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

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 degrees C in the pH-unadjusted (pH = 6.25) solution possibly due to the hydrogen bond, pi-pi stacking, and electrostatic interaction between PCEA-LS and CR. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48640.