The formation and adsorption mechanism studies of 3D hydrangea-like ZnFe-LDHs/FeOOH for the highly efficient removal of phosphate

Phosphate in water can cause a series of problems such as overgrowth of algae and other aquatic organisms, foul-smelling, turbid water and lower dissolved oxygen concentrations, thereby posing a serious threat to human health and environment. To efficiently remove phosphate from water, three-dimensional hydrangea-like ZnFe-layered double hydroxides/FeOOH composites (3D hydrangea-like ZnFe-LDHs/FeOOH) were designed and prepared by a facile urea hydrothermal method. The maximum adsorption capacity of phosphate by 3D hydrangea-like ZnFe-LDHs/FeOOH reached about 200 mg·g−1, much higher than that of ZnFe-LDHs prepared by co-precipitation method (53 mg·g−1) and other reported adsorbents, which confirmed that 3D morphology contributed to the improvement of adsorption capacity. Time-dependent experiments were designed to explore the formation mechanism of 3D hydrangea-like structure and the results indicated directional aggregation and epitaxial growth were two main processes. Batch experiments were conducted to investigate adsorption behavior of phosphate. The adsorption kinetics and isotherms showed that the adsorption process followed the quasi-first-order kinetics and Langmuir model. Besides, 3D hydrangea-like ZnFe-LDHs/FeOOH could be regenerated effectively and recycled at least three times. 3D hydrangea-like ZnFe-LDHs/FeOOH possessed fascinating performance in phosphate removal from real river samples and laundry detergent samples, with the removal rates of 66–100 % and 80–100 %, respectively. Furthermore, 3D hydrangea-like ZnFe-LDHs showed good adsorption performance towards other anionic dyes, including Congo Red and Orange Yellow II, with the maximum adsorption capacity of 867 mg·g−1 and 225 mg·g−1, indicating its widespread applicability. The adsorption mechanism of phosphate by 3D hydrangea-like ZnFe-LDHs was furtherly investigated, mainly containing metal coordination, anion exchange between layers and electrostatic interactions.