The shift of the localized surface plasmon resonance (LSPR) band of gold nanoparticles to shorter wavelengths upon saturation of the hydrosol with hydrogen is used as a tool to study the electrochemical processes on the particle surface. It is shown that dissociative adsorption of hydrogen takes place on the surface of a particle and results in the migration of a proton into the dispersion medium, while the electron remains on the nanoparticle, i.e., a hydrogen-like nanoelectrode is formed. It is shown that Au(iii) ions can be reduced on the gold nanoelectrodes. A thermodynamic scheme explaining the shift of the LSPR band is used to explain the peculiarities of the Au(iii) ion reduction. The reduction rate does not depend on the ion concentration and varies linearly with pH. The observed correlations are explained in terms of a simple model of electrochemical processes taking place on the nanoparticle as an electrode. It is shown that with an increase in the particle size, its capacity for dissociative adsorption of hydrogen decreases and the Au(iii) reduction slows down.
The impact of the size of gold nanoparticles on the magnitude of the bathochromic shift of their plasmon resonance peak upon ozone adsorption is revealed and analyzed. Namely, the plasmon band position of 7, 10, 14 and 32 nm nanoparticles shifts toward longer wavelengths by 51, 35, 23 and 9 nm respectively, i.e. the smaller the nanoparticles, the greater the shift of the band. Thus, the sensor efficiency of gold hydrosol increases with a decrease in the nanoparticle size. The shift of the Fermi level is a linear function of the inverse radius of nanoparticles. The observed alterations in the gold nanoparticle plasmonic properties and the Fermi level position are explained by a decrease in the electron density of nanoparticles caused by the electrons' partial binding by adsorbed O3 molecules. The insignificance of oxygen and nitrous oxide effects on plasmonic properties of gold hydrosol is observed.
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