This study investigates the use of three specific carboxylic acids, citric acid (CA), malic acid (MA), and tartaric acid (TA), as cross-linkers to develop adsorbents for water treatment that integrate the distinctive characteristics of magnetic kraft lignin (MKL) and beta-cyclodextrin (β-CD), thereby achieving improved efficiency and stability. The adsorbents were synthesized via the esterification method and characterized using various analytical techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), and a vibrating sample magnetometer (VSM). Response surface methodology (RSM) was used to design experiments and optimize conditions to achieve the optimal parameters of pH, contact time, and solid-to-solution ratio (dose) in the removal of methylene blue. The results indicated that methylene blue removal could reach approximately 97% under optimal conditions: pH 11, a contact time of 30 min, and a dose of 0.2 g.L−1. The Langmuir model provided the best fit for the equilibrium data, with a maximum adsorption capacity of 454.54 mg.g−1. Kinetic analysis revealed that the sorption process adhered to a pseudo-second-order model. The obtained results highlight the excellent potential of β-CD-TA-MKL as an efficient and sustainable adsorbent for the removal of methylene blue. Notable advantages of β-CD-TA-MKL compared to other reported adsorbents include its higher adsorption capacity, remarkable stability over five regeneration cycles with minimal loss in performance, rapid adsorption kinetics, and the utilization of environmentally friendly, cost-effective materials.

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