Temperature driven structural transition in the nickel-based catalytic graphitization of coconut coir

Abstract

Biomass waste is considered as a renewable, low-cost, and environmental friendly carbon source. However, converting a largely disordered carbon materials from biomass wastes into a highly crystalline graphitic carbon nanostructure with low-energy consumption process remains a challenge. Here, we report a simple and low energy process to transform the amorphous carbon structure of coconut coir from Indonesian biomass waste into graphitic nanostructure. A high crystalline graphitic nanostructure has been successfully obtained through two-step process consisting of (1) carbonization process at 500 °C to produce amorphous charcoal, followed by (2) nickel-based catalytic graphitization process at various temperature of 1000 °C to 1300 °C. It is important to note that the temperature process is a main factor in the structural transformation from amorphous to graphitic nanostructures. The structural transformation during catalytic graphitization process was investigated as a function of heat treatment temperature using X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The results show that the carbon structure of coconut coir start to transform from amorphous to ordered graphitic nanostructure at 1200 °C, a temperature lower than that of conventional graphite production, with the highest degree of graphitization (82.16%) and IG/ID ratio of 1.16. Observation using high resolution transmission electron microscopy (HRTEM) reveal the well-defined lattice fringes of graphitic nanostructures with an interplanar distance of 0.3369 nm corresponding to the (0 0 2) crystal plane of pure graphite (0.3354 nm) and less than the disorder carbon (0.3440 nm). In conclusion, this simple process and low energy successfully convert the coconut coir waste into a higher value-added product of graphitic materials as well as reduce the environmental impact of coconut waste.