Reduction of supported metal ions by a safe atmospheric pressure alcohol cold plasma method

Abstract

Abstract Atmospheric pressure (AP) hydrogen cold plasma has been proved to be an efficient method for synthesizing supported metal catalysts. However, explosive hydrogen gas is generally required, and it is hard to be stored and transported. In this work, a safe AP alcohol cold plasma was developed and employed to reduce Deggusa P25 TiO2 supported metal (Au, Pd, Ag, Pt) ions with the assistance of methanol and ethanol instead of hydrogen gas. Obvious color changes are observed for the samples after AP alcohol cold plasma processing, and enhanced visible light absorption is detected according to the UV–vis diffuse reflectance spectra (UV–vis DRS). These indicate that AP alcohol cold plasma can reduce the noble metal ions into their metallic states, which are further confirmed by the results of X-ray photoelectron spectroscopy (XPS). Gold ions reduction is selected to further investigate the difference between AP alcohol and hydrogen cold plasma. The results reveal that gold ions can be reduced into metallic gold nanoparticles by AP cold plasma. Interestingly, compared to Au/P25-HP, the blueshift of the surface plasmon resonance (SPR) peaks for Au/P25-MP and Au/P25-EP is observed, attributing to the smaller size of gold nanoparticles (ca. 1.6 nm) and the influence of carbon species formed by alcohol dissociation during AP cold plasma. Optical emission spectroscopy (OES) is also used to diagnose the active species in AP cold plasma, and the mechanism of AP alcohol cold plasma for reducing the supported metal ions is discussed. AP alcohol cold plasma is proved to be an alternative safe method for synthesizing supported metal catalysts using methanol and ethanol instead of explosive hydrogen gas, and smaller size of metal nanoparticles can be obtained.