A comparative adsorption study of activated carbon and Fe-modified activated carbon for trinitrotoluene removal

Background Activated carbon (AC) is commonly used to remove many pollutants from water due to its appealing adsorption properties. However, the pristine surface properties of AC limit its ability to effectively remove 2,4,6-trinitrotoluene (TNT, a widely used explosive water contaminant). Modifying AC with Fe nanoparticles (NPs) can significantly improve the surface properties of the Fe/AC composite, thereby enhancing its adsorption capabilities. Method Commercial charcoal-based AC was modified with Fe NPs via wet impregnation followed by a one-step carbothermal synthesis (labeled Fe-AC-800). A detailed characterization of Fe-AC-800 and its counterparts, pristine AC and thermally modified AC (AC-800, without Fe NPs doping) was performed using XRD, Raman Spectroscopy, SEM, EDS, BET, XPS, and FTIR. Then, the adsorption characteristics and performances of Fe-AC-800 were analyzed to determine its effectiveness in removing TNT and compared to AC and AC-800, considering the impact of in-situ Fe-modification and carbothermal treatment. Significant findings Fe-AC-800 displayed a higher adsorption capacity for TNT (387.74 mg/g) than the pristine AC (265.52 mg/g) but only slightly higher than AC-800 (339.64 mg/g). This was ascribed to the combined effect of the carbothermal treatment and Fe NPs doping, which constructed a richer porous structure that improved the Fe-AC-800 surface features and favored TNT removal. The optimal adsorption capacity of Fe-AC-800 was 464.13 mg/g under ambient conditions. TNT adsorption onto Fe-AC-800 and AC-800 conformed to only the Langmuir isotherm model, indicating uniform monolayer adsorption, whereas on the pristine AC, it satisfied both Langmuir and Freundlich isotherm models, respectively. The primary mechanism of TNT adsorption onto Fe-AC-800 was physical adsorption through pore filling, hydrogen bonding, and π-π EDA interactions, respectively.