Two-dimensional hydrophilic ZIF-L as a highly-selective adsorbent for rapid phosphate removal from wastewater

Abstract

Recently zeolitic imidazolate framework-8 (ZIF-8) is considered as a promising adsorbent for phosphate removal, due to their huge surface area from high porosity and strong affinity of Zn (II) centers to PO43− ions. However, the three-dimensional structure and hydrophobicity of commonly micron-sized ZIF-8 material result in a low capacity and a slow kinetics for phosphate adsorption. To overcome these shortcomings, a two-dimensional hydrophilic leaf-like ZIF (ZIF-L) adsorbent was prepared by a simple precipitation method. These features of ZIF-L led to a rapid phosphate-adsorbed rate of 0.0376 g mg−1 min−1, but just 0.0050 g mg−1 min−1 for ZIF-8. Compared to many reported ZIF-8 materials (38.22–41.7 mg g−1), a larger phosphate adsorption capacity of 75.18 ± 2.65 mg g−1 for 2D ZIF-L was mainly benefitting from abundant Zn-OH defects to form Zn-O-P bond, high zeta positive potential to generate electrostatic attraction and hydrophilic surface to expose active sites. Moreover, about 100% of phosphate was selectively adsorbed by ZIF-L from the real influent (1.61 mg L−1) and effluent (0.12 mg L−1) of sewage plant. Such an excellent phosphate removal performance of ZIF-L adsorbent enables its practical application in wastewater treatment.