Synthesis And Properties Of Natural Material/NiAl Layered Double Hydroxides Composite For Fluoride Removal

Layered double hydroxides (LDHs) as adsorbent have a wide range of applications inwater treatment. The aim of this paper was to effectively remove fluoride from aqueoussolution by adsorption of NiAl-LDHs. Non-thermal plasma modified NiAl-LDHs,chitosan-based NiAl-LDHs composite and shell powder-based NiAl-LDHs compositewere prepared by simple methods, and their adsorption capacity for fluoride in water wereinvestigated, respectively.Firstly, NiAl-LDHs was synthesized via traditional coprecipitation at constant pH,and modified by non-thermal plasma. The physical and chemical properties of synthesizedmaterials were characterized by X-ray diffraction (XRD), transmission electronmicroscopy (TEM), Fourier transform infrared (FT-IR) spectrum, thermogracimetricanalysis and N2adsorption-desorption isotherm. The batch adsorption method forevaluating the removal of fluoride on NiAl-LDHs was investigated, where the impact ofoperational parameters such as calcination temperature, adsorbent dose, pH value,coexisting anions, adsorption temperature and adsorption time were evaluated. The resultsshowed that non-thermal plasma modified materials had a larger surface, which wasbeneficial for improve adsorption capacity. The pseudo-second-order kinetic model agreesvery well with the dynamical experimental data and the adsorption isotherm models werewell fit with Langmuir model, the adsorption process was thermodynamicallyspontaneous.Then, the chitosan-based NiAl-LDHs were prepared by coprecipitation andmicrowave assisted methods. The XRD results showed that the materials had a higherdegree of crystallinity which prepared by microwave methods, while a higher adsorptioncapacity of materials prepared by coprecipitation. The adsorption performance was betterin acidic conditions via the protonation of chitosan. The adsorption was very fast andbecame almost asymptotic after30min. In order to understand the mechanism ofadsorption, thermodynamic parameters such asΔG,ΔH,Δ S and Ea were calculated.Finally, the shell powder-based NiAl-LDHs were prepared by microwave-assistedmethod. The scanning electron microscopy (SEM) showed that materials had a relatively uniform3D flowerlike microspheres structure and the microspheres were1~1.5μmdiameters. Materials with2.0g shell powder and microwave radiation2.0h exhibitedbetter performance for fluoride adsorption. The pseudo–second–order and intra-particlediffusion models played a significant role in the adsorption process and thethermodynamic data were better fit by the Freündlich model.