Synthesis of CuO and Cu2O nano/microparticles from a single precursor: effect of temperature on CuO/Cu2O formation and morphology dependent nitroarene reduction

Abstract

CuO and Cu₂O nano/microparticles with pure phases have been synthesized from the same precursor by a hydrothermal method. Hydrothermal heating of Cu(OAc)₂ produced CuO at 125 °C whereas pure Cu₂O was obtained at 175 °C. Heating at 150 °C gave a CuO/Cu₂O mixture. In contrast, Cu(acac)₂ produced only Cu₂O at all three temperatures. The pure phases of Cu₂O and CuO nano/microparticles were confirmed by PXRD and XPS characterization. The mechanistic studies indicate that decomposition of the organic anion/ligand of the Cu-precursor played a key role in the formation of CuO/Cu₂O nano/microparticles from Cu(OAc)₂/Cu(acac)₂. FE-SEM studies revealed the formation of CuO with a microsphere morphology (125 °C) and a micro-cup for Cu₂O at 175 °C. Nanowires and micron-sized elliptical cylinders were observed for Cu₂O synthesized from Cu(acac)₂. However, calcination of Cu(OAc)₂, Cu(acac)₂ and Cu(NO₃)₂ at 500 °C produced crystalline CuO nano/microparticles with various sizes and morphologies. Further, CuO nano/microparticles investigated for industrially important aromatic nitro to amine conversion showed morphology dependent nitro group reduction. Smaller spherical CuO nano/microparticles obtained from Cu(acac)₂ exhibited the highest catalytic activity. The reusability studies indicate that CuO nano/microparticles can be used for up to six cycles. Thus we have presented a simple method to synthesize Cu₂O or CuO from the same precursor and demonstrated the morphology dependent catalytic activity of CuO nano/microparticles.