| Graphene,as a special two-dimensional(2D)material,has a broad range of application in energy storage,drug delivery systems,biosensors and environment applications owing to its excellent properties such as high specific surface area,high strength and strong conductivity.However,graphene sheets would easy to agglomerate due to π-π interaction between them,leading to a large decrease in its conductivity.So self-assembling 2D graphene into a three-dimensional(3D)structure has been recognized as one of the most effective strategies.Therefore,in this study,graphene oxide and waste activated sludge were used to prepare 3D bio-graphene hydrogel(BGH).After the treatment,it was used as the electrode material of supercapacitor to explore the possibility for application in the field of energy storage.Finally,the preparation mechanism of BGH was studied.The main results are as follows:Firstly,graphene oxide(GO)was prepared by a modified Hummers method.Then,the suspension of GO was mixed with domesticated waste activated sludge,after 6 days,the mixture was separated from the aqueous phase and formed activated sludge graphene hydrogel(SGH),X-ray diffraction,infrared spectroscopy,X-ray electron spectroscopy and Raman spectroscopy demonstrated that GO was reduced to conductive reduced graphene oxide(rGO)during formation of hydrogel,indicating that the reducing ability of microorganisms in the waste activated sludge.The formation of rGO enabled the application of SGH in the field of energy storage.Scanning electron microscopy verified that the activated sludge graphene aerogel(SGA)and annealed activated sludge graphene aerogel(ANSGA)had a loose and porous structure,and the porosity of the ANSGA was greater than SGA.By comparing the electrochemical properties of them,it was found that the specific capacitance of ANSGA(174 F/g)was 22 times that of SGA(8 F/g)at a current density of 2 A/g,which proved the importance of annealing modification in argon atmosphere to improve the electrochemical performance of electrode materials.In addition,the excellent rate capability,close to 100%coulomb efficiency and outstanding cycling stability(over 72%capacitance retention after 12000 cycles even at a high current density of 21 A/g),makes ANSGA suitable for high-performance supercapacitor electrode materials.We selected Shewanella xiamenensis BC01(BC01)and co-cultured with GO with different physicochemical properties to explore the interaction between bacteria and GO and the physicochemical properties of GO on BGH formation.The results showed that among various interrelated physicochemical properties of GO,the sheet area determines the BC01 survival and the gelation potential.For biocompatible GO above 0.30 μm2,the larger GO,the higher speed of GO and BC01 self-assembling into BGH.Only 22 h was needed to obtain BGH using GO with average area of 1.83 μm2.GO oxidation degree was found another critical factor that affects whether BGH formed or not,resulting a referential threshold of C/O>1.75.Finally,adhesion of GO was detected and correlated with the bacteria adhesion behavior.It was proved for the first time that the self-assembly of BGH was due to the interaction of hydrophobic force,electrostatic force and adhesion force between GO and BC01,moreover,the large GO in low oxidation state has high resultant force to attract bacteria.All these findings pave a promising way to develop novel GO-bacteria complex to apply in many fields such as energy storage,environment and catalysis. |
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