In order to characterize a representative natural bionanomaterial, present day centric diatom samples (diameter, 175-310 µm) have been analyzed and imaged by infrared (IR) micro-spectroscopy and scanning electron microscopy (SEM). Because diatom silica frustules have complex microscopic morphology, including many void areas such as micro- or nano-pores, the effects of voids on the spectral band shapes were first evaluated. With increasing void area percentage, 1220 cm(-1)/1070 cm(-1) peak height ratio (Si-O polymerization index) increases and 950 cm(-1)/800 cm(-1) peak height ratio (Si-OH/Si-O-Si) decreases, both approaching 1. Based on the void area percentage of representative diatom samples determined using SEM image analyses (51.5% to 20.5%) and spectral simulation, the 1220 cm(-1)/1070 cm(-1) ratios of diatom samples are sometimes affected by the void effect, but the 950 cm(-1)/800 cm(-1) ratios can indicate real structural information of silica. This void effect should be carefully evaluated for IR micro-spectroscopy of micro-nano-porous materials. Maturity of diatom specimens may be evaluated from: (1) void area percentages determined by SEM; (2) average thicknesses determined by optical microscope; and (3) average values of 1220 cm(-1)/1070 cm(-1) peak height ratios (opposite trend to the void effect) determined by IR micro-spectroscopy. Microscopic heterogeneities of chemical structures of silica were obtained by IR micro-spectroscopic mapping of four representative diatoms. The 950 cm(-1)/800 cm(-1) ratios show that large regions of some diatoms consist of hydrated amorphous immature silica. The successful analysis of diatoms by IR micro-spectroscopic data with careful void effect evaluation may be applied to physicochemical structures of many other bionanomaterials.

Interfacial water among silica particles were measured on silica colloid suspensions (0-31.1 vol.%) by transmission infrared micro-spectroscopy. The difference absorption index k spectra from the pure water of silica colloid suspensions with varying volume fractions have residual components in the O-H stretching region: the 3060 cm −1 component increased linearly with the silica volume fraction, while the 3620 cm −1 component increased and the 3380 cm −1 component decreased with much less linearity. The 3060 and 3620 cm −1 components are considered to be characteristic to the surface silanol and interfacial water and affected by overlapping diffuse electrical double layers among silica particles.

A method was developed to obtain the absorption coefficient spectrum of a grain of coal (as small as 10(-7)) in the region of aliphatic and aromatic C-H stretching bands (2700-3200 cm(-1)) using infrared transflection microspectroscopy. In this method, the complex refractive index n - ik was determined using an optimization algorithm with the Kramers-Kronig transform so that the calculated transflection spectrum from the Fresnel equation corresponded to the measured one. The obtained absorption coefficients were compared with the bulk values determined from the potassium bromide (KBr) pellet measurement method.