Preparation Of Graphene Oxide Composites And Study On Their Adsorption And Antibacterial Properties

Water pollution has become one of major environmental threats due to industrial development,many kinds of pollutions existed in water environment,including microorganism,metal ions,organics,dyes,and so on.The treatment of dye-contaminated water is a serious environmental problem because dye wastewater always comes as large quantities,complex composition,color depth,and is of high toxicity.Adsorption is an attractive method for treatment of dye wastewater due to its low-cost and simple post-processing,so it is important to design novel adsorbents with a high adsorption capacity.Microbial contamination has always been one of challenges that threat the health of human beings because many kinds of bacteria can lead to seriously and even deadly infections for people.Therefore,it is significant and necessary to develop effective and broad-spectrum antibacterial agent.Graphene,a two-dimensional,single sheet of carbon atoms,has been intensively studied since it was first discovered.Graphene oxide(GO),as one of graphene derivatives,is decorated with a large number of oxygen groups such as carboxyl,hydroxyl,and epoxy groups.Due to the structural characteristics of GO,it shows a lot of excellent properties.In recent years,it has been reported that GO and GO-based composites present powerful antibacterial effect or adsorption capacity.Although tremendous explorations have been achieved,a facile synthesis of GO-based composites with excellent performances is still highly desirable.Staring from the property of GO,this study analyses deeply the characteristics of GO,and systematically discuss the adsorption and antibacterial activity of GO.Based on the structure and properties of GO,chitosan(CS)with excellent antibacterial property and adsorption capacity,was employed to modified GO for the purpose of improving its adsorption and antibacterial activity.The Fe3O4 nano-particles were used to separate the adsorbent from water after application.In order to improve the antibacterial activity of GO,guanidine polymer was employed to functionalize GO.Then starting from the idea of avoiding the agglomeration of GO-guanidine composite,polyethylene glycol(PEG)and chitosan(CS)was used to functionalize GO respectively.Two kinds of GO based composites with enhanced antibacterial activity and aqueous stability was synthesized.The detailed contents are described as follows:1.The GO was prepared by the modified Hummers’ method,and its chemical structure and morphology was characterized.In the antibacterial experiment,the influence of experimental parameters such as contact time and concentration of GO on the antibacterial ability was investigated.The results demonstrate that the antibacterial activity improves with the increasing of GO concentration in the certain range.GO shows the best antibacterial activity at the concentration of 2000 μg/m L.The sterilizing rate increases with the contact time increasing.The MIC value of GO was measured by using E.coli and S.aureus as model bacteria,the MIC experimental results demonstrate that the GO exhibited stronger antibacterial activity against E.coli than that against S.aureus.In the batch adsorption experiment,the adsorption capacity of GO on methylene blue(MB)and rhodamine B(RhB)was studied.The results shows that the adsorption capacity of GO is better than that of activated carbon(one of the traditional adsorbents).The adsorption capacity of GO on MB and RhB is related to the initial concentrations,the maximum adsorption capacity of GO on MB was found at initial concentrations of 200 mg/L(the one for RhB is 300 mg/L).The adsorption of MB and RhB was fitted to the pseudo-second-order kinetic model very well.2.The GO-mCS composite was synthesized by functionalizing GO with magnetic chitosan(mCS).The structure,morphology and properties were characterized by using various measurements.The antibacterial experiment was carried out to study the antibacterial ability of GO-mCS composite.The experimental results show that the antibacterial ability of GO-mCS against E.coli and S.aureus is better than that of the single component(GO and mCS).GO-mCS shows the improved antibacterial ability.The adsorption experiment was carried out to study the adsorption properties of GO-mCS.The experimental results show that the adsorption ability of GO-mCS is better than that of GO.The adsorption quantities for MB and RhB are 258 mg/g and 153 mg/g,respectively.The optimal pH value for the adsorption of MB and RhB is about 5.The adsorption kinetics analysis show that the adsorption of MB and RhB was fitted the pseudo-second-order kinetic model very well,demonstrating that the adsorption for GO-mCS to MB and RhB is controlled by chemical adsorption.The magnetic test experiment shows that GO-mCS has superparamagnetism,demonstrating that the GO-mCS has the ability of magnetic recycle.In conclusion,the GO-mCS composite,combining the adsorption ability,antibacterial capacity and magnetic separation property,as a multi-functional composite,has great potential in environmental application.3.The GO-PEG-PHGC composite was synthesized by conjugating polyethylene glycol(PEG)and polyhexamethylene guanidine hydrochloride(PHGC)to the surface of GO sheets,and its structure,morphology and properties were characterized subsequently.GO-PEG-PHGC holds the layer structure which is similar to GO.The existence of PEG renders high aqueous stability to GO-PEG-PHGC in solution.The antibacterial experiment was carried out to investigate the antibacterial activity of GO-PEG-PHGC against E.coli and S.aureus.The results reveal that antibacterial activity of GO-PEG-PHGC is better than that of GO-PHGC.The improved antibacterial activity was described to be related to a better dispersion of GO-PEG-PHGC in the presence of PEG.The GO-PEG-PHGC shows obviously enhanced antibacterial ability.4.The GO-CS-PHGC composite was synthesized by conjugating CS-PHGC complexes onto the surface of GO sheets,and its structure,morphology and properties were characterized subsequently.GO-CS-PHGC holds the layer structure which is similar to GO.The existence of CS prevents the GO-CS-PHGC composite from agglomerating.The antibacterial activity of GO-CS-PHGC against E.coli and S.aureus was studied by antibacterial experiment.The experimental results indicate that GO-CS-PHGC composite shows higher antibacterial efficiency than that of any single component(GO,CS,PHGC and CS-PHGC).The MIC value of GO-CS-PHGC aganist E.coli is 32 μg/mL,which is lower than that of the mixture of GO and CS-PHGC,and the mixture of GO,CS and PHGC.This phenomenon demonstrates the significant antibacterial activity of GO-CS-PHGC is not due to a simple addition of contributions from individual components,but rather due to the unique physical and chemical characteristics of all components which contribute together in a synergistic manner to reveal a novel,remarkable efficient antibacterial activity.