Facile Synthesis of Sustainable Tannin/Sodium Alginate Composite Hydrogel Beads for Efficient Removal of Methylene Blue

To meet the requirement of sustainable development, bio-based adsorbents were developed for the removal of dye contaminant. To improve the adsorption capacity of pure sodium alginate (SA) adsorbent for the removal of methylene blue (MB), aromatic bio-based tannin (Tan) was incorporated through the cross-linking with calcium ion. The obtained Tan/SA composite hydrogel beads were characterized with SEM, FTIR and TG, demonstrating that millimeter-sized beads were obtained through calcium cross-linking with enhanced thermal stability. The maximum capacity (247.2 mg/g) at optimal condition (pH = 12, T = 45 degrees C) was obtained for the 40%Tan/SA adsorbents, with a removal efficiency of 82.4%. This can be ascribed to the electrostatic attraction between SA and MB, as well as the formation of pi-pi stacking between Tan and MB. The adsorption process for MB is endothermic, and chemical adsorption, the removal efficiency was exceeded 90% after five cycles.