Optical measurements of oxidation behavior of silver nanometer particle within pores of silica host

The oxidation behavior of silver (Ag) nanometer particles (about 3 nm in diameter) within pores of a silica host in ambient air (298 K) was investigated from optical absorption measurements. Thermodynamic analysis indicates that Ag nanoparticles can be oxidized in air at room temperature. Exposure to air results in a blueshift of the absorption edge with time, which is attributed to the surface oxidation of Ag nanoparticles. On this basis, we present a new method to investigate the oxidation process of Ag nanoparticles. Further experiments show that in air at room temperature oxidation occurs in surface layers of Ag particles in the form of a dense Ag2O film. Once the dense film is formed, further oxidation is restrained. A high relative humidity in the air results in fast surface oxidation. In air with a relative humidity 80% at room temperature, a dense film can be formed in 2 h. When the relative humidity is <30%, no measurable oxidation was found even after several months. (C) 1998 American Institute of Physics. [S0021-8979(98)00903-7].