Ficus-mediated green synthesis of manganese oxide nanoparticles for adsorptive removal of malachite green from surface water

Abstract The extract of ficus leaves was used to prepare manganese (IV) oxide nanoparticles (MnO 2 NPs) for the first time. Several different analytical techniques were used to characterize the prepared MnO 2 NPs. MnO 2 has spherical crystals that are ~ 7 nm on average in size and have 149.68 m 2 /g of surface area and 0.91 cm 3 /g of total pore volume. Malachite green (MG) dye was then taken out of the water by adsorption using MnO 2 NPs. Optimization of various adsorption parameters resulted in 188.68–277.78 mg/g maximum adsorption capacities at 298–328 K tested temperatures and 99.6% removal of 50 mg/L MG within 90 min using MnO 2 dose of 0.01 g at pH 10 and 298 K. The results were tested using pseudo-first order, pseudo-second order, intraparticle diffusion, Elovich, and Liquid film kinetic models as well as Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models. The most likely models to describe the adsorption process at 298 K are pseudo-second-order kinetics ( R 2 = 0.997) with a rate constant of 4 × 10 −4 g/(mg.min) and Langmuir isotherm ( R 2 = 0.973). Additionally, the positive values of enthalpy change (3.91–67.81 kJ/mol) and the negative values of Gibb’s free energy (− 3.38 to − 19.7 kJ/mol) indicate that the process is endothermic, spontaneous, and thermodynamically feasible. MnO 2 NPs sustained their adsorption efficiency at 90.4% after 5 sorption cycles. MnO 2 appears to be more selective for MG in studies examining the adsorption of various cationic dyes. Lately, the biosynthesized MnO 2 NPs can be utilized to remove MG from aqueous solutions effectively.