New strategy to remove phosphate from low concentration solution by MOFs-modified resin: High affinity and thermal desorption
Qiong Tang, Zhonglong Yin, Ruoding Wang, Wei Zhu, Zepeng Zhang, Yue Wang, Zhen Yang, Fuqiang Liu, Weiben Yang
Abstract
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 Fe 3+ and phosphate via the formation of Fe-O-P, leading to much lower adsorption binding energy (E ads ) 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.