The impact of ethylenediaminetetraacetic acid (EDTA) additive on anodization of copper in KHCO3 – hindering Cu2+ re-deposition by EDTA influences morphology and composition of the nanostructures

Copper was anodized in 0.01 M KHCO3 with no additive, with 10−4 M EDTA, 10−3 M EDTA and 10−2 M EDTA as additive, at voltages ranging from 10 to 60 V with a 10 V step. It was found that for EDTA-free electrolyte and electrolyte containing 10−4 M EDTA, nanorods are formed (diameter ranging from 34.2 to 58.4 nm), while for greater content of EDTA in the electrolyte, nanoparticles (diameter ranging from 32.1 to 290.2 nm) are obtained. Moreover, at 10 V in an electrolyte containing 10−2 M EDTA, nanopores, with an average diameter of 23.8 nm, were formed. Chemical composition analysis, based on Raman spectroscopy, revealed that the greater the concentration of EDTA in the electrolyte, the less the CuO in the formed nanostructures. Moreover, X-ray diffraction data show that increase of EDTA content in the electrolyte causes formation of less tenorite (CuO) vs. cuprite (Cu2O). Additionally, the more the EDTA in the electrolyte, the smaller the tenorite crystallites in the nanostructures. In electrolytes containing 10−2 M EDTA CuO was found to be mainly amorphous. Therefore, it was shown that addition of EDTA into the anodizing electrolyte hinders re-deposition of Cu2+ species, like Cu(OH)2 and CuO. Thus, the growth of the nanorods by copper anodizing is a sum of two driving forces: oxidation of copper and re-deposition of Cu(OH)2 and CuO from the electrolyte. A strong impact of re-deposition halting on morphology, chemical composition and crystallinity of the formed nanostructures was shown.