Adsorption and reduction coupling of permanganate on MoS2: Water treatment and metal ion separation

Permanganate (MnO4-) ions were adsorbed on the surface of MoS2 nanosheet and then reacted with it. In this work, effects of pH, temperature, initial MnO4- concentration and ionic strength on this process were studied. The adsorption sites of MoS2 were Mo(IV)-S pairs located in its micropores (abbreviated as MI). Before starting reaction, MoS2 acted as a high capacity adsorbent for MnO4- ions at a certain time. Under various conditions, MnO4- ions were adsorbed on the surface of MoS2 during different time periods (20-180 min) and then reacted with it. The maximum adsorption capacity of MnO4- ions on MoS2 surface in water at 328 K was 368.3 mg g(-1) (2.33 mmol g(-1)). Adsorption isotherms were analyzed by the ARIAN model and it was recognized that in the pH range of 1-11, adsorption isotherms were composed from regions I and II and Delta H values of the process for regions I and II in neutral water were 31.4 kJ mol(-1) and 9.9 kJ mol(-1), respectively. At pH = 12, adsorption isotherm was only formed from region I. In the pH range of 1-12, after completion of adsorption process, reaction of adsorbed MnO4- ions with adsorbent obeyed ARIAN-Hinshelwood mechanism. In the pH range of 1-11, water molecules and at pH = 12, OH- ions and water molecules acted as nucleophiles, respectively. Finally, MoS2 adsorbent was used for separation of Cr2O72- and Ni(2+ )ions from MnO4- ions in water.