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

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), N 2 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 (NO 3 −, Cl −). The Langmuir monolayer adsorption capacities of K-birnessite and H-birnessite samples in 0.1 M NaNO 3 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. ► The presence of NO 3 − in birnessite samples is of academic importance. ► NO 3 − in birnessite could be utilized as an exchangeable site for other anions. ► H + treatment increases total pore volume, which does not come from the increase in micropores. ► The works related to Pb(II) adsorption on birnessite are scarce. ► The change in the intensity of Mn–O band is also linked to Pb(II) adsorption.