CuGaS2 hollow spheres from Ga–CuS core–shell nanoparticles

• We synthesized CuGaS2 hallow sphere from Ga@CuS nanoparticles.
• We used ultrasound to prepare gallium colloidal with small size and good stability.
• Ga@CuS were synthesized by deposition of CuS layer on Ga droplets by ultrasound.
• Ga@CuS transformed into chalcopyrite CuGaS2 hallow sphere after sulfurization at 450 °C.
• CuGaS2 hallow spheres showed 430 nm outer diameter and 120 nm shell thickness.

A liquid gallium emulsion was prepared as a starting material using ultrasound treatment in ethylene glycol. Core–shell particles of Ga@CuS were successfully synthesized by deposition of a CuS layer on gallium droplets through sonochemical deposition of copper ions and thiourea in an alcohol media. The core and shell of Ga@CuS products were composed of amorphous gallium metal and covellite phase CuS, which transformed into chalcopyrite CuGaS2 hollow spheres after sulfurization at 450 °C, which was the lowest crystallization temperature. The formation of hollow nanostructures was ascribed to the Kirkendall mechanism, in which liquid gallium particles play an important role as reactive templates. In conclusion, we obtained CuGaS2 hollow spheres with a 430 nm outer diameter and 120 nm shell thickness that had the same crystal structure and electrical properties as bulk CuGaS2.