A new insight into the generation of hydrogen peroxide from carmine degradation by cryptomelane as a catalyst, oxidant, and adsorbent

Carmine, as a widely used dye, is one kind of refractory organic pollutants that endanger the water environment. Finding an efficient and environmentally friendly degradation method is a crucial step to treat dye-containing wastewater. Using a one-step hydrothermal synthetic method, cryptomelane was synthesized, characterized, and investigated for its ability to degrade carmine in an aqueous solution. Under the optimum conditions of a 2 g/L cryptomelane dosage and an initial pH of 6.8, 97.87% of 100 mg/L carmine degraded within 240 mins. Cryptomelane exhibited excellent reusability after three cycles, with a decolorization efficiency of 85.39%. Cryptomelane accommodated a board working pH range. The carmine was efficiently decolorized via an interaction of oxidation, catalysis, and adsorption of cryptomelane in a ratio of 46.85:47.11:3.90, respectively. The existence of oxygen vacancies on cryptomelane was responsible for H 2 O 2 generation, and O 2 •- and 1 O 2 active species were involved in the carmine degradation by cryptomelane. A low reaction activation energy ( E a  = 6.36 kJ/mol) caused efficient removal of carmine by cryptomelane at ambient temperature. These findings notably distinguish three roles of cryptomelane as an adsorbent, oxidant, and catalyst in a pollutant removal system, and prove that cryptomelane may have extensive and promising utilization on refractory organic wastewater treatment without the need to add extra oxidants.