Studies On The Sorption Mechanism And Environmental Fate Of Atrazine And Nicosulfuron By Modified Biochar Materials

In this study,agricultural waste peanut shell was selected as raw material to produce biochar,and biochar at different pyrolysis temperatures,montmorillonite-peanut shell composite biochar?MMT/BC?and phosphoric acid-modified biochar?H₃PO₄-BC?were successfully prepared and characterized by element analysis.The removal efficiency,influence factors and mechanism of biochar materials on atrazine and nicosulfuron sorption were systematically studied.In addition,the effects of MMT/BC and H₃PO₄-BC on the dissipation of atrazine and the effects of phosphoric acid-modified biochar on the microbial community structure in soil were investigated.This research will provide theoretical basis and method for control and remediation of pesticides by biochar and it composites.The main results of this study including:?1?Nine kinds of peanut shell biochar with different pyrolysis temperatures?300?,450?and600??and different ash removal treatments?no ash removal,water washing and acid cleaning?were prepared.With the increase of pyrolysis temperature,specific surface area increased,accompanied by the enhancement of aromaticity and decreased polarity of biochar.The sorption results showed that the sorption of atrazine and nicosulfuron by biochar depends on multiple mechanisms,i.e.,hydrophobicity distribution,pore filling,hydrogen bond,and electron donor-receptor.The effect of each part was determined by the carbonization degree of biochar and the concentration of atrazine and nicosulfuron.Acid is better than water for ash removal,ash can bind to atrazine and nicosulfuron through specific interactions,but it usually has influence on sorption capacities,especially with high temperature biochar.?2?Montmorillonite-peanut shell composite biochar?MMT/BC?was prepared.Compared to biochar?BC?,MMT/BC showed different physical and chemical properties,i.e.,pore volume and pore size increased,accompanied by decreased specific surface area and aromaticity.The sorption capacity of the MMT/BC to atrazine and nicosulfuron was three times higher than that of BC.The joint reaction mechanisms of MMT/BC and BC on atrazine and nicosulfuron include hydrophobic partition,pore-filling,hydrogen bond,p/?-?electron donor-receptor interaction,and electrostatic interaction.For MMT/BC,the surface sorption and layer interaction of montmorillonite dominated the sorption of atrazine and nicosulfuron.?3?Phosphoric acid-modified peanut shell biochar?H₃PO₄-BC?was successfully prepared with greater specific surface area and pore volume,more microporous structures and functional groups,great aromaticity and thermal stability.The sorption was the result of various mechanisms,including hydrophobic partition,pore-filling,hydrogen bond,p/?-?electron donor-receptor interaction and electrostatic interaction.The sorption capacity of H₃PO₄-BC on atrazine and nicosulfuron was two orders of magnitude higher than that of BC,as H₃PO₄-BC provided more sorption sites and hydrogen bond donors by larger surface area,greater pore structure,oxygen-containing groups and aromatic structure.?4?The dissipation of atrazine and nicosulfuron in different soils,soil-MMT/BC and soil-H₃PO₄-BC amendments was conducted.The results showed that the dissipation of atrazine was inhibited by the strong sorption of MMT/BC and H₃PO₄-BC,accompanied by the increased dissipation of nicosulfuron.The addition of MMT/BC promoted the biodegradation of nicosulfuron in soil,and the addition of H₃PO₄-BC promoted the microbial degradation of nicosulfuron as a result of stimulating microbial activities.?5?Illumina MiSeq high-throughput sequencing technology were used to illuminate the effects of three treatments on soil bacterial diversity and community structure by indoor soil culture experiment.The results showed decreasing diversity of soil bacterial community by atrazine treatment and to some extent,the addition of H₃PO₄-BC could alleviate the inhibition.Compared with blank soil,both atrazine treatment and H₃PO₄-BC treatment had significant effects on the bacteria at the phylum level,however,the effects were basically recovered before the end of the experiment.The results of LefSe showed that the level of Sphingomonas and Nocardioides,which have the potential for the degradation of atrazine,increased in atrazine-treatment soil.With the addition of H₃PO₄-BC,the number of bacterial species increased,such as Sphingomonas and Nocardioides.In addition,the level of phosphate-solubilizing bacterial strain Bacillus enhanced,which can transfer immobilized phosphorus to plant-absorbable free phosphorus.