Ultrahigh and efficient removal of Methyl orange, Eriochrom Black T and acid Blue 92 by triazine based cross-linked polyamine resin: Synthesis, isotherm and kinetic studies

The synthesis of a novel triazine based resin (TRIAZ-PA) has been accomplished for the ultrahigh and efficient removal of Methyl orange (MO), Eriochrom Black T (EBT) and Acid Blue 92 (AB92) from aqueous solution. At room temperature, the mesoporous TRIAZ-PA exhibited excellent adsorptive performance, displaying maximum adsorption capacities (Q_max) of 620.5 mg g⁻¹, 198.3 mg g^-1 and 239.6 mg g⁻¹ for MO, EBT and AB92, respectively. Examination of the experimental adsorption data by non-linear curve fitting of four isotherm models suggested that Langmuir and Freundlich isotherms were the best-fit models in describing the adsorption of these dyes. The kinetics studies revealed faster rate of adsorption, as the equilibrium was achieved within the first 4 h. Moreover, thermodynamics calculations suggested that adsorption was spontaneous, exothermic and physical in nature. The adsorptive performance of the resin at varied pH indicates that beside electrostatic forces and hydrogen-bonding, other adsorption mechanism such hydrophobic interaction or π-π stacking interaction are also involved. The thermal stability of the resin was deduced by thermogravimetric analysis (TGA) (T_d < 300 °C) whereas its mesoporous nature was ascertained by Brunauer-Emmett-Teller (BET) analysis. The X-ray photoelectron spectroscopy (XPS) analysis of dye-loaded resins revealed two new peaks due to O 1s and S 2P at around 529.5 eV and 161.2 eV, hinting the adsorption of the sulfur-based dyes onto the resin. The resin exhibits good reusability, retaining adsorption efficiency of 70 % after four cycles of adsorption-desorption process.