<p>The novel adsorbent of KMnO₄-modified spent coffee grounds (KMnO₄-SCGS) was successfully synthesized for the adsorption of Pb(II). Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and other characterization measurements were employed to evaluate the physical and chemical properties of KMnO₄-SCGS. The results demonstrated that the adsorption behavior of Pb(II) was best fitted by the pseudo-second-order, Ritchie, and Langmuir isothermal models, indicating that the surface of KMnO₄-SCGS was composed of homogeneous adsorption. The surface complexes with manganese oxide (MnO_x) and oxygen-containing functional groups, along with electrostatic interaction, physical adsorption, and ion exchange, played significant roles in the adsorption of Pb(II). The Langmuir maximum adsorption capacity for Pb(II) was 203.8&#xa0;mg/g for KMnO₄-SCGS, which was approximately 11.73 times higher than that of SCGS, and it remained over 80% after five cycles. Finally, the Box-Behnken design was utilized to optimize the results. Therefore, the modification of spent coffee grounds by KMnO₄ is a feasible approach for the adsorption of Pb(II).</p> Graphic Abstract <p></p>