Comparative investigation of catalytic application of α/β/γ-MnO2 nanoparticles synthesized by green and chemical approaches

Abstract It is first time reported that three phases (α, β, and γ) of manganese dioxide (MnO2) are successfully stabilized in a single entity. For this purpose, Citrullus colocynthis (bitter apple) extract is used as natural surfactant in green synthesis. MnO2 nanoparticles were synthesized in the presence and absence of plant extract under same conditions. The morphology of both products are analyzed by SEM and STEM to understand the role of plant extract in controlling the morphology of particles. The crystallinity and composition are analyzed by XRD and confirmed that product is comprised of multiple phases α, β, and γ. The reduction of dyes and nitroarenes are studied by using MnO2 nanoparticles (green and chemical products) as a catalyst. Apparent rate constant, percentage reduction, time reduction and reduced concentration are determined to compare the activity of both catalysts. After comparative data analysis, the catalytic reduction of picric acid is found fastest among all the substrates. All the results are analyzed on the basis of structure, functional group and affinity towards catalyst.