Green microwave-assisted synthesis of α-MnO₂ nanoparticles for efficient photocatalytic and adsorptive removal of quaternary dye mixtures

A quick, environmentally friendly microwave-assisted approach (400 W, 180 s) was used to create manganese oxide nanoparticles (α-MnO 2 NPs) utilizing plant extract from Rumex Hastatus . With this green method, faceted α-MnO 2 nanostructures may be precisely formed, facilitating quick nucleation and development. When the photocatalytic and adsorption properties of α-MnO 2 NPs were evaluated, they demonstrated exceptional photocatalytic efficacy under UV and visible light (125 W) as well as efficient adsorption of organic dyes like Methyl Orange (MO), Congo Red (CR), Methylene Blue (MB), Malachite Green (MG), and their quaternary mixture in 60 min. The remarkable degradation efficiency of 86.63% for a quaternary combination under UV light was achieved by α-MnO 2 NPs. Furthermore, the adsorption studies have been examined for the quaternary mixture and showed remarkable performance. The adsorption data were analyzed using the pseudo-first-order and pseudo-second-order kinetic models, as well as the Freundlich and Langmuir isotherm models. A maximum adsorption capacity of 13.73 mg/g was obtained by the Langmuir model. Additionally, the Dubinin-Radushkevich and Temkin isotherm models have been studied. The Dubinin-Radushkevich model states that quaternary mixture adsorption is a physical process. According to the Temkin model, the adsorption is exothermic since the Temkin constant (B) values are positive. Furthermore, the recyclability of α-MnO 2 NPs has been tested and shown efficient adsorption for three cycles. These α-MnO 2 NPs, which were produced by microwave irradiation in about 180 s, have great potential for use in photocatalysis and adsorption to reduce aqueous contaminants.