Lignin-modulated magnetic negatively charged Fe3O4@lignin nanospheres in removing cationic dyes from wastewater

In recent decades, large amounts of wastewater containing toxic dyes have been generated in the industrial process such as fine chemicals, printing, paper, and textiles. In order to overcome the problem of the complex separation process of conventional adsorbents, the lignin-modulated magnetic negatively charged Fe3O4@lignin/phenolic resins nanospheres (Fe3O4@LPF) by a simple reverse-phase emulsion polymerization method was synthesized. The results demonstrate a contributing effect on improving the sphere size and structure of the Fe3O4@lignin nanospheres with the addition of lignin. The Fe3O4@40%lignin/phenolic resins nanospheres (Fe3O4@40%LPF) with optimal adsorption performance were selected for adsorption experiments, kinetic calculations, and isotherm model fitting. Compared with other prepared magnetic adsorbents in this work, the dye removal ratio of the Fe3O4@40%LPF in removing RB can reach 99.80% at 50 °C. Moreover, the maximum experimental adsorption capacity of Rhodamine B (RB) using the Fe3O4@40%LPF is 41.03 mg/g when the concentration of dye is 225 mg/L. The Fe3O4@40%LPF can still maintain a dye uptake of 28.71 31.65, 25.00, and 15.82 mg/g after five cycles of removing RB, MB, CV, and MO, respectively. Also, there is only 0.0009 mg/L of Fe2+ or Fe3+ existed in the solution after the Fe3O4@40%LPF adsorbing RB, suggesting the excellent stability of the Fe3O4@40%LPF. Four kinetic models of the Fe3O4@40%LPF were calculated, suggesting a chemisorption process involving hydrogen bonding interaction. The isotherm models fitting results indicate that the theoretical maximum monolayer adsorption capacity of the Fe3O4@40%LPF adsorbing RB is 207.0 mg/g. The proper adsorption mechanism between the Fe3O4@40%LPF and RB is electrostatic attraction, hydrogen bond interaction, and the π-π interaction. This work demonstrates that the prepared material can be considered a high-efficiency and economic adsorbent. [Display omitted] •The Fe3O4@40%LPF was synthesized through simple reverse-phase emulsion polymerization strategy using low-cost lignin.•The Fe3O4@40%LPF showed a superior experimental adsorption capacity of 41.03 mg/g in removing RB from aqueous solution.•A contributing effect on improving the sphere size and structure of the Fe3O4@lignin nanospheres with the addition of lignin.•The Fe3O4@40%LPF exhibited excellent potential application in the wastewater industry.