Magnetic ternary layered double hydroxides for efficient removal of 1-naphthalene acetic acid from waters: Adsorption behavior and mechanism

The removal of pollutants requires environmental protection technology to use the least energy consumption, realize the reuse of substances, and ensure the health of the ecosystem and human body. Layered double hy-droxides (LDHs) are widely used as adsorbents due to their excellent tunable structure properties and biocom-patibility. In this study, magnetic CoMgAl LDH (C-MLDH) and magnetic FeMgAl LDH (F-MLDH) were prepared by coprecipitation method with adding Co element and Fe element respectively on the basis of classical MgAl LDH for the adsorption of 1-naphthoacetic acid (NAA) in water. The morphology and characteristics of the synthesized LDHs were investigated. The pH, adsorbent concentration, kinetics, temperature, isotherm and thermodynamics of the adsorbent were studied to explore the adsorption mechanism. The results showed that the Liu isotherm model and Avrami kinetic model can fit the adsorption isotherm and kinetic data well, respectively. The both synthesized magnetic ternary LDHs had high adsorption capacity of NAA, which reached 258.5 mg/g and 288.5 mg/g for C-MLDH and F-MLDH, respectively. The adsorption of NAA by C-MLDH and F-MLDH was both spontaneous and endothermic. There were two main adsorption mechanisms, one was adsorption by forming hydrogen bonds with hydroxyl groups on the surface of the adsorbent, and the other was anion ex-change. The adsorption capacity of magnetic ternary LDHs mainly depended on the shell LDHs, the addition of Co and Fe elements could promote the adsorption reaction, enhance the adsorption capacity, and the promotion effect of Fe element was better than Co.

Automated summary

To remove pollutants, environmental protection technology needs to use low energy consumption, realize substance reuse, and ensure ecosystem and human health. Layered double hydroxides (LDHs) are widely used as adsorbents due to their adjustable structure properties and biocompatibility. In this study, magnetic CoMgAl LDH (C-MLDH) and magnetic FeMgAl LDH (F-MLDH) were prepared for the adsorption of 1-naphthoacetic acid (NAA) in water. The synthesized LDHs showed high adsorption capacity for NAA and the adsorption was spontaneous and endothermic. Two main adsorption mechanisms were identified, one involving hydrogen bonding with hydroxyl groups on the adsorbent surface, and the other involving anion exchange. The addition of Co and Fe elements promoted the adsorption reaction and enhanced the adsorption capacity, with Fe having a better promotion effect than Co.