Mechanistic insights of nitrate removal by MgFe/layered double hydroxides prepared by different synthesis pathways

Abstract

In this study, a layered MgFe/double hydroxide (MgFe/LDH) adsorbent for nitrate removal from simulated systems was developed and investigated. Three different synthesis methods were used: coprecipitation at constant pH (CC), conventional hydrothermal (CH), and pre-ultrasonic followed by conventional hydrothermal (UCH). The XRD results indicated that all synthesized samples presented the characteristic structure of LDHs. The analysis of FT-IR spectra before and after nitrate adsorption allowed the analysis of NO3−MgFe/LDH interaction in different adsorbents. Adsorption kinetics showed that all adsorbents reached equilibrium around 120 min, with the adsorption capacity being 6.970, 6.690, and 5.610 mg g−1 for the UCH, CH, and CC, respectively. Pseudo-second order and Langmuir models were the best models for describing the kinetics and isotherm data. The highest maximum adsorption capacity was reached at 330 K, with a value of 21.18 mg g−1 for the UHC. Thermodynamic analysis indicated that the adsorption of nitrate was exothermic and spontaneous despite the system. The results of this study suggest that the MgFe/LDH adsorbent synthesized by the UCH method with hydrothermal treatment presents a promising and efficient way of removing nitrate from polluted water, with potential application in the purification of water for human and environmental use.

Keywords

• Synthetic clays
• Synthesis routes
• Nitrate
• Adsorption