Adsorptive potential of Zn-Al and Mg-Fe layered double hydroxides for the removal of 2-nitrophenol from aqueous solutions

Two layered double hydroxides (LDH) of the type Zn-Al and Mg-Fe were synthesized, characterized and used as adsorbents to uptake 2-nitrophenol (2-NP) from aqueous solutions. XRD, FTIR, SEM, EDS, AFM and N-2 adsorption/desorption curves were used to characterize the Zn-Al-LDH and Mg-Fe-LDH. The potential of both layered double hydroxides to adsorb 2-NP was investigated by adsorption kinetics, equilibrium, thermodynamics and consecutive adsorption/desorption cycles. The characterization indicated a high crystallinity degree and a well-organized and lamellar structure, confirming the efficiency of the synthesis. Elovich was the better kinetic model to describe the 2-NP adsorption onto Zn-Al-LDH, while Pseudo-second order was the best for Mg-Fe-LDH. For both LDHs, the adsorption equilibrium followed the Freundlich model. The process was endothermic, being the maximum adsorption capacities of 290 and 165 mg g(-1) for Zn-Al-LDH and Mg-Fe-LDH, respectively. LDHs can be applied for five adsorption/desorption cycles with excellent adsorption capacities. It can be concluded that Zn-Al-LDH and Mg-Fe-LDH are promising materials to treat waters and wastewaters containing 2-nitrophenol