“…A widely used method is to replace a carbon atom with the doping atom in the graphene sheet. Currently, different doped-graphene sheets have been explored as toxic gas sensors, replacing a carbon atom by a dopant atom [ 55 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 ]. Around 30 elements of the periodic table have been explored for use as doping materials, with N being the most studied element dopant due to its similar atomic radii with C (see Table 4 ).…”