In situ synthesis of gold nanoparticles at the air–water interface. Spontaneous reduction of Au(III) by poly(N-vinyl-2-pyrrolidone) monolayers

This work reports the in situ synthesis of gold nanoparticles at the air water interface through the direct reaction between spread monolayers of poly(N-vinyl-2-pyrrolidone) at the interface and tetrachloroaurate ions in the subphase. For this, a parallel study between the poly(N-vinyl-2-pyrrolidone) monolayers spread at the air–water interface using pure water and tetrachloroaurate aqueous solution as subphases was done. The effects of parameters such as polymeric molecular weights and temperature on the respective monolayers behaviour were monitored. The spread monolayers of poly(N-vinyl-2-pyrrolidone) on tetrachloroaurate solution as subphase show differences in their elasticity and stability respect to the same monolayers on pure water. Considering the interface as a solvent for poly(N-vinyl-2-pyrrolidone) monolayers, differences in the value of the critical exponent of the excluded volume ν were detected when the subphase change from water to tetrachloroaurate aqueous solution. Gold nanoparticles were confirmed by the presence of typical absorption bands of the surface plasmon resonance in UV–Vis spectra of the subphase and by images obtained by scanning electron microscopy.