Cu(II) galvanic reduction and deposition onto iron nano- and microparticles: Resulting morphologies and growth mechanisms

The galvanic reduction of heavy metal ions by zerovalent iron nanoparticles is a key process occurring extensively in wastewater remediation, as well as for the synthesis of materials, including catalysts. In this work, we studied the growth of copper species on nano- and micrometer-sized iron particles and investigated the morphologies of the resulting structures. The growth proceeds via sacrificial oxidation of iron particles and reduction of Cu²⁺ cations from aqueous solutions. Based on the results of transmission and scanning electron microscopy (TEM and SEM), coupled with energy-dispersive X-ray spectroscopy (EDX), electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS), we proposed two growth mechanisms for the morphologies seen for the copper exposed nano- and microiron particles at varying copper/iron ratios. We observed that, in low Cu/Fe ratios (≥1/100), copper particles decorated the oxide shell of the iron nano/microparticles, while in higher Cu/Fe ratios (≥1/10), Cu-rich hollow structures were formed. Iron microparticles also led to the formation of interesting Cu-fern structures. This study provides insight into the fate of particles used in remediation, as well as recommendations for the synthesis of well-defined materials tailored for precise applications.