Lignin-Derived Metal–Organic Frameworks for Effective Removal of Methylene Blue from Water

Methylene blue (MB), the most widely used colorant in the textile industry, pollutes water bodies, rendering them unusable, and produces a global environmental challenge due to its high toxicity and harmful effects. In this study, lignin-based metal organic frameworks (lignin MOFs) are prepared from Organosolv lignin to develop a highly efficient, cost-effective, and environmentally friendly adsorbent for the removal of MB from aqueous solutions. The introduction of a room temperature linker salt approach synthesis method using lignin as a bio ligand will facilitate the formation of porous structures with high surface area in MOFs, and combined with the rich functional groups of lignin will result in a good adsorption process. The resulting material was characterized using Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Thermal Gravimetric Analysis (TGA), and nitrogen adsorption–desorption analysis (BET) to confirm its structure, morphology, and porosity. Batch adsorption experiments were conducted to evaluate the adsorption efficiency of the prepared lignin-MOFs in comparison to conventional MIL53(AL). Adsorption kinetics and isotherms were analyzed using the pseudo-second-order model and the Langmuir model, respectively, to understand the adsorption mechanisms. The synthesized lignin-derived MOFs exhibited nanosized particles with a porous, crystalline structure with a high specific surface area and thermal stability, confirming their suitability as a non-toxic adsorbent compared to conventional organic ligand-derived MOFs. Adsorption experiments showed that the prepared lignin material effectively removed MB. This research successfully reveals the potential of utilizing an eco-friendly and low-cost precursor, lignin, to fabricate highly efficient biobased MOFs for water purification.