Synthesis, characterization and gas-sensing properties of Pd-doped SnO2 nano particles

SnO2 nano particles with various Pd-doping concentrations were prepared using a template-free hydrothermal method. The effects of Pd doping on the crystal structure, morphology, microstructure, thermal stability and surface chemistry of these nano particles were characterized by transmission electron microscope, X-ray diffractometer and X-ray photoelectron spectroscope respectively. It was observed that Pd-doping had little effect on the grain sizes of the obtained SnO2 nano particles during the hydrothermal route. During thermal annealing, Pd-doping could restrain the growth of grain sizes below 500 °C while the grain growth was promoted when the temperature increased to above 700 °C. XPS results revealed that Pd existed in three chemical states in the as-synthesized sample as Pd0, Pd2+ and Pd4+, respectively. Pd4+ was the main state which was responsible for improving the gas-sensing property. The optimal Pd-doping concentration for better gas-sensing property and thermal stability was 2.0%-2.5% (mole fraction).