Adsorption Behavior of Methylene Blue Using Poly( N ‐vinylcarbazole‐co‐ N ‐vinylpyrrolidone) Semiconducting Polymer: Kinetics and Isotherm Studies

ABSTRACT Water contamination and scarcity are worldwide issues with significant techno‐economic impacts on freshwater resources, and addressing these challenges has received increasing scientific attention to ensure a clean and sustainable environment. Conducting polymers, owing to their conjugated π‐electron systems and tunable functional groups, can enhance pollutant removal through multiple interaction mechanisms, including π–π stacking, electrostatic attraction, and hydrogen bonding. In this study, a cross‐linked poly( N ‐vinylcarbazole‐co‐ N ‐vinylpyrrolidone) adsorbent was prepared by free radical copolymerization of N ‐vinylcarbazole with N ‐vinylpyrrolidone, followed by oxidative cross‐linking using ferric chloride as the oxidizing agent. FTIR, 1 H‐NMR, SEM, BET, and pH p zc measurements were used to characterize the resulting material. The adsorption performance toward methylene blue was evaluated by investigating the effects of pH, adsorbent dosage, contact time, initial dye concentration, and ionic strength. Under optimal conditions (pH 6, 10 mg/L initial dye concentration, 30 mg adsorbent dose, and 30 min contact time), a removal efficiency of 95% was achieved. The adsorption kinetics followed the pseudo‐second‐order model, while the equilibrium data were well fitted by the Langmuir isotherm, suggesting monolayer adsorption on relatively homogeneous sites with a maximum capacity of 77.30 mg/g. Adsorption was mainly attributed to electrostatic attraction and π–π interactions.