Mixed Mn oxides loaded biomass waste-based catalysts for methylene blue dye decoloration

Manganese oxides loaded cellulose, lignin, and rice husk catalysts were prepared by in situ reduction of permanganate. CV, FT-IR, SEM-EDS, TGA, XPS, and XRD analyses were applied to characterize the obtained catalysts. Mn 2p band deconvolution revealed Mn2O3 and MnO2 phases for modified rice husk and cellulose, while amorphous Mn3O4 and MnO2 phases were found for modified lignin. The morphology of MnO2/Mn3O4@KL presents micro/nanospherical particles with aggregation, giving rise to large agglomerations. The relative atomic concentrations of total manganese oxides in fresh catalysts are about 2%, 2.6%, and 6.3% for modified lignin, cellulose, and rice husk, respectively. The photocatalytic degradation of methylene blue on the modified lignin catalyst (60%) was higher than those of modified rice husk (40%) and cellulose (26%), due to the surface charge state and the strong adsorption affinity of lignin-based catalysts with dye. At the optimal contact time of 10 min, the decoloration rate of the modified lignin was higher than 98% for 10 mg/L dye concentration with a catalyst dose of 1 g/L. However, an increase in the initial concentration of dye affects the decoloration rate constants of the modified lignin. The pseudo-first-order rate equation described the kinetic decoloration of methylene blue dye with good correlation coefficients. MnO2/Mn3O4@KL as a low-cost and effective material for the removal of methylene blue may become an alternative catalyst to reduce wastewater pollution.

Automated summary

Manganese oxides loaded cellulose, lignin, and rice husk catalysts were prepared by in situ reduction of permanganate. Characterization of the obtained catalysts was done using CV, FT-IR, SEM-EDS, TGA, XPS, and XRD analyses. The different phases and morphology of manganese oxides in the catalysts affected the photocatalytic degradation of methylene blue, with modified lignin showing the highest efficiency.