Si-doped graphene nanosheets (SiGNSs) were constructed via high temperature annealing of the precursor mixture (the graphene oxide and tetraethoxysilane) in a sealed glass ampoule. Si-doped graphene nanosheets annealed at 400 ◦C (SiGNS-400) exhibited excellent NOx sensing ability with a high response value (21.5%–50 ppm of NO2), a fast response (126s), a fast recovery (378s), a broad detectable concentration range (300 ppm~18 ppb) and outstanding selectivity. The doped Si atoms play a key role in NOx sensing. The sensor pre-
pared by SiGNS-400 detected NOx not only in environments with a single harmful gas but also in complex en-
vironments containing several harmful gases. The detectable concentration range of the SiGNS-400 sensor decreased with increasing operating temperature.