N-doping is one of the most promising strategies to improve the adsorption capacity and selectivity of carbon adsorbents. Herein, synthesis, characterization and dye adsorption of a novel N-doped microporous biochar derived from direct annealing of crop straws under NH3 is presented. The resultant products exhibit high microporosity (71.5%), atomic percentage of nitrogen (8.81%), and adsorption capacity to dyes, which is about 15-20 times higher than that of original biochar. Specifically, for the sample NBC800-3 pyrolyzed at 800°C in NH3 for 3 h, its adsorption for acid orange 7 (AO7, anionic) and methyl blue (MB, cationic) is up to 292 mg g(-1) and 436 mg g(-1), respectively, which is among the highest ever reported for carbonaceous adsorbents. The influences of N-doping and porous structure on dye adsorption of the synthesized carbons are also discussed, where electrostatic attraction, π-π electron donor-accepter interaction, and Lewis acid-base interaction mainly contribute to AO7 adsorption, and surface area (especially pore-filling) dominates MB adsorption. The N-doped biochar can be effectively regenerated and reused through direct combustion and desorption approaches.

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Root growth and protective enzymes of Festuca arundinacea L. and Lolium perenne L. under Cu stress were investigated in a hydroponic experiment. Cu stress significantly inhibited root growth (root elongation and dry biomass) of both turfgrasses. Malondialdehyde (MDA) content in roots of both turfgrasses markedly increased under copper stress. In F. arundinacea root, superoxide dismutase (SOD) activity increased greatly with increasing Cu concentration; peroxidase (POD) activity increased at low Cu level and decreased at high Cu level. Increased MDA content indicated the formation of free radicals under Cu stress, while increased SOD activity pointed to the operation of a scavenging mechanism. In roots of L. perenne, however, SOD and POD were not activated by copper. These results demonstrate that turfgrass cultivars clearly differ in tolerance to Cu stress, and that the tolerance depends largely on the enhanced activity of its antioxidant system. K Ke ey y w wo or rd ds s: : Copper stress, Festuca arundinacea L., Lolium perenne L., MDA, antioxidant enzyme.

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