Low temperature synthesis of ZnO particles using a CO₂-driven mechanism under high pressure

Low temperature synthesis of ZnO particles without using reactive materials, solvents and post-treatments is still a serious challenge for both fundamental research and industrial applications. In this research, we report the dry synthesis of ZnO particles only by using Zn(acac)₂ and supercritical CO₂ (scCO₂) at the low temperature of 60 °C. The synthesis was performed using CO₂ and N₂ from 0.1 to 30.0 MPa for 18 h. As a result, ZnO yields increased with a rise in the CO₂ pressure and reached 67% at 30.0 MPa while N₂ medium gave low yields below 4.9% regardless of the pressure. Additionally, the detailed characterization results and the phase behavior observations evidentially showed the formation of zinc-CO/CO₂-organic complexes in the solid phase of Zn(acac)₂ powder under scCO₂, resulting in the accelerated formation of ZnO particles. These findings suggest that scCO₂ has potential value to drive the formation reaction of zinc-CO/CO₂-organic complexes, which allows the low temperature synthesis of ZnO particles under dry conditions without using reactive materials, solvents and post-treatments.