Batch experimental studies on Acid Blue 25 dye removal by synthesized chitosan containing sodium alginate and halloysite nanotubes

An eco-friendly composite material was developed as a cost-effective and efficient adsorbent for removing Acid Blue 25 (AB25) dye from aqueous solutions. Despite extensive research on dye adsorbents, there remains a need for sustainable and high-performance materials. While chitosan and sodium alginate have shown promise individually, their composite with halloysite nanotubes (HNTs) is less explored. In this study, chitosan/sodium alginate (CSA) and chitosan/sodium alginate/halloysite nanotube (CSAH) composites were synthesized and evaluated for AB25 removal under varying conditions, including pH (3-11), contact time (2-120 min), initial dye concentrations (20-600 mg/L), and HNT content (5-30%). Characterization of the adsorbents was carried out using BET, zeta potential, FESEM, FTIR, EDX, and XRD analyses. CSAH adsorbents were prepared by incorporating different HNT ratios (5-30%) into CSA. At pH 3, CSA achieved 80% dye removal after 70 min, while CSAH with 10% HNT content (CSAH10) showed the best performance, removing 94% of dye within 30 min. Adsorption isotherms (Langmuir, Freundlich, Temkin, Redlich-Peterson, Toth) revealed that the Toth model best described the equilibrium behaviour. According to the Langmuir model, the maximum adsorption capacity of CSAH10 was 351 mg/g. Kinetic studies, including pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models, indicated that the adsorption process followed the pseudo-second-order model for both CSA and CSAH adsorbents. Regeneration tests showed a gradual decline in efficiency, with CSAH10 maintaining 58% removal after five cycles, down from 91% initially. Overall, the CSAH10 composite exhibited strong potential for practical AB25 dye removal, combining high efficiency, low cost, and relatively good reusability.