Fabrication of demethylated lignin-based micro-particle for efficient adsorption of malachite green from aqueous solution

Recently, the research on low-cost and renewable lignin-based adsorbent for the effective removal of organic dyes from wastewater has attracted great interest. Herein, a demethylated lignin-based micro-particle (DLMP) adsorbent with high hydroxyl content was prepared by using AlCl 3 as modification reagent, which exhibited an excellent adsorption capacity for malachite green (MG). The results showed that the size distribution of DLMP was about 100–500 nm, the surface area reached 17.35 m 2 /g, and the phenolic hydroxyl (Ar-OH) group content was up to 5.77 mmol/g, which was much better than that of originally organosolv lignin (OL). With this DLMP as the lignin-based adsorbent, all adsorption processes fitted well with the Langmuir isothermal and the Pseudo-second-order kinetic models. The maximum adsorption capacity for MG reached 168.24 mg/g, which was higher than most of the previously published biomass-based adsorbents. Simultaneously, DLMP adsorbent could be easily regenerated, obtaining outstanding recyclability. After eight cycles, the adsorption capacity of DLMP retained at 144.59 mg/g. Finally, the investigation of the possible adsorption mechanism suggested that the synergistic interactions of electrostatic force, hydrogen bonding, π-π stacking and the superior micro-size structure significantly improved the adsorption property. In conclusion, DLMP adsorbent displays a high adsorption capacity and an excellent recyclability for the removal of MG, which might have widespread prospect in the low-cost and renewable biomass-based adsorbent.