Thermodynamic and kinetic adsorption of methyl orange and methylene blue on NZVI particles for wastewater treatment

Schematic illustration of adsorption of methylene blue and methyl orange from aqueous solution using NZVI particles, showing dye interaction, adsorption process, and subsequent kinetic and thermodynamic analysis. The persistent presence of synthetic dyes in industrial wastewater has become a significant environmental concern, particularly under varying physicochemical conditions. Conventional treatment methods are often ineffective at removing dyes such as methyl orange (MO) and methylene blue (MB), which exhibit strong resistance to biodegradation. In this study, nano zero-valent iron (NZVI) was synthesized via chemical reduction to evaluate its adsorption potential for the removal of both MO and MB. Characterization confirmed the presence of surface functional groups and nanoscale morphology of the particles. Operational parameters, including contact time, temperature, dye concentration, and adsorbent dosage, were optimized. Notably, removal efficiencies of 77% for MO within 15 minutes and 98% for MB within three minutes were achieved using only 0.05 g of NZVI. Adsorption followed pseudo-second-order kinetics, with intraparticle diffusion as the primary rate-limiting step. Isotherm analysis revealed that MB adsorption followed the Langmuir model, whereas MO adsorption conformed to the Freundlich model. Thermodynamic parameters (ΔH, ΔS, and ΔG) indicated that the process was spontaneous and exothermic. Overall, these findings highlight the potential of NZVI particles as a mechanically versatile, rapid, and cost-effective adsorbent for dye remediation and demonstrate the advantages of integrating kinetic and thermodynamic modelling in predicting real-world performance.