Surface activity, mechanisms, kinetics, and thermodynamic study of adsorption of malachite green dye onto sulfuric acid–functionalized Moringa oleifera leaves from aqueous solution

In the present study, activated carbon prepared from H 2 SO 4 -functionalized Moringa oleifera leaves (ACMOL) was used as a potential adsorbent for the effective removal of malachite green (MG) dye from aqueous media. FT-IR, SEM, EDS, Zeta potential, XRD, BET, proximate, and CHNS analysis techniques were used for surface characterization of the ACMOL. The adsorption efficiency of the ACMOL was investigated as a function of varying adsorbent dosage (0.02–0.2 g/100 mL), pH (3.0–9.0), ionic strength (0.1–0.5 M KCl), urea concentration (0.1–0.5 M), contact time (30–210 min), and temperature (303–323 K). The representative adsorption isotherms belong to the typical L-type. Maximum percentage removal was found to be 84% (124.40 mg/g) for MG dye concentration (30 mg/L) at pH 7.0 and 303 K with ACMOL dose 0.02 g/100 mL. The adsorption kinetics and equilibrium experimental data of MG dye adsorption on the ACMOL were well explained by the pseudo-second-order kinetics ( R 2 = 0.99) and Langmuir isotherm model ( R 2 = 0.99), respectively. The value of adsorption and desorption coefficient was found to be 0.036 min −1 and 0.025 mg min −1 /L, respectively. Thermodynamic study showed the spontaneous (Δ G ° = − 31.33, − 31.92, and − 32.49 kJ/mol at temperatures 303 K, 313 K, and 323 K, respectively) and exothermic (Δ H ° = − 13.7 kJ/mol) nature of the adsorption with some structural changes occurring on the ACMOL surface (Δ S ° = 58.198 J/K·mol).