Light-assisted recovery for a highly-sensitive NO2 sensor based on RGO-CeO2 hybrids

The poor sensing performance of reduced graphene oxide (RGO) and difficult recovery of RGO-based gas sensors have long been the challenging issues to overcome. In this work, the characteristic properties of cerium oxide (CeO2), including strong absorption in the ultraviolet (UV) range, polymorphism and mixed valence have been taken into consideration to construct RGO-CeO2 hybrid heterostructure for NO2 gas monitoring as well as recovery enhancement by UV light. Small CeO2 nanocrystals (∼3 nm) have been facile anchored onto RGO nanosheets by a controllable solvothermal method to obtain the RGO-CeO2 hybrids. Through the changing of the precipitant, the size of CeO2 nanocrystals on the RGO nanosheets can be adjusted. Especially, with the aid of 365 nm, 0.25 mW/cm2 UV-light illumination, the recovery process can be greatly accelerated to within 258 s. Otherwise the recovery process can typically take several hours to complete. In addition, our experimental results confirm that the as-fabricated sensor exhibits excellent selectivity and sensitivity (4.59-10 ppm NO2, ∼51 times enhancement). The sensor's response has been demonstrated to maintain its stability after recycling for six times or stored non-encapsulated for one year at room temperature, indicating eminent stability of the fabricated RGO-CeO2 hybrids.