Fabrication of Pd/WO3 colloidal nanoparticles by laser ablation in liquid of tungsten for optical hydrogen detection

In this paper, tetragonal WO3 colloidal nanoparticles (NPs) were prepared by pulsed laser ablation in liquid of tungsten target in de-ionized water, followed by adding a PdCl2 solution immediately after the ablation process or hours after aging. X-ray photoelectron spectroscopy revealed that the surface chemical composition is a mixture of W5+, W6+, and O–H groups for which a defective WO2.8 surface composition was calculated. Transmission electron microscope images showed that only when PdCl2 is added immediately, Pd/WO3 core-shell NPs are formed spontaneously. UV-Vis spectrophotometry showed an increase in the optical bandgap due to NPs oxidation throughout the aging period. Thus, the spontaneous formation of the Pd/WO3 core-shell NPs was attributed to the presence of surface oxygen defects in newly formed NPs. With hydrogen exposure (<10%), Pd/WO3 solutions turned blue, indicating a gasochromic coloration ability which was used to detect different hydrogen concentrations below 10%. The dynamic response to different hydrogen concentrations was also studied at 630 nm constant wavelength. The results revealed that Pd/WO3 NPs obtained by the pristine WO3 colloidal solution show a better gasochromic performance, in both the coloration and response time.