Synthesis and use of 3-mercaptopropyl modified MCM-41 for mercury removal from wastewater

Abstract

MCM-41 was synthesized and modified with sulfur-containing functional group (3-mercaptopropyltrimethoxysilane, MPTMS) which has a good affinity towards mercury ions. Three synthesis methods were studied; (i) Conventional hydrothermal templated sol-gel method (Con), (ii) Original stepped template sol-gel method (Step), and (iii) Grafting method that was divided into grafting method using MCM-41 prepared by conventional hydrothermal templated sol-gel method (Graft-con) and by original stepped template sol-gel method (Graft-step). The amount of MPTMS was varied in the synthesis. The efficiency of the method in ligand loading on the adsorbents was evaluated and compared. The ligand loading efficiency followed the order: Con method > Graft-step method > Step method > Graft-con method. The adsorption efficiency for mercury ions of the obtained products (MP-MCM-41) was evaluated and compared. The order adsorption efficiency of products followed MP-MCM-41 (Graft-step) > MP-MCM-41 (Graft-con) > MP-MCM-41 (Step) > MP-MCM-41 (Con). The Graft-step method was the most suitable method despite of fairly good ligand loading efficiency compared to other methods. All the obtained adsorbents were characterized by XRD, FT-IR, surface area analysis and thermal analysis. The factors that affect mercury(II) ions adsorption by MP-MCM-41 were studied i.e. the pH of solution, contact time, interfering ions. The suitable pH for adsorption was 5-8. Adsorption reached the equilibrium within 20 min. The presence of chloride ions (0.1 and 1.0 M) reduced the removal efficiency up to 24-41%. The adsorption behavior of mercury on MP-MCM-41 at equilibrium followed Langmuir isotherm and the maximum mercury(II) ions adsorption capacity was 1.25 mmol/g. This material could be reused at least 4 cycles and it could remove mercury in real wastewater from refinery processes.