Iron Oxides Nanoparticles Langmuir-Schaeffer Multilayers for Chemoresistive Gas Sensing

Gas sensors based on mixtures of iron oxides nanoparticles (NPs) modified with Pd NPs at the different NPs Pd: Fe3O4/c-Fe2O3 proportions were prepared and characterized. Nanoparticles diameter was 6-7 nm. NPs films were deposited from the mixtures of Fe3O4/c-Fe2O3 and Pd NPs colloidal solutions by modified Langmuir-Schaeffer technique onto alumina substrates. Samples were composed from 4 Fe3O4/c-Fe2O3 NP monolayers (MLs). Sensors were tested toward acetone vapors and NO2 at concentration range of 5-200 and 0.5-12 ppm respectively in dry air, and at different working temperatures. Pd-doped Fe3O4/c-Fe2O3 sensors showed p-type gas response, higher conductance and higher conduction activation energies compared to pure Fe3O4/c-Fe2O3 sensor that gives n-type gas response. Results were tentatively explained in terms of surface interactions with oxidizing and reducing species, and Nearest Neighbor Hopping conduction model (NNH).