Facile Synthesis Of Mgal Layered Double Hydroxides By A Co-Precipitation Method For Efficient Nitrate Removal From Water: Kinetics And Mechanisms

Recently, layered double hydroxides (LDH) have been proven to be promising adsorbents in the field of wastewater treatment mainly due to their unique characteristics. In this study, a series of MgxAl-LDH (x is the molar ratio of Mg/Al) were synthesized via a supersaturated co-precipitation method and used for the removal of low concentration nitrate (NO3-). Based on the results, Mg5Al-LDH showed a significantly enhanced adsorption capacity of 9.76 mg g(-1), and the removal efficiency of NO3- (C-0 = 1 mg L-1) reached about 80% after 6 h at 25 degrees C and neutral pH. As proved by various characterization studies, changes in the molar ratio of Mg/Al would influence the surface active groups and layer distance of the synthesized LDH, thereby affecting the adsorption of NO3-. In addition, the synthesized LDH presented a mesoporous structure, which can reduce the obstruction for adsorbing NO3-. Studies on the reaction kinetics indicated that the NO3- adsorption behavior of Mg5Al-LDH can be well fitted by the pseudo-second-order kinetic and Langmuir models, demonstrating that the resultant adsorption is a spontaneous, exothermic and entropy decreasing process with physical and chemical effects simultaneously. By further clarifying the mechanisms of NO3- removal, the synthesized Mg5Al-LDH could be thought of as an efficient, environmentally friendly, and low-cost adsorbent to remove NO3- from the aquatic environment.