In the pH range of 3–7, the adsorbent surface became protonated and positively charged, and thus would more significantly attract the negatively charged phosphate anions H2PO4.
The attractive forces between the Fe3O4@LDHs surface sites and anionic H2PO4 easily resulted in the formation of metal–ligand magnetic composite complexes.
The surface hydroxyl groups (M–OH) could be exchanged by the adsorbed phosphate, forming outer-sphere complex (M–O–P).
Also, carbonatewas known to convert to bicarbonate which was more labile in the interlamellar space at low pH. Such labile structure enhanced the uptake capacity of the LDHs .
Ion exchange was easily occurred between phosphate anions H2PO4 and interlayer anions.
Therefore, the removal efficiency of phosphate was more than80% at pH 3–7.