<p>This study explores the adsorptive removal of Ni (II) ions using laboratory–synthesized graphene oxide (GO), thoroughly characterizing the adsorbent before and after adsorption. The impact of key operational variables, including initial Ni (II) concentration, solution pH, adsorbent dosage, contact time, and temperature, is systematically analysed. Experimental data indicate that the pseudo-second-order kinetic model (R² &gt; 0.99) and the Langmuir isotherm model (R² &gt; 0.98) best describe the adsorption process, with GO achieving a maximum adsorption capacity of 32.95 mg/g at pH 6.5 and 318 K. Further mathematical analysis determines the effective diffusivity (5 × 10^–16 m²/s) and external mass transfer coefficient (8.583 × 10^–11 m/s) for an initial Ni (II) concentration of 50 mg/L. Fourier transform infrared spectroscopy (FTIR) and NaNO₃ interference studies highlight the role of electrostatic interactions, with C=O and O–H functional groups serving as active adsorption sites. Thermodynamic analysis confirms that the adsorption process is endothermic (ΔH = 14.88 kJ/mol) and spontaneous (ΔG = –3.88 kJ/mol at 318 K). Moreover, density functional theory (DFT) calculations justify that Ni (II) ions preferentially bind to oxygen-containing functional groups on GO. Reusability studies reveal a 22.89% decrease in adsorption capacity after five successive adsorption–desorption cycles, underscoring the material’s potential for practical wastewater treatment applications.</p> Graphical abstract <p><i> Synopsis</i> Being synthesized using Tours’ method, Graphene oxide (GO) is used as an adsorbent for the removal of Ni (II) from aqueous solutions. Oxygenated functional groups on the GO surface are primarily responsible for Ni (II) adsorption.</p>