Adsorption Characteristics Of Tetracycline On Biochar Modified By Vitamin C In Water

With the gradual development of the times and the continuous progress of the animal husbandry and medical industry,the excessive and non-standard use of tetracycline（TC）enters the natural environment from various ways.Due to the characteristics of biodegradability,tetracycline has a certain impact on the ecological balance and natural security,even damage.There are various ways for tetracycline to enter the natural environment,including medical industry,animal husbandry,aquatic aquaculture,surface runoff,which is difficult to control,and the pollution chain is long.How to repair the pollution of tetracycline in the environment and protect the environment is particularly important.Therefore,this study used the waste crayfish shell as raw material to prepare preliminary biochar with different pyrolysis temperatures（Crayfish shell biochar,abbreviated as CSB）.Due to the excellent difference of biochar under different pyrolysis conditions,a variety of carbons are screened to ensure good effect.In order to obtain adsorption materials with higher adsorption capacity,the original biochar was modified to study the removal capacity.At the same time,as a new pollutant in nature,microplastics（MPs）can become the carrier of organic pollutants,which has a certain impact on the process of removing pollutants by biochar.Therefore,this study further discussed the impact of microplastics on the adsorption performance of biochar for tetracycline removal.（1）In this paper,tetracycline was used as the representative pollutant,and crayfish shell was used as the raw material to prepare raw biochar（CSB-500,CSB-700,CSB-900）at different pyrolysis temperatures.With the gradual increase of pyrolysis temperature,the properties of the biochar changed,the C content decreased,and the H/C decreased.The pore folds on the surface of biochar gradually decrease,calcium carbonate gradually forms steadily,the number and types of surface functional groups decrease,and the nature of biochar has a great impact on the adsorption capacity.The results showed that the adsorption rate of three kinds of biochar was faster,the adsorption amount reached the peak at p H=6,and the adsorption amount was higher at p H=8-9under alkaline conditions.CSB-500,CSB-700 and CSB-900 are more consistent with Langmuir isotherm adsorption model.The pseudo-second-order kinetic model can better describe the adsorption process of three adsorption materials.（2）According to the chemical modification of biochar at different pyrolysis temperatures to enhance the adsorption capacity,the original biochar CSB-700 with the best adsorption capacity was selected,and it was chemically modified with vitamin C,and three kinds of biochar(CSB-VC₁（g VC/g CSB=1）,CSB-VC₂（g VC/g CSB=2）,CSB-VC₃（g VC/g CSB=3）were prepared according to the different impregnation ratio of vitamin C and CSB.The modification of vitamin C will not affect the mineral phase composition of Ca CO₃,but can enrich the types of surface functional groups.The adsorption process of CSB-VC₁,CSB-VC₂and CSB-VC₃is more in line with the pseudo-second-order kinetic model.Unlike the original biochar CSB-700,the three impregnations are more in line with the Freundlich isotherm adsorption model than the modified biochar,which is dominated by multilayer adsorption.The maximum adsorption capacities of CSB-VC₁,CSB-VC₂and CSB-VC₃were 221.61 mg/g,276.02 mg/g and 187.38 mg/g,respectively,which were higher than 168.52 mg/g of the original biochar,indicating that the modification of vitamin C could effectively enhance the adsorption and removal of tetracycline by biochar.The adsorption capacity of CSB and CSB-VCs at different temperatures（288.15 K,298.15 K and 308.15 K）was studied.At 308.15 K,the maximum adsorption capacity of CSB-VC₂could reach an astonishing 293.36mg/g.The optimum impregnation ratio CSB-VC₂improved the adsorption performance of the modified resin to 70.4%of the original adsorption performance.Hydrogen bond,p-p conjugation,pi-pi electron donor-receptor effect andπ-πinteraction are the main adsorption mechanisms.The study found that VC modification is very effective in a wide range of p H and high ion concentration.（3）In view of the emerging pollutants in the current water environment-microplastics,consider the impact of microplastics on the removal of tetracycline in water by biochar.Based on the carrier effect of microplastics,three typical microplastics PE,PP and PVC were selected to be added into the best biochar adsorption experiment in the previous study.CSB-VC₂was added with three kinds of micro-plastic PE,PP and PVC at 1:1,and the system was CSB-VC-PE,CSB-VC-PP and CSB-VC-PVC.After adding three kinds of microplastics,the adsorption process are more in line with the pseudo-second-order kinetic model,indicating that the adsorption process is dominated by chemical adsorption,and the Freundlich isotherm adsorption model better describes the adsorption process as multi-layer adsorption.The addition of three kinds of microplastics all enhanced the adsorption of tetracycline by biochar,with an increase of 4.5%for PE,5.3%for PP and 11.9%for PVC.CSB-VCs have excellent adsorption capacity and recycling performance,and also show strong ability to deal with pollution in actual water,providing new insights for the chemical modification of biochar and the recycling of different types of biomass.In view of the current complex and diverse environmental pollution problems,the addition of adsorbents faces various challenges.The synergy mechanism of biochar and microplastics can lay a foundation for comprehensive research on environmental protection and remediation.