Si-doped graphene in geopolymer: Its interfacial chemical bonding, structure evolution and ultrastrong reinforcing ability

Low-cost synthesis of silicon-doped graphene (Si-graphene) is attractive for the development of new graphene/ geopolymer nanocomposites. In this work, a new insight into the properties of Si-graphene and the working mechanisms of Si-graphene in geopolymer is provided via molecular dynamics simulations. It is shown that Si- doping deteriorates the mechanical properties of graphene as Si-doping creates point defects, but it improves the surface hydrophilicity, which promotes its dispersion in aqueous media. By studying the polymerization process of Al(OH)₄/Si(OH)₄ monomers on Si-graphene, it is found that Si-graphene can be chemically bonded with geopolymer matrix by typical condensation reactions. Structural analysis reveals that the interfacial bonding has a beneficial effect on condensing the geopolymer composites, due to a denser interphase region. The tensile test reveals that the Young’s modulus of 10% Si-graphene/geopolymer nanocomposites is twice larger than that of graphene/geopolymer nanocomposites. In addition, the interfacial bonding can strengthen the interfacial structure and arrest crack formation in geopolymer matrices.