Easy synthesis of 4-quinonimine functionalized gold nanoparticles in stable aqueous colloidal state

Abstract

A single step process was developed for successful synthesis of 4-quinonimine functionalized gold nanoparticles in aqueous colloidal state using 4-aminophenol as both reducing agent and stabilizer. As per the proposed mechanism, the gold(III) ion of tetrachloroauric(III) acid was reduced to gold(0) nanoparticles by 4-aminophenol which was oxidized to 4-quinonimine in order to stabilize the small spherical gold nanoparticles through surface functionalization. The purple-red aqueous colloid of 4-quinonimine functionalized gold nanoparticles with average diameter of 10 nm was found to have characteristic surface plasmon resonance absorption at 540 nm. Stability of the aqueous colloid of gold nanoparticles was explained from the zeta potential value of −27 mv with average hydrodynamic size of 60 nm. The stability of the aqueous colloid was increased in the order acidic, neutral to basic pH. Further, it was found to be stable for up to 120 days under gravitational force at room conditions.