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Manganese dioxide nanoparticles are loaded onto the surface of chitosan (CS) in order to enhance their adsorption properties. Various theoretical models and spectroscopic analytical methods are used to investigate the equilibrium isotherm, kinetics, and mechanisms of the removal of lead(II) from the aqueous solution. The kinetic studies based on a pseudo-second-order model show that the uptake of lead(II) occurs via three stages depending on the reaction time. The experimental data are fitted using four nonlinear isotherm models, namely the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models. The results obtained within the Langmuir model gave the highest R², the smallest root-mean-squared error (RMSE), and the best nonlinear chi-square test (χ²) values, indicating that this model is the most appropriate approach for describing the adsorption of lead(II) onto the MnO₂/CS nanomaterials. It is …