Complexation of Hg(II) ions with a functionalized adsorbent: A thermodynamic and kinetic approach

A new functionalized hybrid adsorbent is prepared by covalent grafting of thiosemicarbazide to the silica surface for the abatement of environmental mercury. The material was characterized using spectral techniques like SEM, TGA, FTIR, EDX and BET surface area analysis. The EDX images showed that the chelating ligand was successfully grafted on the surface. The material is analyzed as Hg(II) extractant by using radiotracer in batch experiments. Maximum adsorption capacity for the adsorbent is about 4.83 mg g−1 at pH 7, pHzpc 6.5 and equilibration time of 30 min. The kinetics are best described by Pseudo second order kinetic model (R2 > 0.99). The equilibrium adsorption data are modeled with Langmuir, D-R and Freundlich isotherms. The adsorption capacity (0.05 mmol g−1) calculated from Freundlich model is in agreement with the experimental results (0.023 mmol g−1). Freundlich isotherm predicted heterogeneous nature of the sorbent surface and infinite surface coverage. The adsorption process of mercury is endothermic (ΔH = 27.53 J K−1 mol−1), favorable (ΔS = 106.13 J K−1 mol−1) and spontaneous (ΔG = − 3695.83 J mol−1) in nature, as suggested by thermodynamic investigations.