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

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. Pseudosecond 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.