Preparation of nanosize copper recycled from an electroplating wastewater

To better utilize copper recovered from an electroplating (EP) wastewater, a simple method of preparing valuable nanoparticles has been developed in the present work. Experimentally, about 40-50% of copper in the wastewater can be chelated with β-cyclodextrin (β-CD). The β-CD-Cu²⁺ complex was dried at 373 K for 24 hours and carbonized at 573 K for at least two hours to obtain the nanosize metallic copper (Cu) encapsulated in the carbon shells (Cu@C). The images observed by transmission electron microscopy (TEM) also indicate that the size of Cu in the Cu@C is in the range of 10-60 nm. The component fitted X-ray absorption near edge structure (XANES) spectra suggest that the chelated Cu²⁺ is reduced to form Cu as the hydroxyl groups of the β-CD are oxidized to H₂O vapor during carbonization. By extended X-ray absorption fine structure (EXAFS) spectroscopy, it is found that the average coordination number (CN) of Cu in the Cu@C nanoparticles decreases along with the decrease of the size of Cu, i.e. the CN of the nanosize Cu (23 nm) is reduced to 8 comparing to 12 of the bulky Cu.