Synthesis of oxidation resistant copper nanoparticles in aqueous phase and efficient phase transfer of particles using alkanethiol

Stable and oxidation resistant copper nanoparticles are prepared in aqueous phase using sodium borohydride as a reducing agent. No surfactant has been used to stabilize the sol and the sol is found to bear negative charge. The hydrosol is resistant to oxidation by atmospheric oxygen for a couple of hours. The stability and oxidation resistant found to be due to excess sodium borohydride. The aqueous sol has been found to be stable for days when kept in a refrigerator in an airtight container. UV–Visible, TEM and zeta potential measurements confirm the presence of spherical copper nanoparticles of 2-4 nm in the hydrosol. The charged particles are transferred from the aqueous phase to toluene using dodecanethiol as a phase transfer surfactant. No additional surfactant has been used during the transfer. It has been found that thiol coated particles form a stable colloid in toluene. TEM studies confirm that the particles preserve their shape and size during phase transfer and EDX spectra shows that the particles are metallic copper without any significant amount of oxide formation. Optimization of various parameters of the entire synthesis process has resulted in a well reproducible protocol for synthesis of thiol coated copper nanoparticles in organic phase using surfactant free phase transfer.