Comparative Study of Removing Anionic Contaminants by Layered Double Hydroxides with Different Paths

Abstract A comparative study of anionic contaminants removal using layered double hydroxides (LDHs) by three different paths (ion-exchange, reconstruction and one-pot method) was investigated. The removal of targeted contaminants methyl orange (MO) and methyl red (MR) with similar structure from wastewater by these three methods were tested, respectively. The results of SEM revealed that LDHs obtained by the three methods showed different layered morphologies and the concentration of contaminant almost has no influence to the morphologies. In kinetic study, the removal behaviors of three methods were well described by pseudo-second-order model, and showed different patterns in intraparticle diffusion model, revealing that accessible active sites on the adsorbent were the main factor for different adsorption capacity of these methods. The isotherm experiments manifested that all removal data were well fitted by Langmuir models and revealed a charge-limited process. The adsorption capacity of MO was higher than that of MR by all these methods, and the one pot method had the largest adsorption capacity for MO and MR, which were 2.87 and 2.25 mmol/g respectively. The obtained samples were characterized by XRD and different interlayer spacings were observed by these three methods, which was caused by the amount and the arrangement of MO or MR. Molecular simulation was selected to calculate the change of chemical bond, electron transfer and bonding energy, explaining the different removal capacity of MO and MR.