New strategy to remove phosphate from low concentration solution by MOFs-modified resin: High affinity and thermal desorption

Adsorption process was usually torn between higher affinity and easier regeneration. Herein, for removing phosphate from low concentration solution, a new strategy was developed to break this tradeoff by metal organic frameworks (MOFs) confined in resins. For comparison, a series of metal oxide modified resins were prepared as adsorbents together with MOFs modified resins (transformation from corresponding oxides). MIL-101(Fe) presents higher adsorption capacity (41.79 mg/g) than Oxide(Fe)@201(36.07 mg/g), as well as high anti-interference ability with removal efficiency of 99.8% (2 mg/L phosphate), even if the loading amounts of iron in Oxide(Fe)@201 is almost twice of that in MIL-101(Fe)@201. Instrumental analysis and molecular dynamics simulations show that the higher adsorption affinity is mainly due to direct interaction between Fe3+ and phosphate via the formation of Fe-O-P, leading to much lower adsorption binding energy (Eads) of phosphate on MIL-101(Fe)@201 (-42.48 kcal/mol) than Oxide(Fe)@201; In desorption process, the MOFs structure can be stably restored with push of organic salt and high temperature (60 °C) around neutral pH due to the reversible structural transformation of MOFs. Moreover, MIL-101(Fe)@201 can continuously purify wastewater containing low concentration phosphate in fixed bed system after multiple regeneration, the water treatment capacity remained above ∼3000 BV and the regenerants can be intermittently recycled with precipitation of calcium phosphate from the solutions.