Figure 13.

(a) Preparation route and the N doping sites of the hierarchical porous carbon materials prepared from crab shells [105]. Reprinted with permission from Ref. [105]. Copyright 2018 Royal Society of Chemistry. (b) Fabrication scheme and SEM image of hollow carbon fiber networks prepared from discarded bamboo chopsticks [106]. Reprinted with permission from Ref. [106]. Copyright 2012 Royal Society of Chemistry. (c) TEM, SEM images and the photograph of the self-supporting sulfur-doped porous carbon sandwich membrane prepared from loofah pulp [107]. Reprinted with permission from Ref. [107]. Copyright 2012 Royal Society of Chemistry.