Synthesis and enhanced adsorption for F− by three novel high entropy LDHs using TEA-assisted hydrothermal technology

Abstract

Nowadays the design, preparation and application of high entropy LDHs (HE-LDHs) has already become research hotspots. In this paper, three types of high entropy ZnCoCrMgZr-LDHs (HE-LDHs-1, 2 and 3) were successfully prepared for the first time using TEA as alkali source by simple hydrothermal synthesis, and characterized by XRD, TG, SEM, X-ray photoelectron spectroscopy, BET and zeta potential. The effect of triethanolamine (TEA) on the formation of high entropy LDHs and their adsorption behaviour for F− were investigated. Research showed that high content of TEA can maintain and provide more hydroxyl groups required for the formation of LDHs, while the introduction of high valence Zr4+ breaks the regular arrangement of LDHs themselves. Three types of high entropy LDHs have excellent adsorption performance for F− with the maximum adsorption capacities of 113.78 mg/g, 142.12 mg/g and 128.24 mg/g, respectively. They also have strong resistance to anionic interference. The adsorption process is the transition from physical adsorption to chemical adsorption in the F− adsorption process from HE-LDHs-1 to 3. The adsorption isotherm models of LDHs-1 exhibit high R2 values which shown that their F− adsorption behaviour is the result of the combined effect of physical and chemical adsorption. The adsorption behaviour of LDHs-2 and 3 is more in line with the quasi second-order kinetic model and Langmuir model, indicating that the F− adsorption process is a single-layer adsorption based on chemical reaction-controlled kinetics. The lower temperatures are more conducive to the process for all three adsorbents adsorption process generates heat. FLDHs can still re-adsorb the dye CR after four cycles of adsorbing fluoride ions. HE-LDHs exhibit high adsorption, selectivity, and good reuse performance for fluoride ions, making them promising for wastewater treatment applications.