Theoretical Study On The Adsorption Characteristics Of Sulfonamides On Carbon Nanotubes And The Influence Of Acid-base Environment

With the development of society,people’s demand for and consumption of sulfonamides is increasing.These drugs have the advantages of stable properties,low prices,diverse varieties,easy to use and sufficient yield.In clinical practice,sulfonamides are widely used to prevent and treat infectious diseases.In veterinary clinics and animal husbandry,they can be used as feed additives or animal disease treatment drugs.However,the unreasonable use and disposal of sulfonamides also cause certain harm to human health and the ecological environment.In order to solve this problem,more and more researchers have begun to focus on the detection,removal,adsorption and degradation of sulfonamides.Carbon nanotubes have become a popular new carbon nanomaterial due to its good corrosion resistance,excellent electrical conductivity,unique spatial structure,and large specific surface area.The most important thing is that carbon nanotubes have excellent adsorption properties.Its properties also make it a new type of adsorbent for the removal of sulfonamides in the environment.In this paper,through the calculations of density functional theory,the adsorption characteristics of carbon nanotubes on five sulfonamides--sulfanilamide,sulfadiazine,sulfamerazine,sulfamethazine and sulfamethoxazole were deeply discussed.The main findings are as follows:（1）The adsorption characteristics of sulfanilamide,sulfadiazine,sulfamerazine,sulfamethazine and sulfamethoxazole on carbon nanotubes in vacuum environment were studied.According to the adsorption energies,adsorption bond lengths,electron density maps and frontier molecular orbital values,it is observed that five drugs on carbon nanotubes are all physical adsorption.By analyzing the charge numbers of some atoms in the drug molecule,it is known that the adsorption performance of the drug molecule has a certain correlation with the charge distribution of the molecule.According to the adsorption energy,the order of adsorption strength of five drugs on carbon nanotubes is: sulfamethazine > sulfadiazine > sulfamerazine >sulfamethoxazole > sulfanilamide.（2）Based on the vacuum model,the adsorption of five drugs on carbon nanotubes in water environment was studied.By analyzing adsorption configurations,adsorption energies,adsorption bond lengths,it was found that five drugs in the water environment were still physical adsorption,which provided theoretical support for carbon nanotubes used as a recyclable adsorbent.In addition,the adsorption strength of the five drugs in the water environment has improved,and the order of the adsorption strength of the five drugs is still as follows: sulfamethazine >sulfadiazine > sulfamerazine > sulfamethoxazole > sulfanilamide.（3）In order to study the effect of carbon nanotubes on the adsorption of five drugs in acid-base environments,we set up acid-base environment models with different intensities by introducing one HCl,two HCls,one Na OH,and two Na OHs into the water model.The effects of carbon nanotubes on the adsorption of five drugs under different acid-base environments were explored.The changes of the adsorption properties of carbon nanotubes to five drugs in different acid-base environments were calculated.Under the acid-base environment,the adsorption effect of carbon nanotubes on the five drug molecules decreased,and the alkaline environment was more unfavorable for the adsorption of carbon nanotubes than the acidic environment.Our study explores the use conditions of carbon nanotubes for environmental treatment and separation of five antibiotic drugs,namely sulfanilamide,sulfadiazine,sulfamerazine,sulfamethazine and sulfamethoxazole,hoping to provide an effective theoretical basis for environmental treatment of sulfonamide antibiotic residues.