Sustainable Remediation of Dye‐Contaminated Water: <i>Phragmites australis</i> Leaves (Reed) as a Low‐Cost Biosorbent for Brilliant Cresyl Blue

ABSTRACT This study examines Phragmites australis leaves (LPA) as a biosorbent for removing brilliant cresyl blue (BCB) dye from aqueous solutions. Batch experiments evaluated the effects of pH (2–10), contact time (0–180 min), adsorbent dose (0.05–1 g), initial dye concentration (30 –150 mg/L), and temperature (298‐328 K). Maximum BCB removal (&gt;67%) was achieved at pH 8, with an equilibrium time of 30 min and an adsorbent dose of 0.6 g, consistent with the point of zero charge (pHpzc = 6.8). Characterization revealed a porous structure (SEM), an oxygen‐rich functional group surface (FTIR), and a specific surface area of 2.4276 ± 0.0467 m 2 /g (BET). The adsorption kinetics followed the pseudo‐second‐order model (R 2 &gt; 0.99), and the equilibrium data were best described by the Freundlich isotherm, with a maximum adsorption capacity of 66.28 mg/g at 318 K. Thermodynamic analysis indicated ΔG &gt; 0 and ΔH &gt; 0, confirming a non‐spontaneous and endothermic process. The positive value of ΔS suggests an increase in the randomness/disorder at the solid–liquid interface during the adsorption process. These results demonstrate the potential of Phragmites australis leaves as a cost‐effective and eco‐friendly biosorbent for dye removal, combining natural abundance with competitive adsorption capacity. Future studies should investigate its performance in continuous‐flow systems and real wastewater matrices.