Freestanding Nitrogen-Doped Carbons with Hierarchical Porosity for Environmental Applications: A Green Templating Route with Bio-Based Precursors.

Powdery hierarchical porous carbons serve as cost-effective, functional materials in various fields, namely energy storage, heterogeneous catalysis, electrochemistry, and water/wastewater treatment. Such powdered activated carbons (PAC) limit new module designs and require further preparation steps, for example, adding polymeric binders, to be shaped into a standalone geometry. Polymeric binders, however, can block PACs' catalytic and active sites and, more importantly, pose the risk of secondary pollution for environmental purposes, especially in the context of clean water supply. This study introduces a novel synthesis method for fabricating freestanding nitrogen-doped carbons with hierarchical porosity using chitosan and sucrose as green precursors. Chitosan supplies nitrogen and acts as a backbone, giving a freestanding geometry to the final product, and sucrose is a carbon-rich precursor. The proposed method employs ice- and hard-templating for macropores and mesopores and combines carbonization and activation steps with no required activating agent. Final freestanding carbons function as adsorbents for removing persistent pollutants, as binder-free electrodes with high specific surface area and capacitive current, and as tubular gas diffusion electrodes for oxygen reduction reactions. These freestanding carbons enable new module designs and can be scaled-up by numbering-up, serving as bio-based functional materials for a wide range of applications involving porous heteroatom-doped carbons.