Research On The Adsorption Properties And Mechanism Of Antibiotics By Graphene Oxide And Its Functional Materials In Multicomponent

In recent years,more and more countries use antibiotics to resist diseases and protect human and animal health.The extensive use of antibiotics will not only lead to side effects,but also lead to the emergence of drug-resistant strains,which pose serious harm to the ecological environment and hum an health.However,antibiotics are difficult to metabolize in the body and will eventually be discharged into the natural water.Therefore,it is important to find a suitable method to remove antibiotics from water for protecting the ecological environmen t and human health.Adsorption is considered as a promising method for antibiotic wastewater removal because of its high efficiency,simple operation,low cost and no secondary pollution.Graphene oxide is a kind of two-dimensional single-layer carbon nanomaterial,which has a huge delocalized?electronic structure and m any active groups,and has a great advantage in the adsorption of antibiotics.However,in practical application,graphene oxide has some disadvantages,such as difficult solid-liquid separation and limited adsorption capacity.The separation performance of graphene oxide can be improved by coupling magnetic nanoparticles.In addition,by further using chelating agents with more nitrogen and oxygen groups to functionalize the magnetic graphe ne oxide,the adsorption capacity of antibiotics can be improved.In the actual water body,it is often very complex,a variety of organic and inorganic substances coexist.These components have great influence on antibiotic adsorption.Therefore,it is of great theoretical significance to investigate the influence of coexisting antibiotics,inorganic nanoparticles,electrolyte ions,heavy metals and other components on the adsorption of antibiotics by graphene oxide and its functional materials.In this st udy,graphene oxide was used as the basic material to study its ads orption performance and related mechanism for tetracycline and ciprofloxacin.In order to achieve good solid-liquid separation and adsorption performance,functional modification was carrie d out by coupling and grafting.The modified magnetic graphene oxid e material was applied to the adsorption of tetracycline and ciprofloxacin in the multicomponent.The main purpose was to explore the influence and mechanism of coexisting antibiotics,inorganic nanoparticles,electrolyte ions,heavy metals and other compo nents on the adsorption of tetracycline and ciprofloxacin.The main research work and achievements of this paper included the following five aspects:(1)In the first part,graphene oxide w as successfully prepared,and its morphology,specific surface area and pore size,element and functional group composition were analyzed by TEM,SEM,BET,XPS and FTIR measurements.The prepared graphene oxide was applied to the adsorption of tetracycline(TC)and ciprofloxacin(CIP)in water.Kinetic study showed that t he adsorption process of tetracycline and ciprofloxacin could be better described by the pseudo-second-order kinetic model,indicating that chemical adsorption played a major role.Langmuir and Freundlich models could describe the adsorption process well.According to Langmuir model,the maximum adsorption capacity of tetracycline and ciprofloxacin were 283.98 and 268.44 mg/g,respectively.It was confirmed that graphene oxide had good adsor ption capacity for tetracycline and ciprofloxacin.However,there w ere still some problems in the process of antibiotic wastewater removal,such as limited adsorption capacity and difficulty in solid-liquid separation.(2)In the second part,in order to improve the solid-liquid separation ability of graphene oxide,magnetic graphene oxide was prepared.In order to improve its adsorption performance,magnetic graphene oxide was functionalized by aminotriacetic acid,and the functional magnetic graphene oxid e material(NDMGO)was prepared,which was used as an adsorbent for tetracycline(TC)removal in water.The materials were characterized by TEM,SEM,BET,XPS,TG-DTA,FTIR,Raman,XRD,VSM and zeta potential measurements.The results showed that the adsor ption capacity of NDMGO to 50 mg/L tetracycline was 212 mg/g at pH 4.0,which was about twice and three times that of graphene oxide(109 mg/g)and magnetic graphene oxide(72 mg/g).Several experimental conditions(solution pH,adsorption time,temperature,ionic strength and foreign ions)affecting the adsorption proces s were investigated.The results showed that the adsorption capacity of tetracycline increased first and then decreased in the range of pH 2.0-11.0,and the highest adsorption capacity was at pH 4.The time needed for adsorption to reach equilibrium was ab out1000 minutes,and the pseudo-second-order kinetics provided the better correlation for the experiment data.With the increase of temperature,the adsorption capacity of tetracycline increased gradually.Various thermodynamic parameters indicated that t he adsorption was a spontaneous and endothermic process.When the concentration of Na Cl was less than 0.01 mol/L,the adsorption amount of 10 and 50 mg/L tetracycline by NDMGO increased with the increase of Na Cl concentration.When the concentration of Na Cl was more than 0.01 mol/L,the increase of adsorption efficiency was not obvious.The presence of background electrolytes in the solution had a slight influence on tetracycline adsorption.The regeneration experiment demonstrated that this nanomaterial possessed an excellent regeneration performance.Hydrogen bonds,amidation reaction,?-?and cation-?interaction between NDMGO and tetracycline could be used to explain the adsorption mechan ism.The results show that the NDMGO was a high-efficiency and reusable adsorbent for tetracycline pollution control.(3)In the third part,in order to further improve the solid-liquid separation and adsorption performance of graphene oxide,diethylenetri aminepentaacetic acid-functionalized magnetic graphene oxide(DDMGO)was prepared,and it was applied to adsorb tetracycline(TC)and ciprofloxacin(CIP)in single and binary systems.The materials were characterized by TEM,SEM,XPS,FTIR,XRD and zeta potential measurements.The adsorption kinetics and equilibrium data of single antibiotic were well fitted by pseudo-second-order and Freundlich isotherm models,respectively.Negative?G° values hinted the spontaneous nature of tetracycline and ciprofloxacin sorption.Moreover,different?H^o indicated that tetracycline adsorption was endothermic and ciprofloxacin adsorption was exothermic.The maximum adsorption capacity of tetracycline and ciprofloxacin in the single system occurred at pH 3.0 and 8.0,respectively.The results showed that the lower ionic strength(0-0.01mol/L)inhibited the adsorption of ciprofloxacin,but had little effect on the adsorption of tetracycline.With the increase of Na Cl concentration,the removal capacity of tetracycline and ciprofloxacin increased gradually.The increase of SO ₄^2-concentration significantly enhanced the adsorption of DDMGO to both antibiotics.The existence of low concentration of K⁺and Mg²⁺will lead to the decrease of the removal ability of the adsorbent for ciprofloxacin.However,the presence of K⁺had no significant effect on the adsorption of tetracycline.However,the presence of Mg²⁺inhibited the adsorption of tetracycline by DDMGO.When ciprofloxacin and tetracycline coexist in the solution,the adsorption capacity of ciprofloxacin was almost not affected by the presence of tetracycline,but tetracycline had obvious inhibition on DDMGO by the presence of ciprofloxacin,which showed that the main competitive effect was related to the affini ty of the compound to the adsorbent.The reusability experiment revealed that the material had an excellent regeneration performance in single and binary systems.The removal mechanism was mainly dependent on?-?interaction,hydrogen bonds and amidation reaction.Besides,tetracycline and ciprofloxacin uptake could also be explained by cation-?and electrostatic interaction,respectively.These findings showed that DDMGO was an efficient and reusable adsorbent for antibiotics elimination.(4)The fourth part was devoted to examine the adsorption of tetracycline(TC)on graphene oxide(GO)in the presence of inorganic nanoparticles(m-NPs).Inorganic nanoparticles included metal oxides(ZnO and Fe₂O₃)and clays(kaolin and montmorillonite).The experimental results proved that the existence of m-NPs greatly enhanced the tetracycline adsorption onto graphene oxide and lengthened the adsorption equilibrium time.The enhanced adsorption amount of tetracycline with increasing m-NPs/GO ratio was primarily due to the adsorption of tetracycline onto m-NPs.In the synergistic system of graphene oxide and m-NPs,tetracycline removal efficiency was higher than that of graphene oxide and m-NPs alone,and the adsorption was not equal to the sum of the two,which might be attributed to the possible enhancing performance of graphene oxide induced by m-NPs.In different pH range,the presence of m-NPs was beneficial to the adsorption of tetracycline by GO.Moreover,the heteroaggregation of graphene oxide with di fferent m-NPs was studied in aqueous phase by TEM and DLVO theory.Analysis showed that the electrostatic attraction between negatively charged graphene oxide and positively charged ZnO were likely to first heteroaggregate in binary systems of graphene oxide and ZnO.However,graphene oxide was prone to homoaggregate owing to electrostatic repulsion with the same negatively charged montmorillonite(or kaolin).Besides,Fe₂O₃ tended to first homoaggregate and then heteroaggregate with graphene oxide.This report elucidated complex interactions between graphene oxide and inorganic nanoparticles,which was crucial to understand the migration and transformation of graphene oxide and inorganic nanoparticles in actual water.(5)The fifth part was to study the effect of Cu(?)on the adsorption of ciprofloxacin(CIP)by NDMGO.Adsorption results exhibited that the presence of Cu(?)obviously enhanced the ciprofloxacin adsorption capability through Cu(?)bridging effect.The adsorption capacity for ciprofloxacin was stronger in the(CIP-Cu(?))-NDMGO system than in the(NDMGO-Cu(?))-CIP and(NDMGO-CIP)-Cu(?)systems.Moreover,NDMGO also had good adsorption properties for Cu(?).In addition to Cu(?)bridge enhancement,the mechanism c ould also be explained by hydrogen bonds,amidation reaction,electrostatic and?-?interaction.These results provided valuable information for the removal of ciprofloxacin and improved our understanding on reaction mechanism of antibiotics by NDMGO in the presence of metal ions,demonstrated that NDMGO could be developed as an effective adsorbent to simultaneously removal metal ions and organic substances.