Preparation of graphite-like biochars derived from straw and newspaper based on ball-milling and TEMPO-mediated oxidation and their supersorption performances to imidacloprid and sulfadiazine

Abstract In this study, graphite-like biochars were successively prepared by pyrolyzing modified newspaper and maize straw with ball-milling and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)- mediated oxidation at a pyrolysis temperature of 900 °C and their physico-chemical properties and adsorption performances towards imidacloprid (IMI) and sulfadiazine (SUL) in aqueous solution were all explored. The results showed that the successive modification by ball-milling and TEMPO-mediated oxidation completely open the fibers of the newspaper and porous stereoscopic structures of the maize straw. The obtained graphite-like biochars contained planar structures and abundant O-containing functional groups, and exhibited a great degree of graphitization and specific surface areas reaching up to 871.5 and 1065 m2/g, making them super adsorbents. Furthermore, hydrophobic partitioning provided a limited contribution to the sorption on biochars for IMI and SUL as revealed by dual-mode model fitting. The graphite-like biochars adsorbed IMI and SUL, mainly through pore-filling, H-bonding, cation/p/π-π EDA interactions, and electrostatic interactions and cation-π EDA interactions further enhanced the sorption of cationic IMI. Additionally, the adsorption efficiency of biochars pretreated with ball-milling and TEMPO-mediated oxidation for IMI and SUL was>85%, even after five consecutive recycling process. Thus, this study provides excellent graphite-like biochar adsorbents pretreated with a combined ball-milling and oxidation modification method, making them efficient for removing hydrophilic pesticides and antibiotics from polluted water.