Methylene Blue–Cu2O Reaction Made Easy in Acidic Medium

Abstract

Truncated Cu2O cubes with well-defined morphology have been successfully synthesized using a stable Cu(II)–EDTA precursor and glucose as the reducing agent in alkaline conditions under 5 min of microwave irradiation. The truncated cubic Cu2O particles as a solid powder were characterized by different physical methods. Curiously enough, upon the addition of Cu2O particles, the blue-colored methylene blue (MB) in aqueous acidic (pH ≈ 1.0) solution successively bleaches to colorless leuco-MB (LMB). The redox reaction generates a colorless solution which easily reverts back to blue in air. The reaction has been quantitatively monitored by UV–vis spectrophotometry. The reversible color change, i.e., oscillation between a blue MB solution and colorless LMB solution happens to be a periodic phenomenon for more than 50 cycles and is reproducibly demonstrated as a simple “clock reaction”. Acidic (pH ≈ 3.0) conditions favor zeroth-order kinetics for the underlying redox phenomena. Dilute H2SO4 has been proven to be the best choice to provide a passive reaction medium, and the undisturbed reaction mixture showed oscillatory behavior even after one month.