ZIF-8 derived porous adsorbent for phosphate adsorption from water

Abstract

Abstract

Two new zinc based adsorbents (Zn4-MIm and Zn2-Et-4-MIm) were synthesized by introducing methyl groups at the fourth position. The resulting materials, designated as Zn4-MIm and Zn2-Et-4-MIm, were characterized using a variety of techniques to elucidate their surface properties and structural features. Preliminary synthesis attempts were made by adjusting the ratio of ligand to metal, and the results showed that similar crystalline products can only be obtained at specific stoichiometric ratios: the Zn: 4-MIm ratio of Zn4-MIm is 4:1, and the Zn: 2-Et-4-MIm ratio of Zn2-Et-4-MIm is 2:1. However, the product yield at these ratios was prohibitively low. Therefore, both materials were subsequently synthesized using a higher ligand to metal ratio of 8:1 (ligand: Zn). Although this method successfully produced a large amount of materials, SEM and XRD analysis showed that the morphology of the product was mainly spherical, lacking a clear crystal structure. Under the experimental conditions (298 K, Cphosphate = 50 mg·(P)·L−1, Cadsorbent = 0.2 g·L−1), Zn4-MIm (qmax = 76.63 ± 3.97 mg·g−1) and Zn2-Et-4-MIm (qmax = 93.20 ± 0.70 mg·g−1) both showed good adsorption performance. The Langmuir model and PSO are more in line with the processes of these two materials. Besides, both materials demonstrated high reusability, retaining 75.76% (Zn4-MIm) and 92.15% (Zn2-Et-4-MIm) of their initial adsorption capacity after four cycles. The adsorption mechanism controlled by Zn-O-P complexation and electrostatic interactions was revealed by comparing FT-IR and XPS.