Water vapour-induced enhancement of the surface plasmon resonance for Ag nanoparticles dispersed within pores of mesoporous silica

The optical evolution for monolithic mesoporous silica soaked in Ag+ ion solution (0.01-0.06 M) and annealed in air or water vapour is investigated. Heat treatment in air results in the absence of the surface plasmon resonance (SPR) peak of Ag nanoparticles. However, water vapour annealing induces a strong Ag SPR peak, exhibiting a strong reduction effect on Ag+ ions and an enhancement effect on the SPR absorption. The enhancement and weakening of the SPR can be controlled through annealing in water vapour and air alternately. This finding indicates the possibility that Ag nanoparticles dispersed in silica may be useful in optical sensors for humid environment use at high temperature.