Adsorption Efficiency Mechanism Of Graphene Based Aerogels On Sulfonamide Antibiotics

The sulfonamides that exist in surface water mainly come from industrial wastewater,domestic sewage,medical and aquaculture wastewater,fecal composting and garbage disposal,which have high organic concentration,high ammonia nitrogen,high salinity,and have some biological toxicity.Antibiotics in the environment can induce bacteria to produce drug resistance genes,which is the root cause of bacterial resistance and will pose a serious threat to human health and ecosystem.In this paper,a low concentration of sulfonamides contained in the water body was used as the research object.The preparation materials,the adsorption efficiency and the analytical mechanism were studied,which provided the theoretical and technical support for the rapid adsorption and removal of trace antibiotics in the surface water.Graphene oxide was prepared by Hummers method,and graphene aerogels with different GO concentrations were prepared by hydrothermal reduction method.The adsorption efficiency of four common sulfa sulfamines,sulfadiazine,sulfaisoxazole,sulfamethoxazole and sulfadiazine was studied.The adsorption kinetics showed that the adsorption equilibrium time was about 90 min,and when the concentration of GO was 3 mg/m L,the adsorption effect of GA was the best.At 100 ?g/L,the removal rates of four sulfonamides were 80.92%,74.82%,66.2% and 61.4% respectively,and the adsorption process accorded with the pseudo two kinetic adsorption model.The adsorption isotherm showed that the adsorption isotherm equation of GA for sulfonamides was combined with Langmuir adsorption isotherm equation,the adsorption capacities were 20.46,17.40,15.26 and 13.42 mg/g respectively.The adsorption capacity of four antibiotics was not significantly different;-40 k J/mol <?G0<-20 k J/mol,this process was spontaneous endothermic process and high temperature was beneficial to sucking.In the process,physical adsorption and chemical adsorption were existing simultaneously.Acid condition was more beneficial to the adsorption of sulfonamides by graphene aerogels.With the increase of p H,the adsorption capacity gradually decreased.The adsorption capacity decreased rapidly when 2 < p H < 7,and the decline was slower when p H > 7.The stability of GA-3 was the highest.In order to improve the mechanical strength of GA,GA doped with carbon nanotubes was prepared.The amount of carbon nanotube doping was 10-40%.The results showed that when the content of carbon nanotubes was 20%,the modulus of GA/CNT was the smallest and the mechanical strength was the strongest.The adsorption kinetics showed that the equilibrium time was about 90 min and the adsorption effect was best,and the removal rate increased by 6.9%~9.8% when the adsorption equilibrium was reached;The adsorption of GA/CNT on sulfonamide antibiotics conformed to pseudo two order kinetics.The adsorption process was similar to the adsorption process of GA and was completed in three stages.The adsorption isotherm resulted show that the adsorption of sulfonamides by GA/CNT was combined with Langmuir adsorption isotherm equation,and the adsorption capacities of four antibiotics was 38.80,35.43,32.67 and 27.63 mg/g,respectively.High temperature was beneficial to the process of adsorption.?G0<-10 k J/mol,physical adsorption and chemical adsorption was existing simultaneously.The effect of p H on the adsorption amount was the same as that of GA.The stability of aerogel after adding carbon nanotubes was greatly improved.In order to achieve selective adsorption of sulfonamide antibiotics,carbon nanotube was prepared by carboxylation and amination,and then the composite aerogels GA/CNTCOOH and GA/CNT-NH2 were prepared.The results showed that the adsorption equilibrium time was about 60 min,30 min shorter than that of GA/CNT,and the removal rate of sulfadiazine was above 95%.The internal diffusion model showed that the adsorption process was completed in two stages.The adsorption process of the two materials for sulfadiazine was in accordance with the Langmuir adsorption isotherm equation and the adsorption capacity was 267.79 mg/g and 224.66 mg/g.The adsorption heat-304.60 k J/mol <?G0<-196.89 k J/mol,belonged to chemical adsorption.Acidic condition was more conducive to the adsorption of sulfadiazine by materials.Low ionic strength promoted the adsorption of GA/CNT-COOH on sulfadiazine.When the concentration of ion was 0.01mol/L,the adsorption capacity of Na+ system was increased by 11.4%,the adsorption capacity of Ca2+ system was increased by 15.49%,and humic acid and sulfadiazine were competing for the adsorption site,naturally there wass The presence of organic matter reduced the adsorption capacity of GA/CNT-COOH to sulfadiazine.By analyzing the adsorption mechanism of graphene based aerogels on sulfonamides,it could find that the molecular size of antibiotics is less than the average pore size of GA,and the adsorbate can enter the adsorbent smoothly through the pore structure.The adsorbent and the adsorbate formed a ?-? covalent bond to form a strong binding force,which enhanced the adsorption.The oxygen in sulfanilamide molecules formed hydrogen bonds with-OH in the aerogel structure of graphene to enhance adsorption.The carboxyl group in GA/CNT-COOH could be combined with the amino group in the sulfa antibiotic structure.The amino group in GA/CNT-NH2 could react violently with the sulfone group,so the adsorption process was accelerated and the adsorption capacity of the material is greatly improved.