Three-dimensional (3D) hierarchical reduced graphene oxide (rGO) aerogel with a finely tuned C/O ratio of 11.8 can be used for various applications because of its hih specific surface area (925.27 m(2) g(-1) specific pore volume of 6.46 cm(3) g(-1), and light weight as well as excellent electrical conductivity and electrochemical property. The permselectivity of the 3D rGO aerogels with different C/O ratios was investigated using neutral, positive, and negative redox mediators. The neutral and cationic redox mediators permselectively adsorb within the rGO aerogels via pi-pi and noncovalent electrostatic interactions, respectively. In contrast, the anionic redox mediator does not adsorb within the 3D rGO aerogels due to the repulsion force. The 3D rGO can be used as an absorbent for toxic dye removal such as methylene blue (MB). The in situ electrochemical spectroscopy suggests that the 3D rGO prefers to adsorb the reduced form of MB. For lithium-storage capability, the 3D rGO aerogel is ideal since it can be used as the high-energy anode of lithium batteries. It can provide a reversible specific capacity of over 600 mAh g(-1) at 0.5 A g(-1) and over 1000 mAh g(-1) at 0.1 A g(-1), which are much higher than a theoretical maximum value (372 mAh g(-1)) of graphite.