Adsorption of micropollutants from wastewater using iron and nitrogen co-doped biochar: Performance, kinetics and mechanism studies

In this study, a novel iron and nitrogen co-doped biochar (Fe/N-biochar) was successfully prepared and employed as an efficient adsorbent for micropollutants. The maximum adsorption capacity of Fe/N-biochar for bisphenol A (BPA) was 54 mg/g, which is significantly better than that of commercial graphene (19 mg/g) and activated carbon (6 mg/g). Additionally, for eight other common micropollutants (e.g., phenol, acetaminophen, and sulfamethoxazole), Fe/N-biochar also exhibited highly enhanced adsorption performance. The results of adsorption kinetics and isotherms studies showed that the adsorption of micropollutants onto Fe/N-biochar is by monolayer coverage. Thermodynamic studies further suggested that the adsorption process is feasible, spontaneous, and chemical in nature. The adsorption mechanism was investigated by correlation analysis between the adsorption capacity and the physiochemical properties of Fe/N-biochar. The results demonstrated that the strengthening of π–π electron donor-acceptor interactions between the organics and the adsorbent caused by the co-doping of iron and nitrogen was the dominant driving force behind the efficient adsorption of micropollutants. Furthermore, graphitic N and Fe−N_x were identified as the major adsorption sites. Simple heat treatment could effectively restore the adsorption capacity of Fe/N-biochar that had reached adsorption equilibrium. In view of its simple preparation method, highly enhanced adsorption capacity, and excellent recyclability, the prepared Fe/N-biochar can be regarded as a promising candidate for wastewater treatment.