Removal of toxic ammonium ions from water using nanographene sheets

This paper describes the removal of toxic ammonium ions from model and real water samples using nanographene sheets (NGs). NGs were characterized by using a scanning electron microscope, a transmission electron microscope, X-ray diffraction, and surface area analysis. The results showed that NGs exist as plate-like overlapped transparent wrinkled sheets of graphene with different dimensions and characterized with high Brunauer-Emmett-Teller specific surface area. The effect of different experimental conditions, NGs mass, removal time, solution temperature, and ionic strength, affecting the removal efficiency of NH4+ by NGs from synthetic water sample, was studied and optimized. The adsorption experiments showed that NGs could remove most of the ammonium ions within few minutes, with adsorption capacity of 11.6 mg of NH4+/g of NGs at ambient conditions. The removal of ammonium ions on NGs was explored kinetically and thermodynamically, and the results revealed the suitability of the pseudo-second-order kinetic model for describing the adsorption process. Also, the adsorption process was spontaneous, exothermic in nature, and negative entropy change indicated the decrease in the degree of freedom at the solid-liquid interface. The applicability of the NGs for the adsorption of ammonium ions was explored using different real environmental water samples, and the results indicated that the NGs have great potential to remove ammonium ions from aqueous solution.