Characterization of peanut-shell biochar and the mechanisms underlying its sorption for atrazine and nicosulfuron in aqueous solution

Abstract
      The aim of the present study was to investigate the sorption of atrazine and nicosulfuron onto several experimentally produced biochars, as well as to understand the influence of biochar structure on sorption mechanisms. Nine biochars were generated by pyrolyzing peanut shell at 300, 450, or 600 C and exposing samples to each of the several deashing treatments: none, water or HCl. The sorption of atrazine and nicosulfuron by the nine biochars were evaluated. Biochars were characterized via elemental analyzer, BET-N2 surface area, FTIR and XPS. Three kinetic models were used to fit the sorption kinetics data and both the Freundlich and dual-mode models described the sorption isotherms well. All the biochar samples exhibited high sorption affinity for both atrazine and nicosulfuron. The sorption mechanisms of the biochar included hydrophobic partition, p-p electron donor-acceptor interactions, H-bonding, and pore-filling mechanism, and these mechanisms were dependent on both the degree of biochar carbonization and the concentration of atrazine or nicosulfuron. Ash could bind to atrazine and nicosulfuron by specific interactions but played a negative role in the sorption, especially on high pyrolyzing temperature biochars. These results will facilitate the roduction of efficient and cheap adsorbents for reducing the risk of atrazine and nicosulfuron.