Size controlled synthesis of gold nanoparticle/carbon nanotube composites by atmospheric-pressure microplasma

Gold nanoparticles (AuNPs) have a superior catalytic activity. It has been reported that AuNPs with a diameter of 10 nm or less exhibit not only CO oxidation at room temperature but also glucose oxidation in liquid phase. On the other hand, carbon nanotubes (CNTs) have excellent electrical conductivity, chemical stability and large surface/ volume ratio. Gold nanoparticle/carbon nanotube composites (AuNPs@CNT), therefore, have attracted much attention as a high-sensitive biosensor. AuNPs@CNT have been synthesized by chemical reduction or plasma reduction, due to electrons and H radicals, of a HAuCl₄ aqueous solution using -COOH functionalized CNTs. However, it is an important issue to synthesize size-controlled and monodispersed AuNPs. In this study, AuNPs@CNT are synthesized by atmospheric-pressure He microplasma irradiation to a small amount of a HAuCl₄ aqueous solution (0.80 mM/L) of 100μL with adding CNTs dispersed ethanol of 200 µL. A microplasma was generated by a RF (13.56 MHz) driven narrow metal pipe electrode with He gas flow rate of 550 sccm. Plasma irradiation time was varied from 1 min to 5 min. AuNPs@CNT with an average AuNPs size of 5.3 nm and a standard deviation of 2,6 nm have been successfully synthesized at a plasma irradiation time of 1 min. An average size and standard deviation of AuNPs increase with increasing plasma irradiation time. Both the volume of CNTs dispersed HAuCl4 solution and plasma irradiation time play an important role in the size controlled synthesis of AuNPs.