Activated carbon microspheres derived from waste cotton textiles for efficient removal of methylene blue

Upcycling cellulose-rich waste cotton textiles into high-performance adsorbents can couple textile-waste diversion with water remediation, but routes that generate porous carbon microspheres under relatively mild hydrothermal conditions remain limited. Here, waste cotton textiles were hydrothermally carbonized at 200 °C for 6 h in the presence of ZnCl 2 and then pyrolytically activated at 900 °C for 2 h. With 8 wt% ZnCl 2 , carbon microspheres were obtained, and HWC-8-900 reached a BET specific surface area of 1706 m 2 g − 1 and obtained the maximum MB adsorption capacity of 705 mg/g. The Langmuir separation factor indicated favorable adsorption over the tested concentration range. The pseudo-second-order model gave the best kinetic fit, and HWC-8-900 had the highest calculated initial adsorption rate. Negative △ G and positive △ S values indicated spontaneous, endothermic adsorption over 298–318 K. These results identify ZnCl 2 -assisted hydrothermal carbonization followed by pyrolytic activation as an effective route for converting waste cotton into high-surface-area microspherical adsorbents, while practical validation still requires replicate-level uncertainty analysis, real-water testing, and regeneration assessment.