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Hydrothermal Preparation and Characterization of Structure of Reduced Graphene Oxide-based Hybrids and Their Properties of Absorption and Photocatalysis

Author: ZhouXun
Tutor: ShiTieJun
School: Hefei University of Technology
Course: Materials Science
Keywords: GO RGO Hummers method Hydrothermal Mesoporous SiO2 Methylene blue Photocatalytic degradation ZnO TiO2nanotubes Lyophilization Stability
CLC: O613.71
Type: PhD thesis
Year: 2013
Downloads: 272
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Graphene as a new carbon material is a flat monolayer of carbon atoms packed tightly into atwo-dimensional honeycomb lattice. The outstanding electronic, thermal, optical and mechanicalproperties of graphene have made graphene and its hybrids become the most important focus withinthe field of material.In this dissertation, reduced graphene oxide (RGO) was synthesized under hydrothermalcondition with graphene oxide (GO) as raw material. Three sorts of SiO2/RGO, ZnO/RGO and TiO2nanotube/RGO (TNT/RGO) hybrids have been fabricated through synthetical combination ofhydrothermal-reduced method and in-situ hybridization. The structure and morphology of thehybrids was characterized. Meanwhile, we explored the potential applications of the hybrids inaspects of absorption and photocatalytic degradation.1) The single-layer GO prepared by Hummers’ method was harvested through washing,centrifugation and ultrasound. Under hydrothermal condition, GO was reduced to RGO with theassistance of ammonia or concentrated NaOH solution. Based on XRD, Raman spectra, FT-IR andXPS investigations, the basic chemical structure and intrinsic properties of GO and RGO wasanalysed comparably, and the results deduced that hydrothermal technology was a liable approachto reduce GO for preparing RGO.2) SiO2/RGO hybrid was gained with GO and tetraethoxysilane (TEOS) as raw materials byhydrothermal-reduced method and in-situ hybridization. The characterization of XRD, Ramanspectra, TEM, FE-TEM, FT-IR, XPS and AFM was utilized to analyse the structure and propertiesof SiO2/RGO hybrids. The result showed that reduction of GO and hybridization of SiO2nanoparticles and RGO sheets were accomplished within one-pot hydrothermal treatment. Theamorphous SiO2nanoparticles attached to RGO can obstruct the natural face-to-face aggregation ofRGO.The outcome of nitrogen adsorption/desorption isotherms curves conformed that the surfacearea of the as-prepared SiO2/RGO hybrids corresponded was335,524,371and244m2/g, the poresize located in mesoporous range and was centred at8.91,9.34,43.87and69.26nm, as the massratios of TEOS to GO was25:3,50:3,100:3and200:3, respectively. By adjusting the mass ratios ofTEOS to GO, the surface area, pore size and its distribution can be tunable and controllable. TheSiO2/RGO hybrid owns the biggest surface area as high as524.61m2/g, when the mass ratio ofTEOS to GO was50:3. What is more, with the increase of mass ratios of TEOS to GO, the surfacearea of SiO2/RGO hybrids was extended firstly and declined then, the pore size was enlarged from8.98to69.26nm and its distribution showed a broad tendency. 3) ZnO/RGO hybrid was fabricated with GO, zinc nitrate hexahydrate and ammonia asbeginning materials by hydrothermal-reduced method and in-situ hybridization. The XRD, XPS,FE-SEM, TEM and PL were carried out to understand the basic structure and substaintial propertiesof ZnO/RGO hybrids. It was proven that reduction of GO and hybridization of ZnO and RGOsheets were accomplished within one-pot hydrothermal treatment. The hexagonal-phase wurtziteZnO attached to RGO can prevent the natural face-to-face accumulation of RGO sheets. As theincreasing the mass ratios of zinc nitrate hexahydrate to GO, the morphology of ZnO in ZnO/RGOhybrids was changed from nanoparticle to nanorod, and the extent of tightness of RGO’sentrapment toward ZnO decreased.The apparent rate constant of the relative as-obtained ZnO/RGO hybrids for photocatalyticdegradation of methylene blue (MB) was0.0094,0.0117,0.0108,0.0039and0.0020min-1, as themass ratios of zinc nitrate hexahydrate to GO was1:1,2:1,5:1,10:1and20:1, respectively. Yet, theapparent rate constant of ZnO was0.0014min-1. Comparably, the photocatalytic efficiency ofZnO/RGO hybrid was superior to pure ZnO, mainly due to that the RGO sheets in ZnO/RGOhybrid can accept and transfer photoelectrons to block the recombination of elicitor. Thephotocatalytic apparent rate constant of ZnO/RGO hybrids increased firstly and dropped then as themass ratios of zinc nitrate hexahydrate to GO increased. While the mass ratio of zinc nitratehexahydrate to GO was2:1, the photocatalytic apparent rate constant of ZnO/RGO hybrid can be asbig as0.0117min-1. More meaningfully, the ZnO/RGO hybrid also exhibited a high stability andreproducibility on photocatalytic degradation of MB.4) TNT/RGO hybrid was assembled with TiO2powders, GO and concentrated NaOH solutionas raw materials through successive operations such as hydrothermal reaction, washing with HCl,lyophilization and heat treatments. Through characterizing TNT/RGO hybrid by XRD, Ramanspectra, XPS, TEM, FE-SEM and PL, it was indicated that reducing GO and hybridizing werecompleted within the one-pot hydrothermal treatment. After heat treatment, the anatase TNTattached to RGO can halt the natural face-to-face accumulation of RGO sheets. At the same time,the (001) lattice plane of anatase TNT of TNT/RGO hybrids was exposed, which was in favour ofimproving the photocatalytic efficiency.Analyzing the results of nitrogen adsorption/desorption isotherms curve, the surface area ofZnO/RGO hybrid lyophilized was210m2/g, however, the surface area of ZnO/RGO hybrid withoutlyophilization was113m2/g, which indicated that lyophilization process as the reliable technologycan retain the structure of TNT/RGO hybrid loose and enhance the surface area for photocatalyticdegradation.As the mass ratios of TiO2powder to GO was0.5:1,1:1,2:1and5:1, the apparent rateconstant of the relative as-assembled TNT/RGO hybrids for photocatalytic degradation of MB was 0.0375,0.0408,0.0584and0.0407min-1, respectively. But, the apparent rate constant of pure TNTwas0.0142min-1. By contrast, the photocatalytic efficiency of TNT/RGO hybrids was superior topure TNT, mainly ascribed to that the RGO sheets in TNT/RGO hybrid can accept and transferphotoelectrons to compress the recombination of elicitor. As the mass ratios of TiO2powders to GOincreased, the apparent rate constant of TNT/RGO hybrids ascended firstly and dropped then. Theapparent rate constant of TNT/RGO hybrid for photocatalytic degradation can be as big as0.0584min-1under the condition that the mass ratio of TiO2powders to GO was2:1.More importantly, after four-cycles circular experiments of photocatalytic degradation, theapparent rate constant of TNT/RGO hybrid was0.0584,0.0576,0.0572and0.0560min-1, whichdemonstrated that TNT/RGO hybrid also exhibited a high stability and reproducibility onphotocatalytic degradation of MB.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Non-metallic elements and their compounds > Part Ⅳ family of non-metallic elements (carbon and silicon ) and its compounds > Carbon C
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