Effects Of Biochars On Photodegradation Behavior Of Typical Antibiotics On The Surface Soil Layer

The"pseudo persistence"caused by the continuous input of antibiotics into the soil environment poses a threat to the security of agricultural ecosystems.As a porous material with good electron transfer ability,biochar can not only serve as a carrier for carrying photocatalytic materials,but also affect the degradation of pollutants by producing active species.The mechanism of its impact on the migration and transformation of antibiotics in soil needs further exploration.In view of this,this article uses sawdust（S）,rice husk（R）,and tobacco（T）straw as biomass raw materials to prepare biochar through pyrolysis.Based on the influence of biochar on the adsorption and vertical migration behavior of typical antibiotics tetracycline（TC）,sulfamerazine（SM1）,and enrofloxacin（ENR）,the photolysis laws and main influencing factors of typical antibiotic pollutants in shallow soil modified with different biochar were explored,And analyzed the intermediate products and degradation pathways of antibiotic degradation;By modifying biochar,the photochemical properties and environmental application potential of biochar materials were explored.The main research findings are as follows:（1）Five kinds of biochar（S700,S500,S300,T500 and R500）were prepared at 300,500and 700℃.S700 has the strongest aromaticity,the most developed specific surface area and pore structure,with a C/H of 64.40,a specific surface area of 511.75 m²/g,and a total pore volume of 0.28 cm³/g;Five types of biochar all detected oxygen-containing functional groups such as-OH,C-O,and C=O;The biochar prepared at 500℃has the strongest EPR signal,reaching 10⁶.（2）The results of batch adsorption experiments indicate that the Freundlich equation can relatively best describe the adsorption behavior of typical antibiotics in biochar soil（R²>0.9）,and the adsorption of antibiotics in biochar soil tends to be multi-layer adsorption and is influenced by physical adsorption.S700 has the best adsorption effect on SM1 in soil,with a removal rate of about 40%and a K_d value of 234.11.SM1 has the strongest vertical migration ability,with a maximum concentration of 325μg/kg detected in soil depths of 15-20 cm;S700 biochar can effectively resist the vertical migration of SM1,and the biochar soil has the most obvious immobilization effect on antibiotics when the leaching solution is neutral.（3）Conducting experiments on the photolysis kinetics of antibiotics in shallow soil under simulated sunlight,the results showed that the photolysis of typical antibiotics in biochar soil surface follows a quasi first-order reaction kinetics law（R²>0.9）.After adding R500,the photolysis rate constants(K_obs)of the three antibiotics（TC,SM1,and ENR）were 0.0127 h^-1,0.00801 h^-1,and 0.0826 h^-1,respectively,with t_1/2 shortened by 47.0%,11.7%,and 17.0%,respectively.³DOM*,·OH,h⁺,and ¹O₂ all participate in the photolysis reactions of the three antibiotics to varying degrees.The degradation rate of TC and ENR reaches its maximum at p H neutral,while the photolysis rate of SM1 reaches its maximum at p H=9.The photolysis of three antibiotics in soil includes both direct and indirect photolysis.（4）After alkali modification,the specific surface area and total pore volume of R500biochar（KBC）increased to 406.56 m²/g and 0.35 cm³/g,respectively;The types of oxygen-containing functional groups on the surface increase and the signal enhances;After acid/alkali modification,the adsorption of TC and ENR by R500 weakened,with lg K_f of only 2.42 and3.68,respectively.The adsorption of SM1 was enhanced,with lg K_f of 1.68.The photocatalytic performance of R500 loaded with Fe₃O₄ was enhanced for typical antibiotics,with removal rates of 47.13%,34.30%,and 36.25%for the three antibiotics,respectively;After urea doping,R500 biochar showed the most significant increase in the removal rate of three typical antibiotics,with removal rates of 52.76%,49.09%,and 39.90%,respectively.In this research,the addition of S700 biochar effectively adsorbed SM1 and impeded its vertical migration.Adding R500 biochar to the soil can effectively shorten the t1/2 of three antibiotics under simulated sunlight.Biochar loaded with Fe₃O₄ or nitrogen doped biochar enhances the photocatalytic ability of biochar,reducing the ecological risk of antibiotic pollutants in the soil environment,and is beneficial for protecting China’s agricultural ecological environment Developing environmentally friendly repair materials has important theoretical and practical significance.