Thio-groups decorated covalent triazine polyamide (TTPA) for Hg²⁺ adsorption: Efficiency and mechanism

In this work, the thio-modified covalent triazine polyamides, TTPA-1 (1.5/1) and TTPA-2 (1/1), were successfully synthesized from the diester containing S and melamine, and applied to the adsorption of Hg2+ in the aqueous solution. We have systematically investigated the factors that can affect the adsorption process, such as the dosage of the adsorbent, the contact time, the temperature of the heavy metal solution, the initial concentration of the ions, the pH, the co-existing substances, and the desorption. The pseudo-second-order kinetic model can describe the adsorption of Hg2+ well, and the equilibrium adsorption time is 180 min, respectively. The most appropriate adsorption isotherm model is Langmuir, and the maximum Hg2+ adsorption capacities calculated at 25 degrees C are 685 (TTPA-1) and 657 (TPPA-2) mg g(-1). Repeatable experiments have shown that it can be reused more than 10 times without any loss. The adsorption mechanism of TTPA-1 (-2) was elucidated by combining experimental results, spectral characterization (SEM and XPS, etc.) and the density-functional-theory (DFT) calculations. These results indicate that TTPA-1 (-2) could have a good potential for the removal of the Hg2+ metal ions from wastewater.