Fig. 6.

a SEM image of the sensor after assembly of SnO₂ nanocrystals onto the MWCNTs (inset is the HRTEM image of a MWCNT uniformly coated with SnO₂ nanocrystals). Reproduced with permission [59]. Copyright 2009, Wiley–VCH. b TEM image of SnO₂ QDs/rGO hybrids; and c sensor responses to 50 ppm of different gas at RT. Reproduced with permission [109]. Copyright 2016, American Chemical Society. d Enlarged TEM image demonstrating the MoS₂ coating of the few-layer graphene scaffold. e Sensor response to 0.5 ppm NO₂ at different microheater temperatures, improving response and recovery time. Reproduced with permission [61]. Copyright 2016, Wiley–VCH. f Sensitivities of NO₂ sensor for the three devices (inset is a schema of the mechanism of NO₂ sensing of rGO-Cu₂O). Reproduced with permission [62]. Copyright 2012, American Chemical Society. g Schema of the sensing mechanism of rGO-PANI hybrids. h NH₃ responses of PANI, rGO and their hybrids at different concentrations. i Repeated NH₃ responses of PANI, rGO and their hybrids at 10 ppm. Reproduced with permission [63]. Copyright 2016, Royal Society Chemistry