Triazine-based sulphur-containing polymers for Hg2+ adsorption: Efficiency and mechanism

Abstract

Recently the research on the materials for removal of heave metals is surging rapidly. Here we have studied four triazine-based sulfur-containing polymers with different linkers, namely PDT1, PDT2, EDT1, and EDT2. They have been successfully synthesized by the nucleophilic substitution reaction of cyanuric chloride with propane-1,3-dithiol (PDT1 and PDT2) and ethane-1,2-dithiol (EDT1 and EDT2) in different ratios. The physical and chemical properties of these polymers were characterized by scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, porous structure analysis and X-ray photoelectron spectroscopy. The optimized adsorption condition was established by examining dosing, co-existing substances, contact time, concentration, temperature and pH values. The adsorbing properties, which was mainly described by the pseudo-second-order kinetic and Langmuir isothermal model, indicated that the sorption of Hg2+ was the chemical adsorption. The maximum Hg2+ sorption capacities of PDT1, PDT2, EDT1 and EDT2 were 1440.97 mg g−1, 715.99 mg g−1, 237.87 mg g−1 and 181.48 mg g−1, respectively. Thermodynamically, the adsorption of Hg2+ by the adsorbent is a spontaneous process. Cyclic experiments demonstrated that all the adsorbents could be reused in five successive adsorption cycles without significant losses in performance. Our density functional theory calculations in combination with relevant experimental results revealed the coordination geometry of Hg and hence mercury-adsorbent chelation mechanism. These results suggested that triazine-based sulfur-containing polymers could be utilized as effective adsorbents for the removal of Hg2+ from polluted water.