Ultrahigh removal of methyl orange, acid blue-92 and malachite green by a novel triazine-based polyamine resin: synthesis, isotherm and kinetic studies

A novel triazine-based resin (APP-TRIAZ) has been synthesised for the highly efficient and rapid removal of methyl orange (MO), acid blue 92 (AB92) and malachite green (MG) from aqueous solution. The mesoporous APP-TRIAZ displayed excellent adsorptive performance with maximum adsorption capacities (Q_max) of 454.96 mg g⁻¹, 329.56 mg g⁻¹ and 424.81 mg g⁻¹ for MO, AB92 and MG, respectively. The experimental adsorption data were examined by non-linear curve fitting of four isotherm models which hinted that Lagergren’s pseudo-second-order model as a best-fitted kinetics model in describing adsorption of these dyes. The kinetics studies indicated a faster rate of adsorption for these dyes, with adsorption capacities ~ 90%, in the first 4 hours. The thermodynamics calculations revealed that adsorption was exothermic and physical in nature. Adsorption at varied pH indicated that electrostatic forces, hydrogen-bonding and π-π stacking interaction are the main adsorption mechanisms involved. The APP-TRIAZ is thermally stable(T_d = 375 °C) and mesoporous in nature, established by thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) analysis, respectively. The X-ray photoelectron spectroscopy (XPS) analysis of MO- and AB92-loaded resins revealed two additional peaks owing to S 2p and O 1s at around 164.80 eV and 529.13 eV, suggesting the presence of sulphur-based function on the surface of the loaded resin. The resin exhibits good reusability, retaining adsorption efficiency of 61–76% after four cycles of adsorption-desorption process. The APP-TRIAZ extensively characterised by field emission scanning electron spectroscopy (FESEM), solid state ¹³C (CP-MAS) NMR, FT-IR,and energy dispersion spectroscopic (EDS) analysis.