Graphene Nanosheets (GNs) have been successfully added to the palm oil fuel ash (POFA) based geopolymer with KOH activator to improve the geopolymer compressive strength. The graphene was synthesized using turbulence assisted shear exfoliation (TASE) method and identified using Raman spectroscopy. The influence of concentrations and weight percent of graphene against the compressive strength, porosity, and morphological properties were investigated. The crystallinity phases of geopolymer and graphene were also identified using XRD. Raman spectroscopy revealed that graphene produced by TASE method had ≥ 3 layers (graphene nanosheets, GNs). Furthermore, Raman maping constructed by the intensity D band showed the graphene had different atomic arrangements at the edge (armchair and zigzag). The compressive strength and the porosity tests showed that increasing the concentration and the weight percent of graphene increased the compressive strength and reduced the porosity. The highest compressive strength and the lowest porosity (10.8 MPa and 5.92%, respectively) were exhibited by the geopolymer synthesized using 0.7 wt% graphene with concentrations of 30 mg/ml. The SEM micrographs indicated that the graphene reduced the porosity of geopolymers with a pores fulfilling mechanism due to of very small of graphene nanosheets size (∼60 - ∼80 nm).

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The compressive strength of coal fly ash-based geopolymers has been improved by integrating the graphene nanosheets (GNs) as additive. Proximate analysis and crystal structure were also investigated using atomic absorption spectroscopy (AAS) and X-ray diffractometer. The geopolymer composites were created by mixing the solid fly ash and sand (weight ratio of 1:3) with 10 M NaOH and sodium silicate (Na2SiO3) solutions (weight ratio of 1: 2.5), where the liquid to solid weight ratio reached an economical composition of 1: 4. Low-cost GNs with various concentrations of 5 – 20 mg/ml was then added to the mixtures. The prepared mixtures were poured into mortar molds and allowed to stand for few hours at room temperature before heat treatment (curing) in the oven at various temperatures of 40°C, 60°C, and 80°C for 24 hours. Investigation results showed that the average compressive strength of geopolymer increased about 113.8 % or more than double compared to geopolymer without the addition of GNs. The highest compressive strength (29.5 MPa) was shown by a sample with GNs of 20 mg/mL and a curing temperature of 8°C. Meanwhile, geopolymer without GNs showed the lowest compressive strength in all curing temperatures. Proximate analysis showed that fly ash used in this work was the high calcium of type-C fly ash with the CaO content of 11.18%. XRD analysis results indicated that the GNs had integrated well in the geopolymer matrix. The presence of graphene-like structure was also detected, but it was not agglomerated with GNs. Good compressive strength and inexpensive production processes make this geopolymer very prospective for further development.

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Few-layer wrinkled graphene (FLwG) has been synthesized from a coconut-shell-based charcoal using a high-voltage plasma method. Raman spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used for characterizations. Molecular dynamic simulation was also performed for further atomic/molecule movement analysis in the system. The plasma was supplied in the air gap between the electrodes. The graphite rod was used as the high voltage electrode and the aluminum plate was used as the co-electrode. The charcoal powder was arranged on the aluminum electrode surface in the air gap with a distance of ~3 cm to the graphite electrode. Raman spectroscopy analysis indicated that an FLwG had been produced. TEM analysis confirmed the presence of FLwG with a wrinkled and folded structure with an average size of 48.03 nm. XRD revealed that the produced graphene did not undergo any oxidations. Molecular dynamic simulation predicted that the FLwG formation was mainly led by the combination of ionization and deionization of air molecules under high temperatures and plasma stressing.