Critical review on development of methylene blue degradation by wet catalytic methods

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Abstract The development of textile, agriculture, and other related industries has increased the risk of excessive methylene blue (MB) emissions, making efficient treatment of MB an urgent issue in terms of the economy and environment. The most commonly used chemical treatment methods were wet catalytic methods, including catalytic wet air oxidation (CWAO), catalytic wet peroxide oxidation (CWPO), and photocatalysis. CWAO and CWPO both show fast reaction rates and are environmentally friendly. CWAO uses air as an oxidant at a relatively low cost and can effectively solve the leaching problem of the catalyst. CWPO employs inorganic peroxides like hydrogen peroxide (H2O2) as oxidants to form radicals, showing high efficiency. Photocatalytic degradation utilizes light energy to transform pollutants into harmless molecules with fast kinetic. The selection and application of different methods are analyzed basing on the balance among cost, scale, and efficiency. Finally, the perspective of the effective removal of MB is summarized, containing multiple method combinations, catalyst synthesis optimization, and practical application with less side reaction and instrument loss. More promising technology should be considered in the future for better degradation of MB in the industrial field.