Adsorption/Fenton-like Oxidative Degradation Of Sulfonamides By Carbon Nanotube-based Materials

A large number of sulfonamide antibiotics are discharged into water bodies with excreta in the form of the original drugs or metabolites,causing serious harm to the ecological environment and human health.In order to effectively remove sulfonamides from water,techniques combining adsorption and Fenton-like oxidation based on carbon nanotubes（CNTs）have been extensively studied.However,these studies have two shortcomings: first,usually only one or two sulfonamide antibiotics were tested,and the reaction law of the adsorption/degradation sulfonamide pollutants has not been systematically studied;second,although metal modified CNTs showed enhanced sulfonamide removal efficiency,the interaction between CNTs and metals was weak,thus their catalytic activity need to be further improved.In order to solve the above two problems,CNTs-Fe3O4 and Al0-CNTs-Fe3O4 composites were prepared by ball milling and high temperature melting combined with ball milling strategies,respectively.And two Fenton-like systems were constructed: CNTs-Fe3O4 catalyzed H2O2 Fenton-like system（CNTs-Fe3O4/H2O2）and Al0-CNTs-Fe3O4 activated O2 in situ to produce H2O2 Fenton-like system（Al0-CNTs-Fe3O4/O2）.Furthermore,the adsorption/degradation behaviors and mechanisms of six sulfonamides based on the two systems were discussed in this study.The main conclusions are as follows:A large number of sulfonamide antibiotics are discharged into water bodies with excreta in the form of the original drugs or metabolites,causing serious harm to the ecological environment and human health.In order to effectively remove sulfonamides from water,techniques combining adsorption and Fenton-like oxidation based on carbon nanotubes（CNTs）have been extensively studied.However,these studies have two shortcomings:first,usually only one or two sulfonamide antibiotics were tested,and the reaction law of the adsorption/degradation sulfonamide pollutants has not been systematically studied;second,although metal modified CNTs showed enhanced sulfonamide removal efficiency,the interaction between CNTs and metals was weak,thus their catalytic activity need to be further improved.In order to solve the above two problems,CNTs-Fe₃O₄ and Al⁰-CNTs-Fe₃O₄ composites were prepared by ball milling and high temperature melting combined with ball milling strategies,respectively.And two Fenton-like systems were constructed:CNTs-Fe₃O₄ catalyzed H₂O₂ Fenton-like system（CNTs-Fe₃O₄/H₂O₂）and Al⁰-CNTs-Fe₃O₄ activated O₂ in situ to produce H₂O₂ Fenton-like system（Al⁰-CNTs-Fe₃O₄/O₂）.Furthermore,the adsorption/degradation behaviors and mechanisms of six sulfonamides based on the two systems were discussed in this study.The main conclusions are as follows:（1）The adsorption processes of the six sulfonamides on CNTs and CNTs-Fe₃O₄could be described by pseudo-second-order kinetics and Langmuir model.Under the optimum conditions,the maximum adsorption capacities of SMD on CNTs and CNTs-Fe₃O₄ reached 132.281 mg g^-1 and 101.370 mg g^-1,respectively.The adsorption equilibrium capacity,maximum adsorption capacity and adsorption rate constant of SMD were highly correlated with the highest occupied molecular orbital energy and dipole moment parameters of sulfonamides.For CNTs,these correlations could be expressed as:y=0.204–0.008/(1+e^{（x-129.955）/1.268}),y=0.204–0.008/(1+e^{（x–1.71）/0.036}),y=0.173×e^{（x/0.917）}+6.24 and y=28.781–21.812/(1+e^{（x–204.832）/17.209});For CNTs-Fe₃O₄ could be expressed as:y=-0.194–0.010/(1+e^x-0.110/0.008),y=-0.195–0.009/(1+e^x–91.344/1.488),y=1.691 × e^x/0.011and y=11.169+4.148/(1+e^x–95.928/2.199).（2）The ball milling conditions greatly affected the catalytic activity of CNTs-Fe₃O₄.CNTs-Fe₃O₄ prepared under the conditions of CNTs/Fe₃O₄ mass ratio of 1:1,ball milling time of 90 min,ball milling rate of 420 rpm,and ball/powder mass ratio of1:100 had high catalytic activity:when the dosage of CNTs-Fe₃O₄ was 1 g L^-1 and p H was 3,the removal efficiency for 40 mg L^-1 SMR could reach 100%within 15 min.Compared with the physical mixed CNTs/Fe₃O₄,the catalytic and degradation activity of CNTs-Fe₃O₄ was increased by 80.45%.The degradation rates of the six sulfonamides in the CNTs-Fe₃O₄/H₂O₂ Fenton-like oxidation system were related to their molecular structures.The relationship between the degradation rate constant of most antibiotics and their Mulliken charge could be expressed as:y=-28.719x+15.670.（3）In the Al⁰-CNTs-Fe₃O₄/O₂ Fenton-like system,Al⁰-CNTs activated O₂ to produce H₂O₂ in situ by forming corrosive cells,then Fe₃O₄ catalyzed the generated H₂O₂ into hydroxyl radicals to achieve efficient degradation of sulfonamides.Under the conditions of p H 1.5,SMR concentration of 40 mg L^-1 and catalyst dosage of 0.5 g L^-1,the oxidative degradation efficiency of SMR reached 93%within 12 min.The degradation process of sulfonamides in the Al⁰-CNTs-Fe₃O₄/O₂ Fenton-like system was fitted well with the First-order kinetic model.For most sulfonamide molecules,the relationship between the degradation rate constant and the molecular Mulliken charge could be quantified as follows:y=-21.786x+1.750.In this study,CNTs were used as the matrix material to prepare highly bonded CNTs-Fe₃O₄ and Al⁰-CNTs-Fe₃O₄ through ball milling or melting strategy.The prepared composites had strong adsorption/catalytic activity to effectively remove sulfonamides antibiotics from water and provided a new idea for the development of CNTs-based materials.The establishment of the quantitative relationship between the adsorption/degradation behavior of sulfonamides and their molecular structural parameters also provided a new method for predicting and evaluating the adsorption/degradation behavior of other sulfonamides.