Preparation of ZTCs via the hard template method. (a) Schematic diagram of the typical zeolite template method. Adapted with permission from ref. [120]. Copyright 2020 American Chemical Society. (b) An open graphene framework model for ZTC [Model-I]. (c) A long-range ordered 3D graphene geometric structure model with more structural heterogeneity for ZTC [Model-II]. Adapted with permission from ref. [118]. Copyright 2018 Elsevier. (d–f) 3D electron-density map of the carbon framework formed after carbon deposition in zeolite FAU at 600°C. (g–i) TEM images and (insets) Fourier diffractions of template-free carbon, generated using a template of La³⁺-ion-exchanged (g) FAU, (h) EMT or (i) beta zeolites. Adapted with permission from ref. [28]. Copyright 2016 Springer Nature.