Improvements in the Bleaching Effects of Electrolyzed Water and Sodium Hypochlorite by the Addition of Sodium Chloride

Abstract

In this study the bleaching effect of electrolyzed water prepared from sodium chloride (NaCl) solutions was investigated by bleaching tea-stained cotton cloths. The bleaching performance of the electrolyzed water was higher than that of a sodium hypochlorite (NaOCl) solution with the identical available chlorine concentration (ACC) and pH, but the bleaching performance of NaOCl solution was increased to close to that of the electrolyzed water by adding NaCl. Interestingly, the effect of electrolyzed water also increased with the increase of initial NaCl concentration, even when keeping the ACC constant. These phenomena suggested that the improvements in the bleaching effect are caused by coexistent NaCl. It could be explained by Le Chatelier’s principle, that is, non-ionized NaOCl which has higher bleaching effect than ionized NaOCl (OCl⁻) would be produced by the shift of equilibrium (Na⁺+OCl⁻+NaCl→NaOCl+Na⁺+Cl⁻). This behavior was also indicated from the UV absorption spectra before and after adding NaCl to the NaOCl solution.