Persistent organic pollutants removal via hierarchical flower-like layered double hydroxide: Adsorption behaviors and mechanism investigation

Nanostructured hierarchical flower-like MgAl layered double hydroxide (HMA-LDH) was synthesized via the one-pot soft-template method and employed for the adsorption of persistent organic pollutants: anionic methyl orange (MO) and non-ionic naphthalene (NAP). The adsorption performance and mechanism comparison of MO and NAP were investigated via adsorption kinetics, isotherms, thermodynamics, and microstructural characterization. The maximum adsorption capacity of MO and NAP could reach 380.2 and 43.7 mg.g(-1) at 298 K, respectively. The kinetic studies illustrated that the adsorption equilibria reached in 2 and 1 h for MO and NAP, respectively. The adsorption isotherms indicated that HMA-LDH fitted the Langmuir model toward MO removal, while partition model for NAP. The comparative mechanism between MO and NAP were determined by X-ray diffraction (XRD), Fourier transform spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Anion exchange dominated the MO adsorption, whereas partition was deemed as the predominated mechanism for NAP. Furthermore, the recycle performance stated that HMA-LDH could be reused in five cycles in MO adsorption, while failed after two cycles for NAP. This study provided a theoretical foundation for the practical application of hierarchical flower-like LDH in the adsorption of persistent organic pollutants in the aquatic environment.