Biochar adsorbent was produced by pyrolyzing traditional Chinese medicinal herb residue at 300, 500 and 750 °C (referred to as biochar-300, biochar-500 and biochar-750). Basic physical and chemical analyses, Fourier transform infrared spectroscopy (FT-IR), and thermodynamic analyses were performed to elucidate adsorption and properties of biochar. Biochar adsorption capacity of herbicide metolochlor, as measured by batch-type adsorption experiments by Freundlich constant Kf (mg1−n Ln kg−1), followed the order: biochar-750 > biochar-300 > biochar-500. Thermodynamic analysis suggested that adsorption of metolachlor on biochar was a spontaneous process. The adsorption isotherm for the biochar produced at the highest pyrolysis temperature was characteristic for adsorption process driven by a high surface area of biochar (85.30 m2 g−1), while the adsorption process for the biochar produced at the lowest temperature was controlled by its higher content of organic matter (39.06%) and abundant functional groups. The FT-IR spectra also showed that the biochar prepared at the lowest temperature had the highest number of surface groups. In general, pore-filling induced by the large surface area of the biochar was the dominant adsorption mechanism. When the H/C value was >0.5, the adsorption mechanism of biochar was dominated by surface chemical bond, while pore-filling played a major role when the H/C value was <0.5.
Bibliographical noteFunding Information:
This work was supported by Pearl River S&T Nova Program of Guangzhou , China ( 201610010131 ); the National Natural Science Foundation of China ( 41401353 , 41571313 , 41807454 , 21577131 ); Natural Science Foundation of Guangdong Province , China ( 2015A030313570 , 2016A030313772 , and 2017A030311019 ); Department of Science and Technology of Guangdong Province , China ( 2017B020203002 , 2016B070701009 , and 2016A020210034 ); and President Foundation of Guangdong Academy of Agricultural Sciences, China ( 201716 ); Special fund for scientific innovation strategy-construction of high level Academy of Agriculture Science ( R2016PY-QY010 , R2016PY-JX006 ).
© 2020 Elsevier Inc.
- Adsorption mechanism
- Chinese medicinal herb residue
- Functional groups
- H/C ratio
ASJC Scopus subject areas
- Environmental Science(all)