Synthesis, structural characterization and Pb(II) adsorption behavior of K- and H-birnessite samples Original Research Article

This paper presents the synthesis, structural characterization and Pb(II) adsorption behavior of K-birnessite and H-birnessite samples. Changes in the surfaces and structure of birnessite samples were characterized by means of infrared spectroscopy (IR), N2 gas adsorption and thermal analysis (TG–DTA) techniques. Adsorption of Pb(II) by samples was investigated as a function of the initial Pb(II) concentration, solution pH, ionic strength, temperature and inorganic ligand (NO3−, Cl−). The Langmuir monolayer adsorption capacities of K-birnessite and H-birnessite samples in 0.1 M NaNO3 solution at 298 K were estimated as 164.30 and 133.17 mg/g, respectively. Thermodynamic parameters such as change in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were evaluated for K-birnessite and H-birnessite to be −22.43 kJ/mol (at 298 K), 23.90 kJ/mol, 155 J/mol K, and −18.50 kJ/mol (at 298 K), 10.57 kJ/mol, 98 J/mol K, respectively.