Pt-doped In2O3 nanoparticles prepared by flame spray pyrolysis for NO2 sensing

Undoped In2O3 and 0.25-1.00 wt% M (M=Pt, Nb, and Ru)-doped/loaded In2O3 nanoparticles were successfully synthesized in a single-step flame spray pyrolysis technique using indium nitrate, platinum (II) acetylacetonate, niobium ethoxide, and ruthenium (III) acetylacetonate precursors. The undoped In2O3 and M-doped In2O3 nanoparticles were characterized by Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), and scanning and transmission electron microscopy (SEM & TEM). The BET average diameter of spherical nanoparticles was found to be in the range of 10.2-15.2 nm under 5/5 (precursor/oxygen) flame conditions. All XRD peaks were confirmed to correspond to the cubic structure of In2O3. TEM images showed that there is no Pt nanoparticle loaded on In2O3 surface, suggesting that Pt should form solid solution with the In2O3 lattice. Gas sensing studies showed that 0.5 wt% Pt doping in In2O3 nanoparticles gave a significant enhancement of NO2 sensing performances in terms of sensor response and selectivity. 0.5 wt% Pt/In2O3 exhibited a high NO2 response of similar to 1904 to 5 ppm NO2 at 250 degrees C and good NO2 selectivity against NO, H2S, H-2, and C2H5OH. In contrast, Nb and Ru loading resulted in deteriorated NO2 response. Therefore, Pt is demonstrated to be an effective additive to enhance NO2 sensing performances of In2O3-based sensors.