Abstract
Hollow carbon nanofibers (HCNFs) were found to have formed during microwave pyrolysis of palm kernel shell (PKS) at 500 and 600°C. The formation of HCNFs was only observed during microwave pyrolysis and not the fixed-bed pyrolysis, indicating that microwave played a key role in formation of HCNFs. X-ray diffraction (XRD) analysis of microwave bio-chars showed typical carbon diffractions at 2θ=26.3° and 43.2°, indicating good graphitic structure of HCNFs, especially for bio-chars prepared at 600°C. High resolution transmission electron microscope (HRTEM) results revealed multiwall nature of the HCNFs with carbon layer spacing of 0.34nm. Two major tubular and bamboo-shape structures were observed for HCNFs. With increasing microwave pyrolysis temperature from 500 to 600°C, the yield of HCNFs increased from 5.85wt.% to 9.88wt.%. Raman spectroscopy analysis showed that with increasing pyrolysis temperature to 600°C, the ID/IG ratio decreased from 0.95 to 0.86, indicating higher order of the carbon layers of the HCNFs. Energy dispersive X-ray spectroscopy (EDS) showed the presence of Fe, K, and Ca in HCNFs structure which may have played a catalytic role during their formation and growth. Mechanism of formation and growth of HCNFs under microwave irradiation were proposed and discussed. The HCNFs-coated bio-char has great potential for removal of heavy metals from waste water.
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