Composite Catalysts Based on Manganese Carbonate Ore for Environmental Ozone Decomposition and Decolourization of Malachite Green Dye

Environmental pollution from ozone and wastewaters containing dyes from various industries is an important problem for humanity. In this study, novel composite catalysts based on manganese carbonate ore from the Obrochishte deposit, Bulgaria, were used successfully in two environmentally relevant catalytic processes—the ozone decomposition and photocatalytic decolourization of Malachite Green (MG) dye under UV illumination. Manganese carbonate ore/NiO, manganese oxides, and silver-containing composites were synthesized via co-precipitation, followed by calcination at 500 °C or hydrothermal treatment at 160 °C, and then thermal treatment. The phase and elemental composition, structure, morphology, and textural characteristics of the obtained composites were investigated using powder X-ray diffraction analysis, wavelength-dispersive X-ray fluorescence, Fourier-transform infrared spectroscopy, scanning electron microscopy, nitrogen adsorption–desorption isotherms, and the BET method. The materials exhibit a mesoporous structure. The results established that the thermally treated MnCO3 ore/NiO, manganese oxides, and Ag-containing composites demonstrate a higher catalytic efficiency for the removal of ozone (85%, 93%, and 99%) in comparison with hydrothermally treated analogues—79%, 66%, and 98%, respectively. The thermally treated manganese carbonate ore/silver-containing composite exhibits the highest photocatalytic ability (83% degree of decolourization of MG dye) compared to the other investigated catalysts.