Optimized single-step synthesis of graphene-based carbon nanosheets from palm oil fuel ash

Recycling palm oil fuel ash (POFA) into lucrative holey graphene nanosheets will not only save resources but will also prove to be a great solution to avoid the hazards of environmental pollution. The present research aims on studying the effects of temperature and ratio of potassium hydroxide (KOH) during the chemical activation reaction of POFA, resulting in porous graphene sheets with great scope in a variety of industrial applications. These two parameters were studied because of their major influence on the yield, surface area, porosity, and quality of the produced graphene sheets. Porous graphene sheets were prepared by optimizing different activation temperatures (700 degrees C, 800 degrees C, and 900 degrees C) and POFA to KOH impregnation ratios (1:2, 1:3, 1:4, and 1:5). The optimal conditions for producing the best POFA-derived holey graphene in terms of the number of layers, surface area, and porosity were found with impregnation ratio of 1:3 and at temperature of 800 degrees C. From scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM) analyses, it was found that the resulting few layer nanosheets have more uniform porosity at these optimized conditions. We found Brunauer-Emmett-Teller (BET) surface area, pore volume and carbon percentage of 1506.64 m2/g, 0.88 cm3/g and 99% respectively which are comparable to the previous findings using other biomass sources. It was also found that a higher temperature and higher KOH ratio resulted into pore widening and increasing the surface area, but at temperatures beyond the optimized conditions, the surface area and pore volume were reduced due to more vigorous reactions, and volatilization, which led to pore destruction. The present work emphasizes that these parameters have major impact on POFA activation, and their optimisation resulted into good quality graphene nanosheets in a greener and sustainable way, which can be used for many applications including inexpensive energy-storage and water purification applications.