Study On The Effects And Mechanism Of Several Biological Reaction Systems On Graphite And Graphene Oxide Materials

In recent years,with the extensive research and application of graphene and related carbon materials,the natural environment,living organisms and human health were inevitably influenced.As a result,scientists have increasingly attached importance to the research on the adaptability and the interaction between graphene materials and living organisms.As the raw material to prepare graphene and related carbon nanomaterials by the top-down method,graphite shows excellent chemical stability so that its study was limited only to physical and chemical domains.The enhancement of the reaction activity of graphite with defects as well as its potential interaction with the biological system has always been neglected.In this dissertation,some typical microorganisms,which have representative oxidation or reduction ability,were selected to study microbial oxidation of graphite,oxidation or degradation of graphene oxide(GO),biological nitrogen doped graphene and their reaction mechanisms.The first principle theory was used to study the simplified molecular models of graphene and biological enzymes.Compared with other methods especially the chemical method using toxic reagents and showing high energy consumption,biological method is mild,green,and environmental friendly in large-scale production of graphene and N-doped graphene.The prepared porous graphene and N-doped graphene can be widely used in the fields of biomedicine,energy storage materials and so on.The main contributions of this dissertation are described as follows:Microbial oxidation of graphite by Acidithiobacillus ferrooxidans and its mechanism study.Acidithiobacillus ferrooxidans is isolated from acid mine drainage in an extremely thermophilic bacilli sour.It is widely used in biological leaching and microbial processing of metal sulfide ore and other mineral materials.Acidithiobacillus ferrooxidans CFMI-1 preserved in our laboratory was selected in this dissertation.Graphite was added to the bio-culture system in order to domesticate the microorganism.Then,the graphite-adaptable strains were obtained.The biological oxidation graphite was prepared by the domestication of Acidithiobacillus ferrooxidans CFMI-1 in the home-made biological reaction system(5L glass reaction kettle)after multiple continuous microbiological functions.The purified biologically converted graphite oxide(BCGO)was collected and dispersed homogeneously in ethanol.However,the oxidation degree of the graphite is low,according to the black color and its water contact angle of 85°.The BCGO samples were characterized by X-ray photoelectron spectroscopy(XPS),energy dispersive X-ray(EDX)and Raman spectroscopy(Raman).There was a small amount of oxygen element in the sample,which was from the groups of-OH,C-O-C and-COOH.The BCGO samples were characterized by transmission electron microscopy(TEM)and atomic force microscopy(AFM).It was found that a small part of graphite layers,which were few-layers in thickness and several nanometers in size,were exfoliated on the edge.Also,many nanoscaled holes on the surface of graphene oxide were found after biological treatment of graphene oxide.The above results indicated that graphite and GO were biologically eroded by Acidithiobacillus ferrooxidans bio-system reaction.The experimental study on the action mechanism of Acidithiobacillus ferrooxidans and the graphite sheet showed that defects on the graphite or GO surface and direct contact between cells and graphite were two important conditions for biological erosion or oxidation.Microbial oxidation of graphite study by nitrifying bacteria.The biological effect of nitrifying bacteria 2011.2 on the graphite was studied.Bio-oxidation graphite was obtained after biological treatment.The good dispersion in ethanol and the black color of the as-prepared graphite revealed its low oxidation degree.The water contact angle of graphite was 78°,indicating that nitrifying bacteria 2011.2 had the ability to oxidize graphite.The as-prepared samples were characterized by XPS and Raman spectroscopy,which showed that the bio-oxidation was a weaker oxidation process compared to chemical oxidation method.The as-prepared samples were characterized by TEM and AFM.It was found that the obtained graphite oxide nanosheets possessed the thickness of 2-3 layers and the size of 50-300 nm.The obtained nano carbon particles possessed the size of 20-60 nm and the height of 2-4 nm.Microbial reduction/synchronous N-doping study of graphene oxide by denitrifying bacteria.To investigate N-doped graphene,the graphene oxide was firstly prepared by improved Hummers methods.Microbial reduction/synchronous N doping study of graphene oxide by denitrifying bacteria CFMI-1 under anaerobic conditions was investigated.The deep yellow GO solution turned black and GO began to accumulate after 5 days of culture under anaerobic conditions,which suggested that graphene oxide could be reduced to graphene with denitrifying bacteria CFMI-1.The obtained samples were characterized by XPS and FTIR,which indicated that the prepared samples contained relatively high proportion of N element during the reduction of graphene oxide.It was found that nitrogen element was mainly in the form of pyridinic N,amino N and pyrrolic N,not including graphitic N.According to the morphology observed,N-doped graphene sheets stacking phenomenon is obvious with the size distribution from nano to micron level.It was also showed that the extracellular secretion by denitrifying bacteria played an important role in biological reduction and N doping.The cell itself had no obvious reduction or N doping effectiveness.Microbial oxidation and biodegradation study of graphite/graphene oxide by white rot fungi.Bacterial cellulose(BC)membrane,which was produced by fermentation process,functioned as the immobilized carrier for white rot fungus CFMI-1.The immobilized white rot fungi were used to micro-oxidate or biodegradate GO and graphite.The results showed that the fungal mycelia could be evenly coated on the surface of a certain size of BC membrane block.The mycelia mesh was sparse,which was beneficial to the dissolution of oxygen and nutrient transport for white rot fungus.Graphite or GO,added to the liquid culture containing immobilized white rot fungi,were rapidly adsorbed on the membrane surface.It was found that "mycelium-graphite-mycelium" or "mycelium-GO-mycelium"sandwich structure was formed on the BC membrane surface.Microbial graphite was obtained after the bio-oxidation process.After biological treatment,the oxygen groups of graphene oxide were reduced.Meanwhile,a large number of nanoscale holes,the diameter of more than 75%of which was below 200 nm,were generated.Therefore,it was proved to be degraded.At last,two kinds of peroxidase were found to be related to the reaction mechanism.Density functional theory study of graphene models and biological enzyme active centers.The density functional theory study of graphene oxide,enzyme active center heme,veratryl alcohol and its cation radical models based on first principle of graphene,was conducted and the molecular models were optimized using Gaussian 09 software.The results show that the small size of graphene HOMO orbits are concentrated on the edge carbon atoms.Thus,the reaction activity of the graphene edges is higher.The catalytic activity and the reaction site of the heme molecules are located in Fe atom.The reaction activity of the veratryl alcohol is located in the oxygen atom of the methoxy group and carbon atoms of aromatic ring.In the end,the action mechanism of water molecules in the catalytic cycle of peroxidase was studied,and the importance of water molecules on the catalytic activity of the peroxidase was demonstrated.The above theoretical calculation proves that active center of the enzyme,small molecule electron mediator and water molecule play important roles in the bio-oxidation and biodegradation of carbon materials such as graphite and graphene oxide.