Although iron nanoparticles have been extensively examined for heavy metal-contaminated groundwater remediation, their transformation mechanisms and fate have not been clearly understood. The research manifests copper nanostructure formation via galvanic replacement and Kirkendall growth from nanoscale zero-valent iron (nZVI) nanoparticles after they react with Cu(II) at a concentration of 1000 mg/L. Copper core–shell nanostructures and nanobubbles from nZVI at the same Cu(II) concentration are visualized by energy-dispersive spectra mappings, which were collected using spherical aberration-corrected transmission electron microscopy equipped with energy-dispersive X-ray spectrometry. X-ray diffraction analysis of Cu(II)-nZVI products shows that Cu(0) and Cu<sub>2</sub>O are dominant at the initial Cu(II) concentrations up to 500 mg/L or much larger, while maghematite/magnetite, Cu(0), and Cu<sub>2</sub>O comprise the major components when Cu(II) concentrations are smaller than 250 mg/L. The different shapes and compositions of copper nanostructures depict the multiple pathways contributing to the morphology evolution, such as galvanic displacement and Kirkendall growth. This work provides vividly proofs on the galvanic replacement reaction between nZVI and Cu(II), as well as the Kirkendall growth for the formation of nanostructural materials, and preliminary information regarding the potential fate of nZVI for Cu(II)-contaminated groundwater remediation.

Copper nanostructure genesis via galvanic replacement and Kirkendall growth from nanoscale zero-valent iron

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