Highly efficient and sustainable alginate/carboxylated lignin hybrid beads as adsorbent for cationic dye removal

In this study, chemically modified lignin and alginate (Alg) hybrid spherical adsorbents exhibiting highly effective adsorption performance for cationic dyes were simply prepared. Carboxylated lignin (C-Lig) was prepared by simple peracetic acid oxidation. Thereafter, through encapsulation of C-Lig into Alg beads was conducted. As the encapsulated amount of C-Lig increased, a higher methylene blue (MB) removal capacity was observed due to the introduction of carboxylated anions on the surface. The adsorption isotherm of Alg/C-Lig beads followed the Langmuir model and exhibited a high monolayer maximum adsorption capacity (qm) of 613 mg/g due to the driving force which is electrostatic interaction between the cationic dye and the anionic group of C-Lig. According to intraparticle diffusion theory, the adsorption behavior proceeded in surface adsorption and internal diffusion during 6 h of the adsorption process. Desorption of MB molecules was found to occur easily via a change in only the pH condition of the solution, and it was possible to maintain over 80% of stable adsorption efficiency even after 5 repeated adsorption/desorption cycles. The facile fabrication process of the Alg/C-Lig beads and superior MB removal performance imply that the Alg/C-Lig beads show a high possibility to purify dye wastewater especially cationic dye molecules.

Automated summary

The study involved the preparation of chemically modified lignin and alginate hybrid adsorbents for efficient removal of cationic dyes. The encapsulation of carboxylated lignin into alginate beads resulted in higher methylene blue removal capacity due to the introduction of carboxylated anions. The Alg/C-Lig beads exhibited a high monolayer maximum adsorption capacity and stable adsorption efficiency even after multiple adsorption/desorption cycles, making them a promising candidate for dye wastewater purification.