Adsorptive removal of phenol from aqueous solution using natural clay with mechanistic interpretation from kinetics isotherms thermodynamics and pore diffusion modeling

Abstract This study investigates the mechanism describing the adsorptive uptake of phenol onto natural clay adsorbent and its resistance to mass transfer by applying the pore diffusion model. The activated clay adsorbent was characterized via XRD, SEM, BET, and FTIR, respectively. Batch adsorption experiments were carried-out at varying dosage of 1.0–5.0 g, initial concentrations of 50–250 mg/L, temperatures of 20–60 °C, and adsorption time of 10–70 min to examine the sorption behavior of phenol in natural clay. The characterization revealed a pore size of 1.45 nm, pore volume of 0.09, and a large surface area of 54.95 m 2 /g. The results confirmed optimized effects of adsorption parameters at pH 6, corresponding to adsorbent dosage (1.0 g), contact time (20 min), initial concentration (250 mg/L), and temperature (40 °C), translating to 94% phenol removal efficiency. The results confirmed that the adsorption process obeyed the Pseudo-First-Order kinetics, and the Dubinin-Radushkevich isotherm model best describes the adsorptive uptake of phenol onto natural clay surface, with a maximum adsorption capacity of 28.42 mg/g, recorded at a range of 0.989 ≤ R 2 ≤ 0.9898. The pore diffusion modeling confirmed mass transport of the phenol molecule towards the clay surface was influenced by the pore diffusivity coefficient of 1.48 × 10⁻ 6 cm 2 /min, molecular diffusivity of 6.72 × 10⁻ 7 , and a tortuosity of 2.6 respectively, while thermodynamics findings established that the adsorption process is spontaneous, exothermic, and occurred via phyisorption mechanism influenced by hydrogen bonds between the OH of the phenol group and the Si–O–Si group on an heterogeneous surface of natural clay. Graphical Abstract