A karst-inspired hierarchical Mg/Al layered double hydroxide with a high entropy-driven process for interception and storage

Abstract

Karstification plays a crucial role in forming magnificent scenery, and storing oil, natural gas, mineral resources, and water. Through the inspiration of karstification, a hierarchical layered double hydroxide (LDH) with funnel-like and cave-like structures (called Karst-LDH) is formed by the dissolution of acrylic acid/water solution. Meanwhile, the results of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) show that Karst-LDH has complicated and interconnected internal pipe networks. The actual maximum phosphate adsorption capacity of Karst-LDH reaches 126.38 mg g⁻¹ due to the unique structures, protonation, ligand exchange, ion exchange, and hydrogen bonding, which is over ten times that of general LDH with a regular hexagonal structure. The results of isotherms and thermodynamics also indicate that Karst-LDH conforms to more heterogeneous and multilayer adsorption with a higher entropy-driven process. Karst-LDH exhibits good selectivity for chloride and nitrate ions. The change in the frontier orbital interaction between phosphate and different LDHs is a significant reason for quick macropore transmission, mesopore interception, and finally, phosphate storage in Karst-LDH. This work provides an efficient way for the design and fabrication of high adsorption performance materials with unique karst-type structures, which can be used for multiple fields potentially.