Biochars were produced by pyrolyzing herb residue of Danshen (a traditional Chinese medicine) at different temperatures (250-800 oC) and used as sorbents for sulfamethoxazole (SMX). Biochar prepared at 250 oC (B250) exhibited higher (2-7 times) sorption capacity to SMX than high-temperature chars. A negative charge-assisted H-bond (-)CAHB was proposed to play the dominating role in SMX sorption on B250 due to its abundant O-containing groups and comparable pKa (around 5.0) with that of SMX (pKa, 2 = 5.7). The thermodynamic analysis suggested that SMX sorption on the biochars was a spontaneous and endothermic process. The higher increase of enthalpy (?H) and entropy (?S) for low-temperature chars were well related with the strong (-)CAHB between SMX and oxyl groups on the chars. This study indicates that (-)CAHB could more easily form on low-temperature chars rich in oxyl groups, which provides valuable information on the design and synthesis of efficient biochars for various environmental applications.

Physicochemical properties of herb-residue biochar and its sorption to ionizable antibiotic sulfamethoxazole

247th National Meeting (2014)

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