Melamine Thiourea Chemically Modified Activated Carbon Derived from Water Hyacinth  as an Efficient Adsorbent for the Removal of Hg(II), Pb(II) and Cd(II) Ions from Aqueous Solution

Abstract

The purpose of this work was to incorporate amine and thiol groups onto the surface of activated carbon (MT-MAC) derived from water hyacinth through amidation reaction between the amino groups of melamine thiourea (MT) and the carboxyl groups of activated carbon (OAC) in presence of dicyclohexylcarbodiimide as a coupling agent. The prepared MT-MAC exhibited extensive potential for the extraction of toxic metal ions Hg(II), Pb(II) and Cd(II) from wastewater. The prepared MT-MAC was characterized by different techniques like BET, SEM, XPS, and FTIR analysis. The results displayed that the total pore volume and surface area of OAC were found to be 864.52 m2 g-1 and 0.5216 m3 g-1, respectively and decreased up on modification with melamine thiourea to 493.78 m2 g-1 and0.2916 m3 g-1.FTIR spectra confirmed the incorporation of amine and thiol groups on the surface of OAC by the appearance of new peaks at 1625 cm-1 and 3332 cm-1 corresponding to the C=O stretching vibration of the NHCO (amide), and N-H stretching vibration, respectively. XPS displayed two new peaks due to S2p and N1s in the MT-MAC survey scan. The MT-MAC adsorbent showed high capacities for the removal of Hg(II) ( 292.6 mg.g-1), Pb(II) (237.4 mg.-1) and Cd(II) (97.9 mg.g-1) from aqueous solution at pH 5.5, agitation time 60 min and 298 K.The experimental sorption data could be fitted well with Langmuir isotherm model suggesting a monolayer adsorption behavior. Chemisorption mechanism via melaminethiourea groups grafted on the surface of activated carbon is suggested based on the excellent agreement of the kinetic data with pseudo–second-order model. The MT-MAC exhibited high stability over three adsorption-desorption cycles. The results also revealed that MT-MAC is a promising adsorbent for the extraction of Hg(II), Pb(II) and Cd(II) ions from polluted water.