Enhancing the Sustainability of Cotton Spinning Mill Waste Through Thermochemical Processes: Converting Waste into Carbon Materials

Cotton spinning mills generate considerable waste containing residual fibers, typically divided into useable and unusable fractions. With increasing emphasis on sustainability, repurposing the unusable portion of cotton waste (CW) has become a promising approach. In this study, CW was converted into carbon materials through chemical activation using ZnCl₂ and KOH, as well as steam activation. Among the samples, ZnCl₂ activation at 800 °C (CZ800) yielded the highest BET surface area (698.31 m² g^-1) and a mesoporous structure with an average pore diameter of 1.84 nm. In contrast, KOH-activated samples (e.g., CK800) exhibited a broader pore distribution and higher fixed carbon content. Sample yield varied based on the activation method and temperature, with porosity development generally inversely related to carbon yield. Adsorption performance was assessed using methylene blue (MB) as a model pollutant. Langmuir isotherm analysis revealed maximum adsorption capacities of 73.53 mg g^-1 for CZ800 and 45.45 mg g^-1 for CK800, attributed to differences in surface area, pore size, and oxygen-containing functionalities. Notably, pore size compatibility and surface chemistry played key roles in adsorption capacity. Statistical optimization using a central composite design (CCD) confirmed that the activating agent significantly influenced surface area development (<i>p</i> = 0.0046), while temperature had no statistically significant effect. Both materials demonstrated high adsorption efficiency over five reuse cycles, indicating strong regeneration potential. These findings support the feasibility of converting cotton waste into effective, sustainable adsorbents for environmental remediation.