Adsorption,Degradation And Phytotoxicity Assessment Of Fomesafen By Biochar/g-C₃N₄

As a type of diphenyl ether herbicide,Fomesafen（FSA）is commonly used for weed control in peanut and soybean crops after emergence.Because of its anionic and hydrophilic properties,the herbicides could persist for a long time in soil and water environments,posing harmful impacts on non-target species,surface-water and groundwater through the runoff and leaching.Thus,a green and efficient approach was developed to eliminate residue pesticides in the environment that is critical to remedy the ecological risks.In detail,the biochar-based carbon nitride（Biochar/g-C₃N₄,CNC）was prepared via a two-step hydrothermal and pyrolysis process using agricultural waste（corn cobs）and agricultural fertilizer（urea）as raw materials.It performed well in the removal of residues from the aquatic environment.Then the plant growth and development experiments were conducted to examine the toxic effects including the corn seed germination,seedling growth,antioxidant enzyme activity and plant metabolism.The specific research contents were written as follows.（1）The structural composition and physicochemical properties of Biochar and Biochar/g-C₃N₄（CNC）were characterized by SEM,BET,XRD and FT-IR.The adsorption kinetics and isothermal curves of CNC on FSA were calculated in accordance with the Elovich and Sips models respectively.The removal rate of FSA under visible-light irradiation was found to be over 84%,which was significantly higher compared to pure g-C₃N₄.Its photodegradation behavior was in line with the secondary kinetic model.（2）Predicted on the Gaussian software using density functional theory（DFT）calculations,the possible photodegradation sites and pathways of FSA were simulated and explain the distribution of degradation products by LC-MS.It was found that FSA may undergo degradation processes such as hydrolysis,ether cleavage,photocatalytic oxidation,hydroxylation,and dehalogenation.Free radical quenching experiments further indicated that the hole（h⁺）and hydroxyl radical（·OH）were the crucial active species involved to the photocatalytic degradation.（3）Remedy of FSA on the growth,development and metabolization of corn seedlings were investigated on the biochar-based carbon nitride.The results showed that CNC significantly reduced the toxicity of FSA on the growth of corn seedlings,making an increase in chlorophyll content,altering the activity levels of antioxidant enzymes,reducing the content of malondialdehyde and weakening the growth stress of FSA on corn seedlings.Non-targeted analysis of metabolites in the leaves of corn seedlings treated with FSA and CNC repaired group was carried out over the UHPLC-TOF-MS.The results revealed 84 identified metabolites.Compared with the control group,54 metabolites were increased and 13 metabolites were decreased within the treatment group,including the amino acids phenylpropanoic acid,polyketone,and organic acids.Within the remedy group by CNC,only 13 metabolites were significantly altered,specifically,6 metabolites being accumulated and 7 metabolites being decreased.Further analysis on the metabolic pathway showed that the growth of corn seedlings finally adapted to the FSA stress through initiating aminoacyl-t RNA biosynthesis,biosynthesis of amino acids,ABC transporters,cyanoamino acid metabolism and carbon metabolism.And there is still a little effect on the corn seedlings via the hormone signal transduction and carbon metabolism.