A Facile Acid Etching to Create Unsaturated-Coordinate Zn-Defects on Zif-L Surface for Highly-Selective Phosphate Removal from Wastewater

Abstract

Defects, as the specific chemical bonding sites with phosphate, played a key role in the P-selective adsorption on zeolitic imidazolate frameworks (ZIFs). In this study, numerous unsaturated-coordinate Zn defects were created by a facile acid etching method on leaf-like ZIF (ZIF-L) surface for highly-selective phosphate removal from wastewater. Our acid-etched ZIF-L (ae-ZIF-L) exhibited a much better phosphate adsorption performance of 164.4 mg/g than original ZIF-L (73.5 mg/g), attributing to the specific chemical bonding of richer P-adsorbing-active Zn defects and strong electrostatic attraction from higher surface zeta potential. More importantly, under the strong interfering effect of competitive SO42− and CO32−, ae-ZIF-L possessed outstanding capacity retention rates of 93.8−97.5% (only 77.2−95.7% for ZIF-L) and selectivity coefficients of 8.93−11.12 (only 1.61−2.18 for ZIF-L), mainly thanks to the specific PO43−–adsorbing ability of unsaturated coordinate Zn-defects. Finally, column filtration experiments further demonstrated the application potential of ae-ZIF-L with ~725 BV of actual wastewater treatment to meet the effluent-P standard of 0.5 mg/L, much higher than ~455 BV of ZIF-L. Hence, surface defect engineering via a facile etching method would inspire more interesting works on the design of highly-selective phosphate adsorbent for advanced treatment of wastewater.

Keywords: Zeolitic imidazolate frameworks (ZIFs), acid etching, unsaturated-coordinate Zn defects, phosphate adsorption, high selectivity