Adsorption kinetics and isotherms of malachite green removal from aqueous solution using TiO2 loaded on f-MWCNTs nanocomposite

This study investigated the removal of toxic Malachite Green (MG) dye from aqueous solution using a nanocomposite of TiO₂ loaded on functionalized multi-walled carbon nanotubes (TiO₂/f-MWCNT). The nanocomposite was synthesized via a hydrothermal method and characterized using XRD, FESEM, FTIR, BET, and EDS. The optimal adsorption conditions were determined as pH = 8, adsorbent dose of 0.005 g, equilibrium time of 10 min, and temperature of 293 K. Under these conditions, the maximum adsorption capacity reached 38.61 mg/g with a removal efficiency exceeding 95%. Kinetic data showed an excellent fit to the pseudo-second-order model (R 2 = 0.99), indicating a chemisorption-controlled process. The equilibrium adsorption behavior was well described by the Langmuir-2 isotherm model (R 2 = 0.99), confirming monolayer formation on a homogeneous surface. Additionally, the Freundlich, Temkin, and Elovich models also showed favorable fitting (R 2 ≥ 0.98), suggesting a combined physical–chemical adsorption mechanism on a heterogeneous surface. The adsorbent was effectively regenerated with a 1 M NaOH solution, achieving 99% recovery. These results demonstrate the rapid and efficient performance of TiO₂/f-MWCNT as a promising adsorbent for the treatment of wastewater containing cationic dyes.