possessing micro-nano porous structure has been successfully prepared by further carbonization (Co@N-PC). The catalytic ability of Co@N-PC was studied by activating potassium peroxomonosulfate (PMS) to remove methylene blue (MB). The results indicate the degradation efficiency on MB of Co@N-PC can reach 100% within 30 min which shows excellent catalytic performance. The boosted MB degradation ability mainly results from its unique micro-nano porous structure facilitating efficient material transfer and electron transfer during degradation process. At the same time, a possible catalytic mechanism was proposed. Moreover, Co@N-PC can be easy to separate and reuse from the solution by an external magnet, and performed decent stability. This work not only provides a simple and effective strategy to design large-scale and commercially viable biomass/MOF derived catalysts for water treatment, but also offers a decent alternative for high value utilization of waste biomass.