Removal characteristics of emerging pollutant F-53B by three common a ctivated carbons

As a substitute for traditional perfluorooctane sulfonate(PFOS) substances, chlorinated polyfluoroalkyl ether sulfonate acid(6∶2 Cl-PFAES, F-53B) has been widely adopted in China's electroplating industry. It should be noted that current emission limits and treatment standards for this compound remain undeveloped,leading to its continuous accumulation in environmental media and potentially causing significant ecological risks and health hazards. This study systematically investigated the adsorption characteristics of F-53B by three typical activated carbon materials(coconut shell-based, coal-based,and bamboo-based activated carbons). Experimental results demonstrated that for an initial F-53B concentration of 1 mg/L, coconut shell activated carbon(250 mg/L) achieved adsorption equilibrium within 24 hours(F-53B removal efficiency of 99.9%, residual concentration of 1.31 μg/L), with a maximum adsorption capacity of 261.64 mg/g, which was significantly higher than that of coal-based(93.37 mg/g) and bamboo-based activated carbons(10.77 mg/g). The adsorption behavior of F-53B was better fitted by the Langmuir isotherm model(R²>0.83) and pseudo-second-order kinetic model(R²>0.97). To investigate the rate-limiting steps,the intra-particle diffusion model suggested a three-stage adsorption process for coconut shell-based and coal-based activated carbons, involving surface adsorption,pore diffusion, and adsorption equilibrium,while bamboo-based activated carbon only exhibited the first two stages. Further physicochemical characterization revealed that coconut shell-based activated carbon exhibited the highest specific surface area(1 042.66 m²/g), surpassing coal-based(705.09 m²/g) and bamboo-based activated carbons(163.12 m²/g). Nitrogen adsorption isotherm analysis indicated that coconut shell-based activated carbon displayed characteristic Type Ⅰ behavior according to IUPAC classification, while both coal-based and bamboo-based activated carbons showed typical Type Ⅳ isotherms. Pore structure analysis further revealed that both coconut shell-based and coal-based activated carbons were predominantly microporous, whereas bamboo-based activated carbon was dominated by mesopores and macropores. Additionally,surface chemical characterization demonstrated that coconut shell-based activated carbon possessed the highest quantity of basic functional groups and the lowest acidic functional groups,with a point of zero charge(pHzpc) of 4.49 higher than that of coal-based(4.30) and bamboo-based activated carbons(2.42). These distinct physicochemical properties collectively explained why coconut shell-based activated carbon exhibited optimal F-53B adsorption performance, showing significantly superior removal efficiency compared to both coal-based and bamboo-based activated carbons.