High efficiency of phosphate adsorption by yolk-shell Mn–La binary nanocomposites from aqueous solution: Adsorption and mechanism studies

In this work, yolk-shell Mn La binary nanocomposites were successfully prepared by a simple two-step precipitation procedure in order to enhance the utilization efficiency of La for sequestering phosphate from water. Advanced techniques including XRD, FTIR, SEM-EDX, BET and zeta potential analysis were employed to characterize the synthesized yolk-shell Mn La binary nanocomposites, indicating δ-MnO 2 in the yolk and La(OH) 3 in the shell. Batch adsorption experiments revealed that the Mn La binary nanocomposites exhibited a relatively rapid adsorption process in the first 1.5 h. The q max of phosphate increased with the increase of La contents in the nanocomposites, and the increase of solution pH apparently reduced the removal efficiency of phosphate. Mn La binary nanocomposites were considered effective even in the presence of coexisting anions, and exhibited an acceptable adsorption reusability. The mechanisms of phosphate removal involved ligand exchange reactions, electrostatic attraction and surface coprecipitation to form LaPO 4 nanocrystals. Lanthanum hydroxide in the shell was vital for phosphate removal. Based on the curve fitting results of FTIR, the phosphate configurations on the Mn La binary nanocomposites transformed from doubly protonated species at pH 3 to singly protonated species at pH 9. This study provides a potential approach for phosphate treatment from aqueous environments. • A series of yolk-shell Mn–La binary nanocomposites were successfully prepared. • The removal performance of phosphate was investigated. • Lanthanum hydroxide in the shell was vital for phosphate removal. • LaPO 4 was formed after phosphate removal. • Phosphate configurations were diprotonated and monoprotonated.