Study On Adsorption Characteristics Of Typical Sulfonamides In Aquatic Solutions By Modified Activated Carbon

Sulfonamide antibiotics are widely used in human and animal health care due to their low cost,obvious effect and wide antimicrobial spectrum.Most of them are released into the environment through animal feces and urine in the form of the original drug or metabolites.The properties of sulfonamides in the water environment are relatively stable,which can exist for a long time in the environment.Thus,they are highly detected in the soil,surface water,groundwater and even drinking water.In this study,two modified activated carbons were prepared with Iron chloride hexahydrate?FeCl₃·6H₂O?and Hexadecyl trimethyl ammonium bromide?CTAB?,respectively.Multiple characterization techniques were used to analysis the properties of modified activated carbon including Scanning Electron Microscope?SEM?,Transmission Electron Microscope?TEM?,Energy Dispersive Spectrometer?EDS?,Fourier transform infrared spectroscopy?FT-IR?,specific surface area analyzer?BET?,Raman spectroscopy and X-ray diffraction?XRD?.The adsorption characteristics and mechanisms of sulfonamides on modified activated carbon were investigated by adsorption isotherms,adsorption kinetics,adsorption thermodynamics and adsorption activation energy.And On the basis of the analysis of the content and reduction of sulfonamides in each section of sewage treatment plant,the adsorption effect of sulfonamides by modified activated carbon was explored.The main research results are as follows:?1?The SEM and TEM characterization showed that surface holes and pore structure of MAC-1 were increased.And the pore structure of MAC-2 was decreased,where it can be attributed to hole blockage by CTAB.The BET analysis showed that the surface area,total pore volume,micropore volume and mesopore volume of MAC-1 were all increased to some extent after modification by Fe³⁺.However,the specific surface area,total pore volume,mesopore volume and micropore volume of MAC-2 were observably decreased.The FT-IR analysis showed that the oxygen functional groups of MAC-1 and MAC-2 were all increased.It was obvious that the flexural vibration peaks of unsaturated C-H and the characteristic absorption peaks of Fe OOH were clearly observed on MAC-1.And the antisymmetric stretching vibration peak of-CH₂ and symmetrical stretching vibration peak of-CH₃ are found on MAC-2.?2?Batch adsorption experiments for Sulfamethazine?SMX?and Sulfamethoxazole?SMZ?were conducted at different pH value,ionic strength,soluble humic acid?HA?and different heavy metals.It is shown that the adsorption of SMX on original and modified activated carbon first increased and then decreased for pH values between 3.0 and 10.0,while the adsorption of SMZe was decreased with increasing pH value.Well,the effect of ionic strength on the adsorption of sulfonamides on original and modified activated carbon is relatively weak,suggesting that the electrostatic interaction is not the main mechanism for adsorption of sulfonamides by activated carbon.The adsorption of sulfonamides was obviously inhibited by HA,where the adsorption coefficient of MAC-1 and MAC-2 on SMX,with the maximum inhibitory concentration of HA of 20 mg·L^-1,were decreased by81.03%and 71.74%,respectively,and adsorption coefficient of SMZ were decreased by 89.04%and 64.12%,respectively.Cd²⁺can promote the adsorption ability of Sulfamethazine,where Cr⁶⁺inhibits the adsorption of SMX.?3?The Langmuir model can fit the adsorption process of sulfonamides on MAC-1 well,where the maximum adsorption amount of SMX and SMZ were 17.483mg·g^-1 and 19.646 mg·g^-1,respectively.However,the Freundlich model can better describe the adsorption process of sulfonamides on MAC-2,and the adsorption capacity of SMZ is higher than that of SMX,where the K_F value were 12.249 and9.190 mg^1-1/n·L^1/n·g^-1,respectively.The kinetic adsorption process of SMX and SMZ on MAC-1 and MAC-2 were all conformed Pseudo first-order model,where the diffusion process can be divided into three stages.The adsorption of SMX and SMZ is exothermic process,where low temperature is conducive to the adsorption of sulfonamides.?4?It can be observed that the adsorption of sulfonamides on MAC-1 was mainly ascribed to chemical adsorption by calculation of adsorption activation energy.It was also extrapolated that the adsorption mechanisms included micropore capture,hydrogen bonding interaction,?-?electron donor-acceptor?EDA?interaction and coordination interactions by various characterizations.Meanwhile,the adsorption of sulfonamides on MAC-2 was also mainly ascribed to chemical adsorption,where the adsorption mechanisms were included hydrogen bonding interaction and?-?electron donor-acceptor?EDA?interaction.There might be hydrophobic interaction between oxazole ring of SMZ and benzene ring on the surface of modified activated carbon,resulting that the adsorption efficiency of SMZ was higher that SMX.?5?Ten sulfonamide antibiotics were detected in raw influent,effluent of primary sedimentation tank,effluent of biochemical reaction tank,effluent of secondary sedimentation tank and final effluent,where the concentrations were in the range of0.09³56.91 ng·L^-1,0.08²69.25 ng·L^-1,0.07³21.93 ng·L^-1,0.05²47.69 ng·L^-1,0.06²57.08 ng·L^-1,respectively.Besides TMP,the wastewater treatment plant has a certain removal effect on sulfonamides,where removal difference of each section is evident with the total removal rate of 12.15%⁶0%.