Abstract
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.
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