Comparative study of layered double hydroxides intercalated by MoS42− and Mo3S132− on removal of Cu(II) and Pb(II): Adsorption mechanism and environmental stability

MgAl layered double hydroxides (LDHs) intercalated by Mo3S132− and MoS42− (Mo3S13-LDHs/MoS4-LDHs) were prepared through the ion exchange method and compared their removing ability of Cu(II), Pb(II) from wastewater. When the batch experiment conducted at dosage 0.3 g/L, pH neutral, contact time 360 min, concentration 6 mmol/L and temperature 298 K, the adsorption capacity of Cu(II)/Pb(II) onto Mo3S13-LDHs and MoS4-LDHs was 2.76, 4.85 and 2.15, 4.66 mmol/g, Mo3S13-LDHs showed a higher adsorption capacity, which was because the larger amount of adsorption sites on Mo3S132−. In mixed systems, Mo3S13-LDHs/MoS4-LDHs exhibited the preferential selectivity of Pb(II). When Mo3S13-LDHs/MoS4-LDHs adsorbed the low concentrations of Cu(II)/Pb(II), Mo3S132−/MoS42− first captured heavy metals and fixed into the interlayer. With the increase of concentration, Cu(II)/Pb(II) were still captured by the interlayered Mo3S132− unlike MoS4-LDHs that hydroxyl groups onto LDHs began to capture Cu(II)/Pb(II). In the dynamic adsorption experiment, Mo3S13-LDHs could treat a larger volume of sewage than MoS4-LDHs. Mo3S13-LDHs exhibited better selectivity for Cu(II)/Pb(II) under the interference of organic and other metal ions in wastewater, and heavy metals after the treatment by Mo3S13-LDHs were more stable in the environment. Therefore, Mo3S13-LDHs could be considered as an environmentally stable adsorbent to remove heavy metals from wastewater compared to MoS4-LDHs. [Display omitted] •Mo3S13-LDH held massive binding sites in the interlayer to capture heavy metals.•Mo3S13-LDH exhibited excellent adsorption capacities and environmental stability.•The preferential selectivity of Pb onto Mo3S13-LDH/MoS4-LDH in the mixed solution.•The removal mechanism was interlayer fixation and additional precipitation for MoS4-LDH.