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 WO_2.8 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. [ABSTRACT FROM AUTHOR]