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TiO2 is the most widely used photocatalytic material to degrade waste compounds. To improve the photocatalytic performance of TiO2, graphene nanoplatelets were used as doping on TiO2. Graphene nanoplatelets are a hybrid between graphene and graphite. Graphene nanoplatelets have attractive features, including mechanical toughness, and for composite material applications. In this report, we investigate the effect of calcination on the synthesis of graphene nanoplatelets-TiO2 synthesis material for photocatalytic processes. Graphene nanoplatelets-TiO2 composites were prepared by stirring and evaporation methods. Then the composite was calcined at a temperature of 400°C, 500°C 600°C at intervals for 1, 2, 3 hours respectively. The composites were confirmed by X-ray diffraction (XRD), FTIR, SEM, BET, and UV-vis. The effect of calcination temperature on the surface, morphology, microstructure and photocatalytic activity of the graphene nanoplatelets-TiO2 composite was investigated further. The photocatalytic performance of the graphene nanoplatelets-TiO2 composite was evaluated for the photodegradation of phenol in an aqueous solution under a mercury lamp. Based on the results of the performance test in degrading phenol, the best results were obtained at a calcination temperature of 500°C for 3 hours. From the results of the characterization, it can be explained that 500°C calcination of this composite can improve the photocatalytic process in degrading of phenol.

The flexural strength of geopolymer has been improved by the addition of few layers graphene (FLG). The composites were made by mixing coal fly ash, alkaline activator, fine aggregate and FLG. FLG was obtained from a simple, low-cost and environmentally friendly liquid shear exfoliation method using a kitchen blender. Flexural strength and morphological properties were characterized using hydraulic concrete beam testing, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The interaction between the geopolymer matrix and the FLG were also discussed through the density functional theory (DFT) approach. The flexural strength of composites increased with the increasing FLG content, and reached a maximum increase of 14.9% when 12% of FLG was added. SEM micrographs showed that the FLG addition changed the surface profile of geopolymers, from a grain-containing surface to a grain-less surface. TEM figures confirmed the existence of FLG, where various sizes of FLG were distributed and embedded in the matrix. The optimized structure through the DFT calculations revealed the emergence of several types of secondary bonds between carbon atoms on the FLG surface and the nearest oxygen (O), sodium (Na) and silicon (Si) atoms that strengthen the composite. Unexpectedly, this geopolymer composite could maintain its high flexural strength after exposure to a temperature of 300 °C. Overall, low-cost FLG is a promising additive for manufacturing high flexural strength geopolymers for industrial scale and for expanding their catalog of contemporary applications.