Sodium chloride assists copper release, enhances antibacterial efficiency, and introduces atmospheric corrosion on copper surface

Sodium chloride (NaCl) is commonly found in physiological buffers. This study found out its additional but important role in antibacterial efficiency test by better corroding metallic copper surface. Combined with multiple characterisation methods including scanning electron microscopy, grazing incidence X-ray diffractometry, and inductively coupled plasma mass spectrometry, 0.9% saline was observed to cause localised corrosion attacks on copper surface, enhancing release of copper content. The 1 h killing rate against Escherichia coli was thus promoted from 22% (when re-suspended in pure water) to 98%. By a long-term observation (3-week), residual NaCl crystals on 0.9% saline treated copper surface were found partially disappeared in atmospheric environment, contributing to an additional Cu2O layer forming above the treated surface. Besides, formation of oxygen-containing species was observed on fresh copper surface exposed by focused ion beam after saline treatment, suggesting a chloride-assisted atmospheric corrosion process.