Palladium/gamma-Fe2O3 nanoparticle mixtures for acetone and NO2 gas sensors

The functionalization of Fe3O4/gamma-Fe2O3 nanoparticles (NPs) gas sensors with Pd NPs was studied. NPs films were deposited from the mixtures of Fe3O4/gamma-Fe2O3 and Pd NPs colloidal solutions by modified Langmuir-Schaefer technique onto Al2O3 substrates, the NP size being 6-7 nm. Samples were composed from 4 Fe3O4/gamma-Fe2O3 NP monolayers (MLs), either pure or doped by Pd at the different NPs Pd: Fe3O4/gamma-Fe2O3 proportions. NPs and films were studied by DLS, GI XRD, SEM and EDS. Sensors were tested toward acetone vapors and NO2 at concentration range of 5-200 ppm and 0.5-12 ppm respectively in dry air and under working temperatures range 200-500 degrees C. Before testing 1 nm, surfactant capping was removed by UV irradiation. Pd-doped Fe3O4/,gamma-Fe2O3 sensors showed p-type gas response, higher conductance and higher conduction activation energies compared to pure Fe3O4/gamma-Fe2O3 sensor that gives n-type gas response. Results are explained in terms of surface interactions with oxidizing and reducing species, and electrical conduction mechanisms. (C) 2016 Elsevier B.V. All rights reserved.