Enhanced removal of Pb2+ and Congo red from aqueous solutions using hierarchically porous melamine sponge/polyvinyl alcohol/Zr-MOF composites

Conventional adsorbent materials are usually limited by low adsorption capacity, difficult regeneration, and long processing time. The construction of hierarchically porous composites is expected to solve these limitations. In this work, a novel strategy for immobilizing Zr-MOF on melamine sponge (MS) using polyvinyl alcohol (PVA) was developed, and melamine sponge/polyvinyl alcohol@UIO-66-TETA composite (MPUT) was prepared. The prepared hierarchically porous material MPUT combines the advantages of MS (large pore size and easy separation) and Zr-MOF (high specific surface area, numerous adsorption sites). It could efficiently separate Pb2+ and Congo Red (CR) in aqueous solution. The Pb2+ adsorption performance was investigated by static adsorption experiments and dynamic column adsorption experiments. The theoretical maximum adsorption capacity of MPUT for Pb2+ and CR could reach 326.80 and 303.95 mg/g, respectively. The excellent removal efficiency is attributed to the hierarchical porous structure and the high density of binding sites. There is a synergistic effect of MPUT on Pb2+ and CR adsorption in the mixed system, which can enhance the removal efficiency. Additionally, MPUT has excellent reusability properties. Experimental data and density functional theory (DFT) calculations show that MPUT adsorbs Pb2+ mainly through chelation and electrostatic interactions, and adsorbs CR through hydrogen bonding and π-π interactions. Overall, MPUT has great potential for application in the separation of Pb2+ and CR from water for environmental remediation.