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

[Display omitted] •The DLMP has an outstanding adsorption capacity of 168.24 mg/g for MG.•The DLMP is a full-lignin based adsorbent without any other introduced stuff.•The DLMP has a good stability and reusability for MG adsorption.•The DLMP with micro-particle structure is much suitable for the adsorption of MG. 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 AlCl3 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 m2/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.