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

Abstract

The functionalization of Fe3O4/γ-Fe2O3 nanoparticles (NPs) gas sensors with Pd NPs was studied. NPs films were deposited from the mixtures of Fe3O4/γ-Fe2O3 and Pd NPs colloidal solutions by modified Langmuir-Schaefer technique onto Al2O3 substrates, the NP size being 6–7nm. Samples were composed from 4 Fe3O4/γ-Fe2O3 NP monolayers (MLs), either pure or doped by Pd at the different NPs Pd: Fe3O4/γ-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 5–200ppm and 0.5–12ppm respectively in dry air and under working temperatures range 200–500°C. Before testing 1nm, surfactant capping was removed by UV irradiation. Pd-doped Fe3O4/γ-Fe2O3 sensors showed p-type gas response, higher conductance and higher conduction activation energies compared to pure Fe3O4/γ-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.