Iron-activated bermudagrass-derived biochar for adsorption of aqueous sulfamethoxazole: Effects of iron impregnation ratio on biochar properties, adsorption, and regeneration

This work focused on the impacts of FeCl3 impregnation ratio on the properties of FeCl3-activated bermudagrass (BG)-derived biochars (IA-BCs), adsorption of sulfamethoxazole (SMX) onto IA-BCs and regeneration of SMX-spent IA-BC. Compared with the control BC (85.82 m2/g), IA-BCs made via pyrolysis with FeCl3 to BG mass ratio between 1 and 3 (1-3 g FeCl3/g BG) resulted in significantly enhancing surface area (1014-1035 m2/g), hydrophobicity, Fe content in IA-BCs (3.87-7.27%), and graphitized carbon. The properties of IA-BCs supported magnetic separation and higher adsorption (32-265 mg SMX/g BC) than the control BC (6-14 mg SMX/g BC) at various pH. Adsorption experiments indicated various adsorption mechanisms between SMX and IA-BCs via π-π EDA, hydrophobic interactions, and hydrogen bond with intraparticle diffusion limitation. The adsorption was also found to be spontaneous and exothermic. The IA-BC made at FeCl3 to BG mass ratio of 2 (IA-BC2.0) showed the maximum adsorption capacity for SMX (253 mg SMX/g BC) calculated from Langmuir isotherm model. Additionally, both NaOH desorption and thermal oxidation showed effective regeneration of SMX-saturated IA-BC2.0 over multiple cycles. After three cycles of adsorption-regeneration, 64% and 62% of regeneration efficiencies were still achieved under thermal treatment at 300 °C and desorption with 0.1 M NaOH solution, respectively, indicating a cost-efficient adsorbent for the elimination of SMX in water.