Efficient removal of Congo red from pH‐unregulated aqueous solutions by lignosulfonate‐based polycatecholamine

ABSTRACT Lignosulfonate‐based polycatecholamine (PCEA‐LS) was synthesized by a two‐stage approach involving Mannich and catechol–amine reactions, and it was directly used to adsorb Congo red (CR) from the pH‐unadjusted aqueous solution. PCEA‐LS was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), and X‐ray photoelectron spectroscopy (XPS). Various factors affecting on removal of CR by PCEA‐LS were investigated in depth, including contact time, adsorbent dosage, and initial concentration of CR and adsorption temperature. The adsorption kinetics, isotherm, and thermodynamics of PCEA‐LS for CR were explored in detail, and then its adsorption mechanism was systematically elucidated. Results indicated that the removal process of CR followed the pseudo‐second‐order kinetic model, and the isotherm data fitted the Langmuir model well. The maximum adsorption capacity reached 972.6 mg g −1 at 30°C in the pH‐unadjusted (pH = 6.25) solution possibly due to the hydrogen bond, π–π stacking, and electrostatic interaction between PCEA‐LS and CR. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137 , 48640.