Highly efficient removal of Mn(II) and organic pollutant by adipate functionalized Ca-Al layered double hydroxides: Capture behavior and mechanism

Abstract

In this work, Ca-Al LDHs were modified via co-precipitation method utilizing two distinct chemical forms of adipic acid (adipate salt and adipic acid) as intercalation agents, with the resulting materials denoted as At-LDHs (adipate-intercalated LDHs) and Aa-LDHs (adipic acid-intercalated LDHs). The results indicated that At-LDHs and Aa-LDHs all exhibit a sheet-like porous structure stacked with each other. Due to the different synthesis conditions, the sheet structure of Aa-LDHs is smaller than that of At-LDHs. The kinetic and isotherm simulation results indicated that the capture capacity of At-LDHs for Mn^2 + was up to 227.53 mg·g⁻¹ when the pH value was 7, while that of Aa-LDHs for naphthol green B reached to 132.73 mg·g⁻¹ at a pH value of 9. The kinetic and thermodynamic simulation results indicated that the capture of Mn²⁺ by At-LDHs conformed to the pseudo-first-order kinetic model and the Langmuir isotherm model, and the capture of naphthol green B by Aa-LDHs conformed to the Elovich kinetic model and the Temkin isotherm model. In addition, the capture process of both was a spontaneous exothermic reaction. Benefiting from the excellent adsorption properties of At-LDHs composites (Ion exchange, electrostatic attraction, adsorption precipitation, functional group chelation), the adsorption effect on Mn²⁺ was better. Aa-LDHs have good adsorption effect on naphthol green B in solution through electrostatic attraction, dipole-dipole hydrogen bond, Yoshida hydrogen bond and n-π interaction. At-LDHs and Aa-LDHs have great potential to be employed as the materials for the removal of organic and inorganic composite pollutants from wastewater.