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Background & Aims of the Study: Malachite Green (MG) is the most commonly used substance for dying cotton, food & pharmacy industries, paper, leather and silk. On inhalation it can cause difficult breathing, while on the direct contact it may cause permanent injury of the eyes of human and animals, burning sensations, nausea, vomiting, profuse sweating, mental confusion and methemoglobinemia; also it can causes cancer in livers. The aim of this study is  the removal of Malachite Green (MG) dye from aqueous solutions, using MnFe₂O₄/Al₂O₃ nanophotocatalyst by UV/H₂O₂ process which was used as a low cost method.

Materials & Methods: In this research, photocatalytic decomposition of malachite green in water was done by nanocatalyst MnFe₂O₄/Al₂O₃ in discontinuous photoreactor under UV light and the injection of H₂O₂. In order to identify and analyze the provided catalyst, SEM image and XRD diffraction pattern were used. The effect of operational factors in the photocatalytic decomposition of the desired pollutant such as pH, the initial thickness of the dye, the thickness of H₂O₂ and the quantity of the catalyst were investigated.

Results: The finding showed that the right conditions for the elimination of the pollutant included pH equals 4, the initial thickness of the dye being 10 ppm, the thickness of H₂O₂ being 250ppm, the amount of catalyst being 50mg, the Correlation Coefficient being 0.998 and the dye removal was 94 percent at the end of the experiment. the reaction of Malachite green decomposition was in terms of kinetics investigated through integral method as well; also it showed the kinetic reaction is the first type and the constant speed rate is K=0.047 min^-1 .