Controllable Dispersion Of Graphene Oxide And Its Impact On Structure And Properties Of Cement-based Composites

Graphene oxide(GO)is a derivative of graphene.Because of the large specific surface and various oxygen-containing groups,GO is widely used in the preparation of composites.As a kind of nanomaterials,GO sheets tend to aggregate due to the small size and strong Van der Waals force,resulting in inefficient improvement of properties of composite materials.In previous studies,we found that GO can control the hydration products of cement,which made its shape aggregate structure tend to be regulate.And then,the mechanical properties and durability of cement composites were improved significantly.However,as the additive of cement,GO cannot disperse uniformly in a few layers of cement matrix,resulting in uneven structure of cement composites.In this paper,in order to solve the problem of GO dispersion,a few sheets,small size and uniformly dispersed GO was prepared by chemical modification.The influence of GO dispersion on the structure and properties of cement composites was further investigated.(1)The graphene oxide nanosheets were prepared by improved Hummers method,and SGO,CGO,AGO,VGO and KGO were prepared by the modification of GO with thioglycolic acid,azobisisobutyronitrile,acrylic acid,vinyltriethoxysilane and γ-propyltrimethoxysilane respectively.Also,the dispersibility of modified GO in aqueous system was discussed.The composition,structure and the dispersibility in aqueous system of modified GO were characterized by XRD,FTIR,Raman,SEM,TEM,AFM and UV-vis.The results showed that the crystallinity and regularity of modified GO was low.The disordered structure and the content of polar groups on the sheets of modified GO increased providing a guarantee for the dispersion in aqueous system.The dispersibility in aqueous system of GO and modified GO was VGO>CGO>SGO>AGO>KGO>GO.In addition,the thickness of VGO,CGO,SGO,AGO,KGO,GO sheets were 0.4-1.0 nm(1-2 sheets),0.6-1.0 nm(1-2 sheets),1.4-1.9 nm(2-4 sheets),1.4-1.9 nm(3-4 sheets),1.3-1.6 nm(2-3 sheets)and 1.4-2.8 nm(3-7 sheets),respectively.(2)The cement composites were prepared by mixing GO,SGO,CGO,AGO,VGO or KGO with cement.The structure and properties of cement composites were characterized by anti-bending and compression testing,FTIR,SEM,EDS,XRD and automatic mercury porosimeter.The results showed that GO can regulate the shape and aggregation structure of cement hydration products to form a uniform structure with cross-linked and a dense morphology,and this can achieve the effect of repairing defects and improving compactness.The addition of GO improved the strength,toughness and durability of the composites.The structure and properties were related to the dispersion of graphene oxide.When the content of VGO is 0.03wt%,the compressive and flexural strength of cement composites was 90.45 MPa and 9.2 MPa,increased by 72.91% and 41.54%.The average pore size of cement composites was 9.9 nm and the porosity was 9.07%,which increased by 70.18% and 38.05%,respectively.(3)The lightweight cement composites were prepared by adding VGO into the cement system.The holes structure,microstructure and mechanical properties of lightweight cement composites were tested.The results indicated that the mechanical properties of lightweight cement composites were related to the holes structure.The addition of VGO controlled the shape and size of the holes and reduced the existence of perforating holes.However,the mechanical properties of cement composites were not changed by adding 30wt% of the fly ash.At the same time,the lightweight cement composites can be used as adsorption materials for removing the dye wastewater containing methyl orange.The optimal adsorption conditions as followed: the content of VGO was 0.03wt%,the pH of 7,the reaction time of 120 min and then the maximum adsorption capacity can reach 0.485 mg/g.The adsorption process of methyl orange on lightweight cement composites was a homogeneous and monolayer adsorption process with a uniform distribution of binding sites providing a technical basis for the application of lightweight cement composites.The innovation of this paper is that the dispersibility of GO in aqueous phase was increased by chemical modification.And the effect of GO dispersion on the structure and properties of cement composites was discussed.We have also prepared the VGO lightweight cement composites and investigated their properties and hole structure.The adsorption properties of lightweight cement composites were also discussed.These studies have found a new application of lightweight cement composites containing graphene oxide as a dye-containing wastewater adsorbent.