Removal of tetrabromobisphenol A from water by four activated carbons: adsorption performance and implications for engineering practice

Tetrabromobisphenol A (TBBPA) is one of the most commonly used and high-risk flame retardants, and it is ubiquitous in the aqueous environment. It can be removed efficiently by carbon nanotubes, graphene oxide, and derived activated carbons (ACs) from water; however, the engineering feasibility is limited due to the high cost. Herein, the adsorption performance of commercial adsorbents on TBBPA removal in aqueous solutions needs to be adequately understood for water treatment applications. Four commercial, cost-effective, and coal-based ACs with different chemical properties and functions were used to remove TBBPA from water. The adsorption of TBBPA onto the four ACs fit well with the pseudo-second-order kinetic model and reached equilibrium within 72 h. Adsorption isotherms indicated that coal-based ACs had a high potential for effective TBBPA removal from water, with adsorption capacities of up to 292, 422, 544, and 1379 mg/g, according to the Dubinin–Ashtakhov model. The TBBPA adsorption capacity of ACs could be enhanced under neutral or weakly alkaline conditions. An approximately linear relationship between adsorption capacity and surface area (r = 0.995), micropore volume (V_mic) (r = 0.993), or total pore volume (V_t) (r = 0.997) was observed. The same situation was observed between adsorption affinity and surface area (r = 0.990), V_mic (r = 0.989), or V_t (r = 0.998), indicating that the pore size distribution and surface area of the ACs dominated the adsorption of TBBPA. The micropore-filling mechanism explained that the micropores (pore size from 0.7 nm to 2.0 nm) played a major role during the adsorption. The higher surface area of AC would endow itself with a larger proportion of micropores and hence show better affinity to TBBPA due to the size effect and the hydrophobic, π–π, and hydrogen bonding. Electrostatic interactions affected the adsorption energy between TBBPA and ACs (25.8–57.3 kJ/mol), which could promote the enrichment of TBBPA on the AC surface.