(A) Possible mechanisms of NO _x photocatalytic purification [36]; (B) calculated reaction pathway and structures of initial states, transitional states, and final states for NO photooxidation by on CN and Au@CN [40]; (C) design diagram for localized excess electrons that decrease the reaction activation energies and increase the photocatalysis efficiency [41]; (D) DFT calculated adsorption energy and bond length of several major intermediate adsorption products (upward for CN and downward for Sr intercalated CN), all lengths are given in Å [42]; (E) detailed mechanism of photocatalytic NO oxidation on -OH intercalated BiOI [43]; (F) diagram of the reduction of the surface by NO and e⁻ [44]; (G) proposed schematic diagram for the separation and transfer of photogenerated carriers and the photocatalytic process over the insulator–semiconductor heterojunction [45].