Structures of Green Culms and Charcoal of Bambusa multiplex

Abstract

Bambusa multiplex (Lour.) Raeusch that is bamboo native to southern Asia and naturalized in other areas of Asia and America has a straight culm of a height of 5~8 m and a diameter of 0.03~0.05 m with small lumens between internodes of a length of 0.2~0.3 m. The culm is thick and heavy. It has been used as wood pulp and is expected to be the useful material for cellulose nanofibers. Its charcoal would be the promising carbon material for new fabricated devices. Therefore, we studied the structures of the green culm and the charcoal of Bambusa multiplex, mainly by X-ray diffraction (XRD) and fluorescent element analysis (XRF), analytical scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). Culms of Bambusa multiplex were sampled and seasoned in Thailand. Some of culms, cut off their branches and leaves, were carbonized around 700 o C for 3 h in a conventional charcoal kiln. SEM energy dispersive X-ray spectroscopy (EDS) mapping was performed using large depth of focus (LDF) mode with a JSM-7200F operated at 15 kV. For TEM/STEM, two aberration corrected microscopes, JEM-ARM 200F and JEM-3100F R05 were used and operated at 200 kV and 80 kV, respectively with a cold field emission gun. Both were configured with a Gatan US-1000 camera and a GIF Quantum ER energy filter for image recording and electron energy loss spectroscopy (EELS). Fig. 1 shows a light microscopy image of a transverse section of a green culm of Bambusa multiplex. Bambusa multiplex has a typical anatomical structure of bamboo [1] and resembles Phragmites australis (common reed) [2] and Arundo donax (giant reed) [3], which also belong to Poaceae Family, although it is different from those reeds in scale of outer shape and size of cells. Fig. 2(a) and Fig. 3 show the XRD and XRF results for different points a and b of a green culm and points A-E of a charcoal tube, as shown in Fig. 2(c). The culm and the charcoal tube are indicated in Fig. 2(b). XRD revealed that the green culm comprises amorphous cellulose and natural crystalline cellulose. XRF revealed that it contains Si atoms in and near its skin. With these results, we concluded that neither carbonization nor graphitization was completed for the charcoal at the present low carbonized temperature. The outside of the charcoal tube B still contained a large amount of Si like the green bamboo skin, which was confirmed by SEM EDS mapping in Fig. 4. Fig. 5(a) shows TEM image of a flake of the charcoal powder. The EELS fine structure of C-K edge obtained from the area enclosed by the circle is shown in Fig. 5(b). The excitation peaks π* and σ* related with the π and σ bonds appear in the amorphous charcoal. The charcoal powder is composed of carbon nanotubes or nanofibers disorderly distributed and graphite crystallites in very small areas, as seen in Fig. 6.

Structural investigations on green culms and charcoal of Bambusa multiplex

“…Ep , epidermis; Cor , cortex; Cc , central cylinder; Vb , vascular bundle; Bs , vascular bundle sheath; Pa , parenchyma cell; P , phloem; X , xylem; Pc , pith cavity. [(c) is reprinted with permission from Kawasaki et al (). Copyright: M & M (Cambridge University Press, 2017)] [Color figure can be viewed at http://wileyonlinelibrary.com]…”

“…D and E are the points on the outer surface and a transversal section of a node in another charcoal piece, respectively. [This figure is reprinted with permission from Kawasaki et al, . Copyright: M & M (Cambridge University Press, 2017)] [Color figure can be viewed at http://wileyonlinelibrary.com]…”

“…The experiments were performed with JEM‐ARM (UHR) attached with Ultra Scan US 1000 and GIF Quantum. [(c) and (d) are reprinted with permission from Kawasaki et al, . Copyright: M & M (Cambridge University Press, 2017)] [Color figure can be viewed at http://wileyonlinelibrary.com]…”

“…The observation was performed with JEM 3100F R05 operated at 80 kV. [This figure is reprinted with permission from Kawasaki et al, . Copyright: M & M (Cambridge University Press, 2017)]…”

“…Therefore, we studied structures of the culms of Bambusa multiplex and its charcoal by X‐ray diffraction (XRD), X‐ray fluorescent elemental analysis (XRF) and different analytical electron microscopy techniques. Preliminary results were reported at Microscopy & Microanalysis 2017 Meeting (Kawasaki et al, ). This paper describes the details of the structural characterization of the bamboo, its charcoal, and also Ag‐doped carbon powders produced using this charcoal.…”