High-efficient removal of dye across a wide pH range over alkali lignin-based adsorbent: Batch experiments and DFT mechanistic analysis

Abstract

As the primary byproduct of paper making industry, alkali lignin can lead to biological anoxia and disrupt aquatic ecosystems. Application of it in wastewater treatment can not only realize its high value utilization, but realizing reduction of carbon emission. In this study, a renewable alkali lignin-modified MOFs adsorbent AL@PCN-250 was prepared by in-situ synthesis strategy and was used to adsorb and remove Methylene blue (MB) and Rhodamine B (RhB) from textile wastewater. The effects of adsorbent dosage, pH, contact time, and initial concentration on the adsorption behavior of RhB and MB by AL@PCN-250 were investigated to evaluate its adsorption capacity and reusability. The results showed that the maximum adsorption capacities of AL@PCN-250 for RhB and MB were 299.292 mg g⁻¹ and 209.260 mg g⁻¹, respectively. The Sips models fitted the adsorption isotherms well, indicating that the adsorption sites on the surface of AL@PCN-250 are heterogeneous, with varying affinities for the adsorbates. Notably, after six cycles, the removal efficiency of AL@PCN-250 for the two dyes remained above 80 %. Experimental and theoretical calculations revealed that adsorption mainly involved hydrogen bonding, Van der Waals’ force, π-π interactions, and electrostatic interactions. This study provides new insights into the high-value utilization of lignin and the synthesis of efficient adsorbents.