Phenoxy herbicide removal from aqueous solutions using fast pyrolysis switchgrass biochar

The release of herbicides is known to negatively impact humans and the environment. We report the use of a low cost biochar (prepared through fast pyrolysis) to successfully remove phenoxy herbicides from aqueous solutions. The biochar was characterized using: FT-IR, SEM, pH(pzc), elemental analysis, and surface area measurements. Sorption experiments were run at pH values from 2 to 10, adsorbate concentrations from 25 to 300 mg/L and temperatures from 25 to 45 degrees C. Adsorption isotherms were evaluated from 25 to 45 degrees C using both two parameter (Freundlich and Langmuir) and three parameter (Redlich-Peterson and Toth) adsorption isotherm models. The maximum adsorption capacities for 2,4dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) were Q(sGB)(0) similar or equal to 134 mg/g and Q(SGB)(0)similar or equal to 50 mg/g, respectively, at pH 2. This low surface area switchgrass biochar (1.1 m(2)/g) can adsorb far more MCPA per unit of measured surface area (45 mg/m(2)) than high surface area commercial activated carbons (1050-1150 m(2)/g) which absorb only 0.08-0.11 mg/m(2), and are also expensive. This indicates that biochar three dimensional swelling occurs in an aqueous environment and adsorbates are imbibed and adsorbed at additional sorption sites. (C) 2017 Elsevier Ltd. All rights reserved.