Utilization of Coal-Based Activated Carbon (JA) for the Adsorption of Methyl Orange Azo Dye in Wastewater

Currently, the mainstream methods for dye removal internationally include advanced oxidation, catalytic degradation, and adsorption. Catalytic and oxidation methods are costly and unsuitable for large-scale application. While adsorption is straightforward, selecting and modifying raw materials poses significant challenges. Therefore, identifying readily available and inexpensive adsorbents is crucial for dye removal. This study utilized Type A coal as raw material to prepare a series of specialized activated carbon (JA) for adsorbing methyl orange from wastewater, followed by optimization. The optimized screening results indicated that JA-12 exhibited the highest methyl orange removal rate (90.54%). This performance is attributed to its larger micropore structure and increased pore volume. Further analysis revealed that the adsorption process follows pseudo-second-order kinetics and the Langmuir adsorption isotherm model (R² ≈ 0.999). Compared to the theoretical adsorption capacity calculated based on specific surface area, the adsorption capacity calculated based on pore volume (270.66 mg/g) was closer to the actual adsorption capacity, indicating that the pore structure of JA-12 plays a dominant role in the adsorption process. Combined with the Langmuir adsorption model, it can be inferred that dye molecules in solution adsorb onto the inner surface of JA-12 in a monolayer form. Surface functional group analysis revealed that protonation enhances JA-12’s adsorption capacity for the azo dye methyl orange. Collectively, our findings elucidate the removal mechanism of methyl orange using readily available coal as raw material to prepare low-cost specialty activated carbon, providing a framework for cost-effective, large-scale dye removal.