Simultaneous removal of Hg2+, Pb2+ and Cd2+ from aqueous solutions on multifunctional MoS2

In this work, multifunctional MoS2 prepared by hydrothermal method was studied as an adsorbent for the simultaneous removal of He2+, Pb2+ and Cd2+ in aqueous solutions. This study was performed through the adsorption experiments in single- and multi-metal systems. It was shown that MoS2 exhibited a highest adsorption capacity for Hg2+, and lowest for Cd2+, which was mainly attributed to the different affinities between the S sites and the heavy metals. Based on the results of XPS and Zeta potential, the adsorption mechanisms were investigated in depth, which involved oxidation-reduction between Hg2+ and MoS2, electrostatic attraction between positively charged heavy metals and negatively charged MoS2 , complexation of Hg-S, Pb-S, Cd-S, Hg-O and Pb-MoO4 and ion-exchange reaction occurred on -SH and -OH. In the coexistence of Hg2+, Pb2+ and Cd2+, the excess MoO3 generated during the oxidation-reduction between MoS2 and Hg2+ resulted in a higher adsorption capacity for Pb2+ compared with the condition in single-metal system. However, the adsorption sites of S on MoS2 would be occupied competitively by the three heavy metals so that it caused lower adsorption capacities for Hg2+ and Cd2+. These findings would make a great significance in the field of water treatment by MoS2. (C) 2019 Elsevier B.V. All rights reserved.