Phosphate Adsorption from Reclaimed Water via External Cage Expansion on CD-MOF Micro-Interface

As an essential element for all living organisms, excessive phosphate ranks as a primary contributor to eutrophication in aquatic regions. Coordinative modification of metal-organic frameworks (MOFs) with porous molecular cages can enhance their adsorption selectivity for phosphate. In this study, a novel MOF@porous coordination cages (MOF@PCCs) was developed by modifying PCCs with s-triazine, 2,4,6-tris(2-pyridyl)-s-triazine (tpt), and 2,4,6-tris[4-(pyridin-4-ylmethoxy)phenyl][1,3,5]triazine (tpypt). The results indicated that cyclodextrin-MOF@PCC-L (CD-MOF@PCC-L) prepared with tpypt reached an equilibrium adsorption capacity of 164.5 mg/g within 3 min. Notably, factors such as acidic-neutral pH and low concentrations of anions had negligible effects on phosphate adsorption, while humic acid and methyl orange exhibited a noticeable inhibitory effect on phosphate adsorption. CD-MOF@PCC-L can last for ∼2486 bed volumes before the phosphate concentration in the secondary effluent exceeds the average limit of 0.5 mg/L. Superior phosphorus removal efficiency in adsorption/desorption experiments highlights its potential for effective reclaimed water treatment applications. Comprehensive spectroscopic and computational analyses elucidate the multifaceted phosphate adsorption mechanisms on CD-MOF@PCC-L. Subsequently, the study proposed the application of CD-MOF@PCC after phosphate adsorption for further adsorption removal of humic acid and methyl orange. This study provides innovative insights into microinterface adsorption and an effective strategy for the sequential removal of pollutants via employing phosphate as a bridge.