New strategy to enhance heavy metal ions removal from synthetic wastewater by mercapto-functionalized hydrous manganese oxide via adsorption and membrane separation.

The development of efficient materials and methods for the elimination of heavy metals contamination from water bodies is increasingly demanded as these toxic cations can acute diseases to humans or make serious threat to the environment. The aim of this research is to evaluate the effectiveness of the organosilane coupling agent for the modification of hydrous manganese oxide and the application of the functionalized nanoadsorbent for the removal of nickel and copper ions from synthetic wastewater samples. The synthesized thiol-functionalized hydrous manganese oxide was characterized in terms of their morphology, surface area, functional groups, surface elemental compositions, and the structural properties. In the adsorption process of Ni(II) and Cu(II), the effective parameters including the initial metal cation concentration (20-150 mg/L), operation temperature (298-318 K), and the contact time at the optimum pH were investigated. The uptake of Ni(II) and Cu(II) ions on the prepared adsorbents followed by the Freundlich isotherm model reveals the heterogeneous adsorption, with the adsorption capacities of 24.96 mg/g and 31.2 mg/g for the modified adsorbent and 23.92 mg/g and 29.6 mg/g for the virgin adsorbent, respectively. Based on the results, both the virgin and the functionalized adsorbents exhibited high affinity to copper ions than nickel in the single-component system. Kinetic experiments of both metal ions clarified that the experimental data was well predicted by pseudo-second-order model and the equilibrium was achieved after 10 min of contact time. Additionally, the incorporation of the as-prepared adsorbents in the electrospun nanofibers membrane matrix showed the promising potential for the removal of metal cations. The nickel and copper removal efficiency by the membranes containing 1.5 wt% of the modified adsorbent was 80% and 89%, respectively which implying that the modified adsorbent could be employed more efficiently in other treatment techniques for the removal of metallic pollutants. The modification of hydrous manganese oxide by the functional mercaptosilane increases the adsorption sites for trapping the metal ions and improves the adsorption capacity, making high capability for the removal of metal ions from the effluent.