Efficient adsorption of Congo red (CR) dye onto novel lignin-based magnetic core-shell adsorbent: Synthesis, characterization and experimental studies

Background: Furfural residue is a by-product in the furfural production from the biomass, and enriched in cellulose and lignin. Lignin is considered efficient candidates for the preparation of bio-based adsorbents because of a variety of functional groups and reactive sites involved. Methods: In this study, we prepared the tunable covalent binding of the aldehyde-based furfural residue lignin onto amine-functionalized Fe3O4 magnetic nanoparticles using cyanuric chloride as a chemoselective crosslinker. The novel lignin-based magnetic adsorbent in core-shell structure was reported for the first time to remove Congo red from aqueous solution. Significant Findings: A distinct core-shell structure is formed, according to the SEM, TEM, FTIR, BET, XPS, and VSM techniques. Adsorption studies suggested that endothermic processes occured for CR adsorption onto AFRL@AMNP, and both pseudo-first and pseudo-second order models could provide a good description of the adsorption kinetics. The Langmuir model estimated the qmax of CR by AFRL@AMNP were 218.2 mg/g at 290 K. According to FTIR, XPS, and DFT calculations, electrostatic interactions, hydrogen bonds, and it-it interactions were identified as main mechanisms for CR onto AFRL@AMNP. More importantly, due to the incorporation of Fe3O4 magnetic nanoparticle, AFRL@AMNP can be easier to separate from the aqueous solutions and be reused.