Coal-derived physically activated carbon for methylene blue adsorption in waste water

In this study, methylene blue (MB) dye adsorption from aqueous solution was simulated using coal-derived physically activated carbons (ACs) created with CO2 gas. ACs were produced by varying activation temperatures, maintaining a fixed activation time of 1 h under CO2 flow. Characterization was carried out using BET (Brunauer-Emmett-Teller), FTIR (Fourier transform infrared spectroscopy), SEM (scanning electron microscopy), TGA (thermogravimetric analysis), and XRD (X-ray diffraction). FTIR confirmed functional groups before and after activation, while TGA demonstrated coal char conversion around 560°C. XRD of raw coal, pyrolyzed coal, and activated samples confirmed amorphous structure. At 900°C, ACs showed the highest BET surface area of 779.40 m2/g. SEM images revealed a porous structure. ACs were tested for MB dye removal, and adsorption kinetics and equilibrium were studied under different conditions. Optimal removal (84.8%) was achieved at 50 mg/L dye concentration, 120-min contact time, and pH 8. Langmuir and Freundlich isotherms were applied; the Langmuir model fit best (R2 = 0.99), with a Langmuir affinity constant (KL) of 0.35 L/mg and a maximum adsorption capacity (qm) of 56.63 mg/g. Adsorption followed pseudo-second-order kinetics with R2 = 0.998. Coal-derived ACs are cost-effective and exhibit strong potential as efficient adsorbents for cationic dye removal.