Raman, infrared and XPS study of bamboo phytoliths after chemical digestion

Raman, infrared and X-ray photoelectron spectroscopies have been used to examine the effect of various chemical digestion methods on the composition of bamboo phytoliths. Intact bilobate phytoliths, suitable for interrogation by Raman microprobe analysis, were isolated by a microwave wet ashing technique using hydrogen peroxide with nitric and hydrochloric acids. The occluded phytolith carbon presented evidence of cellulose, lignin and carboxylic acids. Nitrate from the nitric acid used in the digestion was observed in homogenized samples of the isolated phytoliths; in addition to nitrogen of plant origin occluded within the phytolith, which was observed as amine nitrogen and ammonia. Intact bilobate phytoliths were not observed following an exothermic hydrogen peroxide/sulfuric acid digest, suggesting that these structures ruptured during this digestion procedure. The silicate network was significantly altered during isolation using the exothermic hydrogen peroxide/sulfuric digest, with surface hydroxyls undergoing condensation to form a SiO3 ring structure.

Raman microprobe spectra at 633 nm of internal structure of phytoliths isolated using: (a) μ-H2O2/HNO3/HCl; (b) μ-H2O2/HNO3; and (c) H2O2/H2SO4. Band positions of defect modes D1 and D2 are highlighted.Figure optionsDownload as PowerPoint slideHighlights
► Bamboo phytoliths after chemicaldigestion were examined using Raman, FTIR and XPS.
► Occluded phytolith carbon showed evidence of cellulose, lignin and carboxylic acids.
► Nitrogen was observed from residual nitric acid and from that of plant origin.
► SiO3ring structure was observed in phytolithsilicate after digestion in H2O2/H2SO4.