where 𝑛(𝐶) ≈ 28.7 𝜇𝑚𝑜𝑙 (here we made assumption that the contribution of H element to mass of GOM is negligible). Compared with the intercalated cations (0.2 µmol), the number of carbon atoms are ~144 times more than cations. This means that very limited number of cations existed in the nanochannels, indicating weak the steric hindrance of cations.